Add Osmo-CC library to replace MNCC

22 files changed, 6408 insertions, 2 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 5f2bad4..b342db1 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -28,7 +28,8 @@ SUBDIRS = \
 	libclipper \
 	libserial \
 	libv27 \
-	libmtp
+	libmtp \
+	libosmocc
 
 if HAVE_ALSA
 SUBDIRS += \
diff --git a/src/libdebug/debug.c b/src/libdebug/debug.c
index 43fb56c..334b2b4 100755
--- a/src/libdebug/debug.c
+++ b/src/libdebug/debug.c
@@ -56,7 +56,7 @@ struct debug_cat {
 	{ "eurosignal", "\033[1;34m" },
 	{ "frame", "\033[0;36m" },
 	{ "call", "\033[0;37m" },
-	{ "mncc", "\033[1;32m" },
+	{ "cc", "\033[1;32m" },
 	{ "database", "\033[0;33m" },
 	{ "transaction", "\033[0;32m" },
 	{ "dms", "\033[0;33m" },
diff --git a/src/libdebug/debug.h b/src/libdebug/debug.h
index 2061ce2..ff8cba7 100644
--- a/src/libdebug/debug.h
+++ b/src/libdebug/debug.h
@@ -20,6 +20,7 @@
 #define DFRAME		13
 #define DCALL		14
 #define DMNCC		15
+#define DCC		15
 #define DDB		16
 #define DTRANS		17
 #define DDMS		18
diff --git a/src/libosmocc/Makefile.am b/src/libosmocc/Makefile.am
new file mode 100644
index 0000000..27c0f6c
--- /dev/null
+++ b/src/libosmocc/Makefile.am
@@ -0,0 +1,15 @@
+AM_CPPFLAGS = -Wall -Wextra -g $(all_includes)
+
+noinst_LIBRARIES = libosmocc.a
+
+libosmocc_a_SOURCES = \
+	message.c \
+	socket.c \
+	cause.c \
+	screen.c \
+	endpoint.c \
+	session.c \
+	sdp.c \
+	rtp.c \
+	helper.c
+
diff --git a/src/libosmocc/cause.c b/src/libosmocc/cause.c
new file mode 100644
index 0000000..4a3a41e
--- /dev/null
+++ b/src/libosmocc/cause.c
@@ -0,0 +1,252 @@
+/* OSMO-CC Processing: convert causes
+ *
+ * (C) 2019 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+#include <arpa/inet.h>
+#include "message.h"
+#include "cause.h"
+
+/* stolen from freeswitch */
+/* map sip responses to QSIG cause codes ala RFC4497 section 8.4.4 */
+static uint8_t status2isdn_cause(uint16_t status)
+{
+	switch (status) {
+	case 200:
+		return 16; //SWITCH_CAUSE_NORMAL_CLEARING;
+	case 401:
+	case 402:
+	case 403:
+	case 407:
+	case 603:
+		return 21; //SWITCH_CAUSE_CALL_REJECTED;
+	case 404:
+		return 1; //SWITCH_CAUSE_UNALLOCATED_NUMBER;
+	case 485:
+	case 604:
+		return 3; //SWITCH_CAUSE_NO_ROUTE_DESTINATION;
+	case 408:
+	case 504:
+		return 102; //SWITCH_CAUSE_RECOVERY_ON_TIMER_EXPIRE;
+	case 410:
+		return 22; //SWITCH_CAUSE_NUMBER_CHANGED;
+	case 413:
+	case 414:
+	case 416:
+	case 420:
+	case 421:
+	case 423:
+	case 505:
+	case 513:
+		return 127; //SWITCH_CAUSE_INTERWORKING;
+	case 480:
+		return 180; //SWITCH_CAUSE_NO_USER_RESPONSE;
+	case 400:
+	case 481:
+	case 500:
+	case 503:
+		return 41; //SWITCH_CAUSE_NORMAL_TEMPORARY_FAILURE;
+	case 486:
+	case 600:
+		return 17; //SWITCH_CAUSE_USER_BUSY;
+	case 484:
+		return 28; //SWITCH_CAUSE_INVALID_NUMBER_FORMAT;
+	case 488:
+	case 606:
+		return 88; //SWITCH_CAUSE_INCOMPATIBLE_DESTINATION;
+	case 502:
+		return 38; //SWITCH_CAUSE_NETWORK_OUT_OF_ORDER;
+	case 405:
+		return 63; //SWITCH_CAUSE_SERVICE_UNAVAILABLE;
+	case 406:
+	case 415:
+	case 501:
+		return 79; //SWITCH_CAUSE_SERVICE_NOT_IMPLEMENTED;
+	case 482:
+	case 483:
+		return 25; //SWITCH_CAUSE_EXCHANGE_ROUTING_ERROR;
+	case 487:
+		return 31; //??? SWITCH_CAUSE_ORIGINATOR_CANCEL;
+	default:
+		return 31; //SWITCH_CAUSE_NORMAL_UNSPECIFIED;
+	}
+}
+
+static uint16_t isdn2status_cause(uint8_t cause, uint8_t location)
+{
+	switch (cause) {
+	case 1:
+		return 404;
+	case 2:
+		return 404;
+	case 3:
+		return 404;
+	case 17:
+		return 486;
+	case 18:
+		return 408;
+	case 19:
+		return 480;
+	case 20:
+		return 480;
+	case 21:
+		if (location == OSMO_CC_LOCATION_USER)
+			return 603;
+		return 403;
+	case 22:
+		//return 301;
+		return 410;
+	case 23:
+		return 410;
+	case 26:
+		return 404;
+	case 27:
+		return 502;
+	case 28:
+		return 484;
+	case 29:
+		return 501;
+	case 31:
+		return 480;
+	case 34:
+		return 503;
+	case 38:
+		return 503;
+	case 41:
+		return 503;
+	case 42:
+		return 503;
+	case 47:
+		return 503;
+	case 55:
+		return 403;
+	case 57:
+		return 403;
+	case 58:
+		return 503;
+	case 65:
+		return 488;
+	case 69:
+		return 501;
+	case 70:
+		return 488;
+	case 79:
+		return 501;
+	case 87:
+		return 403;
+	case 88:
+		return 503;
+	case 102:
+		return 504;
+	case 111:
+		return 500;
+	case 127:
+		return 500;
+	default:
+		return 468;
+	}
+}
+
+static uint8_t socket2isdn_cause(uint8_t sock)
+{
+	switch (sock) {
+	case OSMO_CC_SOCKET_CAUSE_FAILED:
+		return 47;
+	case OSMO_CC_SOCKET_CAUSE_BROKEN_PIPE:
+		return 41;
+	case OSMO_CC_SOCKET_CAUSE_VERSION_MISMATCH:
+		return 38;
+	case OSMO_CC_SOCKET_CAUSE_TIMEOUT:
+		return 41;
+	default:
+		return 31;
+	}
+}
+
+void osmo_cc_convert_cause(struct osmo_cc_ie_cause *cause)
+{
+	/* complete cause, from socket cause */
+	if (cause->socket_cause && cause->isdn_cause == 0 && ntohs(cause->sip_cause_networkorder) == 0)
+		cause->isdn_cause = socket2isdn_cause(cause->socket_cause);
+
+	/* convert ISDN cause to SIP cause */
+	if (cause->isdn_cause && ntohs(cause->sip_cause_networkorder) == 0) {
+		cause->sip_cause_networkorder = htons(isdn2status_cause(cause->isdn_cause, cause->location));
+	}
+
+	/* convert SIP cause to ISDN cause */
+	if (ntohs(cause->sip_cause_networkorder) && cause->isdn_cause == 0) {
+		cause->isdn_cause = status2isdn_cause(ntohs(cause->sip_cause_networkorder));
+	}
+
+	/* no cause at all: use Normal Call Clearing */
+	if (cause->isdn_cause == 0 && ntohs(cause->sip_cause_networkorder) == 0) {
+		cause->isdn_cause = OSMO_CC_ISDN_CAUSE_NORM_CALL_CLEAR;
+		cause->sip_cause_networkorder = htons(486);
+	}
+}
+
+void osmo_cc_convert_cause_msg(osmo_cc_msg_t *msg)
+{
+	void *ie;
+	uint8_t type;
+	uint16_t length;
+	void *value;
+
+	/* search for (all) cause IE and convert the values, if needed */
+	ie = msg->data;
+	while ((value = osmo_cc_msg_sep_ie(msg, &ie, &type, &length))) {
+		if (type == OSMO_CC_IE_CAUSE && length >= sizeof(struct osmo_cc_ie_cause)) {
+			osmo_cc_convert_cause(value);
+		}
+	}
+}
+
+uint8_t osmo_cc_collect_cause(uint8_t old_cause, uint8_t new_cause)
+{
+	/* first cause */
+	if (old_cause == 0)
+		return new_cause;
+
+	/* first prio: return 17 */
+	if (old_cause == OSMO_CC_ISDN_CAUSE_USER_BUSY
+	 || new_cause == OSMO_CC_ISDN_CAUSE_USER_BUSY)
+		return OSMO_CC_ISDN_CAUSE_USER_BUSY;
+
+	/* second prio: return 21 */
+	if (old_cause == OSMO_CC_ISDN_CAUSE_CALL_REJECTED
+	 || new_cause == OSMO_CC_ISDN_CAUSE_CALL_REJECTED)
+		return OSMO_CC_ISDN_CAUSE_CALL_REJECTED;
+
+	/* third prio: return other than 88 and 18 (what ever was first) */
+	if (old_cause != OSMO_CC_ISDN_CAUSE_INCOMPAT_DEST
+	 && old_cause != OSMO_CC_ISDN_CAUSE_USER_NOTRESPOND)
+		return old_cause;
+	if (new_cause != OSMO_CC_ISDN_CAUSE_INCOMPAT_DEST
+	 && new_cause != OSMO_CC_ISDN_CAUSE_USER_NOTRESPOND)
+		return new_cause;
+
+	/* fourth prio: return 88 */
+	if (old_cause == OSMO_CC_ISDN_CAUSE_INCOMPAT_DEST
+	 || new_cause == OSMO_CC_ISDN_CAUSE_INCOMPAT_DEST)
+		return OSMO_CC_ISDN_CAUSE_INCOMPAT_DEST;
+
+	/* fith prio: return 18 */
+	return OSMO_CC_ISDN_CAUSE_USER_NOTRESPOND;
+}
+
diff --git a/src/libosmocc/cause.h b/src/libosmocc/cause.h
new file mode 100644
index 0000000..22319f4
--- /dev/null
+++ b/src/libosmocc/cause.h
@@ -0,0 +1,5 @@
+
+void osmo_cc_convert_cause(struct osmo_cc_ie_cause *cause);
+void osmo_cc_convert_cause_msg(osmo_cc_msg_t *msg);
+uint8_t osmo_cc_collect_cause(uint8_t old_cause, uint8_t new_cause);
+
diff --git a/src/libosmocc/endpoint.c b/src/libosmocc/endpoint.c
new file mode 100644
index 0000000..83dd475
--- /dev/null
+++ b/src/libosmocc/endpoint.c
@@ -0,0 +1,1476 @@
+/* Endpoint and call process handling
+ *
+ * (C) 2019 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include <arpa/inet.h>
+#include <unistd.h>
+#include "../libtimer/timer.h"
+#include "../libdebug/debug.h"
+#include "endpoint.h"
+
+osmo_cc_endpoint_t *osmo_cc_endpoint_list = NULL;
+
+static osmo_cc_call_t *call_new(osmo_cc_endpoint_t *ep, uint32_t callref)
+{
+	osmo_cc_call_t *call, **cp;
+
+	call = calloc(1, sizeof(*call));
+	if (!call) {
+		PDEBUG(DCC, DEBUG_ERROR, "No memory for call process instance.\n");
+		abort();
+	}
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Creating new call with callref %u.\n", callref);
+
+	call->ep = ep;
+	call->callref = callref;
+
+	/* attach to call process list */
+	cp = &ep->call_list;
+	while (*cp)
+		cp = &((*cp)->next);
+	*cp = call;
+
+	/* return new entry */
+	return call;
+}
+
+static void call_delete(osmo_cc_call_t *call)
+{
+	osmo_cc_call_t **cp;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Destroying call with callref %u.\n", call->callref);
+
+	/* detach from call process list */
+	cp = &call->ep->call_list;
+	while (*cp != call)
+		cp = &((*cp)->next);
+	*cp = call->next;
+
+	/* flush message queue */
+	while (call->sock_queue) {
+		osmo_cc_msg_t *msg = osmo_cc_msg_list_dequeue(&call->sock_queue, NULL);
+		osmo_cc_free_msg(msg);
+	}
+
+	/* free remote peer */
+	free((char *)call->attached_name);
+	free((char *)call->attached_host);
+
+	free(call);
+}
+
+static const char *state_names[] = {
+	"IDLE",
+	"INIT-OUT",
+	"INIT-IN",
+	"OVERLAP-OUT",
+	"OVERLAP-IN",
+	"PROCEEDING-OUT",
+	"PROCEEDING-IN",
+	"ALERTING-OUT",
+	"ALERTING-IN",
+	"CONNECTING-OUT",
+	"CONNECTING-IN",
+	"ACTIVE",
+	"DISCONNECTING-OUT",
+	"DISCONNECTING-IN",
+	"DISCONNECT-COLLISION",
+	"RELEASING-OUT",
+	"ATTACH-SENT",
+	"ATTACH-OUT",
+	"ATTACH-WAIT",
+	"ATTACH-IN",
+};
+
+static void new_call_state(osmo_cc_call_t *call, enum osmo_cc_state new_state)
+{
+	PDEBUG(DCC, DEBUG_DEBUG, "Changing call state with callref %u from %s to %s.\n", call->callref, state_names[call->state], state_names[new_state]);
+	call->state = new_state;
+}
+
+/* helper to forward message to lower layer */
+static void forward_to_ll(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	if (call->lower_layer_released)
+		return;
+
+	if (msg->type == OSMO_CC_MSG_SETUP_REQ
+	 || msg->type == OSMO_CC_MSG_SETUP_RSP) {
+		/* screen towards lower layer */
+		msg = osmo_cc_screen_msg(call->ep, msg, 0, NULL);
+	}
+
+	osmo_cc_msg_list_enqueue(&call->ep->ll_queue, msg, call->callref);
+}
+
+static void sock_reject_msg(osmo_cc_socket_t *os, uint32_t callref, uint8_t location, uint8_t socket_cause, uint8_t isdn_cause, uint16_t sip_cause)
+{
+	osmo_cc_msg_t *msg;
+
+	/* create message */
+	msg = osmo_cc_new_msg(OSMO_CC_MSG_REJ_IND);
+
+	/* add cause */
+	osmo_cc_add_ie_cause(msg, location, isdn_cause, sip_cause, socket_cause);
+	osmo_cc_convert_cause_msg(msg);
+
+	/* message to socket */
+	osmo_cc_sock_send_msg(os, callref, msg, NULL, 0);
+}
+
+static void ll_reject_msg(osmo_cc_call_t *call, uint8_t location, uint8_t socket_cause, uint8_t isdn_cause, uint16_t sip_cause)
+{
+	osmo_cc_msg_t *msg;
+
+	/* create message */
+	msg = osmo_cc_new_msg(OSMO_CC_MSG_REJ_REQ);
+
+	/* add cause */
+	osmo_cc_add_ie_cause(msg, location, isdn_cause, sip_cause, socket_cause);
+	osmo_cc_convert_cause_msg(msg);
+
+	/* message to lower layer */
+	forward_to_ll(call, msg);
+}
+
+static int split_address(const char *address, const char **host_p, uint16_t *port_p)
+{
+	const char *portstring;
+
+	*host_p = osmo_cc_host_of_address(address);
+	if (!(*host_p)) {
+		PDEBUG(DCC, DEBUG_ERROR, "Host IP in given address '%s' is invalid.\n", address);
+		return -EINVAL;
+	}
+	portstring = osmo_cc_port_of_address(address);
+	if (!portstring) {
+		PDEBUG(DCC, DEBUG_ERROR, "Port number in given address '%s' is not specified or invalid.\n", address);
+		return -EINVAL;
+	}
+	*port_p = atoi(portstring);
+
+	return 0;
+}
+
+/* helper to forward message to upper layer */
+static void forward_to_ul(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	const char *address = NULL, *host = NULL;
+	uint16_t port;
+	int rc;
+
+	if (call->upper_layer_released)
+		return;
+
+	if (msg->type == OSMO_CC_MSG_SETUP_IND
+	 || msg->type == OSMO_CC_MSG_SETUP_CNF) {
+		/* screen towards upper layer */
+		msg = osmo_cc_screen_msg(call->ep, msg, 1, &address);
+	}
+
+	/* no socket: forward message to upper layer */
+	if (call->ep->ul_msg_cb) {
+		call->ep->ul_msg_cb(call, msg);
+		return;
+	}
+
+	/* if remote peer is included in the setup message */
+	if (address && msg->type == OSMO_CC_MSG_SETUP_IND) {
+		rc = split_address(address, &host, &port);
+		if (rc < 0) {
+			PDEBUG(DCC, DEBUG_ERROR, "Given remote peer's address '%s' in setup message is invalid, rejecting call.\n", address);
+reject:
+			/* reject, due to error */
+			osmo_cc_free_msg(msg);
+			new_call_state(call, OSMO_CC_STATE_IDLE);
+			ll_reject_msg(call, call->ep->serving_location, 0, OSMO_CC_ISDN_CAUSE_DEST_OOO, 0);
+			call_delete(call);
+			return;
+		}
+		PDEBUG(DCC, DEBUG_DEBUG, "Using host IP '%s' and port '%d' from setup message.\n", host, port);
+	}
+
+	/* for attach message, use remote peer */
+	if (msg->type == OSMO_CC_MSG_ATTACH_IND) {
+		host = call->ep->remote_host;
+		port = call->ep->remote_port;
+		PDEBUG(DCC, DEBUG_DEBUG, "Using host IP '%s' and port '%d' from remote address for attach message.\n", host, port);
+	}
+
+	/* if there is no remote peer in the setup message, use remote peer */
+	if (!address && msg->type == OSMO_CC_MSG_SETUP_IND && call->ep->remote_host) {
+		host = call->ep->remote_host;
+		port = call->ep->remote_port;
+		PDEBUG(DCC, DEBUG_DEBUG, "Using host IP '%s' and port '%d' from remote address for setup message.\n", host, port);
+	}
+
+	/* if there is no remote peer set, try to use the interface name */
+	if (!host && msg->type == OSMO_CC_MSG_SETUP_IND) {
+		char interface[256];
+		osmo_cc_call_t *att;
+
+		rc = osmo_cc_get_ie_called_interface(msg, 0, interface, sizeof(interface));
+		if (rc < 0)
+			interface[0] = '\0';
+		/* check for incoming attachment */
+		for (att = call->ep->call_list; att; att = att->next) {
+			if (att->state != OSMO_CC_STATE_ATTACH_IN)
+				continue;
+			/* no interface given, just use the attached peer */
+			if (!interface[0])
+				break;
+			/* no interface name given on attached peer, ignore it */
+			if (!att->attached_name || !att->attached_name[0])
+				continue;
+			/* interface given, use the attached peer with the same interface name */
+			if (!strcmp(interface, att->attached_name))
+				break;
+		}
+		if (!att && !interface[0]) {
+			PDEBUG(DCC, DEBUG_ERROR, "No remote peer attached, rejecting call.\n");
+			goto reject;
+		}
+		if (!att) {
+			PDEBUG(DCC, DEBUG_ERROR, "No remote peer attached for given interface '%s', rejecting call.\n", interface);
+			goto reject;
+		}
+		host = att->attached_host;
+		port = att->attached_port;
+		PDEBUG(DCC, DEBUG_DEBUG, "Using host IP '%s' and port '%d' from attached peer for setup message.\n", host, port);
+	}
+
+	/* add local interface name to setup message */
+	// FIXME: should we do that if there is already an interface name given?
+	if (msg->type == OSMO_CC_MSG_SETUP_IND && call->ep->local_name)
+		osmo_cc_add_ie_calling_interface(msg, call->ep->local_name);
+
+	/* forward message to socket */
+	osmo_cc_sock_send_msg(&call->ep->os, call->callref, msg, host, port);
+}
+
+/* send attach indication to socket */
+void send_attach_ind(struct timer *timer)
+{
+	osmo_cc_endpoint_t *ep = (osmo_cc_endpoint_t *)timer->priv;
+	osmo_cc_call_t *call;
+	osmo_cc_msg_t *msg;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Trying to attach to remote peer \"%s\".\n", ep->remote_host);
+
+	/* create new call for attachment */
+	call = osmo_cc_call_new(ep);
+
+	/* create attach message */
+	msg = osmo_cc_new_msg(OSMO_CC_MSG_ATTACH_IND);
+
+	/* set interface name and address */
+	osmo_cc_add_ie_calling_interface(msg, ep->local_name);
+	osmo_cc_add_ie_socket_address(msg, ep->local_address);
+
+	/* message to socket */
+	forward_to_ul(call, msg);
+
+	/* set state */
+	new_call_state(call, OSMO_CC_STATE_ATTACH_SENT);
+}
+
+void attach_rsp(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	PDEBUG(DCC, DEBUG_INFO, "Attached to remote peer \"%s\".\n", call->ep->remote_address);
+
+	/* set state */
+	new_call_state(call, OSMO_CC_STATE_ATTACH_OUT);
+
+	/* drop message */
+	osmo_cc_free_msg(msg);
+}
+
+void attach_rel(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* (re-)start timer for next attachment */
+	if (call->state == OSMO_CC_STATE_ATTACH_SENT
+	 || call->state == OSMO_CC_STATE_ATTACH_OUT) {
+		timer_start(&call->ep->attach_timer, OSMO_CC_ATTACH_TIMER);
+		PDEBUG(DCC, DEBUG_INFO, "Attachment to remote peer \"%s\" failed, retrying.\n", call->ep->remote_address);
+	}
+
+	if (call->attached_name)
+		PDEBUG(DCC, DEBUG_INFO, "Peer with remote interface \"%s\" detached from us.\n", call->attached_name);
+
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_IDLE);
+
+	/* unset interface */
+	free((char *)call->attached_name);
+	call->attached_name = NULL;
+	free((char *)call->attached_host);
+	call->attached_host = NULL;
+
+	/* drop message */
+	osmo_cc_free_msg(msg);
+
+	/* destroy */
+	call_delete(call);
+}
+
+void attach_req(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	char address[256];
+	char interface[256];
+	const char *host;
+	uint16_t port;
+	int rc;
+
+	/* get peer from message */
+	rc = osmo_cc_get_ie_socket_address(msg, 0, address, sizeof(address));
+	if (rc < 0)
+		address[0] = '\0';
+	if (!address[0]) {
+		PDEBUG(DCC, DEBUG_ERROR, "Attachment request from remote peer has no remote address set, rejecting.\n");
+
+rel:
+		/* change to REL_REQ */
+		msg->type = OSMO_CC_MSG_REL_IND;
+		PDEBUG(DCC, DEBUG_INFO, "Changing message to %s.\n", osmo_cc_msg_name(msg->type));
+
+		/* message to socket */
+		forward_to_ul(call, msg);
+
+		/* destroy */
+		call_delete(call);
+
+		return;
+	}
+	rc = split_address(address, &host, &port);
+	if (rc < 0) {
+		PDEBUG(DCC, DEBUG_ERROR, "Given remote peer's address '%s' in attach message is invalid, rejecting call.\n", address);
+		goto rel;
+	}
+	free((char *)call->attached_host);
+	call->attached_host = strdup(host);
+	call->attached_port = port;
+
+	rc = osmo_cc_get_ie_calling_interface(msg, 0, interface, sizeof(interface));
+	if (rc < 0)
+		interface[0] = '\0';
+	if (interface[0]) {
+		free((char *)call->attached_name);
+		call->attached_name = strdup(interface);
+	}
+
+	PDEBUG(DCC, DEBUG_INFO, "Remote peer with socket address '%s' and port '%d' and interface '%s' attached to us.\n", call->attached_host, call->attached_port, call->attached_name);
+
+	/* changing to confirm message */
+	msg->type = OSMO_CC_MSG_ATTACH_CNF;
+	PDEBUG(DCC, DEBUG_INFO, "Changing message to %s.\n", osmo_cc_msg_name(msg->type));
+
+	/* message to socket */
+	forward_to_ul(call, msg);
+
+	/* set state */
+	new_call_state(call, OSMO_CC_STATE_ATTACH_IN);
+}
+
+static void setup_req(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_INIT_OUT);
+
+	/* to lower layer */
+	forward_to_ll(call, msg);
+}
+
+static void setup_ind(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_INIT_IN);
+
+	/* to upper layer */
+	forward_to_ul(call, msg);
+}
+
+static void rej_req(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_IDLE);
+
+	/* to lower layer */
+	forward_to_ll(call, msg);
+
+	/* destroy */
+	call_delete(call);
+}
+
+static void rej_ind(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_IDLE);
+
+	/* to upper layer */
+	forward_to_ul(call, msg);
+
+	/* destroy */
+	call_delete(call);
+}
+
+static void setup_ack_req(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_OVERLAP_IN);
+
+	/* to lower layer */
+	forward_to_ll(call, msg);
+}
+
+static void setup_ack_ind(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_OVERLAP_OUT);
+
+	/* to upper layer */
+	forward_to_ul(call, msg);
+}
+
+static void proc_req(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_PROCEEDING_IN);
+
+	/* to lower layer */
+	forward_to_ll(call, msg);
+}
+
+static void proc_ind(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_PROCEEDING_OUT);
+
+	/* to upper layer */
+	forward_to_ul(call, msg);
+}
+
+static void alert_req(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_ALERTING_IN);
+
+	/* to lower layer */
+	forward_to_ll(call, msg);
+}
+
+static void alert_ind(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_ALERTING_OUT);
+
+	/* to upper layer */
+	forward_to_ul(call, msg);
+}
+
+static void setup_rsp(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_CONNECTING_IN);
+
+	/* to lower layer */
+	forward_to_ll(call, msg);
+}
+
+static void setup_cnf(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_CONNECTING_OUT);
+
+	/* to upper layer */
+	forward_to_ul(call, msg);
+}
+
+static void setup_comp_req(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_ACTIVE);
+
+	/* to lower layer */
+	forward_to_ll(call, msg);
+}
+
+static void setup_comp_ind(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_ACTIVE);
+
+	/* to upper layer */
+	forward_to_ul(call, msg);
+}
+
+static void info_req(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* to lower layer */
+	forward_to_ll(call, msg);
+}
+
+static void info_ind(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* to upper layer */
+	forward_to_ul(call, msg);
+}
+
+static void progress_req(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* to lower layer */
+	forward_to_ll(call, msg);
+}
+
+static void progress_ind(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* to upper layer */
+	forward_to_ul(call, msg);
+}
+
+static void notify_req(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* to lower layer */
+	forward_to_ll(call, msg);
+}
+
+static void notify_ind(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* to upper layer */
+	forward_to_ul(call, msg);
+}
+
+static void disc_req(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_DISCONNECTING_OUT);
+
+	/* to lower layer */
+	forward_to_ll(call, msg);
+}
+
+static void disc_ind(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_DISCONNECTING_IN);
+
+	/* to upper layer */
+	forward_to_ul(call, msg);
+}
+
+static void rel_req(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* terminate process, if there is no lower layer anmore */
+	if (call->lower_layer_released) {
+		/* change state */
+		new_call_state(call, OSMO_CC_STATE_IDLE);
+
+		/* drop message */
+		osmo_cc_free_msg(msg);
+
+		/* destroy */
+		call_delete(call);
+
+		return;
+	}
+
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_RELEASING_OUT);
+
+	/* to lower layer */
+	forward_to_ll(call, msg);
+}
+
+static void rel_ind(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_IDLE);
+
+	/* to upper layer */
+	forward_to_ul(call, msg);
+
+	/* destroy */
+	call_delete(call);
+}
+
+static void rel_cnf(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_IDLE);
+
+	/* drop message */
+	osmo_cc_free_msg(msg);
+
+	/* destroy */
+	call_delete(call);
+}
+
+static void disc_collision_ind(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* release to lower layer wheen there is no upper layer */
+	if (call->upper_layer_released) {
+		/* change state */
+		new_call_state(call, OSMO_CC_STATE_RELEASING_OUT);
+
+		/* change to REL_REQ */
+		msg->type = OSMO_CC_MSG_REL_REQ;
+		PDEBUG(DCC, DEBUG_INFO, "Changing message to %s.\n", osmo_cc_msg_name(msg->type));
+
+		/* to lower layer */
+		forward_to_ll(call, msg);
+
+		return;
+	}
+
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_DISC_COLLISION);
+
+	/* to upper layer */
+	forward_to_ul(call, msg);
+}
+
+static void disc_collision_req(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* release to upper layer wheen there is no lower layer */
+	if (call->lower_layer_released) {
+		/* change to REL_REQ */
+		msg->type = OSMO_CC_MSG_REL_IND;
+		PDEBUG(DCC, DEBUG_INFO, "Changing message to %s.\n", osmo_cc_msg_name(msg->type));
+
+		/* to upper layer */
+		forward_to_ul(call, msg);
+
+		/* destroy */
+		call_delete(call);
+
+		return;
+	}
+
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_DISC_COLLISION);
+
+	/* to lower layer */
+	forward_to_ll(call, msg);
+}
+
+static void rel_collision(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	if (call->state != OSMO_CC_STATE_IDLE)
+		new_call_state(call, OSMO_CC_STATE_IDLE);
+
+	/* drop message */
+	osmo_cc_free_msg(msg);
+
+	/* destroy */
+	call_delete(call);
+}
+
+static void rej_ind_disc(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_IDLE);
+
+	/* change to REL_IND */
+	msg->type = OSMO_CC_MSG_REL_IND;
+	PDEBUG(DCC, DEBUG_INFO, "Changing message to %s.\n", osmo_cc_msg_name(msg->type));
+
+	/* to upper layer */
+	forward_to_ul(call, msg);
+
+	/* destroy */
+	call_delete(call);
+}
+
+static void rej_req_disc(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_IDLE);
+
+	/* change to REL_REQ */
+	msg->type = OSMO_CC_MSG_REL_REQ;
+	PDEBUG(DCC, DEBUG_INFO, "Changing message to %s.\n", osmo_cc_msg_name(msg->type));
+
+	/* to lower layer */
+	forward_to_ll(call, msg);
+
+	/* destroy */
+	call_delete(call);
+}
+
+static void rel_ind_other(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	// FIXME: does this event really happens in this state?
+	// just to be safe we handle it
+	/* if thereis no upper layer, we are done */
+	if (call->upper_layer_released) {
+		/* drop message */
+		osmo_cc_free_msg(msg);
+
+		/* destroy */
+		call_delete(call);
+
+		return;
+	}
+
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_DISCONNECTING_IN);
+
+	/* change to DISC_IND */
+	msg->type = OSMO_CC_MSG_DISC_IND;
+	PDEBUG(DCC, DEBUG_INFO, "Changing message to %s.\n", osmo_cc_msg_name(msg->type));
+	call->lower_layer_released = 1;
+
+	/* to upper layer */
+	forward_to_ul(call, msg);
+}
+
+static void rel_req_other(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	// FIXME: does this event really happens in this state?
+	// just to be safe we handle it
+	/* if thereis no lower layer, we are done */
+	if (call->lower_layer_released) {
+		/* drop message */
+		osmo_cc_free_msg(msg);
+
+		/* destroy */
+		call_delete(call);
+
+		return;
+	}
+
+	/* change state */
+	new_call_state(call, OSMO_CC_STATE_DISCONNECTING_OUT);
+
+	/* change to DISC_REQ */
+	msg->type = OSMO_CC_MSG_DISC_REQ;
+	PDEBUG(DCC, DEBUG_INFO, "Changing message to %s.\n", osmo_cc_msg_name(msg->type));
+	call->upper_layer_released = 1;
+
+	/* to lower layer */
+	forward_to_ll(call, msg);
+}
+
+#define SBIT(a) (1 << a)
+#define ALL_STATES (~0)
+
+static struct statemachine {
+	uint32_t	states;
+	int		type;
+	void		(*action)(osmo_cc_call_t *call, osmo_cc_msg_t *msg);
+} statemachine_list[] = {
+	/* attachment states */
+	{SBIT(OSMO_CC_STATE_ATTACH_SENT),
+	 OSMO_CC_MSG_ATTACH_RSP, attach_rsp},
+	{SBIT(OSMO_CC_STATE_ATTACH_OUT) | SBIT(OSMO_CC_STATE_ATTACH_SENT),
+	 OSMO_CC_MSG_REL_REQ, attach_rel},
+	{SBIT(OSMO_CC_STATE_IDLE),
+	 OSMO_CC_MSG_ATTACH_REQ, attach_req},
+	{SBIT(OSMO_CC_STATE_ATTACH_IN),
+	 OSMO_CC_MSG_REL_REQ, attach_rel},
+
+	/* call setup toward lower layer protocol */
+	{SBIT(OSMO_CC_STATE_IDLE),
+	 OSMO_CC_MSG_SETUP_REQ, setup_req},
+	{SBIT(OSMO_CC_STATE_INIT_OUT),
+	 OSMO_CC_MSG_SETUP_ACK_IND, setup_ack_ind},
+	{SBIT(OSMO_CC_STATE_INIT_OUT) | SBIT(OSMO_CC_STATE_OVERLAP_OUT),
+	 OSMO_CC_MSG_PROC_IND, proc_ind},
+	{SBIT(OSMO_CC_STATE_INIT_OUT) | SBIT(OSMO_CC_STATE_OVERLAP_OUT) |
+	 SBIT(OSMO_CC_STATE_PROCEEDING_OUT),
+	 OSMO_CC_MSG_ALERT_IND, alert_ind},
+	{SBIT(OSMO_CC_STATE_INIT_OUT) | SBIT(OSMO_CC_STATE_OVERLAP_OUT) |
+	 SBIT(OSMO_CC_STATE_PROCEEDING_OUT) | SBIT(OSMO_CC_STATE_ALERTING_OUT),
+	 OSMO_CC_MSG_SETUP_CNF, setup_cnf},
+	{SBIT(OSMO_CC_STATE_OVERLAP_OUT) | SBIT(OSMO_CC_STATE_PROCEEDING_OUT) |
+	 SBIT(OSMO_CC_STATE_ALERTING_OUT),
+	 OSMO_CC_MSG_PROGRESS_IND, progress_ind},
+	{SBIT(OSMO_CC_STATE_OVERLAP_OUT),
+	 OSMO_CC_MSG_INFO_REQ, info_req},
+	{SBIT(OSMO_CC_STATE_PROCEEDING_OUT) | SBIT(OSMO_CC_STATE_ALERTING_OUT),
+	 OSMO_CC_MSG_NOTIFY_IND, notify_ind},
+	{SBIT(OSMO_CC_STATE_CONNECTING_OUT),
+	 OSMO_CC_MSG_SETUP_COMP_REQ, setup_comp_req},
+
+	/* call setup from lower layer protocol */
+	{SBIT(OSMO_CC_STATE_IDLE),
+	 OSMO_CC_MSG_SETUP_IND, setup_ind},
+	{SBIT(OSMO_CC_STATE_INIT_IN),
+	 OSMO_CC_MSG_SETUP_ACK_REQ, setup_ack_req},
+	{SBIT(OSMO_CC_STATE_INIT_IN) | SBIT(OSMO_CC_STATE_OVERLAP_IN),
+	 OSMO_CC_MSG_PROC_REQ, proc_req},
+	{SBIT(OSMO_CC_STATE_INIT_IN) | SBIT(OSMO_CC_STATE_OVERLAP_IN) |
+	 SBIT(OSMO_CC_STATE_PROCEEDING_IN),
+	 OSMO_CC_MSG_ALERT_REQ, alert_req},
+	{SBIT(OSMO_CC_STATE_INIT_IN) | SBIT(OSMO_CC_STATE_OVERLAP_IN) |
+	 SBIT(OSMO_CC_STATE_PROCEEDING_IN) | SBIT(OSMO_CC_STATE_ALERTING_IN),
+	 OSMO_CC_MSG_SETUP_RSP, setup_rsp},
+	{SBIT(OSMO_CC_STATE_OVERLAP_IN) | SBIT(OSMO_CC_STATE_PROCEEDING_IN) |
+	 SBIT(OSMO_CC_STATE_ALERTING_IN),
+	 OSMO_CC_MSG_PROGRESS_REQ, progress_req},
+	{SBIT(OSMO_CC_STATE_OVERLAP_IN),
+	 OSMO_CC_MSG_INFO_IND, info_ind},
+	{SBIT(OSMO_CC_STATE_PROCEEDING_IN) | SBIT(OSMO_CC_STATE_ALERTING_IN),
+	 OSMO_CC_MSG_NOTIFY_REQ, notify_req},
+	{SBIT(OSMO_CC_STATE_CONNECTING_IN),
+	 OSMO_CC_MSG_SETUP_COMP_IND, setup_comp_ind},
+
+	/* active state */
+	{SBIT(OSMO_CC_STATE_ACTIVE),
+	 OSMO_CC_MSG_NOTIFY_IND, notify_ind},
+	{SBIT(OSMO_CC_STATE_ACTIVE),
+	 OSMO_CC_MSG_NOTIFY_REQ, notify_req},
+	{SBIT(OSMO_CC_STATE_ACTIVE),
+	 OSMO_CC_MSG_INFO_IND, info_ind},
+	{SBIT(OSMO_CC_STATE_ACTIVE),
+	 OSMO_CC_MSG_INFO_REQ, info_req},
+
+	/* call release */
+	{SBIT(OSMO_CC_STATE_INIT_OUT) | SBIT(OSMO_CC_STATE_INIT_IN) |
+	 SBIT(OSMO_CC_STATE_OVERLAP_OUT) | SBIT(OSMO_CC_STATE_OVERLAP_IN) |
+	 SBIT(OSMO_CC_STATE_PROCEEDING_OUT) | SBIT(OSMO_CC_STATE_PROCEEDING_IN) |
+	 SBIT(OSMO_CC_STATE_ALERTING_OUT) | SBIT(OSMO_CC_STATE_ALERTING_IN) |
+	 SBIT(OSMO_CC_STATE_CONNECTING_OUT) | SBIT(OSMO_CC_STATE_CONNECTING_IN) |
+	 SBIT(OSMO_CC_STATE_ACTIVE),
+	 OSMO_CC_MSG_DISC_REQ, disc_req},
+	{SBIT(OSMO_CC_STATE_INIT_OUT) | SBIT(OSMO_CC_STATE_INIT_IN) |
+	 SBIT(OSMO_CC_STATE_OVERLAP_OUT) | SBIT(OSMO_CC_STATE_OVERLAP_IN) |
+	 SBIT(OSMO_CC_STATE_PROCEEDING_OUT) | SBIT(OSMO_CC_STATE_PROCEEDING_IN) |
+	 SBIT(OSMO_CC_STATE_ALERTING_OUT) | SBIT(OSMO_CC_STATE_ALERTING_IN) |
+	 SBIT(OSMO_CC_STATE_CONNECTING_OUT) | SBIT(OSMO_CC_STATE_CONNECTING_IN) |
+	 SBIT(OSMO_CC_STATE_ACTIVE),
+	 OSMO_CC_MSG_DISC_IND, disc_ind},
+	{SBIT(OSMO_CC_STATE_INIT_OUT),
+	 OSMO_CC_MSG_REJ_IND, rej_ind},
+	{SBIT(OSMO_CC_STATE_INIT_IN),
+	 OSMO_CC_MSG_REJ_REQ, rej_req},
+	{SBIT(OSMO_CC_STATE_DISCONNECTING_OUT),
+	 OSMO_CC_MSG_REL_IND, rel_ind},
+	{SBIT(OSMO_CC_STATE_DISCONNECTING_IN),
+	 OSMO_CC_MSG_REL_REQ, rel_req},
+	{SBIT(OSMO_CC_STATE_RELEASING_OUT),
+	 OSMO_CC_MSG_REL_CNF, rel_cnf},
+
+	/* race condition where disconnect is received after disconnecting (disconnect collision) */
+	{SBIT(OSMO_CC_STATE_DISCONNECTING_OUT),
+	 OSMO_CC_MSG_DISC_IND, disc_collision_ind},
+	{SBIT(OSMO_CC_STATE_DISCONNECTING_IN),
+	 OSMO_CC_MSG_DISC_REQ, disc_collision_req},
+	{SBIT(OSMO_CC_STATE_DISC_COLLISION),
+	 OSMO_CC_MSG_REL_IND, rel_ind},
+	{SBIT(OSMO_CC_STATE_DISC_COLLISION),
+	 OSMO_CC_MSG_REL_REQ, rel_req},
+
+	/* race condition where release is received after releasing (release collision) */
+	{SBIT(OSMO_CC_STATE_RELEASING_OUT),
+	 OSMO_CC_MSG_REL_IND, rel_collision},
+	{SBIT(OSMO_CC_STATE_IDLE),
+	 OSMO_CC_MSG_REL_REQ, rel_collision},
+
+	/* race condition where reject is received after disconnecting */
+	{SBIT(OSMO_CC_STATE_DISCONNECTING_OUT),
+	 OSMO_CC_MSG_REJ_IND, rej_ind_disc},
+	{SBIT(OSMO_CC_STATE_DISCONNECTING_IN),
+	 OSMO_CC_MSG_REJ_REQ, rej_req_disc},
+
+	/* turn release into disconnect, so release is possible in any state */
+	{ALL_STATES,
+	 OSMO_CC_MSG_REL_IND, rel_ind_other},
+	{ALL_STATES,
+	 OSMO_CC_MSG_REL_REQ, rel_req_other},
+};
+
+#define STATEMACHINE_LEN \
+	(sizeof(statemachine_list) / sizeof(struct statemachine))
+
+static void handle_msg(osmo_cc_call_t *call, osmo_cc_msg_t *msg)
+{
+	int i;
+
+	/* Find function for current state and message */
+	for (i = 0; i < (int)STATEMACHINE_LEN; i++)
+		if ((msg->type == statemachine_list[i].type)
+		 && ((1 << call->state) & statemachine_list[i].states))
+			break;
+	if (i == STATEMACHINE_LEN) {
+		PDEBUG(DCC, DEBUG_INFO, "Message %s unhandled at state %s (callref %d)\n",
+			osmo_cc_msg_name(msg->type), state_names[call->state], call->callref);
+		osmo_cc_free_msg(msg);
+		return;
+	}
+
+	PDEBUG(DCC, DEBUG_INFO, "Handle message %s at state %s (callref %d)\n",
+		osmo_cc_msg_name(msg->type), state_names[call->state], call->callref);
+	statemachine_list[i].action(call, msg);
+}
+
+static int handle_call(osmo_cc_call_t *call)
+{
+	/* may handle only one message, since call may be destroyed when handling */
+	if (call->sock_queue) {
+		osmo_cc_msg_t *msg = osmo_cc_msg_list_dequeue(&call->sock_queue, NULL);
+		handle_msg(call, msg);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int osmo_cc_handle_endpoint(osmo_cc_endpoint_t *ep)
+{
+	int work = 0;
+	uint32_t callref;
+	osmo_cc_call_t *call;
+
+	/* may handle only one message, since call may be destroyed when handling */
+	if (ep->ll_queue) {
+		osmo_cc_msg_t *msg = osmo_cc_msg_list_dequeue(&ep->ll_queue, &callref);
+		ep->ll_msg_cb(ep, callref, msg);
+		work |= 1;
+	}
+
+	/* handle only one call, because it might have been removed */
+	for (call = ep->call_list; call; call = call->next) {
+		work |= handle_call(call);
+		if (work)
+			break;
+	}
+
+	return work;
+}
+
+/* main handler
+ * note that it must be called in a loop (with ohter handlers) until no work was done
+ */ 
+int osmo_cc_handle(void)
+{
+	int work = 0;
+	osmo_cc_endpoint_t *ep;
+
+	for (ep = osmo_cc_endpoint_list; ep; ep = ep->next) {
+		work |= osmo_cc_handle_endpoint(ep);
+		work |= osmo_cc_handle_socket(&ep->os);
+	}
+
+	return work;
+}
+
+osmo_cc_call_t *osmo_cc_call_by_callref(osmo_cc_endpoint_t *ep, uint32_t callref)
+{
+	osmo_cc_call_t *call;
+
+	if (!callref)
+		return NULL;
+
+	for (call = ep->call_list; call; call = call->next) {
+		if (call->callref == callref) {
+			return call;
+		}
+	}
+
+	return NULL;
+}
+
+
+void osmo_cc_ll_msg(osmo_cc_endpoint_t *ep, uint32_t callref, osmo_cc_msg_t *msg)
+{
+	osmo_cc_call_t *call;
+
+	if (!(msg->type & 1)) {
+		PDEBUG(DCC, DEBUG_ERROR, "Received message from lower layer that is not an _IND nor _CNF, please fix!\n");
+		osmo_cc_free_msg(msg);
+		return;
+	}
+
+	call = osmo_cc_call_by_callref(ep, callref);
+	if (call) {
+		/* complete cause */
+		osmo_cc_convert_cause_msg(msg);
+		handle_msg(call, msg);
+		return;
+	}
+
+	/* if no ref exists */
+}
+
+/* message from upper layer (socket) */
+void osmo_cc_ul_msg(void *priv, uint32_t callref, osmo_cc_msg_t *msg)
+{
+	osmo_cc_endpoint_t *ep = priv;
+	osmo_cc_call_t *call;
+
+	if ((msg->type & 1)) {
+		PDEBUG(DCC, DEBUG_ERROR, "Received message from socket that is not an _REQ nor _RSP, please fix!\n");
+		osmo_cc_free_msg(msg);
+		return;
+	}
+
+	call = osmo_cc_call_by_callref(ep, callref);
+	if (call) {
+		/* if we are not in INIT-IN state, we change a CC-REJ-REQ into CC-REL_REQ.
+		 * this happens, if the socket fails.
+		 */
+		if (call->state != OSMO_CC_STATE_INIT_IN
+		 && msg->type == OSMO_CC_MSG_REJ_REQ)
+			msg->type = OSMO_CC_MSG_REL_REQ;
+
+		osmo_cc_msg_list_enqueue(&call->sock_queue, msg, call->callref);
+		return;
+	}
+
+	/* if no ref exists */
+
+	/* reject and release are ignored */
+	if (msg->type == OSMO_CC_MSG_REJ_REQ
+	 || msg->type == OSMO_CC_MSG_REL_REQ) {
+		osmo_cc_free_msg(msg);
+		return;
+	}
+
+	/* reject if not a setup/attach or release message */
+	if (msg->type != OSMO_CC_MSG_SETUP_REQ
+	 && msg->type != OSMO_CC_MSG_ATTACH_REQ) {
+		sock_reject_msg(&ep->os, callref, ep->serving_location, 0, OSMO_CC_ISDN_CAUSE_INVAL_CALLREF, 0);
+		osmo_cc_free_msg(msg);
+		return;
+	}
+
+	/* create call instance with one socket reference */
+	call = call_new(ep, callref);
+
+	osmo_cc_msg_list_enqueue(&call->sock_queue, msg, call->callref);
+}
+
+static void osmo_cc_help_address(void)
+{
+	printf("Address options:\n\n");
+
+	printf("local <IPv4 address>:<port>\n");
+	printf("local [<IPv6 address>]:<port>\n");
+	printf("remote <IPv4 address>:<port>\n");
+	printf("remote [<IPv6 address>]:<port>\n\n");
+
+	printf("These options can be used to define local and remote IP and port for the socket\n");
+	printf("interface. Note that IPv6 adresses must be enclosed by '[' and ']'.\n\n");
+
+	printf("If no local address was given, the IPv4 loopback IP and port %d is used. If\n", OSMO_CC_DEFAULT_PORT);
+	printf("this port is already in use, the first free higher port is used.\n\n");
+
+	printf("If no remote address is given, the local IP is used. If the local port is %d,\n", OSMO_CC_DEFAULT_PORT);
+	printf("the remote port will be %d. If not, the remote port will be %d. This way it is\n", OSMO_CC_DEFAULT_PORT + 1, OSMO_CC_DEFAULT_PORT);
+	printf("possible to link two interfaces without any IP configuration required.\n\n");
+}
+
+static int osmo_cc_set_address(osmo_cc_endpoint_t *ep, const char *text)
+{
+	const char **address_p, **host_p;
+	uint16_t *port_p;
+	int rc;
+
+	if (!strncasecmp(text, "local", 5)) {
+		text += 5;
+		/* remove spaces after keyword */
+		while (*text) {
+			if (*text > 32)
+				break;
+			text++;
+		}
+		address_p = &ep->local_address;
+		host_p = &ep->local_host;
+		port_p = &ep->local_port;
+	} else if (!strncasecmp(text, "remote", 6)) {
+		text += 6;
+		/* remove spaces after keyword */
+		while (*text) {
+			if (*text > 32)
+				break;
+			text++;
+		}
+		if (!strcasecmp(text, "auto")) {
+			PDEBUG(DCC, DEBUG_DEBUG, "setting automatic remote peer selection\n");
+			ep->remote_auto = 1;
+			return 0;
+		}
+		ep->remote_auto = 0;
+		address_p = &ep->remote_address;
+		host_p = &ep->remote_host;
+		port_p = &ep->remote_port;
+	} else {
+		PDEBUG(DCC, DEBUG_ERROR, "Invalid local or remote address definition '%s'\n", text);
+		return -EINVAL;
+	}
+
+	if (*address_p) {
+		free((char *)*address_p);
+		*address_p = NULL;
+	}
+	if (*host_p) {
+		free((char *)*host_p);
+		*host_p = NULL;
+	}
+	rc = split_address(text, host_p, port_p);
+	if (rc < 0) {
+		/* unset, so that this is not treated with free() */
+		*host_p = NULL;
+		return rc;
+	}
+	*address_p = strdup(text);
+	*host_p = strdup(*host_p);
+
+	return 0;
+}
+
+static void osmo_cc_help_rtp(void)
+{
+	printf("RTP options:\n\n");
+
+	printf("rtp-peer <IPv4 address>\n");
+	printf("rtp-peer <IPv6 address>\n");
+	printf("rtp-ports <first> <last>\n\n");
+
+	printf("These options can be used to alter the local IP and port range for RTP traffic.\n");
+	printf("By default the local IPv4 loopback address is used. To connect interfaces\n");
+	printf("between machines, local machine's IP must be given.\n\n");
+}
+
+static int osmo_cc_set_rtp(const char *text)
+{
+	int peer = 0, ports = 0;
+
+	if (!strncasecmp(text, "rtp-peer", 8)) {
+		text += 8;
+		peer = 1;
+	} else if (!strncasecmp(text, "rtp-ports", 9)) {
+		text += 9;
+		ports = 1;
+	} else {
+		PDEBUG(DCC, DEBUG_ERROR, "Invalid RTP definition '%s'\n", text);
+		return -EINVAL;
+	}
+
+	/* remove spaces after keyword */
+	while (*text) {
+		if (*text > 32)
+			break;
+		text++;
+	}
+
+	if (peer) {
+		enum osmo_cc_session_addrtype addrtype;
+		addrtype = osmo_cc_address_type(text);
+		if (addrtype == osmo_cc_session_addrtype_unknown) {
+			PDEBUG(DCC, DEBUG_ERROR, "Given RTP address '%s' is invalid.\n", text);
+			return -EINVAL;
+		}
+		osmo_cc_set_local_peer(osmo_cc_session_nettype_inet, addrtype, text);
+		return 0;
+	}
+
+	if (ports) {
+		int from = 0, to = 0;
+
+		/* from port */
+		while (*text > ' ') {
+			if (*text < '0' || *text > '9') {
+				PDEBUG(DCC, DEBUG_ERROR, "Given 'from' port in '%s' is invalid.\n", text);
+				return -EINVAL;
+			}
+			from = from * 10 + *text - '0';
+		}
+
+		/* remove spaces after keyword */
+		while (*text) {
+			if (*text > 32)
+				break;
+			text++;
+		}
+
+		/* to port */
+		while (*text > ' ') {
+			if (*text < '0' || *text > '9') {
+				PDEBUG(DCC, DEBUG_ERROR, "Given 'to' port in '%s' is invalid.\n", text);
+				return -EINVAL;
+			}
+			from = from * 10 + *text - '0';
+		}
+
+		osmo_cc_set_rtp_ports(from, to);
+		return 0;
+	}
+
+	return -EINVAL;
+}
+
+void osmo_cc_help(void)
+{
+	osmo_cc_help_screen();
+	osmo_cc_help_address();
+	osmo_cc_help_rtp();
+}
+
+/* create a new endpoint instance */
+int osmo_cc_new(osmo_cc_endpoint_t *ep, const char *version, const char *name, uint8_t serving_location, void (*ll_msg_cb)(osmo_cc_endpoint_t *ep, uint32_t callref, osmo_cc_msg_t *msg), void (*ul_msg_cb)(osmo_cc_call_t *call, osmo_cc_msg_t *msg), void *priv, int argc, const char *argv[])
+{
+	osmo_cc_endpoint_t **epp;
+	int rc;
+	int i;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Creating new endpoint instance.\n");
+
+	if (!!strcmp(version, OSMO_CC_VERSION)) {
+		PDEBUG(DCC, DEBUG_ERROR, "Application was compiled for different Osmo-CC version.\n");
+		return OSMO_CC_RC_VERSION_MISMATCH;
+	}
+
+	memset(ep, 0, sizeof(*ep));
+
+	/* attach to list */
+	epp = &osmo_cc_endpoint_list;
+	while (*epp)
+		epp = &((*epp)->next);
+	*epp = ep;
+
+	if (name)
+		ep->local_name = strdup(name);
+	ep->ll_msg_cb = ll_msg_cb;
+	ep->ul_msg_cb = ul_msg_cb;
+	ep->serving_location = serving_location;
+	ep->priv = priv;
+
+	/* apply args */
+	for (i = 0; i < argc; i++) {
+		if (!strncasecmp(argv[i], "local", 5)) {
+			rc = osmo_cc_set_address(ep, argv[i]);
+			if (rc < 0) {
+				return rc;
+			}
+		} else
+		if (!strncasecmp(argv[i], "remote", 6)) {
+			rc = osmo_cc_set_address(ep, argv[i]);
+			if (rc < 0) {
+				return rc;
+			}
+		} else
+		if (!strncasecmp(argv[i], "rtp", 3)) {
+			rc = osmo_cc_set_rtp(argv[i]);
+			if (rc < 0) {
+				return rc;
+			}
+		} else
+		if (!strncasecmp(argv[i], "screen", 6)) {
+			rc = osmo_cc_add_screen(ep, argv[i]);
+			if (rc < 0) {
+				return rc;
+			}
+		} else {
+			PDEBUG(DCC, DEBUG_ERROR, "Unknown osmo-cc argument \"%s\"\n", argv[i]);
+			return -EINVAL;
+		}
+	}
+
+	/* open socket */
+	if (!ul_msg_cb) {
+		char address[256];
+		const char *host;
+		uint16_t port;
+		enum osmo_cc_session_addrtype addrtype;
+
+		host = ep->local_host;
+		port = ep->local_port;
+		if (!host) {
+			host = "127.0.0.1";
+			PDEBUG(DCC, DEBUG_DEBUG, "No local peer set, using default \"%s\"\n", host);
+		}
+		rc = osmo_cc_open_socket(&ep->os, host, port, ep, osmo_cc_ul_msg, serving_location);
+		if (rc < 0) {
+			return rc;
+		}
+		port = rc;
+		if (!ep->local_host) {
+			ep->local_host = strdup(host);
+			/* create address string */
+			addrtype = osmo_cc_address_type(host);
+			if (addrtype == osmo_cc_session_addrtype_ipv6)
+				sprintf(address, "[%s]:%d", host, port);
+			else
+				sprintf(address, "%s:%d", host, port);
+			ep->local_address = strdup(address);
+		}
+		ep->local_port = port;
+		/* auto configure */
+		if (ep->remote_auto) {
+			free((char *)ep->remote_host);
+			ep->remote_host = strdup(ep->local_host);
+			PDEBUG(DCC, DEBUG_DEBUG, "Remote peer set to auto, using local peer's host \"%s\" for remote peer.\n", ep->remote_host);
+			if (rc == OSMO_CC_DEFAULT_PORT)
+				ep->remote_port = OSMO_CC_DEFAULT_PORT + 1;
+			else
+				ep->remote_port = OSMO_CC_DEFAULT_PORT;
+			PDEBUG(DCC, DEBUG_DEBUG, " -> Using remote port %d.\n", ep->remote_port);
+			/* create address string */
+			free((char *)ep->remote_address);
+			addrtype = osmo_cc_address_type(ep->remote_host);
+			if (addrtype == osmo_cc_session_addrtype_ipv6)
+				sprintf(address, "[%s]:%d", ep->remote_host, ep->remote_port);
+			else
+				sprintf(address, "%s:%d", ep->remote_host, ep->remote_port);
+			ep->remote_address = strdup(address);
+		}
+		/* attach to remote host */
+		timer_init(&ep->attach_timer, send_attach_ind, ep);
+		if (ep->remote_host) {
+			send_attach_ind(&ep->attach_timer);
+		}
+	}
+
+	return 0;
+}
+
+/* destroy an endpoint instance */
+void osmo_cc_delete(osmo_cc_endpoint_t *ep)
+{
+	osmo_cc_endpoint_t **epp;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Destroying endpoint instance.\n");
+
+	/* detach from list >*/
+	epp = &osmo_cc_endpoint_list;
+	while (*epp && *epp != ep)
+		epp = &((*epp)->next);
+	if (*epp)
+		*epp = ep->next;
+
+	/* remove timer */
+	timer_exit(&ep->attach_timer);
+
+	/* flush screen lists */
+	osmo_cc_flush_screen(ep->screen_calling_in);
+	osmo_cc_flush_screen(ep->screen_called_in);
+	osmo_cc_flush_screen(ep->screen_calling_out);
+	osmo_cc_flush_screen(ep->screen_called_out);
+
+	/* free local and remote peer */
+	free((char *)ep->local_name);
+	free((char *)ep->local_address);
+	free((char *)ep->local_host);
+	free((char *)ep->remote_address);
+	free((char *)ep->remote_host);
+
+	/* destroying all child callesses (calls) */
+	while(ep->call_list)
+		call_delete(ep->call_list);
+
+	/* flush message queue */
+	while(ep->ll_queue) {
+		osmo_cc_msg_t *msg = osmo_cc_msg_list_dequeue(&ep->ll_queue, NULL);
+		osmo_cc_free_msg(msg);
+	}
+
+	/* remove socket */
+	osmo_cc_close_socket(&ep->os);
+
+	memset(ep, 0, sizeof(*ep));
+}
+
+/* create new call instance */
+osmo_cc_call_t *osmo_cc_call_new(osmo_cc_endpoint_t *ep)
+{
+	return call_new(ep, osmo_cc_new_callref());
+}
+
+/* destroy call instance */
+void osmo_cc_call_delete(osmo_cc_call_t *call)
+{
+	call_delete(call);
+}
+
+/* check valid IP and return address type (protocol) */
+enum osmo_cc_session_addrtype osmo_cc_address_type(const char *address)
+{
+	struct sockaddr_storage sa;
+	int rc;
+
+	rc = inet_pton(AF_INET, address, &sa);
+	if (rc > 0)
+		return osmo_cc_session_addrtype_ipv4;
+	rc = inet_pton(AF_INET6, address, &sa);
+	if (rc > 0)
+		return osmo_cc_session_addrtype_ipv6;
+
+	return osmo_cc_session_addrtype_unknown;
+}
+
+/* get host from address */
+const char *osmo_cc_host_of_address(const char *address)
+{
+	static char host[256];
+	char *p;
+
+	if (strlen(address) >= sizeof(host)) {
+		PDEBUG(DCC, DEBUG_ERROR, "String way too long!\n");
+		return NULL;
+	}
+
+	if (address[0] == '[' && (p = strchr(address, ']'))) {
+		memcpy(host, address + 1, p - address - 1);
+		host[p - address - 1] = '\0';
+		return host;
+	}
+
+	strcpy(host, address);
+	if ((p = strchr(host, ':')))
+		*p = '\0';
+
+	return host;
+}
+
+/* get port from address */
+const char *osmo_cc_port_of_address(const char *address)
+{
+	const char *p;
+	int i;
+
+	if (address[0] == '[' && (p = strchr(address, ']')))
+		address = p + 1;
+	
+	if (!(p = strchr(address, ':')))
+		return NULL;
+	p++;
+
+	/* check for zero */
+	if (p[0] == '0')
+		return NULL;
+
+	/* check for digits */
+	for (i = 0; i < (int)strlen(p); i++) {
+		if (p[i] < '0' || p[i] > '9')
+			return NULL;
+	}
+
+	/* check for magnitude */
+	if (atoi(p) > 65535)
+		return NULL;
+
+	return p;
+}
+
diff --git a/src/libosmocc/endpoint.h b/src/libosmocc/endpoint.h
new file mode 100644
index 0000000..7145726
--- /dev/null
+++ b/src/libosmocc/endpoint.h
@@ -0,0 +1,128 @@
+#ifndef OSMO_CC_ENDPOINT_H
+#define OSMO_CC_ENDPOINT_H
+
+#include "message.h"
+#include "socket.h"
+#include "cause.h"
+
+/* special osmo-cc error codes */
+#define OSMO_CC_RC_SEE_ERRNO			-1
+#define OSMO_CC_RC_VERSION_MISMATCH		1
+
+#define OSMO_CC_ATTACH_TIMER			2
+
+/* call control state */
+enum osmo_cc_state {
+	OSMO_CC_STATE_IDLE = 0,
+	/* call states */
+	OSMO_CC_STATE_INIT_OUT,			/* outgoing CC-SETUP-REQ sent */
+	OSMO_CC_STATE_INIT_IN,			/* incoming CC-SETUP-IND received */
+	OSMO_CC_STATE_OVERLAP_OUT,		/* received CC-SETUP-ACK-IND on outgoing call */
+	OSMO_CC_STATE_OVERLAP_IN,		/* sent CC-SETUP-ACK-REQ on incoming call */
+	OSMO_CC_STATE_PROCEEDING_OUT,		/* received CC-PROC-IND on outgoing call */
+	OSMO_CC_STATE_PROCEEDING_IN,		/* sent CC-PROC-REQ on incoming call */
+	OSMO_CC_STATE_ALERTING_OUT,		/* received CC-ALERT-IND on outgoing call */
+	OSMO_CC_STATE_ALERTING_IN,		/* sent CC-ALERT-REQ on incoming call */
+	OSMO_CC_STATE_CONNECTING_OUT,		/* received CC-SETUP-CNF on outgoing call */
+	OSMO_CC_STATE_CONNECTING_IN,		/* sent CC-SETUP-RSP on incoming call */
+	OSMO_CC_STATE_ACTIVE,			/* received or sent CC-SETUP-COMPL-* */
+	OSMO_CC_STATE_DISCONNECTING_OUT,	/* sent CC-DISC-REQ */
+	OSMO_CC_STATE_DISCONNECTING_IN,		/* received CC-DISC-IND */
+	OSMO_CC_STATE_DISC_COLLISION,		/* received CC-DISC-IND after sending CC-DISC_REQ */
+	OSMO_CC_STATE_RELEASING_OUT,		/* sent CC-REL-REQ */
+	/* attachment states */
+	OSMO_CC_STATE_ATTACH_SENT,		/* outgoing CC-ATT-REQ sent to socket */
+	OSMO_CC_STATE_ATTACH_OUT,		/* received CC-ATT-RSP on outgoing socket */
+	OSMO_CC_STATE_ATTACH_WAIT,		/* wait for outgoing attachment after failure */
+	OSMO_CC_STATE_ATTACH_IN,		/* incoming CC-ATT-REQ received from socket*/
+};
+
+/* sample type */
+typedef int16_t osmo_cc_sample_t;
+
+#define OSMO_CC_SAMPLE_MILLIWATT 23170 /* peak sine at -3 dB of full sample range */
+#define OSMO_CC_SAMPLE_SPEECH 3672 /* peak speech at -16 dB of milliwatt */
+#define OSMO_CC_SAMPLE_MIN -32768 /* lowest level */
+#define OSMO_CC_SAMPLE_MAX 32767 /* highest level */
+
+struct osmo_cc_call;
+
+typedef struct osmo_cc_screen_list {
+	struct osmo_cc_screen_list *next;
+	int			has_from_type;
+	uint8_t			from_type;
+	int			has_from_present;
+	uint8_t			from_present;
+	char			from[128];
+	int			has_to_type;
+	uint8_t			to_type;
+	int			has_to_present;
+	uint8_t			to_present;
+	char			to[128];
+} osmo_cc_screen_list_t;
+
+/* endpoint instance */
+typedef struct osmo_cc_endpoint {
+	struct osmo_cc_endpoint	*next;
+	void			*priv;
+	void			(*ll_msg_cb)(struct osmo_cc_endpoint *ep, uint32_t callref, osmo_cc_msg_t *msg);
+	void			(*ul_msg_cb)(struct osmo_cc_call *call, osmo_cc_msg_t *msg);
+	osmo_cc_msg_list_t	*ll_queue;	/* messages towards lower layer */
+	struct osmo_cc_call	*call_list;
+	const char		*local_name; /* name of interface */
+	const char		*local_address; /* host+port */
+	const char		*local_host;
+	uint16_t		local_port;
+	const char		*remote_address; /* host+port */
+	const char		*remote_host;
+	uint16_t		remote_port;
+	uint8_t			serving_location;
+	osmo_cc_socket_t	os;
+	osmo_cc_screen_list_t	*screen_calling_in;
+	osmo_cc_screen_list_t	*screen_called_in;
+	osmo_cc_screen_list_t	*screen_calling_out;
+	osmo_cc_screen_list_t	*screen_called_out;
+	int			remote_auto;	/* automatic remote address */
+	struct timer		attach_timer;	/* timer to retry attachment */
+} osmo_cc_endpoint_t;
+
+extern osmo_cc_endpoint_t *osmo_cc_endpoint_list;
+
+/* call process */
+typedef struct osmo_cc_call {
+	struct osmo_cc_call	*next;
+	osmo_cc_endpoint_t	*ep;
+	enum osmo_cc_state	state;
+	int			lower_layer_released;	/* when lower layer sent release, while upper layer gets a disconnect */
+	int			upper_layer_released;	/* when upper layer sent release, while lower layer gets a disconnect */
+	uint32_t		callref;
+	osmo_cc_msg_list_t	*sock_queue;	/* messages from socket */
+	const char		*attached_host;	/* host and port from remote peer that attached to us */
+	uint16_t		attached_port;
+	const char		*attached_name;	/* interface name from remote peer that attached to us */
+} osmo_cc_call_t;
+
+/* returns 0 if ok
+ * returns <0 for error as indicated
+ * returns >=1 to indicate osmo-cc error code
+ */
+
+void osmo_cc_help(void);
+int osmo_cc_new(osmo_cc_endpoint_t *ep, const char *version, const char *name, uint8_t serving_location, void (*ll_msg_cb)(osmo_cc_endpoint_t *ep, uint32_t callref, osmo_cc_msg_t *msg), void (*ul_msg_cb)(osmo_cc_call_t *call, osmo_cc_msg_t *msg), void *priv, int argc, const char *argv[]);
+void osmo_cc_delete(struct osmo_cc_endpoint *ep);
+int osmo_cc_handle(void);
+osmo_cc_call_t *osmo_cc_call_by_callref(osmo_cc_endpoint_t *ep, uint32_t callref);
+void osmo_cc_ll_msg(osmo_cc_endpoint_t *ep, uint32_t callref, osmo_cc_msg_t *msg);
+void osmo_cc_ul_msg(void *priv, uint32_t callref, osmo_cc_msg_t *msg);
+osmo_cc_call_t *osmo_cc_call_new(osmo_cc_endpoint_t *ep);
+void osmo_cc_call_delete(struct osmo_cc_call *call);
+enum osmo_cc_session_addrtype osmo_cc_address_type(const char *address);
+const char *osmo_cc_host_of_address(const char *address);
+const char *osmo_cc_port_of_address(const char *address);
+
+#include "session.h"
+#include "rtp.h"
+#include "sdp.h"
+#include "screen.h"
+
+#endif /* OSMO_CC_ENDPOINT_H */
diff --git a/src/libosmocc/helper.c b/src/libosmocc/helper.c
new file mode 100644
index 0000000..cde8b27
--- /dev/null
+++ b/src/libosmocc/helper.c
@@ -0,0 +1,171 @@
+/* Osmo-CC: helpers to simplify Osmo-CC usage
+ *
+ * (C) 2016 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <sys/time.h>
+#include <inttypes.h>
+#include "../libtimer/timer.h"
+#include "../libdebug/debug.h"
+#include "endpoint.h"
+#include "helper.h"
+
+osmo_cc_session_t *osmo_cc_helper_audio_offer(void *priv, struct osmo_cc_helper_audio_codecs *codecs, void (*receiver)(struct osmo_cc_session_codec *codec, uint16_t sequence_number, uint32_t timestamp, uint8_t *data, int len), osmo_cc_msg_t *msg, int debug)
+{
+	osmo_cc_session_t *session;
+	osmo_cc_session_media_t *media;
+	const char *sdp;
+	int i;
+
+	session = osmo_cc_new_session(priv, NULL, NULL, NULL, 0, 0, NULL, NULL, debug);
+	if (!session)
+		return NULL;
+
+	media = osmo_cc_add_media(session, 0, 0, NULL, osmo_cc_session_media_type_audio, 0, osmo_cc_session_media_proto_rtp, 1, 1, receiver, debug);
+	osmo_cc_rtp_open(media);
+
+	for (i = 0; codecs[i].payload_name; i++)
+		osmo_cc_add_codec(media, codecs[i].payload_name, codecs[i].payload_rate, codecs[i].payload_channels, codecs[i].encoder, codecs[i].decoder, debug);
+
+	sdp = osmo_cc_session_send_offer(session);
+	osmo_cc_add_ie_sdp(msg, sdp);
+
+	return session;
+}
+
+const char *osmo_cc_helper_audio_accept(void *priv, struct osmo_cc_helper_audio_codecs *codecs, void (*receiver)(struct osmo_cc_session_codec *codec, uint16_t sequence_number, uint32_t timestamp, uint8_t *data, int len), osmo_cc_msg_t *msg, osmo_cc_session_t **session_p, osmo_cc_session_codec_t **codec_p, int force_our_codec)
+{
+	char offer_sdp[65536];
+	const char *accept_sdp;
+	osmo_cc_session_media_t *media, *selected_media = NULL;
+	osmo_cc_session_codec_t *codec, *selected_codec = NULL;
+	int rc;
+	int i, selected_i;
+
+	if (*session_p) {
+		PDEBUG(DCC, DEBUG_ERROR, "Session already set, please fix!\n");
+		abort();
+	}
+	if (*codec_p) {
+		PDEBUG(DCC, DEBUG_ERROR, "Codec already set, please fix!\n");
+		abort();
+	}
+
+	/* SDP IE */
+	rc = osmo_cc_get_ie_sdp(msg, 0, offer_sdp, sizeof(offer_sdp));
+	if (rc < 0) {
+		PDEBUG(DCC, DEBUG_ERROR, "There is no SDP included in setup request.\n");
+		return NULL;
+	}
+
+	*session_p = osmo_cc_session_receive_offer(priv, offer_sdp);
+	if (!*session_p) {
+		PDEBUG(DCC, DEBUG_ERROR, "Failed to parse SDP.\n");
+		return NULL;
+	}
+
+	selected_i = -1;
+	osmo_cc_session_for_each_media((*session_p)->media_list, media) {
+		/* only audio */
+		if (media->description.type != osmo_cc_session_media_type_audio)
+			continue;
+		osmo_cc_session_for_each_codec(media->codec_list, codec) {
+			for (i = 0; codecs[i].payload_name; i++) {
+				if (osmo_cc_session_if_codec(codec, codecs[i].payload_name, codecs[i].payload_rate, codecs[i].payload_channels)) {
+					/* select the first matchting codec or the one we prefer */
+					if (selected_i < 0 || i < selected_i) {
+						selected_codec = codec;
+						selected_media = media;
+						selected_i = i;
+					}
+					/* if we don't force our preferred codec, use the preferred one from the remote */
+					if (!force_our_codec)
+						break;
+				}
+			}
+		}
+	}
+	if (!selected_codec) {
+		PDEBUG(DCC, DEBUG_ERROR, "No codec found in setup message that we support.\n");
+		osmo_cc_free_session(*session_p);
+		return NULL;
+	}
+	osmo_cc_session_accept_codec(selected_codec, codecs[selected_i].encoder, codecs[selected_i].decoder);
+	osmo_cc_session_accept_media(selected_media, 0, 0, NULL, 1, 1, receiver);
+	osmo_cc_rtp_open(selected_media);
+	osmo_cc_rtp_connect(selected_media);
+	*codec_p = selected_codec;
+
+	accept_sdp = osmo_cc_session_send_answer(*session_p);
+	if (!accept_sdp) {
+		osmo_cc_free_session(*session_p);
+		return NULL;
+	}
+
+	return accept_sdp;
+}
+
+int osmo_cc_helper_audio_negotiate(osmo_cc_msg_t *msg, osmo_cc_session_t **session_p, osmo_cc_session_codec_t **codec_p)
+{
+	char sdp[65536];
+	osmo_cc_session_media_t *media;
+	int rc;
+
+	if (!(*session_p)) {
+		PDEBUG(DCC, DEBUG_ERROR, "Session not set, please fix!\n");
+		abort();
+	}
+
+	/* once done, just ignore further messages that reply to setup */
+	if (*codec_p)
+		return 0;
+
+	/* SDP IE */
+	rc = osmo_cc_get_ie_sdp(msg, 0, sdp, sizeof(sdp));
+	if (rc < 0)
+		return 0; // no reply in this message
+
+	rc = osmo_cc_session_receive_answer(*session_p, sdp);
+	if (rc < 0)
+		return rc;
+
+	osmo_cc_session_for_each_media((*session_p)->media_list, media) {
+		/* only audio */
+		if (media->description.type != osmo_cc_session_media_type_audio)
+			continue;
+		/* select first codec, if one was accpeted */
+		if (media->codec_list)
+			*codec_p = media->codec_list;
+		if (*codec_p) {
+			osmo_cc_rtp_connect(media);
+			/* no more media streams */
+			break;
+		}
+	}
+	if (!(*codec_p)) {
+		PDEBUG(DCC, DEBUG_ERROR, "No codec found in setup reply message that we support.\n");
+		return -EIO;
+	}
+
+	return 0;
+}
+
diff --git a/src/libosmocc/helper.h b/src/libosmocc/helper.h
new file mode 100644
index 0000000..e3acf0e
--- /dev/null
+++ b/src/libosmocc/helper.h
@@ -0,0 +1,13 @@
+
+struct osmo_cc_helper_audio_codecs {
+	const char *payload_name;
+	uint32_t payload_rate;
+	int payload_channels;
+	void (*encoder)(uint8_t *src_data, int src_len, uint8_t **dst_data, int *dst_len);
+	void (*decoder)(uint8_t *src_data, int src_len, uint8_t **dst_data, int *dst_len);
+};
+
+osmo_cc_session_t *osmo_cc_helper_audio_offer(void *priv, struct osmo_cc_helper_audio_codecs *codecs, void (*receiver)(struct osmo_cc_session_codec *codec, uint16_t sequence_number, uint32_t timestamp, uint8_t *data, int len), osmo_cc_msg_t *msg, int debug);
+const char *osmo_cc_helper_audio_accept(void *priv, struct osmo_cc_helper_audio_codecs *codecs, void (*receiver)(struct osmo_cc_session_codec *codec, uint16_t sequence_number, uint32_t timestamp, uint8_t *data, int len), osmo_cc_msg_t *msg, osmo_cc_session_t **session_p, osmo_cc_session_codec_t **codec_p, int force_our_codec);
+int osmo_cc_helper_audio_negotiate(osmo_cc_msg_t *msg, osmo_cc_session_t **session_p, osmo_cc_session_codec_t **codec_p);
+
diff --git a/src/libosmocc/message.c b/src/libosmocc/message.c
new file mode 100644
index 0000000..126f684
--- /dev/null
+++ b/src/libosmocc/message.c
@@ -0,0 +1,879 @@
+/* Osmo-CC: Message handling
+ *
+ * (C) 2016 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <arpa/inet.h>
+#include "../libdebug/debug.h"
+#include "message.h"
+
+static uint32_t new_callref = 0;
+
+uint32_t osmo_cc_new_callref(void)
+{
+	return (++new_callref);
+}
+
+const char *osmo_cc_msg_name(uint8_t msg_type)
+{
+	switch (msg_type) {
+	case OSMO_CC_MSG_SETUP_REQ:
+		return "CC-SETUP-REQ";
+	case OSMO_CC_MSG_SETUP_IND:
+		return "CC-SETUP-IND";
+	case OSMO_CC_MSG_REJ_REQ:
+		return "CC-REJ-REQ";
+	case OSMO_CC_MSG_REJ_IND:
+		return "CC-REJ-IND";
+	case OSMO_CC_MSG_SETUP_ACK_REQ:
+		return "CC-SETUP-ACK-REQ";
+	case OSMO_CC_MSG_SETUP_ACK_IND:
+		return "CC-SETUP-ACK-IND";
+	case OSMO_CC_MSG_PROC_REQ:
+		return "CC-PROC-REQ";
+	case OSMO_CC_MSG_PROC_IND:
+		return "CC-PROC-IND";
+	case OSMO_CC_MSG_ALERT_REQ:
+		return "CC-ALERT-REQ";
+	case OSMO_CC_MSG_ALERT_IND:
+		return "CC-ALERT-IND";
+	case OSMO_CC_MSG_SETUP_RSP:
+		return "CC-SETUP-RSP";
+	case OSMO_CC_MSG_SETUP_CNF:
+		return "CC-SETUP-CNF";
+	case OSMO_CC_MSG_SETUP_COMP_REQ:
+		return "CC-SETUP-COMP-REQ";
+	case OSMO_CC_MSG_SETUP_COMP_IND:
+		return "CC-SETUP-COMP-IND";
+	case OSMO_CC_MSG_DISC_REQ:
+		return "CC-DISC-REQ";
+	case OSMO_CC_MSG_DISC_IND:
+		return "CC-DISC-IND";
+	case OSMO_CC_MSG_REL_REQ:
+		return "CC-REL-REQ";
+	case OSMO_CC_MSG_REL_CNF:
+		return "CC-REL-CNF";
+	case OSMO_CC_MSG_REL_IND:
+		return "CC-REL-IND";
+	case OSMO_CC_MSG_PROGRESS_REQ:
+		return "CC-PROGRESS-REQ";
+	case OSMO_CC_MSG_PROGRESS_IND:
+		return "CC-PROGRESS-IND";
+	case OSMO_CC_MSG_NOTIFY_REQ:
+		return "CC-NOTIFY-REQ";
+	case OSMO_CC_MSG_NOTIFY_IND:
+		return "CC-NOTIFY-IND";
+	case OSMO_CC_MSG_INFO_REQ:
+		return "CC-INFO-REQ";
+	case OSMO_CC_MSG_INFO_IND:
+		return "CC-INFO-IND";
+	case OSMO_CC_MSG_ATTACH_REQ:
+		return "CC-ATTACH-REQ";
+	case OSMO_CC_MSG_ATTACH_IND:
+		return "CC-ATTACH-IND";
+	case OSMO_CC_MSG_ATTACH_RSP:
+		return "CC-ATTACH-RSP";
+	case OSMO_CC_MSG_ATTACH_CNF:
+		return "CC-ATTACH-CNF";
+	default:
+		return "<unknown>";
+	}
+}
+
+/* create message with maximum size */
+osmo_cc_msg_t *osmo_cc_new_msg(uint8_t msg_type)
+{
+	osmo_cc_msg_t *msg;
+
+	/* allocate message */
+	msg = calloc(1, sizeof(*msg) + 65535);
+	if (!msg) {
+		PDEBUG(DCC, DEBUG_ERROR, "No memory\n");
+		abort();
+	}
+	/* set message type and zero lentgh */
+	msg->type = msg_type;
+	msg->length_networkorder = htons(0);
+
+	return msg;
+}
+
+/* clone message */
+osmo_cc_msg_t *osmo_cc_clone_msg(osmo_cc_msg_t *msg)
+{
+	osmo_cc_msg_t *new_msg;
+
+	new_msg = osmo_cc_new_msg(msg->type);
+	new_msg->length_networkorder = msg->length_networkorder;
+	memcpy(new_msg->data, msg->data, ntohs(msg->length_networkorder));
+
+	return new_msg;
+}
+
+osmo_cc_msg_t *osmo_cc_msg_list_dequeue(osmo_cc_msg_list_t **mlp, uint32_t *callref_p)
+{
+	osmo_cc_msg_list_t *ml;
+	osmo_cc_msg_t *msg;
+
+	ml = *mlp;
+	msg = ml->msg;
+	if (callref_p)
+		*callref_p = ml->callref;
+	*mlp = ml->next;
+	free(ml);
+
+	return msg;
+}
+
+osmo_cc_msg_list_t *osmo_cc_msg_list_enqueue(osmo_cc_msg_list_t **mlp, osmo_cc_msg_t *msg, uint32_t callref)
+{
+	osmo_cc_msg_list_t *ml;
+
+	ml = calloc(1, sizeof(*ml));
+	ml->msg = msg;
+	ml->callref = callref;
+	while (*mlp)
+		mlp = &((*mlp)->next);
+	*mlp = ml;
+
+	return ml;
+}
+
+/* destroy message */
+void osmo_cc_free_msg(osmo_cc_msg_t *msg)
+{
+	free(msg);
+}
+
+static void osmo_cc_debug_ie(osmo_cc_msg_t *msg, int level)
+{
+	uint16_t msg_len, len;
+	uint8_t *p;
+	osmo_cc_ie_t *ie;
+
+	msg_len = ntohs(msg->length_networkorder);
+	p = msg->data;
+
+	PDEBUG(DCC, level, "Debugging Message: type=0x%02x length=%d value=%s\n", msg->type, msg_len, debug_hex(p, msg_len));
+	while (msg_len) {
+		ie = (osmo_cc_ie_t *)p;
+		/* check for minimum IE length */
+		if (msg_len < sizeof(*ie)) {
+			PDEBUG(DCC, level, "****** Rest of message is too short for an IE: value=%s\n", debug_hex(p, msg_len));
+			return;
+		}
+		/* get actual IE length */
+		len = ntohs(ie->length_networkorder);
+		/* check if IE length does not exceed message */
+		if (msg_len < sizeof(*ie) + len) {
+			PDEBUG(DCC, level, "****** IE: type=0x%02x length=%d would exceed the rest length of message (%d bytes left)\n", ie->type, len, msg_len - (int)sizeof(*ie));
+			return;
+		}
+		PDEBUG(DCC, level, "IE: type=0x%02x length=%d value=%s\n", ie->type, len, debug_hex(ie->data, len));
+		p += sizeof(*ie) + len;
+		msg_len -= sizeof(*ie) + len;
+	}
+}
+
+/* search and return information element
+ * we give the IE type we are searching for
+ * we also give the repetition, to find IE that is repeated
+ * the result is stored in *ie_data
+ * the return length is the length that exceeds the given ie_len
+ * if there is an error, a value < 0 is returned
+ */
+int osmo_cc_get_ie_struct(osmo_cc_msg_t *msg, uint8_t ie_type, int ie_repeat, int ie_len, const osmo_cc_ie_t **ie_struct)
+{
+	uint16_t msg_len, len;
+	uint8_t *p;
+	osmo_cc_ie_t *ie;
+
+	msg_len = ntohs(msg->length_networkorder);
+	p = msg->data;
+
+	while (msg_len) {
+		ie = (osmo_cc_ie_t *)p;
+		/* check for minimum IE length */
+		if (msg_len < sizeof(*ie)) {
+			PDEBUG(DCC, DEBUG_ERROR, "MSG short read\n");
+			osmo_cc_debug_ie(msg, DEBUG_ERROR);
+			return -EINVAL;
+		}
+		/* get actual IE length */
+		len = ntohs(ie->length_networkorder);
+		/* check if IE length does not exceed message */
+		if (msg_len < sizeof(*ie) + len) {
+			PDEBUG(DCC, DEBUG_ERROR, "MSG short read\n");
+			osmo_cc_debug_ie(msg, DEBUG_ERROR);
+			return -EINVAL;
+		}
+		/* check if IE matches the one that is searched for */
+		if (ie->type != ie_type) {
+			p += sizeof(*ie) + len;
+			msg_len -= sizeof(*ie) + len;
+			continue;
+		}
+		/* check if IE repetition exists */
+		if (ie_repeat) {
+			--ie_repeat;
+			p += sizeof(*ie) + len;
+			msg_len -= sizeof(*ie) + len;
+			continue;
+		}
+		/* return IE and indicate how many bytes we have more than the given length*/
+		if (ntohs(ie->length_networkorder) < ie_len) {
+			PDEBUG(DCC, DEBUG_ERROR, "IE 0x%02d has length of %d, but we expect it to have at least %d!\n", ie_type, ntohs(ie->length_networkorder), ie_len);
+			return -EINVAL;
+		}
+		*ie_struct = ie;
+		return ntohs(ie->length_networkorder) - ie_len;
+	}
+
+	/* IE not found */
+	return -EINVAL;
+}
+
+/* as above, but return data of IE only */
+int osmo_cc_get_ie_data(osmo_cc_msg_t *msg, uint8_t ie_type, int ie_repeat, int ie_len, const void **ie_data)
+{
+	const osmo_cc_ie_t *ie;
+	int rc;
+
+	rc = osmo_cc_get_ie_struct(msg, ie_type, ie_repeat, ie_len, &ie);
+	if (rc >= 0)
+		*ie_data = ie->data;
+
+	return rc;
+}
+
+/* as above, but return 1 if IE exists */
+int osmo_cc_has_ie(osmo_cc_msg_t *msg, uint8_t ie_type, int ie_repeat)
+{
+	const osmo_cc_ie_t *ie;
+	int rc;
+
+	rc = osmo_cc_get_ie_struct(msg, ie_type, ie_repeat, 0, &ie);
+	if (rc >= 0)
+		return 1;
+
+	return 0;
+}
+
+/* remove IE from message */
+int osmo_cc_remove_ie(osmo_cc_msg_t *msg, uint8_t ie_type, int ie_repeat)
+{
+	const osmo_cc_ie_t *ie;
+	int rc;
+	int msg_len, before_ie, ie_size, after_ie;
+
+	rc = osmo_cc_get_ie_struct(msg, ie_type, ie_repeat, 0, &ie);
+	if (rc < 0)
+		return rc;
+
+	msg_len = ntohs(msg->length_networkorder);
+	before_ie = (void *)ie - (void *)msg->data;
+	ie_size = sizeof(*ie) + ntohs(ie->length_networkorder);
+	after_ie = msg_len - ie_size - before_ie;
+	if (after_ie)
+		memcpy(msg->data + before_ie, msg->data + before_ie + ie_size, after_ie);
+	msg->length_networkorder = htons(msg_len - ie_size);
+
+	return 0;
+}
+
+/* add information element
+ * the type is given by ie_type and length is given by ie_len
+ * the return value is a pointer to the data of the IE
+ */
+void *osmo_cc_add_ie(osmo_cc_msg_t *msg, uint8_t ie_type, int ie_len)
+{
+	uint16_t msg_len;
+	int new_msg_len;
+	uint8_t *p;
+	osmo_cc_ie_t *ie;
+
+	/* get pointer to first IE, if any */
+	p = msg->data;
+	/* expand messasge */
+	msg_len = ntohs(msg->length_networkorder);
+	new_msg_len = msg_len + sizeof(*ie) + ie_len;
+	if (new_msg_len > 65535) {
+		PDEBUG(DCC, DEBUG_ERROR, "MSG overflow\n");
+		return NULL;
+	}
+	msg->length_networkorder = htons(new_msg_len);
+	/* go to end of (unexpanded) message */
+	ie = (osmo_cc_ie_t *)(p + msg_len);
+	/* add ie */
+	ie->type = ie_type;
+	ie->length_networkorder = htons(ie_len);
+	memset(ie->data, 0, ie_len); /* just in case there is something, but it shouldn't */
+
+	return ie->data;
+}
+
+/* gets the information element's data that *iep points to and returns that ie.
+ * if *iep points to msg->data, the first IE's data is returned. (must be set before first call.)
+ * if *iep points to the end of the message, NULL is returned.
+ * if there is no next IE, *iep is set to point to the end of message.
+ */
+void *osmo_cc_msg_sep_ie(osmo_cc_msg_t *msg, void **iep, uint8_t *ie_type, uint16_t *ie_length)
+{
+	uint16_t msg_len;
+	osmo_cc_ie_t *ie;
+
+	/* in case that *iep points to start of message, make it point to first IE */
+	if (*iep == msg)
+		*iep = msg->data;
+	/* case IE */
+	ie = *iep;
+	/* check if it is NULL */
+	if (ie == NULL)
+		return NULL;
+	/* check if it points to the end of message or there is not at least an IE header */
+	msg_len = ntohs(msg->length_networkorder);
+	if ((int)((uint8_t *)ie - msg->data) > (int)(msg_len - sizeof(*ie)))
+		return NULL;
+	/* increment iep and return IE */
+	*ie_type = ie->type;
+	*ie_length = ntohs(ie->length_networkorder);
+	*iep = (uint8_t *)ie + sizeof(*ie) + *ie_length;
+	return ie->data;
+}
+
+/* copy given block to given string with given size */
+static void _ie2string(char *string, size_t string_size, const char *ie_string, int ie_size)
+{
+	int copy_size;
+
+	copy_size = string_size - 1;
+	if (ie_size < copy_size)
+		copy_size = ie_size;
+	memcpy(string, ie_string, copy_size);
+	string[copy_size] = '\0';
+}
+
+/* helper to encode called party number (dialing) */
+void osmo_cc_add_ie_called(osmo_cc_msg_t *msg, uint8_t type, uint8_t plan, const char *dialing)
+{
+	struct osmo_cc_ie_called *ie_called;
+
+	ie_called = osmo_cc_add_ie(msg, OSMO_CC_IE_CALLED, sizeof(*ie_called) + strlen(dialing));
+	ie_called->type = type;
+	ie_called->plan = plan;
+	memcpy(ie_called->digits, dialing, strlen(dialing));
+}
+
+/* helper to decode called party number (dialing) */
+int osmo_cc_get_ie_called(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *type, uint8_t *plan, char *dialing, size_t dialing_size)
+{
+	struct osmo_cc_ie_called *ie_called;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_CALLED, ie_repeat, sizeof(*ie_called), (const void **)&ie_called);
+	if (rc < 0)
+		return rc;
+	*type = ie_called->type;
+	*plan = ie_called->plan;
+	_ie2string(dialing, dialing_size, ie_called->digits, rc);
+	return rc;
+}
+
+/* helper to encode called party sub address (dialing) */
+void osmo_cc_add_ie_called_sub(osmo_cc_msg_t *msg, uint8_t type, const char *dialing)
+{
+	struct osmo_cc_ie_called_sub *ie_called_sub;
+
+	ie_called_sub = osmo_cc_add_ie(msg, OSMO_CC_IE_CALLED_SUB, sizeof(*ie_called_sub) + strlen(dialing));
+	ie_called_sub->type = type;
+	memcpy(ie_called_sub->digits, dialing, strlen(dialing));
+}
+
+/* helper to decode called party sub address (dialing) */
+int osmo_cc_get_ie_called_sub(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *type, char *dialing, size_t dialing_size)
+{
+	struct osmo_cc_ie_called_sub *ie_called_sub;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_CALLED_SUB, ie_repeat, sizeof(*ie_called_sub), (const void **)&ie_called_sub);
+	if (rc < 0)
+		return rc;
+	*type = ie_called_sub->type;
+	_ie2string(dialing, dialing_size, ie_called_sub->digits, rc);
+	return rc;
+}
+
+/* helper to encode called party name (dialing) */
+void osmo_cc_add_ie_called_name(osmo_cc_msg_t *msg, const char *name)
+{
+	struct osmo_cc_ie_called_name *ie_called_name;
+
+	ie_called_name = osmo_cc_add_ie(msg, OSMO_CC_IE_CALLED_NAME, sizeof(*ie_called_name) + strlen(name));
+	memcpy(ie_called_name->name, name, strlen(name));
+}
+
+/* helper to decode called party name (dialing) */
+int osmo_cc_get_ie_called_name(osmo_cc_msg_t *msg, int ie_repeat, char *name, size_t name_size)
+{
+	struct osmo_cc_ie_called_name *ie_called_name;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_CALLED_NAME, ie_repeat, sizeof(*ie_called_name), (const void **)&ie_called_name);
+	if (rc < 0)
+		return rc;
+	_ie2string(name, name_size, ie_called_name->name, rc);
+	return rc;
+}
+
+/* helper to encode called interface name */
+void osmo_cc_add_ie_called_interface(osmo_cc_msg_t *msg, const char *interface)
+{
+	struct osmo_cc_ie_called_interface *ie_interface;
+
+	ie_interface = osmo_cc_add_ie(msg, OSMO_CC_IE_CALLED_INTERFACE, sizeof(*ie_interface) + strlen(interface));
+	memcpy(ie_interface->name, interface, strlen(interface));
+}
+
+/* helper to decode called interface name */
+int osmo_cc_get_ie_called_interface(osmo_cc_msg_t *msg, int ie_repeat, char *interface, size_t interface_size)
+{
+	struct osmo_cc_ie_called_interface *ie_interface;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_CALLED_INTERFACE, ie_repeat, sizeof(*ie_interface), (const void **)&ie_interface);
+	if (rc < 0)
+		return rc;
+	_ie2string(interface, interface_size, ie_interface->name, rc);
+	return rc;
+}
+
+/* helper to encode complete IE */
+void osmo_cc_add_ie_complete(osmo_cc_msg_t *msg)
+{
+	osmo_cc_add_ie(msg, OSMO_CC_IE_COMPLETE, 0);
+}
+
+/* helper to decode complete IE */
+int osmo_cc_get_ie_complete(osmo_cc_msg_t *msg, int ie_repeat)
+{
+	int rc;
+	void *ie_complete;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_COMPLETE, ie_repeat, 0, (const void **)&ie_complete);
+	return rc;
+}
+
+/* helper to encode calling/connected party number (caller ID or connected ID) */
+void osmo_cc_add_ie_calling(osmo_cc_msg_t *msg, uint8_t type, uint8_t plan, uint8_t present, uint8_t screen, const char *callerid)
+{
+	struct osmo_cc_ie_calling *ie_calling;
+
+	ie_calling = osmo_cc_add_ie(msg, OSMO_CC_IE_CALLING, sizeof(*ie_calling) + strlen(callerid));
+	ie_calling->type = type;
+	ie_calling->plan = plan;
+	ie_calling->present = present;
+	ie_calling->screen = screen;
+	memcpy(ie_calling->digits, callerid, strlen(callerid));
+}
+
+/* helper to decode calling/connected party number (caller ID or connected ID) */
+int osmo_cc_get_ie_calling(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *type, uint8_t *plan, uint8_t *present, uint8_t *screen, char *callerid, size_t callerid_size)
+{
+	struct osmo_cc_ie_calling *ie_calling;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_CALLING, ie_repeat, sizeof(*ie_calling), (const void **)&ie_calling);
+	if (rc < 0)
+		return rc;
+	*type = ie_calling->type;
+	*plan = ie_calling->plan;
+	*present = ie_calling->present;
+	*screen = ie_calling->screen;
+	_ie2string(callerid, callerid_size, ie_calling->digits, rc);
+	return rc;
+}
+
+/* helper to encode calling/connected sub address (caller ID or connected ID) */
+void osmo_cc_add_ie_calling_sub(osmo_cc_msg_t *msg, uint8_t type, const char *callerid)
+{
+	struct osmo_cc_ie_calling_sub *ie_calling_sub;
+
+	ie_calling_sub = osmo_cc_add_ie(msg, OSMO_CC_IE_CALLING_SUB, sizeof(*ie_calling_sub) + strlen(callerid));
+	ie_calling_sub->type = type;
+	memcpy(ie_calling_sub->digits, callerid, strlen(callerid));
+}
+
+/* helper to decode calling/connected sub address (caller ID or connected ID) */
+int osmo_cc_get_ie_calling_sub(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *type, char *callerid, size_t callerid_size)
+{
+	struct osmo_cc_ie_calling_sub *ie_calling_sub;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_CALLING_SUB, ie_repeat, sizeof(*ie_calling_sub), (const void **)&ie_calling_sub);
+	if (rc < 0)
+		return rc;
+	*type = ie_calling_sub->type;
+	_ie2string(callerid, callerid_size, ie_calling_sub->digits, rc);
+	return rc;
+}
+
+/* helper to encode calling/connected name (caller ID or connected ID) */
+void osmo_cc_add_ie_calling_name(osmo_cc_msg_t *msg, const char *name)
+{
+	struct osmo_cc_ie_calling_name *ie_calling_name;
+
+	ie_calling_name = osmo_cc_add_ie(msg, OSMO_CC_IE_CALLING_NAME, sizeof(*ie_calling_name) + strlen(name));
+	memcpy(ie_calling_name->name, name, strlen(name));
+}
+
+/* helper to decode calling/connected name address (caller ID or connected ID) */
+int osmo_cc_get_ie_calling_name(osmo_cc_msg_t *msg, int ie_repeat, char *name, size_t name_size)
+{
+	struct osmo_cc_ie_calling_name *ie_calling_name;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_CALLING_NAME, ie_repeat, sizeof(*ie_calling_name), (const void **)&ie_calling_name);
+	if (rc < 0)
+		return rc;
+	_ie2string(name, name_size, ie_calling_name->name, rc);
+	return rc;
+}
+
+/* helper to encode calling interface name */
+void osmo_cc_add_ie_calling_interface(osmo_cc_msg_t *msg, const char *interface)
+{
+	struct osmo_cc_ie_calling_interface *ie_interface;
+
+	ie_interface = osmo_cc_add_ie(msg, OSMO_CC_IE_CALLING_INTERFACE, sizeof(*ie_interface) + strlen(interface));
+	memcpy(ie_interface->name, interface, strlen(interface));
+}
+
+/* helper to decode calling interface name */
+int osmo_cc_get_ie_calling_interface(osmo_cc_msg_t *msg, int ie_repeat, char *interface, size_t interface_size)
+{
+	struct osmo_cc_ie_calling_interface *ie_interface;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_CALLING_INTERFACE, ie_repeat, sizeof(*ie_interface), (const void **)&ie_interface);
+	if (rc < 0)
+		return rc;
+	_ie2string(interface, interface_size, ie_interface->name, rc);
+	return rc;
+}
+
+/* helper to encode network specific caller/connected ID */
+void osmo_cc_add_ie_calling_network(osmo_cc_msg_t *msg, uint8_t type, const char *networkid)
+{
+	struct osmo_cc_ie_network *ie_network;
+
+	ie_network = osmo_cc_add_ie(msg, OSMO_CC_IE_CALLING_NETWORK, sizeof(*ie_network) + strlen(networkid));
+	ie_network->type = type;
+	memcpy(ie_network->id, networkid, strlen(networkid));
+}
+
+/* helper to encode network specific caller/connected ID */
+int osmo_cc_get_ie_calling_network(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *type, char *networkid, size_t networkid_size)
+{
+	struct osmo_cc_ie_network *ie_network;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_CALLING_NETWORK, ie_repeat, sizeof(*ie_network), (const void **)&ie_network);
+	if (rc < 0)
+		return rc;
+	*type = ie_network->type;
+	_ie2string(networkid, networkid_size, ie_network->id, rc);
+	return rc;
+}
+
+/* helper to encode bearer capability */
+void osmo_cc_add_ie_bearer(osmo_cc_msg_t *msg, uint8_t coding, uint8_t capability, uint8_t mode)
+{
+	struct osmo_cc_ie_bearer *ie_bearer;
+
+	ie_bearer = osmo_cc_add_ie(msg, OSMO_CC_IE_BEARER, sizeof(*ie_bearer));
+	ie_bearer->coding = coding;
+	ie_bearer->capability = capability;
+	ie_bearer->mode = mode;
+}
+
+/* helper to decode bearer capability */
+int osmo_cc_get_ie_bearer(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *coding, uint8_t *capability, uint8_t *mode)
+{
+	struct osmo_cc_ie_bearer *ie_bearer;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_BEARER, ie_repeat, sizeof(*ie_bearer), (const void **)&ie_bearer);
+	if (rc < 0)
+		return rc;
+	*coding = ie_bearer->coding;
+	*capability = ie_bearer->capability;
+	*mode = ie_bearer->mode;
+	return rc;
+}
+
+/* helper to encode redirection and redirecting number */
+void osmo_cc_add_ie_redir(osmo_cc_msg_t *msg, uint8_t type, uint8_t plan, uint8_t present, uint8_t screen, uint8_t redir_reason, const char *callerid)
+{
+	struct osmo_cc_ie_redir *ie_redir;
+
+	ie_redir = osmo_cc_add_ie(msg, OSMO_CC_IE_REDIR, sizeof(*ie_redir) + strlen(callerid));
+	ie_redir->type = type;
+	ie_redir->plan = plan;
+	ie_redir->present = present;
+	ie_redir->screen = screen;
+	ie_redir->redir_reason = redir_reason;
+	memcpy(ie_redir->digits, callerid, strlen(callerid));
+}
+
+/* helper to decode redirection and redirecting number */
+int osmo_cc_get_ie_redir(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *type, uint8_t *plan, uint8_t *present, uint8_t *screen, uint8_t *reason, char *callerid, size_t callerid_size)
+{
+	struct osmo_cc_ie_redir *ie_redir;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_REDIR, ie_repeat, sizeof(*ie_redir), (const void **)&ie_redir);
+	if (rc < 0)
+		return rc;
+	*type = ie_redir->type;
+	*plan = ie_redir->plan;
+	*present = ie_redir->present;
+	*screen = ie_redir->screen;
+	*reason = ie_redir->redir_reason;
+	_ie2string(callerid, callerid_size, ie_redir->digits, rc);
+	return rc;
+}
+
+/* helper to encode DTMF tones */
+void osmo_cc_add_ie_dtmf(osmo_cc_msg_t *msg, uint8_t duration_ms, uint8_t pause_ms, uint8_t dtmf_mode, const char *digits)
+{
+	struct osmo_cc_ie_dtmf *ie_dtmf;
+
+	ie_dtmf = osmo_cc_add_ie(msg, OSMO_CC_IE_DTMF, sizeof(*ie_dtmf) + strlen(digits));
+	ie_dtmf->duration_ms = duration_ms;
+	ie_dtmf->pause_ms = pause_ms;
+	ie_dtmf->dtmf_mode = dtmf_mode;
+	memcpy(ie_dtmf->digits, digits, strlen(digits));
+}
+
+/* helper to decode DTMF tones */
+int osmo_cc_get_ie_dtmf(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *duration_ms, uint8_t *pause_ms, uint8_t *dtmf_mode, char *digits, size_t digits_size)
+{
+	struct osmo_cc_ie_dtmf *ie_dtmf;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_DTMF, ie_repeat, sizeof(*ie_dtmf), (const void **)&ie_dtmf);
+	if (rc < 0)
+		return rc;
+	*duration_ms = ie_dtmf->duration_ms;
+	*pause_ms = ie_dtmf->pause_ms;
+	*dtmf_mode = ie_dtmf->dtmf_mode;
+	_ie2string(digits, digits_size, ie_dtmf->digits, rc);
+	return rc;
+}
+
+/* helper to encode keypad press */
+void osmo_cc_add_ie_keypad(osmo_cc_msg_t *msg, const char *digits)
+{
+	struct osmo_cc_ie_keypad *ie_keypad;
+
+	ie_keypad = osmo_cc_add_ie(msg, OSMO_CC_IE_KEYPAD, sizeof(*ie_keypad) + strlen(digits));
+	memcpy(ie_keypad->digits, digits, strlen(digits));
+}
+
+/* helper to decode keypad press */
+int osmo_cc_get_ie_keypad(osmo_cc_msg_t *msg, int ie_repeat, char *digits, size_t digits_size)
+{
+	struct osmo_cc_ie_keypad *ie_keypad;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_KEYPAD, ie_repeat, sizeof(*ie_keypad), (const void **)&ie_keypad);
+	if (rc < 0)
+		return rc;
+	_ie2string(digits, digits_size, ie_keypad->digits, rc);
+	return rc;
+}
+
+/* helper to encode call progress information */
+void osmo_cc_add_ie_progress(osmo_cc_msg_t *msg, uint8_t coding, uint8_t location, uint8_t progress)
+{
+	struct osmo_cc_ie_progress *ie_progress;
+
+	ie_progress = osmo_cc_add_ie(msg, OSMO_CC_IE_PROGRESS, sizeof(*ie_progress));
+	ie_progress->coding = coding;
+	ie_progress->location = location;
+	ie_progress->progress = progress;
+}
+
+/* helper to decode call progress information */
+int osmo_cc_get_ie_progress(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *coding, uint8_t *location, uint8_t *progress)
+{
+	struct osmo_cc_ie_progress *ie_progress;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_PROGRESS, ie_repeat, sizeof(*ie_progress), (const void **)&ie_progress);
+	if (rc < 0)
+		return rc;
+	*coding = ie_progress->coding;
+	*location = ie_progress->location;
+	*progress = ie_progress->progress;
+	return rc;
+}
+
+/* helper to encode notification */
+void osmo_cc_add_ie_notify(osmo_cc_msg_t *msg, uint8_t notify)
+{
+	struct osmo_cc_ie_notify *ie_notify;
+
+	ie_notify = osmo_cc_add_ie(msg, OSMO_CC_IE_NOTIFY, sizeof(*ie_notify));
+	ie_notify->notify = notify;
+}
+
+/* helper to decode notification */
+int osmo_cc_get_ie_notify(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *notify)
+{
+	struct osmo_cc_ie_notify *ie_notify;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_NOTIFY, ie_repeat, sizeof(*ie_notify), (const void **)&ie_notify);
+	if (rc < 0)
+		return rc;
+	*notify = ie_notify->notify;
+	return rc;
+}
+
+/* helper to encode cause */
+void osmo_cc_add_ie_cause(osmo_cc_msg_t *msg, uint8_t location, uint8_t isdn_cause, uint16_t sip_cause, uint8_t socket_cause)
+{
+	struct osmo_cc_ie_cause *ie_cause;
+
+	ie_cause = osmo_cc_add_ie(msg, OSMO_CC_IE_CAUSE, sizeof(*ie_cause));
+	ie_cause->location = location;
+	ie_cause->isdn_cause = isdn_cause;
+	ie_cause->sip_cause_networkorder = htons(sip_cause);
+	ie_cause->socket_cause = socket_cause;
+}
+
+/* helper to deccode cause */
+int osmo_cc_get_ie_cause(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *location, uint8_t *isdn_cause, uint16_t *sip_cause, uint8_t *socket_cause)
+{
+	struct osmo_cc_ie_cause *ie_cause;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_CAUSE, ie_repeat, sizeof(*ie_cause), (const void **)&ie_cause);
+	if (rc < 0)
+		return rc;
+	*location = ie_cause->location;
+	*isdn_cause = ie_cause->isdn_cause;
+	*sip_cause = ntohs(ie_cause->sip_cause_networkorder);
+	*socket_cause = ie_cause->socket_cause;
+	return rc;
+}
+
+/* helper to encode DISPLAY information */
+void osmo_cc_add_ie_display(osmo_cc_msg_t *msg, const char *text)
+{
+	struct osmo_cc_ie_display *ie_display;
+
+	ie_display = osmo_cc_add_ie(msg, OSMO_CC_IE_DISPLAY, sizeof(*ie_display) + strlen(text));
+	memcpy(ie_display->text, text, strlen(text));
+}
+
+/* helper to decode DISPLAY information */
+int osmo_cc_get_ie_display(osmo_cc_msg_t *msg, int ie_repeat, char *text, size_t text_size)
+{
+	struct osmo_cc_ie_display *ie_display;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_DISPLAY, ie_repeat, sizeof(*ie_display), (const void **)&ie_display);
+	if (rc < 0)
+		return rc;
+	_ie2string(text, text_size, ie_display->text, rc);
+	return rc;
+}
+
+/* helper to encode SDP */
+void osmo_cc_add_ie_sdp(osmo_cc_msg_t *msg, const char *sdp)
+{
+	struct osmo_cc_ie_sdp *ie_sdp;
+
+	ie_sdp = osmo_cc_add_ie(msg, OSMO_CC_IE_SDP, sizeof(*ie_sdp) + strlen(sdp));
+	memcpy(ie_sdp->sdp, sdp, strlen(sdp));
+}
+
+/* helper to decode SDP */
+int osmo_cc_get_ie_sdp(osmo_cc_msg_t *msg, int ie_repeat, char *sdp, size_t sdp_size)
+{
+	struct osmo_cc_ie_sdp *ie_sdp;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_SDP, ie_repeat, sizeof(*ie_sdp), (const void **)&ie_sdp);
+	if (rc < 0)
+		return rc;
+	_ie2string(sdp, sdp_size, ie_sdp->sdp, rc);
+	return rc;
+}
+
+/* helper to encode socket addresss */
+void osmo_cc_add_ie_socket_address(osmo_cc_msg_t *msg, const char *address)
+{
+	struct osmo_cc_ie_socket_address *ie_socket_address;
+
+	ie_socket_address = osmo_cc_add_ie(msg, OSMO_CC_IE_SOCKET_ADDRESS, sizeof(*ie_socket_address) + strlen(address));
+	memcpy(ie_socket_address->address, address, strlen(address));
+}
+
+/* helper to decode socket addresss */
+int osmo_cc_get_ie_socket_address(osmo_cc_msg_t *msg, int ie_repeat, char *address, size_t address_size)
+{
+	struct osmo_cc_ie_socket_address *ie_socket_address;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_SOCKET_ADDRESS, ie_repeat, sizeof(*ie_socket_address), (const void **)&ie_socket_address);
+	if (rc < 0)
+		return rc;
+	_ie2string(address, address_size, ie_socket_address->address, rc);
+	return rc;
+}
+
+/* helper to encode private information element */
+void osmo_cc_add_ie_private(osmo_cc_msg_t *msg, uint32_t unique, const uint8_t *data, size_t data_size)
+{
+	struct osmo_cc_ie_private *ie_private;
+
+	ie_private = osmo_cc_add_ie(msg, OSMO_CC_IE_PRIVATE, sizeof(*ie_private) + data_size);
+	ie_private->unique_networkorder = htonl(unique);
+	memcpy(ie_private->data, data, data_size);
+}
+
+/* helper to decode private information element */
+int osmo_cc_get_ie_private(osmo_cc_msg_t *msg, int ie_repeat, uint32_t *unique, uint8_t *data, size_t data_size)
+{
+	struct osmo_cc_ie_private *ie_private;
+	int rc;
+
+	rc = osmo_cc_get_ie_data(msg, OSMO_CC_IE_PRIVATE, ie_repeat, sizeof(*ie_private), (const void **)&ie_private);
+	if (rc < 0)
+		return rc;
+	*unique = ntohl(ie_private->unique_networkorder);
+	memcpy(data, ie_private->data, (rc < (int)data_size) ? rc : (int)data_size);
+	return rc;
+}
+
diff --git a/src/libosmocc/message.h b/src/libosmocc/message.h
new file mode 100644
index 0000000..9dee2c9
--- /dev/null
+++ b/src/libosmocc/message.h
@@ -0,0 +1,437 @@
+#ifndef OSMO_CC_MSG_H
+#define OSMO_CC_MSG_H
+
+#define OSMO_CC_VERSION "OSMOCCv1"
+
+/* call control messages types */
+enum osmo_cc_msg_type {
+	OSMO_CC_MSG_SETUP_REQ =		0x00,
+	OSMO_CC_MSG_SETUP_IND =		0x01,
+	OSMO_CC_MSG_REJ_REQ =		0x10,
+	OSMO_CC_MSG_REJ_IND =		0x11,
+	OSMO_CC_MSG_SETUP_ACK_REQ =	0x20,
+	OSMO_CC_MSG_SETUP_ACK_IND =	0x21,
+	OSMO_CC_MSG_PROC_REQ =		0x30,
+	OSMO_CC_MSG_PROC_IND =		0x31,
+	OSMO_CC_MSG_ALERT_REQ =		0x40,
+	OSMO_CC_MSG_ALERT_IND =		0x41,
+	OSMO_CC_MSG_SETUP_RSP =		0x02,
+	OSMO_CC_MSG_SETUP_CNF =		0x03,
+	OSMO_CC_MSG_SETUP_COMP_REQ =	0x50,
+	OSMO_CC_MSG_SETUP_COMP_IND =	0x51,
+	OSMO_CC_MSG_DISC_REQ =		0x60,
+	OSMO_CC_MSG_DISC_IND =		0x61,
+	OSMO_CC_MSG_REL_REQ =		0x70,
+	OSMO_CC_MSG_REL_CNF =		0x73,
+	OSMO_CC_MSG_REL_IND =		0x71,
+	OSMO_CC_MSG_PROGRESS_REQ =	0x80,
+	OSMO_CC_MSG_PROGRESS_IND =	0x81,
+	OSMO_CC_MSG_NOTIFY_REQ =	0x84,
+	OSMO_CC_MSG_NOTIFY_IND =	0x85,
+	OSMO_CC_MSG_INFO_REQ =		0x88,
+	OSMO_CC_MSG_INFO_IND =		0x89,
+	OSMO_CC_MSG_ATTACH_REQ =	0xf8,
+	OSMO_CC_MSG_ATTACH_IND =	0xf9,
+	OSMO_CC_MSG_ATTACH_RSP =	0xfa,
+	OSMO_CC_MSG_ATTACH_CNF =	0xfb,
+	OSMO_CC_MSG_DUMMY_REQ =		0xfc,
+};
+
+#define OSMO_CC_MSG_MASK		0x03,
+#define OSMO_CC_MSG_REQ			0x00,
+#define OSMO_CC_MSG_IND			0x01,
+#define OSMO_CC_MSG_RSP			0x02,
+#define OSMO_CC_MSG_CNF			0x03,
+
+/* information elements */
+enum osmo_cc_ie_type {
+	OSMO_CC_IE_CALLED =		0x11,
+	OSMO_CC_IE_CALLED_SUB =		0x12,
+	OSMO_CC_IE_CALLED_NAME =	0x13,
+	OSMO_CC_IE_CALLED_INTERFACE =	0x14,
+	OSMO_CC_IE_DTMF =		0x1d,
+	OSMO_CC_IE_KEYPAD =		0x1e,
+	OSMO_CC_IE_COMPLETE =		0x1f,
+	OSMO_CC_IE_CALLING =		0x21,
+	OSMO_CC_IE_CALLING_SUB =	0x22,
+	OSMO_CC_IE_CALLING_NAME =	0x23,
+	OSMO_CC_IE_CALLING_INTERFACE =	0x24,
+	OSMO_CC_IE_CALLING_NETWORK =	0x2f,
+	OSMO_CC_IE_REDIR =		0x31,
+	OSMO_CC_IE_PROGRESS =		0x32,
+	OSMO_CC_IE_NOTIFY =		0x33,
+	OSMO_CC_IE_DISPLAY =		0x34,
+	OSMO_CC_IE_CAUSE =		0x41,
+	OSMO_CC_IE_BEARER =		0x51,
+	OSMO_CC_IE_SDP =		0x52,
+	OSMO_CC_IE_SOCKET_ADDRESS =	0x5e,
+	OSMO_CC_IE_PRIVATE =		0x5f,
+};
+
+/* type of number, see ITU-T Rec. Q.931 */
+#define OSMO_CC_TYPE_UNKNOWN			0
+#define OSMO_CC_TYPE_INTERNATIONAL		1
+#define OSMO_CC_TYPE_NATIONAL			2
+#define OSMO_CC_TYPE_NETWORK			3
+#define OSMO_CC_TYPE_SUBSCRIBER			4
+#define OSMO_CC_TYPE_ABBREVIATED		5
+#define OSMO_CC_TYPE_RESERVED			7
+
+/* numbering plan, see ITU-T Rec. Q.931 */
+#define OSMO_CC_PLAN_UNKNOWN			0
+#define OSMO_CC_PLAN_TELEPHONY			1
+#define OSMO_CC_PLAN_DATA			3
+#define OSMO_CC_PLAN_TTY			4
+#define OSMO_CC_PLAN_NATIONAL_STANDARD		8
+#define OSMO_CC_PLAN_PRIVATE			9
+#define OSMO_CC_PLAN_RESERVED			15
+
+/* presentation indicator, see ITU-T Rec. Q.931 */
+#define OSMO_CC_PRESENT_ALLOWED			0
+#define OSMO_CC_PRESENT_RESTRICTED		1
+#define OSMO_CC_PRESENT_NOT_AVAIL		2
+#define OSMO_CC_PRESENT_RESERVED		3
+
+/* screening indicator, see ITU-T Rec. Q.931 */
+#define OSMO_CC_SCREEN_USER_UNSCREENED		0
+#define OSMO_CC_SCREEN_USER_VERIFIED_PASSED	1
+#define OSMO_CC_SCREEN_USER_VERIFIED_FAILED	2
+#define OSMO_CC_SCREEN_NETWORK			3
+
+/* screening indicator, see ITU-T Rec. Q.931 */
+#define OSMO_CC_REDIR_REASON_UNKNOWN		0
+#define OSMO_CC_REDIR_REASON_CFB		1
+#define OSMO_CC_REDIR_REASON_CFNR		2
+#define OSMO_CC_REDIR_REASON_CD			4
+#define OSMO_CC_REDIR_REASON_CF_OUTOFORDER	9
+#define OSMO_CC_REDIR_REASON_CF_BY_DTE		10
+#define OSMO_CC_REDIR_REASON_CFU		15
+
+/* notification indicator, see ITU-T Rec. Q.931 ff. */
+#define OSMO_CC_NOTIFY_USER_SUSPENDED		0x00    
+#define OSMO_CC_NOTIFY_USER_RESUMED		0x01
+#define OSMO_CC_NOTIFY_BEARER_SERVICE_CHANGE	0x02
+#define OSMO_CC_NOTIFY_CALL_COMPLETION_DELAY	0x03
+#define OSMO_CC_NOTIFY_CONFERENCE_ESTABLISHED	0x42
+#define OSMO_CC_NOTIFY_CONFERENCE_DISCONNECTED	0x43
+#define OSMO_CC_NOTIFY_OTHER_PARTY_ADDED	0x44
+#define OSMO_CC_NOTIFY_ISOLATED			0x45
+#define OSMO_CC_NOTIFY_REATTACHED		0x46
+#define OSMO_CC_NOTIFY_OTHER_PARTY_ISOLATED	0x47
+#define OSMO_CC_NOTIFY_OTHER_PARTY_REATTACHED	0x48
+#define OSMO_CC_NOTIFY_OTHER_PARTY_SPLIT	0x49
+#define OSMO_CC_NOTIFY_OTHER_PARTY_DISCONNECTED	0x4a
+#define OSMO_CC_NOTIFY_CONFERENCE_FLOATING	0x4b
+#define OSMO_CC_NOTIFY_CONFERENCE_DISC_PREEMPT	0x4c	/* disconnect preemted */
+#define OSMO_CC_NOTIFY_CONFERENCE_FLOATING_SUP	0x4f	/* served user preemted */
+#define OSMO_CC_NOTIFY_CALL_IS_A_WAITING_CALL	0x60
+#define OSMO_CC_NOTIFY_DIVERSION_ACTIVATED	0x68
+#define OSMO_CC_NOTIFY_RESERVED_CT_1		0x69
+#define OSMO_CC_NOTIFY_RESERVED_CT_2		0x6a
+#define OSMO_CC_NOTIFY_REVERSE_CHARGING		0x6e
+#define OSMO_CC_NOTIFY_REMOTE_HOLD		0x79
+#define OSMO_CC_NOTIFY_REMOTE_RETRIEVAL		0x7a
+#define OSMO_CC_NOTIFY_CALL_IS_DIVERTING	0x7b
+
+/* coding standard, see ITU-T Rec. Q.931 */
+#define OSMO_CC_CODING_ITU_T			0
+#define OSMO_CC_CODING_ISO_IEC			1
+#define OSMO_CC_CODING_NATIONAL			2
+#define OSMO_CC_CODING_STANDARD_SPECIFIC	3
+
+/* cause, see ITU-T Rec. Q.850 */
+#define	OSMO_CC_ISDN_CAUSE_UNASSIGNED_NR	1
+#define	OSMO_CC_ISDN_CAUSE_NO_ROUTE		3
+#define	OSMO_CC_ISDN_CAUSE_CHAN_UNACCEPT	6
+#define	OSMO_CC_ISDN_CAUSE_OP_DET_BARRING	8
+#define	OSMO_CC_ISDN_CAUSE_NORM_CALL_CLEAR	16
+#define	OSMO_CC_ISDN_CAUSE_USER_BUSY		17
+#define	OSMO_CC_ISDN_CAUSE_USER_NOTRESPOND	18
+#define	OSMO_CC_ISDN_CAUSE_USER_ALERTING_NA	19
+#define	OSMO_CC_ISDN_CAUSE_CALL_REJECTED	21
+#define	OSMO_CC_ISDN_CAUSE_NUMBER_CHANGED	22
+#define	OSMO_CC_ISDN_CAUSE_PRE_EMPTION		25
+#define	OSMO_CC_ISDN_CAUSE_NONSE_USER_CLR	26
+#define	OSMO_CC_ISDN_CAUSE_DEST_OOO		27
+#define	OSMO_CC_ISDN_CAUSE_INV_NR_FORMAT	28
+#define	OSMO_CC_ISDN_CAUSE_FACILITY_REJ		29
+#define	OSMO_CC_ISDN_CAUSE_RESP_STATUS_INQ	30
+#define	OSMO_CC_ISDN_CAUSE_NORMAL_UNSPEC	31
+#define	OSMO_CC_ISDN_CAUSE_NO_CIRCUIT_CHAN	34
+#define	OSMO_CC_ISDN_CAUSE_NETWORK_OOO		38
+#define	OSMO_CC_ISDN_CAUSE_TEMP_FAILURE		41
+#define	OSMO_CC_ISDN_CAUSE_SWITCH_CONG		42
+#define	OSMO_CC_ISDN_CAUSE_ACC_INF_DISCARD	43
+#define	OSMO_CC_ISDN_CAUSE_REQ_CHAN_UNAVAIL	44
+#define	OSMO_CC_ISDN_CAUSE_RESOURCE_UNAVAIL	47
+#define	OSMO_CC_ISDN_CAUSE_QOS_UNAVAIL		49
+#define	OSMO_CC_ISDN_CAUSE_REQ_FAC_NOT_SUBSC	50
+#define	OSMO_CC_ISDN_CAUSE_INC_BARRED_CUG	55
+#define	OSMO_CC_ISDN_CAUSE_BEARER_CAP_UNAUTH	57
+#define	OSMO_CC_ISDN_CAUSE_BEARER_CA_UNAVAIL	58
+#define	OSMO_CC_ISDN_CAUSE_SERV_OPT_UNAVAIL	63
+#define	OSMO_CC_ISDN_CAUSE_BEARERSERV_UNIMPL	65
+#define	OSMO_CC_ISDN_CAUSE_ACM_GE_ACM_MAX	68
+#define	OSMO_CC_ISDN_CAUSE_REQ_FAC_NOTIMPL	69
+#define	OSMO_CC_ISDN_CAUSE_RESTR_BCAP_AVAIL	70
+#define	OSMO_CC_ISDN_CAUSE_SERV_OPT_UNIMPL	79
+#define	OSMO_CC_ISDN_CAUSE_INVAL_CALLREF	81
+#define	OSMO_CC_ISDN_CAUSE_USER_NOT_IN_CUG	87
+#define	OSMO_CC_ISDN_CAUSE_INCOMPAT_DEST	88
+#define	OSMO_CC_ISDN_CAUSE_INVAL_TRANS_NET	91
+#define	OSMO_CC_ISDN_CAUSE_SEMANTIC_INCORR	95
+#define	OSMO_CC_ISDN_CAUSE_INVAL_MAND_INF	96
+#define	OSMO_CC_ISDN_CAUSE_MSGTYPE_NOTEXIST	97
+#define	OSMO_CC_ISDN_CAUSE_MSGTYPE_INCOMPAT	98
+#define	OSMO_CC_ISDN_CAUSE_IE_NOTEXIST		99
+#define	OSMO_CC_ISDN_CAUSE_COND_IE_ERR		100
+#define	OSMO_CC_ISDN_CAUSE_MSG_INCOMP_STATE	101
+#define	OSMO_CC_ISDN_CAUSE_RECOVERY_TIMER	102
+#define	OSMO_CC_ISDN_CAUSE_PROTO_ERR		111
+#define	OSMO_CC_ISDN_CAUSE_INTERWORKING		127
+
+/* location, see ITU-T Rec. Q.931 */
+#define OSMO_CC_LOCATION_USER			0
+#define OSMO_CC_LOCATION_PRIV_SERV_LOC_USER	1
+#define OSMO_CC_LOCATION_PUB_SERV_LOC_USER	2
+#define OSMO_CC_LOCATION_TRANSIT		3
+#define OSMO_CC_LOCATION_PUB_SERV_REM_USER	4
+#define OSMO_CC_LOCATION_PRIV_SERV_REM_USER	5
+#define OSMO_CC_LOCATION_BEYOND_INTERWORKING	10
+
+/* progress description, see ITU-T Rec. Q.931 */
+#define OSMO_CC_PROGRESS_NOT_END_TO_END_ISDN	1
+#define OSMO_CC_PROGRESS_DEST_NOT_ISDN		2
+#define OSMO_CC_PROGRESS_ORIG_NOT_ISDN		3
+#define OSMO_CC_PROGRESS_RETURN_TO_ISDN		4
+#define OSMO_CC_PROGRESS_INTERWORKING		5
+#define OSMO_CC_PROGRESS_INBAND_INFO_AVAILABLE	8
+
+/* information transfer capability, see ITU-T Rec. Q.931 */
+#define OSMO_CC_CAPABILITY_SPEECH		0
+#define OSMO_CC_CAPABILITY_DATA			8
+#define OSMO_CC_CAPABILITY_DATA_RESTRICTED	9
+#define OSMO_CC_CAPABILITY_AUDIO		16
+#define OSMO_CC_CAPABILITY_DATA_WITH_TONES	17
+#define OSMO_CC_CAPABILITY_VIDEO		24
+
+/* transfer mode, see ITU-T Rec. Q.931 */
+#define OSMO_CC_MODE_CIRCUIT			0
+#define OSMO_CC_MODE_PACKET			2
+
+#define OSMO_CC_DTMF_MODE_OFF			0	/* stop tone */
+#define OSMO_CC_DTMF_MODE_ON			1	/* start tone */
+#define OSMO_CC_DTMF_MODE_DIGITS		2	/* play tone(s) with duration and pauses */
+
+#define OSMO_CC_SOCKET_CAUSE_VERSION_MISMATCH	1	/* version missmatch */
+#define OSMO_CC_SOCKET_CAUSE_FAILED		2	/* connection failed */
+#define OSMO_CC_SOCKET_CAUSE_BROKEN_PIPE	3	/* connected socket failed */
+#define OSMO_CC_SOCKET_CAUSE_TIMEOUT		4	/* keepalive packets timeout */
+// if you add causes here, add them in process_cause.c also!
+
+/* network type (network IE) and meaning of 'id' */
+#define OSMO_CC_NETWORK_UNDEFINED		0x00
+#define OSMO_CC_NETWORK_ALSA_NONE		0x01
+#define OSMO_CC_NETWORK_POTS_NONE		0x02
+#define OSMO_CC_NETWORK_ISDN_NONE		0x03
+#define OSMO_CC_NETWORK_SIP_NONE		0x04
+#define OSMO_CC_NETWORK_GSM_IMSI		0x05	/* id has decimal IMSI */
+#define OSMO_CC_NETWORK_GSM_IMEI		0x06	/* id has decimal IMEI */
+#define OSMO_CC_NETWORK_WEB_NONE		0x07
+#define OSMO_CC_NETWORK_DECT_NONE		0x08
+#define OSMO_CC_NETWORK_BLUETOOTH_NONE		0x09
+#define OSMO_CC_NETWORK_SS5_NONE		0x0a
+#define OSMO_CC_NETWORK_ANETZ_NONE		0x80
+#define OSMO_CC_NETWORK_BNETZ_MUENZ		0x81	/* id starts with 'M' */
+#define OSMO_CC_NETWORK_CNETZ_NONE		0x82
+#define OSMO_CC_NETWORK_NMT_NONE		0x83	/* id has decimal password */
+#define OSMO_CC_NETWORK_R2000_NONE		0x84
+#define OSMO_CC_NETWORK_AMPS_ESN		0x85	/* if has decimal ESN (TACS also) */
+#define OSMO_CC_NETWORK_MTS_NONE		0x86
+#define OSMO_CC_NETWORK_IMTS_NONE		0x87
+#define OSMO_CC_NETWORK_EUROSIGNAL_NONE		0x88
+#define OSMO_CC_NETWORK_JOLLYCOM_NONE		0x89	/* call from JollyCom... */
+
+typedef struct osmo_cc_msg {
+	uint8_t type;
+	uint16_t length_networkorder;
+	uint8_t data[0];
+} __attribute__((packed)) osmo_cc_msg_t;
+
+typedef struct osmo_cc_msg_list {
+	struct osmo_cc_msg_list *next;
+	struct osmo_cc_msg *msg;
+	uint32_t callref;
+	char host[128];
+	uint16_t port;
+} osmo_cc_msg_list_t;
+
+typedef struct osmo_cc_ie {
+	uint8_t type;
+	uint16_t length_networkorder;
+	uint8_t data[0];
+} __attribute__((packed)) osmo_cc_ie_t;
+
+struct osmo_cc_ie_called {
+	uint8_t type;
+	uint8_t	plan;
+	char digits[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_called_sub {
+	uint8_t type;
+	char digits[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_called_name {
+	char name[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_called_interface {
+	char name[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_calling {
+	uint8_t type;
+	uint8_t	plan;
+	uint8_t present;
+	uint8_t	screen;
+	char digits[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_calling_sub {
+	uint8_t type;
+	char digits[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_calling_name {
+	char name[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_calling_interface {
+	char name[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_network {
+	uint8_t type;
+	char id[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_bearer {
+	uint8_t coding;
+	uint8_t capability;
+	uint8_t mode;
+} __attribute__((packed));
+
+struct osmo_cc_ie_redir {
+	uint8_t type;
+	uint8_t	plan;
+	uint8_t present;
+	uint8_t	screen;
+	uint8_t redir_reason;
+	char digits[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_dtmf {
+	uint8_t duration_ms;
+	uint8_t pause_ms;
+	uint8_t dtmf_mode;
+	char digits[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_keypad {
+	char digits[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_progress {
+	uint8_t coding;
+	uint8_t location;
+	uint8_t progress;
+} __attribute__((packed));
+
+struct osmo_cc_ie_notify {
+	uint8_t notify;
+} __attribute__((packed));
+
+struct osmo_cc_ie_cause {
+	uint8_t location;
+	uint8_t isdn_cause;
+	uint16_t sip_cause_networkorder;
+	uint8_t socket_cause;
+} __attribute__((packed));
+
+struct osmo_cc_ie_display {
+	char text[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_sdp {
+	char sdp[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_socket_address {
+	char address[0];
+} __attribute__((packed));
+
+struct osmo_cc_ie_private {
+	uint32_t unique_networkorder;
+	uint8_t data[0];
+} __attribute__((packed));
+
+uint32_t osmo_cc_new_callref(void);
+const char *osmo_cc_msg_name(uint8_t msg_type);
+osmo_cc_msg_t *osmo_cc_new_msg(uint8_t msg_type);
+osmo_cc_msg_t *osmo_cc_clone_msg(osmo_cc_msg_t *msg);
+osmo_cc_msg_t *osmo_cc_msg_list_dequeue(osmo_cc_msg_list_t **mlp, uint32_t *callref_p);
+osmo_cc_msg_list_t *osmo_cc_msg_list_enqueue(osmo_cc_msg_list_t **mlp, osmo_cc_msg_t *msg, uint32_t callref);
+void osmo_cc_free_msg(osmo_cc_msg_t *msg);
+int osmo_cc_get_ie_struct(osmo_cc_msg_t *msg, uint8_t ie_type, int ie_repeat, int ie_len, const osmo_cc_ie_t **ie_struct);
+int osmo_cc_get_ie_data(osmo_cc_msg_t *msg, uint8_t ie_type, int ie_repeat, int ie_len, const void **ie_data);
+int osmo_cc_has_ie(osmo_cc_msg_t *msg, uint8_t ie_type, int ie_repeat);
+int osmo_cc_remove_ie(osmo_cc_msg_t *msg, uint8_t ie_type, int ie_repeat);
+void *osmo_cc_add_ie(osmo_cc_msg_t *msg, uint8_t ie_type, int ie_len);
+void *osmo_cc_msg_sep_ie(osmo_cc_msg_t *msg, void **iep, uint8_t *ie_type, uint16_t *ie_length);
+
+void osmo_cc_add_ie_called(osmo_cc_msg_t *msg, uint8_t type, uint8_t plan, const char *dialing);
+int osmo_cc_get_ie_called(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *type, uint8_t *plan, char *dialing, size_t dialing_size);
+void osmo_cc_add_ie_called_sub(osmo_cc_msg_t *msg, uint8_t type, const char *dialing);
+int osmo_cc_get_ie_called_sub(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *type, char *dialing, size_t dialing_size);
+void osmo_cc_add_ie_called_name(osmo_cc_msg_t *msg, const char *name);
+int osmo_cc_get_ie_called_name(osmo_cc_msg_t *msg, int ie_repeat, char *name, size_t name_size);
+void osmo_cc_add_ie_called_interface(osmo_cc_msg_t *msg, const char *interface);
+int osmo_cc_get_ie_called_interface(osmo_cc_msg_t *msg, int ie_repeat, char *interface, size_t interface_size);
+void osmo_cc_add_ie_complete(osmo_cc_msg_t *msg);
+int osmo_cc_get_ie_complete(osmo_cc_msg_t *msg, int ie_repeat);
+void osmo_cc_add_ie_calling(osmo_cc_msg_t *msg, uint8_t type, uint8_t plan, uint8_t present, uint8_t screen, const char *callerid);
+int osmo_cc_get_ie_calling(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *type, uint8_t *plan, uint8_t *present, uint8_t *screen, char *callerid, size_t callerid_size);
+void osmo_cc_add_ie_calling_sub(osmo_cc_msg_t *msg, uint8_t type, const char *callerid);
+int osmo_cc_get_ie_calling_sub(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *type, char *callerid, size_t callerid_size);
+void osmo_cc_add_ie_calling_name(osmo_cc_msg_t *msg, const char *name);
+int osmo_cc_get_ie_calling_name(osmo_cc_msg_t *msg, int ie_repeat, char *name, size_t name_size);
+void osmo_cc_add_ie_calling_interface(osmo_cc_msg_t *msg, const char *interface);
+int osmo_cc_get_ie_calling_interface(osmo_cc_msg_t *msg, int ie_repeat, char *interface, size_t interface_size);
+void osmo_cc_add_ie_calling_network(osmo_cc_msg_t *msg, uint8_t type, const char *networkid);
+int osmo_cc_get_ie_calling_network(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *type, char *networkid, size_t networkid_size);
+void osmo_cc_add_ie_bearer(osmo_cc_msg_t *msg, uint8_t coding, uint8_t capability, uint8_t mode);
+int osmo_cc_get_ie_bearer(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *coding, uint8_t *capability, uint8_t *mode);
+void osmo_cc_add_ie_redir(osmo_cc_msg_t *msg, uint8_t type, uint8_t plan, uint8_t present, uint8_t screen, uint8_t redir_reason, const char *callerid);
+int osmo_cc_get_ie_redir(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *type, uint8_t *plan, uint8_t *present, uint8_t *screen, uint8_t *reason, char *callerid, size_t callerid_size);
+void osmo_cc_add_ie_dtmf(osmo_cc_msg_t *msg, uint8_t duration_ms, uint8_t pause_ms, uint8_t dtmf_mode, const char *digits);
+int osmo_cc_get_ie_dtmf(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *duration_ms, uint8_t *pause_ms, uint8_t *dtmf_mode, char *digits, size_t digits_size);
+void osmo_cc_add_ie_keypad(osmo_cc_msg_t *msg, const char *digits);
+int osmo_cc_get_ie_keypad(osmo_cc_msg_t *msg, int ie_repeat, char *digits, size_t digits_size);
+void osmo_cc_add_ie_progress(osmo_cc_msg_t *msg, uint8_t coding, uint8_t location, uint8_t progress);
+int osmo_cc_get_ie_progress(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *coding, uint8_t *location, uint8_t *progress);
+void osmo_cc_add_ie_notify(osmo_cc_msg_t *msg, uint8_t notify);
+int osmo_cc_get_ie_notify(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *notify);
+void osmo_cc_add_ie_cause(osmo_cc_msg_t *msg, uint8_t location, uint8_t isdn_cause, uint16_t sip_cause, uint8_t socket_cause);
+int osmo_cc_get_ie_cause(osmo_cc_msg_t *msg, int ie_repeat, uint8_t *location, uint8_t *isdn_cause, uint16_t *sip_cause, uint8_t *socket_cause);
+void osmo_cc_add_ie_display(osmo_cc_msg_t *msg, const char *text);
+int osmo_cc_get_ie_display(osmo_cc_msg_t *msg, int ie_repeat, char *text, size_t text_size);
+void osmo_cc_add_ie_sdp(osmo_cc_msg_t *msg, const char *sdp);
+int osmo_cc_get_ie_sdp(osmo_cc_msg_t *msg, int ie_repeat, char *sdp, size_t sdp_size);
+void osmo_cc_add_ie_socket_address(osmo_cc_msg_t *msg, const char *address);
+int osmo_cc_get_ie_socket_address(osmo_cc_msg_t *msg, int ie_repeat, char *address, size_t address_size);
+void osmo_cc_add_ie_private(osmo_cc_msg_t *msg, uint32_t unique, const uint8_t *data, size_t data_size);
+int osmo_cc_get_ie_private(osmo_cc_msg_t *msg, int ie_repeat, uint32_t *unique, uint8_t *data, size_t data_size);
+
+#endif /* OSMO_CC_MSG_H */
diff --git a/src/libosmocc/rtp.c b/src/libosmocc/rtp.c
new file mode 100644
index 0000000..a6de25a
--- /dev/null
+++ b/src/libosmocc/rtp.c
@@ -0,0 +1,399 @@
+/* Osmo-CC: RTP handling
+ *
+ * (C) 2016 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <string.h>
+#include <errno.h>
+#include <sys/socket.h>
+#include <arpa/inet.h>
+#include "../libdebug/debug.h"
+#include "../libtimer/timer.h"
+#include "endpoint.h"
+
+#define RTP_VERSION 2
+
+static uint16_t rtp_port_next = 16384;
+static uint16_t rtp_port_from = 16384;
+static uint16_t rtp_port_to = 32767;
+
+void osmo_cc_set_rtp_ports(uint16_t from, uint16_t to)
+{
+	rtp_port_next = from;
+	rtp_port_from = from;
+	rtp_port_to = to;
+}
+
+struct rtp_hdr {
+	uint8_t byte0;
+	uint8_t byte1;
+	uint16_t sequence;
+	uint32_t timestamp;
+	uint32_t ssrc;
+} __attribute__((packed));
+
+struct rtp_x_hdr {
+	uint16_t by_profile;
+	uint16_t length;
+} __attribute__((packed));
+
+static int rtp_receive(int sock, uint8_t **payload_p, int *payload_len_p, uint8_t *marker_p, uint8_t *pt_p, uint16_t *sequence_p, uint32_t *timestamp_p)
+{
+	static uint8_t data[2048];
+	int len;
+	struct rtp_hdr *rtph = (struct rtp_hdr *)data;
+	uint8_t version, padding, extension, csrc_count, marker, payload_type;
+	struct rtp_x_hdr *rtpxh;
+	uint8_t *payload;
+	int payload_len;
+	int x_len;
+
+	len = read(sock, data, sizeof(data));
+	if (len < 0) {
+		if (errno == EAGAIN)
+			return -EAGAIN;
+		PDEBUG(DCC, DEBUG_DEBUG, "Read errno = %d (%s)\n", errno, strerror(errno));
+		return -EIO;
+	}
+	if (len < 12) {
+		PDEBUG(DCC, DEBUG_NOTICE, "Received RTP frame too short (len = %d).\n", len);
+		return -EINVAL;
+	}
+
+	version = rtph->byte0 >> 6;
+	padding = (rtph->byte0 >> 5) & 1;
+	extension = (rtph->byte0 >> 4) & 1;
+	csrc_count = rtph->byte0 & 0x0f;
+	marker = rtph->byte1 >> 7;
+	payload_type = rtph->byte1 & 0x7f;
+	*sequence_p = ntohs(rtph->sequence);
+	*timestamp_p = ntohl(rtph->timestamp);
+
+	if (version != RTP_VERSION) {
+		PDEBUG(DCC, DEBUG_NOTICE, "Received RTP version %d not supported.\n", version);
+		return -EINVAL;
+	}
+
+	payload = data + sizeof(*rtph) + (csrc_count << 2);
+	payload_len = len - sizeof(*rtph) - (csrc_count << 2);
+	if (payload_len < 0) {
+		PDEBUG(DCC, DEBUG_NOTICE, "Received RTP frame too short (len = %d, csrc count = %d).\n", len, csrc_count);
+		return -EINVAL;
+	}
+
+	if (extension) {
+		if (payload_len < (int)sizeof(*rtpxh)) {
+			PDEBUG(DCC, DEBUG_NOTICE, "Received RTP frame too short for extension header.\n");
+			return -EINVAL;
+		}
+		rtpxh = (struct rtp_x_hdr *)payload;
+		x_len = ntohs(rtpxh->length) * 4 + sizeof(*rtpxh);
+		payload += x_len;
+		payload_len -= x_len;
+		if (payload_len < (int)sizeof(*rtpxh)) {
+			PDEBUG(DCC, DEBUG_NOTICE, "Received RTP frame too short, extension header exceeds frame length.\n");
+			return -EINVAL;
+		}
+	}
+
+	if (padding) {
+		if (payload_len < 1) {
+			PDEBUG(DCC, DEBUG_NOTICE, "Received RTP frame too short for padding length.\n");
+			return -EINVAL;
+		}
+		payload_len -= payload[payload_len - 1];
+		if (payload_len < 0) {
+			PDEBUG(DCC, DEBUG_NOTICE, "Received RTP frame padding is greater than payload.\n");
+			return -EINVAL;
+		}
+	}
+
+	*payload_p = payload;
+	*payload_len_p = payload_len;
+	*marker_p = marker;
+	*pt_p = payload_type;
+
+	return 0;
+}
+
+static void rtp_send(int sock, uint8_t *payload, int payload_len, uint8_t pt, uint16_t sequence, uint32_t timestamp, uint32_t ssrc)
+{
+	struct rtp_hdr *rtph;
+	char data[sizeof(*rtph) + payload_len];
+	int len, rc;
+	
+	rtph = (struct rtp_hdr *)data;
+	len = sizeof(*rtph);
+	rtph->byte0 = RTP_VERSION << 6;
+	rtph->byte1 = pt;
+	rtph->sequence = htons(sequence);
+	rtph->timestamp = htonl(timestamp);
+	rtph->ssrc = htonl(ssrc);
+	len += payload_len;
+	if (len > (int)sizeof(data)) {
+		PDEBUG(DCC, DEBUG_NOTICE, "Buffer overflow, please fix!.\n");
+		abort();
+	}
+	memcpy(data + sizeof(*rtph), payload, payload_len);
+
+	rc = write(sock, data, len);
+	if (rc < 0)
+		PDEBUG(DCC, DEBUG_DEBUG, "Write errno = %d (%s)\n", errno, strerror(errno));
+}
+
+/* open and bind RTP
+ * set local port to what we bound
+ */
+int osmo_cc_rtp_open(osmo_cc_session_media_t *media)
+{
+	int domain = 0; // make GCC happy
+	uint16_t start_port;
+	struct sockaddr_storage sa;
+	int slen = 0; // make GCC happy
+	struct sockaddr_in6 *sa6;
+	struct sockaddr_in *sa4;
+	uint16_t *sport;
+	int flags;
+	int rc;
+
+	media->rtp_ssrc = rand();
+
+	osmo_cc_rtp_close(media);
+
+	switch (media->connection_data_local.addrtype) {
+	case osmo_cc_session_addrtype_ipv4:
+		domain = AF_INET;
+		memset(&sa, 0, sizeof(sa));
+		sa4 = (struct sockaddr_in *)&sa;
+		sa4->sin_family = domain;
+		sa4->sin_addr.s_addr = INADDR_ANY;
+		sport = &sa4->sin_port;
+		slen = sizeof(*sa4);
+		break;
+	case osmo_cc_session_addrtype_ipv6:
+		domain = AF_INET6;
+		memset(&sa, 0, sizeof(sa));
+		sa6 = (struct sockaddr_in6 *)&sa;
+		sa6->sin6_family = domain;
+		sa6->sin6_addr = in6addr_any;
+		sport = &sa6->sin6_port;
+		slen = sizeof(*sa6);
+		break;
+	case osmo_cc_session_addrtype_unknown:
+		PDEBUG(DCC, DEBUG_NOTICE, "Unsupported address type '%s'.\n", media->connection_data_local.addrtype_name);
+		return -EINVAL;
+	}
+
+	/* rtp_port_from/rtp_port_to may be changed at run time, so rtp_port_next can become out of range. */
+	if (rtp_port_next < rtp_port_from || rtp_port_next > rtp_port_to)
+		rtp_port_next = rtp_port_from;
+	start_port = rtp_port_next;
+	while (1) {
+		/* open sockets */
+		rc = socket(domain, SOCK_DGRAM, IPPROTO_UDP);
+		if (rc < 0) {
+socket_error:
+			PDEBUG(DCC, DEBUG_ERROR, "Cannot create socket (domain=%d, errno=%d(%s))\n", domain, errno, strerror(errno));
+			osmo_cc_rtp_close(media);
+			return -EIO;
+		}
+		media->rtp_socket = rc;
+		rc = socket(domain, SOCK_DGRAM, IPPROTO_UDP);
+		if (rc < 0)
+			goto socket_error;
+		media->rtcp_socket = rc;
+
+		/* bind sockets */
+		*sport = htons(rtp_port_next);
+		rc = bind(media->rtp_socket, (struct sockaddr *)&sa, slen);
+		if (rc < 0) {
+bind_error:
+			osmo_cc_rtp_close(media);
+			rtp_port_next = (rtp_port_next + 2 > rtp_port_to) ? rtp_port_from : rtp_port_next + 2;
+			if (rtp_port_next == start_port) {
+				PDEBUG(DCC, DEBUG_ERROR, "Cannot bind socket (errno=%d(%s))\n", errno, strerror(errno));
+				return -EIO;
+			}
+			continue;
+		}
+		*sport = htons(rtp_port_next + 1);
+		rc = bind(media->rtcp_socket, (struct sockaddr *)&sa, slen);
+		if (rc < 0)
+			goto bind_error;
+		media->description.port_local = rtp_port_next;
+		rtp_port_next = (rtp_port_next + 2 > rtp_port_to) ? rtp_port_from : rtp_port_next + 2;
+		/* set nonblocking io */
+		flags = fcntl(media->rtp_socket, F_GETFL);
+		flags |= O_NONBLOCK;
+		fcntl(media->rtp_socket, F_SETFL, flags);
+		flags = fcntl(media->rtcp_socket, F_GETFL);
+		flags |= O_NONBLOCK;
+		fcntl(media->rtcp_socket, F_SETFL, flags);
+		break;
+	}
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Opening media port %d\n", media->description.port_local);
+
+	return 0;
+}
+
+/* connect RTP
+ * use remote port to connect to
+ */
+int osmo_cc_rtp_connect(osmo_cc_session_media_t *media)
+{
+	struct sockaddr_storage sa;
+	int slen = 0; // make GCC happy
+	struct sockaddr_in6 *sa6;
+	struct sockaddr_in *sa4;
+	uint16_t *sport;
+	int rc;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Connecting media port %d->%d\n", media->description.port_local, media->description.port_remote);
+
+	switch (media->connection_data_remote.addrtype) {
+	case osmo_cc_session_addrtype_ipv4:
+		memset(&sa, 0, sizeof(sa));
+		sa4 = (struct sockaddr_in *)&sa;
+		sa4->sin_family = AF_INET;
+		rc = inet_pton(AF_INET, media->connection_data_remote.address, &sa4->sin_addr);
+		if (rc < 1) {
+pton_error:
+			PDEBUG(DCC, DEBUG_NOTICE, "Cannot connect to address '%s'.\n", media->connection_data_remote.address);
+			return -EINVAL;
+		}
+		sport = &sa4->sin_port;
+		slen = sizeof(*sa4);
+		break;
+	case osmo_cc_session_addrtype_ipv6:
+		memset(&sa, 0, sizeof(sa));
+		sa6 = (struct sockaddr_in6 *)&sa;
+		sa6->sin6_family = AF_INET6;
+		rc = inet_pton(AF_INET6, media->connection_data_remote.address, &sa6->sin6_addr);
+		if (rc < 1)
+			goto pton_error;
+		sport = &sa6->sin6_port;
+		slen = sizeof(*sa6);
+		break;
+	case osmo_cc_session_addrtype_unknown:
+		PDEBUG(DCC, DEBUG_NOTICE, "Unsupported address type '%s'.\n", media->connection_data_local.addrtype_name);
+		return -EINVAL;
+	}
+
+	*sport = htons(media->description.port_remote);
+	rc = connect(media->rtp_socket, (struct sockaddr *)&sa, slen);
+	if (rc < 0) {
+connect_error:
+		PDEBUG(DCC, DEBUG_NOTICE, "Cannot connect to address '%s'.\n", media->connection_data_remote.address);
+		osmo_cc_rtp_close(media);
+		return -EIO;
+	}
+	*sport = htons(media->description.port_remote + 1);
+	rc = connect(media->rtcp_socket, (struct sockaddr *)&sa, slen);
+	if (rc < 0)
+		goto connect_error;
+
+	return 0;
+}
+
+/* send rtp data with given codec */
+void osmo_cc_rtp_send(osmo_cc_session_codec_t *codec, uint8_t *data, int len, int inc_sequence, int inc_timestamp)
+{
+	uint8_t *payload = NULL;
+	int payload_len = 0;
+
+	if (!codec || !codec->media->rtp_socket)
+		return;
+
+	if (codec->encoder)
+		codec->encoder(data, len, &payload, &payload_len);
+	else {
+		payload = data;
+		payload_len = len;
+	}
+
+	rtp_send(codec->media->rtp_socket, payload, payload_len, codec->payload_type_remote, codec->media->tx_sequence, codec->media->tx_timestamp, codec->media->rtp_ssrc);
+	codec->media->tx_sequence += inc_sequence;
+	codec->media->tx_timestamp += inc_timestamp;
+
+	if (codec->encoder)
+		free(payload);
+}
+
+/* receive rtp data for given media, return < 0, if there is nothing this time */
+int osmo_cc_rtp_receive(osmo_cc_session_media_t *media)
+{
+	int rc;
+	uint8_t *payload = NULL;
+	int payload_len = 0;
+	uint8_t marker;
+	uint8_t payload_type;
+	osmo_cc_session_codec_t *codec;
+	uint8_t *data;
+	int len;
+
+	if (!media || media->rtp_socket <= 0)
+		return -EIO;
+
+	rc = rtp_receive(media->rtp_socket, &payload, &payload_len, &marker, &payload_type, &media->rx_sequence, &media->rx_timestamp);
+	if (rc < 0)
+		return rc;
+
+	/* search for codec */
+	for (codec = media->codec_list; codec; codec = codec->next) {
+		
+		if (codec->payload_type_local == payload_type)
+			break;
+	}
+	if (!codec) {
+		PDEBUG(DCC, DEBUG_NOTICE, "Received RTP frame for unknown codec (payload_type = %d).\n", payload_type);
+		return 0;
+	}
+
+	if (codec->decoder)
+		codec->decoder(payload, payload_len, &data, &len);
+	else {
+		data = payload;
+		len = payload_len;
+	}
+
+	if (codec->media->receive)
+		codec->media->receiver(codec, media->rx_sequence, media->rx_timestamp, data, len);
+
+	if (codec->decoder)
+		free(data);
+
+	return 0;
+}
+
+void osmo_cc_rtp_close(osmo_cc_session_media_t *media)
+{
+	if (media->rtp_socket) {
+		close(media->rtp_socket);
+		media->rtp_socket = 0;
+	}
+	if (media->rtcp_socket) {
+		close(media->rtcp_socket);
+		media->rtcp_socket = 0;
+	}
+}
+
diff --git a/src/libosmocc/rtp.h b/src/libosmocc/rtp.h
new file mode 100644
index 0000000..47d748c
--- /dev/null
+++ b/src/libosmocc/rtp.h
@@ -0,0 +1,8 @@
+
+void osmo_cc_set_rtp_ports(uint16_t from, uint16_t to);
+int osmo_cc_rtp_open(osmo_cc_session_media_t *media);
+int osmo_cc_rtp_connect(osmo_cc_session_media_t *media);
+void osmo_cc_rtp_send(osmo_cc_session_codec_t *codec, uint8_t *data, int len, int inc_sequence, int inc_timestamp);
+int osmo_cc_rtp_receive(osmo_cc_session_media_t *media);
+void osmo_cc_rtp_close(osmo_cc_session_media_t *media);
+
diff --git a/src/libosmocc/screen.c b/src/libosmocc/screen.c
new file mode 100644
index 0000000..c8e17dc
--- /dev/null
+++ b/src/libosmocc/screen.c
@@ -0,0 +1,684 @@
+/* Endpoint and call process handling
+ *
+ * (C) 2019 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include <arpa/inet.h>
+#include <unistd.h>
+#include "../libtimer/timer.h"
+#include "../libdebug/debug.h"
+#include "endpoint.h"
+#include "message.h"
+
+#define SCREEN_QUESTIONMARK	1
+#define SCREEN_STAR		2
+#define SCREEN_AT		3
+
+void osmo_cc_help_screen(void)
+{
+	printf("Screening options:\n\n");
+
+	printf("screen-calling-in [attrs] <current caller ID> [attrs] <new caller ID>\n");
+	printf("screen-called-in [attrs] <current dialed number> [attrs] <new dialed number>\n");
+	printf("screen-calling-out [attrs] <current caller ID> [attrs] <new caller ID>\n");
+	printf("screen-called-out [attrs] <current dialed number> [attrs] <new dialed number>\n\n");
+
+	printf("These options allow to screen an incoming or outgoing caller ID or dialed\n");
+	printf("number. If 'the current caller ID' or 'current dialed number' matches, it will\n");
+	printf("be replaced by 'new caller ID' or 'new dialed number'.  'incoming' means from\n");
+	printf(" the interface and 'outgoing' means towards the interface.\n\n");
+
+	printf("Attributes prior 'current caller ID' or 'new dialed number' may be used to\n");
+	printf("perform screening only if the attribute match. Attributes prior\n");
+	printf("'new caller ID' or 'new dialed number' may be used to alter them. Attribute to\n");
+	printf("define the type of number can be: 'unknown', 'international', 'national',\n");
+	printf("'network', 'subscriber', 'abbreviated' Attribute to define the restriction of a\n");
+	printf("caller ID: 'allowed', 'restricted'\n\n");
+
+	printf("The current caller ID or dialed number may contain one or more '?', to allow\n");
+	printf("any digit to match. The current caller ID or dialed number may contain a '*',\n");
+	printf("to allow any suffix to match from now on. The new caller ID or dialed number\n");
+	printf("may contain a '*', to append the suffix from the current caller ID or dialed\n");
+	printf("number.\n\n");
+}
+
+char *osmo_cc_strtok_quotes(const char **text_p)
+{
+	static char token[1024];
+	const char *text = *text_p;
+	int i, quote;
+
+	/* skip spaces */
+	while (*text) {
+		if (*text > 32)
+			break;
+		text++;
+	}
+
+	/* if eol, return NULL */
+	if (!(*text))
+		return NULL;
+
+	i = 0;
+	quote = 0;
+	while (*text) {
+		/* escape allows all following characters */
+		if (*text == '\\') {
+			text++;
+			if (*text)
+				token[i++] = *text++;
+			continue;
+		}
+		/* no quote, check for them or break on white space */
+		if (quote == 0) {
+			if (*text == '\'') {
+				quote = 1;
+				text++;
+				continue;
+			}
+			if (*text == '\"') {
+				quote = 2;
+				text++;
+				continue;
+			}
+			if (*text <= ' ')
+				break;
+		}
+		/* single quote, check for unquote */
+		if (quote == 1 && *text == '\'') {
+			quote = 0;
+			text++;
+			continue;
+		}
+	       	/* double quote, check for unquote */
+		if (quote == 2 && *text == '\"') {
+			quote = 0;
+			text++;
+			continue;
+		}
+		/* copy character */
+		token[i++] = *text++;
+	}
+	token[i] = '\0';
+
+	*text_p = text;
+	return token;
+}
+
+int osmo_cc_add_screen(osmo_cc_endpoint_t *ep, const char *text)
+{
+	osmo_cc_screen_list_t **list_p = NULL, *list;
+	const char *token;
+	int no_present = 0, calling_in = 0, star_used, at_used;
+	int i, j;
+
+	star_used = 0;
+	if (!strncasecmp(text, "screen-calling-in", 17)) {
+		text += 17;
+		list_p = &ep->screen_calling_in;
+		no_present = 1;
+		calling_in = 1;
+	} else if (!strncasecmp(text, "screen-called-in", 16)) {
+		text += 16;
+		list_p = &ep->screen_called_in;
+	} else if (!strncasecmp(text, "screen-calling-out", 18)) {
+		text += 18;
+		list_p = &ep->screen_calling_out;
+		no_present = 1;
+	} else if (!strncasecmp(text, "screen-called-out", 17)) {
+		text += 17;
+		list_p = &ep->screen_called_out;
+	} else {
+		PDEBUG(DCC, DEBUG_ERROR, "Invalid screening definition \"%s\". It must start with 'screen-calling-in' or 'screen-called-in' or 'screen-calling-out' or 'screen-called-out'\n", text);
+		return -EINVAL;
+	}
+
+	/* skip space behind screen list string */
+	while (*text) {
+		if (*text > 32)
+			break;
+		text++;
+	}
+
+	list = calloc(1, sizeof(*list));
+	if (!list)
+		return -ENOMEM;
+
+next_from:
+	token = osmo_cc_strtok_quotes(&text);
+	if (!token) {
+		free(list);
+		PDEBUG(DCC, DEBUG_ERROR, "Missing 'from' string in screening definition \"%s\". If the string shall be empty, use double quotes. (\'\' or \"\")\n", text);
+		return -EINVAL;
+	}
+	if (!strcasecmp(token, "unknown")) {
+		list->has_from_type = 1;
+		list->from_type = OSMO_CC_TYPE_UNKNOWN;
+		goto next_from;
+	} else
+	if (!strcasecmp(token, "international")) {
+		list->has_from_type = 1;
+		list->from_type = OSMO_CC_TYPE_INTERNATIONAL;
+		goto next_from;
+	} else
+	if (!strcasecmp(token, "national")) {
+		list->has_from_type = 1;
+		list->from_type = OSMO_CC_TYPE_NATIONAL;
+		goto next_from;
+	} else
+	if (!strcasecmp(token, "network")) {
+		list->has_from_type = 1;
+		list->from_type = OSMO_CC_TYPE_NETWORK;
+		goto next_from;
+	} else
+	if (!strcasecmp(token, "subscriber")) {
+		list->has_from_type = 1;
+		list->from_type = OSMO_CC_TYPE_SUBSCRIBER;
+		goto next_from;
+	} else
+	if (!strcasecmp(token, "abbreviated")) {
+		list->has_from_type = 1;
+		list->from_type = OSMO_CC_TYPE_ABBREVIATED;
+		goto next_from;
+	} else
+	if (!strcasecmp(token, "allowed")) {
+		if (no_present) {
+no_present_error:
+			free(list);
+			PDEBUG(DCC, DEBUG_ERROR, "Error in screening definition '%s'.\n", text);
+			PDEBUG(DCC, DEBUG_ERROR, "Keyword '%s' not allowed in screen entry for called number\n", token);
+			return -EINVAL;
+		}
+		list->has_from_present = 1;
+		list->from_present = OSMO_CC_PRESENT_ALLOWED;
+		goto next_from;
+	} else
+	if (!strcasecmp(token, "restricted")) {
+		if (no_present)
+			goto no_present_error;
+		list->has_from_present = 1;
+		list->from_present = OSMO_CC_PRESENT_RESTRICTED;
+		goto next_from;
+	} else {
+		for (i = j = 0; token[i] && j < (int)sizeof(list->from) - 1; i++, j++) {
+			if (token[i] == '?')
+				list->from[j] = SCREEN_QUESTIONMARK;
+			else
+			if (token[i] == '*') {
+				if (star_used) {
+					free(list);
+					PDEBUG(DCC, DEBUG_ERROR, "Error in screening definition '%s'.\n", text);
+					PDEBUG(DCC, DEBUG_ERROR, "The '*' may be used only once.\n");
+					return -EINVAL;
+				}
+				list->from[j] = SCREEN_STAR;
+				star_used = 1;
+			} else
+			if (token[i] == '\\' && token[i + 1] != '\0')
+				list->from[j] = token[++i];
+			else
+				list->from[j] = token[i];
+		}
+		list->from[j] = '\0';
+	}
+
+	star_used = 0;
+next_to:
+	token = osmo_cc_strtok_quotes(&text);
+	if (!token) {
+		free(list);
+		PDEBUG(DCC, DEBUG_ERROR, "Error in screening definition '%s'.\n", text);
+		PDEBUG(DCC, DEBUG_ERROR, "Missing screening result. If the string shall be empty, use double quotes. (\'\' or \"\")\n");
+		return -EINVAL;
+	}
+	if (!strcasecmp(token, "unknown")) {
+		list->has_to_type = 1;
+		list->to_type = OSMO_CC_TYPE_UNKNOWN;
+		goto next_to;
+	} else
+	if (!strcasecmp(token, "international")) {
+		list->has_to_type = 1;
+		list->to_type = OSMO_CC_TYPE_INTERNATIONAL;
+		goto next_to;
+	} else
+	if (!strcasecmp(token, "national")) {
+		list->has_to_type = 1;
+		list->to_type = OSMO_CC_TYPE_NATIONAL;
+		goto next_to;
+	} else
+	if (!strcasecmp(token, "network")) {
+		list->has_to_type = 1;
+		list->to_type = OSMO_CC_TYPE_NETWORK;
+		goto next_to;
+	} else
+	if (!strcasecmp(token, "subscriber")) {
+		list->has_to_type = 1;
+		list->to_type = OSMO_CC_TYPE_SUBSCRIBER;
+		goto next_to;
+	} else
+	if (!strcasecmp(token, "abbreviated")) {
+		list->has_to_type = 1;
+		list->to_type = OSMO_CC_TYPE_ABBREVIATED;
+		goto next_to;
+	} else
+	if (!strcasecmp(token, "allowed")) {
+		if (no_present)
+			goto no_present_error;
+		list->has_to_present = 1;
+		list->to_present = OSMO_CC_PRESENT_ALLOWED;
+		goto next_to;
+	} else
+	if (!strcasecmp(token, "restricted")) {
+		if (no_present)
+			goto no_present_error;
+		list->has_to_present = 1;
+		list->to_present = OSMO_CC_PRESENT_RESTRICTED;
+		goto next_to;
+	} else {
+		for (i = j = 0; token[i] && j < (int)sizeof(list->to) - 1; i++, j++) {
+			if (token[i] == '*') {
+				if (star_used) {
+					free(list);
+					PDEBUG(DCC, DEBUG_ERROR, "Error in screening definition '%s'.\n", text);
+					PDEBUG(DCC, DEBUG_ERROR, "The '*' may be used only once.\n");
+					return -EINVAL;
+				}
+				list->to[j] = SCREEN_STAR;
+				star_used = 1;
+			} else
+			if (token[i] == '@') {
+				if (!calling_in) {
+					free(list);
+					PDEBUG(DCC, DEBUG_ERROR, "Error in screening definition '%s'.\n", text);
+					PDEBUG(DCC, DEBUG_ERROR, "The '@' may be used only for incoming calls from interface.\n");
+					return -EINVAL;
+				}
+				if (at_used) {
+					free(list);
+					PDEBUG(DCC, DEBUG_ERROR, "Error in screening definition '%s'.\n", text);
+					PDEBUG(DCC, DEBUG_ERROR, "The '@' may be used only once.\n");
+					return -EINVAL;
+				}
+				list->to[j] = SCREEN_AT;
+				at_used = 1;
+			} else
+			if (token[i] == '\\' && token[i + 1] != '\0')
+				list->to[j] = token[++i];
+			else
+				list->to[j] = token[i];
+		}
+		list->to[j] = '\0';
+	}
+
+	token = osmo_cc_strtok_quotes(&text);
+	if (token) {
+		free(list);
+		PDEBUG(DCC, DEBUG_ERROR, "Error in screening definition '%s'.\n", text);
+		PDEBUG(DCC, DEBUG_ERROR, "Got garbage behind screening result.\n");
+		return -EINVAL;
+	}
+
+	/* attach screen entry to list */
+	while (*list_p)
+		list_p = &((*list_p)->next);
+	*list_p = list;
+
+	return 0;
+}
+
+void osmo_cc_flush_screen(osmo_cc_screen_list_t *list)
+{
+	osmo_cc_screen_list_t *temp;
+
+	while (list) {
+		temp = list;
+		list = list->next;
+		free(temp);
+	}
+}
+
+const char *print_rule_string(const char *input)
+{
+	static char output[256];
+	int i;
+
+	for (i = 0; *input && i < (int)sizeof(output) - 1; i++, input++) {
+		switch (*input) {
+		case SCREEN_QUESTIONMARK:
+			output[i] = '?';
+			break;
+		case SCREEN_STAR:
+			output[i] = '*';
+			break;
+		case SCREEN_AT:
+			output[i] = '@';
+			break;
+		default:
+			output[i] = *input;
+		}
+	}
+
+	output[i] = '\0';
+	return output;
+}
+
+static int osmo_cc_screen(const char *what, osmo_cc_screen_list_t *list, uint8_t *type, uint8_t *present, char *id_to, int id_to_size, const char *id_from, const char **routing_p)
+{
+	const char *suffix;
+	int i, j, rule;
+
+	PDEBUG(DCC, DEBUG_INFO, "Screening %s '%s':\n", what, id_from);
+	switch (*type) {
+	case OSMO_CC_TYPE_UNKNOWN:
+		PDEBUG(DCC, DEBUG_INFO, " -> type = unknown\n");
+		break;
+	case OSMO_CC_TYPE_INTERNATIONAL:
+		PDEBUG(DCC, DEBUG_INFO, " -> type = international\n");
+		break;
+	case OSMO_CC_TYPE_NATIONAL:
+		PDEBUG(DCC, DEBUG_INFO, " -> type = national\n");
+		break;
+	case OSMO_CC_TYPE_NETWORK:
+		PDEBUG(DCC, DEBUG_INFO, " -> type = network\n");
+		break;
+	case OSMO_CC_TYPE_SUBSCRIBER:
+		PDEBUG(DCC, DEBUG_INFO, " -> type = subscriber\n");
+		break;
+	case OSMO_CC_TYPE_ABBREVIATED:
+		PDEBUG(DCC, DEBUG_INFO, " -> type = abbreviated\n");
+		break;
+	}
+	if (present) switch (*present) {
+	case OSMO_CC_PRESENT_ALLOWED:
+		PDEBUG(DCC, DEBUG_INFO, " -> present = allowed\n");
+		break;
+	case OSMO_CC_PRESENT_RESTRICTED:
+		PDEBUG(DCC, DEBUG_INFO, " -> present = restricted\n");
+		break;
+	}
+
+	rule = 0;
+	while (list) {
+		rule++;
+		PDEBUG(DCC, DEBUG_INFO, "Comparing with rule #%d: '%s':\n", rule, print_rule_string(list->from));
+		if (list->has_from_type) switch (list->from_type) {
+		case OSMO_CC_TYPE_UNKNOWN:
+			PDEBUG(DCC, DEBUG_INFO, " -> type = unknown\n");
+			break;
+		case OSMO_CC_TYPE_INTERNATIONAL:
+			PDEBUG(DCC, DEBUG_INFO, " -> type = international\n");
+			break;
+		case OSMO_CC_TYPE_NATIONAL:
+			PDEBUG(DCC, DEBUG_INFO, " -> type = national\n");
+			break;
+		case OSMO_CC_TYPE_NETWORK:
+			PDEBUG(DCC, DEBUG_INFO, " -> type = network\n");
+			break;
+		case OSMO_CC_TYPE_SUBSCRIBER:
+			PDEBUG(DCC, DEBUG_INFO, " -> type = subscriber\n");
+			break;
+		case OSMO_CC_TYPE_ABBREVIATED:
+			PDEBUG(DCC, DEBUG_INFO, " -> type = abbreviated\n");
+			break;
+		}
+		if (list->has_from_present) switch (list->from_present) {
+		case OSMO_CC_PRESENT_ALLOWED:
+			PDEBUG(DCC, DEBUG_INFO, " -> present = allowed\n");
+			break;
+		case OSMO_CC_PRESENT_RESTRICTED:
+			PDEBUG(DCC, DEBUG_INFO, " -> present = restricted\n");
+			break;
+		}
+		suffix = NULL;
+		/* attributes do not match */
+		if (list->has_from_type && list->from_type != *type) {
+			PDEBUG(DCC, DEBUG_INFO, "Rule does not match, because 'type' is different.\n");
+			continue;
+		}
+		if (present && list->has_from_present && list->from_present != *present) {
+			PDEBUG(DCC, DEBUG_INFO, "Rule does not match, because 'present' is different.\n");
+			continue;
+		}
+		for (i = 0; list->from[i] && id_from[i]; i++) {
+			/* '?' means: any digit, so it machtes */
+			if (list->from[i] == SCREEN_QUESTIONMARK) {
+				continue;
+			}
+			/* '*' means: anything may follow, so it machtes */
+			if (list->from[i] == SCREEN_STAR) {
+				suffix = id_from + i;
+				break;
+			}
+			/* check if digit doesn't matches */
+			if (list->from[i] != id_from[i])
+				break;
+		}
+		/* if last checked digit is '*', we have a match */
+		/* also if we hit EOL at id_from and next check digit is '*' */
+		if (list->from[i] == SCREEN_STAR)
+			break;
+		/* if all digits have matched */
+		if (list->from[i] == '\0' && id_from[i] == '\0')
+			break;
+		PDEBUG(DCC, DEBUG_INFO, "Rule does not match, because %s is different.\n", what);
+		list = list->next;
+	}
+
+	/* if no list entry matches */
+	if (!list)
+		return -1;
+
+	/* replace ID */
+	if (list->has_to_type) {
+		*type = list->to_type;
+	}
+	if (present && list->has_to_present) {
+		*present = list->to_present;
+	}
+	for (i = j = 0; list->to[i]; i++) {
+		if (j == id_to_size - 1)
+			break;
+		/* '*' means to use suffix of input string */
+		if (list->to[i] == SCREEN_STAR && suffix) {
+			while (*suffix) {
+				id_to[j++] = *suffix++;
+				if (j == id_to_size - 1)
+					break;
+			}
+			continue;
+		/* '@' means to stop and return routing also */
+		} else if (list->to[i] == SCREEN_AT) {
+			*routing_p = &list->to[i];
+			break;
+		}
+		/* copy output digit */
+		id_to[j++] = list->to[i];
+	}
+	id_to[j] = '\0';
+
+	PDEBUG(DCC, DEBUG_INFO, "Rule matches, changing %s to '%s'.\n", what, print_rule_string(id_to));
+	if (list->has_to_type) switch (list->to_type) {
+	case OSMO_CC_TYPE_UNKNOWN:
+		PDEBUG(DCC, DEBUG_INFO, " -> type = unknown\n");
+		break;
+	case OSMO_CC_TYPE_INTERNATIONAL:
+		PDEBUG(DCC, DEBUG_INFO, " -> type = international\n");
+		break;
+	case OSMO_CC_TYPE_NATIONAL:
+		PDEBUG(DCC, DEBUG_INFO, " -> type = national\n");
+		break;
+	case OSMO_CC_TYPE_NETWORK:
+		PDEBUG(DCC, DEBUG_INFO, " -> type = network\n");
+		break;
+	case OSMO_CC_TYPE_SUBSCRIBER:
+		PDEBUG(DCC, DEBUG_INFO, " -> type = subscriber\n");
+		break;
+	case OSMO_CC_TYPE_ABBREVIATED:
+		PDEBUG(DCC, DEBUG_INFO, " -> type = abbreviated\n");
+		break;
+	}
+	if (list->has_to_present) switch (list->to_present) {
+	case OSMO_CC_PRESENT_ALLOWED:
+		PDEBUG(DCC, DEBUG_INFO, " -> present = allowed\n");
+		break;
+	case OSMO_CC_PRESENT_RESTRICTED:
+		PDEBUG(DCC, DEBUG_INFO, " -> present = restricted\n");
+		break;
+	}
+
+	return 0;
+}
+
+osmo_cc_msg_t *osmo_cc_screen_msg(osmo_cc_endpoint_t *ep, osmo_cc_msg_t *old_msg, int in, const char **routing_p)
+{
+	osmo_cc_msg_t *new_msg;
+	char id[256], calling[256], called[256], redir[256];
+	uint8_t calling_type, calling_plan, calling_present, calling_screen;
+	uint8_t called_type, called_plan;
+	uint8_t redir_type, redir_plan, redir_present, redir_screen, redir_reason;
+	int calling_status = 0, called_status = 0, redir_status = 0;
+	int rc;
+	void *ie, *to_ie;
+	uint8_t ie_type;
+	uint16_t ie_length;
+	void *ie_value;
+
+	if (in && ep->screen_calling_in) {
+		rc = osmo_cc_get_ie_calling(old_msg, 0, &calling_type, &calling_plan, &calling_present, &calling_screen, id, sizeof(id));
+		if (rc >= 0) {
+			rc = osmo_cc_screen("incoming caller ID", ep->screen_calling_in, &calling_type, &calling_present, calling, sizeof(calling), id, routing_p);
+			if (rc >= 0)
+				calling_status = 1;
+		} else {
+			calling_type = OSMO_CC_TYPE_UNKNOWN;
+			calling_plan = OSMO_CC_PLAN_TELEPHONY;
+			calling_present = OSMO_CC_PRESENT_ALLOWED;
+			calling_screen = OSMO_CC_SCREEN_NETWORK;
+			rc = osmo_cc_screen("incoming caller ID", ep->screen_calling_in, &calling_type, &calling_present, calling, sizeof(calling), "", routing_p);
+			if (rc >= 0)
+				calling_status = 1;
+		}
+		rc = osmo_cc_get_ie_redir(old_msg, 0, &redir_type, &redir_plan, &redir_present, &redir_screen, &redir_reason, id, sizeof(id));
+		if (rc >= 0) {
+			rc = osmo_cc_screen("incoming redirecting number", ep->screen_calling_in, &redir_type, &redir_present, redir, sizeof(redir), id, routing_p);
+			if (rc >= 0)
+				redir_status = 1;
+		}
+	}
+	if (in && ep->screen_called_in) {
+		rc = osmo_cc_get_ie_called(old_msg, 0, &called_type, &called_plan, id, sizeof(id));
+		if (rc >= 0) {
+			rc = osmo_cc_screen("incoming dialed number", ep->screen_called_in, &called_type, NULL, called, sizeof(called), id, NULL);
+			if (rc >= 0)
+				called_status = 1;
+		} else {
+			called_type = OSMO_CC_TYPE_UNKNOWN;
+			called_plan = OSMO_CC_PLAN_TELEPHONY;
+			rc = osmo_cc_screen("incoming dialed number", ep->screen_called_in, &called_type, NULL, called, sizeof(called), "", NULL);
+			if (rc >= 0)
+				called_status = 1;
+		}
+	}
+	if (!in && ep->screen_calling_out) {
+		rc = osmo_cc_get_ie_calling(old_msg, 0, &calling_type, &calling_plan, &calling_present, &calling_screen, id, sizeof(id));
+		if (rc >= 0) {
+			rc = osmo_cc_screen("outgoing caller ID", ep->screen_calling_out, &calling_type, &calling_present, calling, sizeof(calling), id, NULL);
+			if (rc >= 0)
+				calling_status = 1;
+		} else {
+			calling_type = OSMO_CC_TYPE_UNKNOWN;
+			calling_plan = OSMO_CC_PLAN_TELEPHONY;
+			calling_present = OSMO_CC_PRESENT_ALLOWED;
+			calling_screen = OSMO_CC_SCREEN_NETWORK;
+			rc = osmo_cc_screen("outgoing caller ID", ep->screen_calling_out, &calling_type, &calling_present, calling, sizeof(calling), "", NULL);
+			if (rc >= 0)
+				calling_status = 1;
+		}
+		rc = osmo_cc_get_ie_redir(old_msg, 0, &redir_type, &redir_plan, &redir_present, &redir_screen, &redir_reason, id, sizeof(id));
+		if (rc >= 0) {
+			rc = osmo_cc_screen("outgoing redirecting number", ep->screen_calling_out, &redir_type, &redir_present, redir, sizeof(redir), id, NULL);
+			if (rc >= 0)
+				redir_status = 1;
+		}
+	}
+	if (!in && ep->screen_called_out) {
+		rc = osmo_cc_get_ie_called(old_msg, 0, &called_type, &called_plan, id, sizeof(id));
+		if (rc >= 0) {
+			rc = osmo_cc_screen("outgoing dialed number", ep->screen_called_out, &called_type, NULL, called, sizeof(called), id, NULL);
+			if (rc >= 0)
+				called_status = 1;
+		} else {
+			called_type = OSMO_CC_TYPE_UNKNOWN;
+			called_plan = OSMO_CC_PLAN_TELEPHONY;
+			rc = osmo_cc_screen("outgoing dialed number", ep->screen_called_out, &called_type, NULL, called, sizeof(called), "", NULL);
+			if (rc >= 0)
+				called_status = 1;
+		}
+	}
+
+	/* nothing screened */
+	if (!calling_status && !called_status && !redir_status)
+		return old_msg;
+
+	new_msg = osmo_cc_new_msg(old_msg->type);
+
+	/* copy and replace */
+	ie = old_msg->data;
+        while ((ie_value = osmo_cc_msg_sep_ie(old_msg, &ie, &ie_type, &ie_length))) {
+		switch (ie_type) {
+		case OSMO_CC_IE_CALLING:
+			if (calling_status) {
+				osmo_cc_add_ie_calling(new_msg, calling_type, calling_plan, calling_present, calling_screen, calling);
+				calling_status = 0;
+				break;
+			}
+			goto copy;
+		case OSMO_CC_IE_CALLED:
+			if (called_status) {
+				osmo_cc_add_ie_called(new_msg, called_type, called_plan, called);
+				called_status = 0;
+				break;
+			}
+			goto copy;
+		case OSMO_CC_IE_REDIR:
+			if (redir_status) {
+				osmo_cc_add_ie_redir(new_msg, redir_type, redir_plan, redir_present, redir_screen, redir_reason, redir);
+				redir_status = 0;
+				break;
+			}
+			goto copy;
+		default:
+			copy:
+			to_ie = osmo_cc_add_ie(new_msg, ie_type, ie_length);
+			memcpy(to_ie, ie_value, ie_length);
+		}
+        }
+
+	/* applend, if not yet in message (except redir, since it must exist) */
+	if (calling_status)
+		osmo_cc_add_ie_calling(new_msg, calling_type, calling_plan, calling_present, calling_screen, calling);
+	if (called_status)
+		osmo_cc_add_ie_called(new_msg, called_type, called_plan, called);
+
+	free(old_msg);
+	return new_msg;
+}
+
diff --git a/src/libosmocc/screen.h b/src/libosmocc/screen.h
new file mode 100644
index 0000000..29f4515
--- /dev/null
+++ b/src/libosmocc/screen.h
@@ -0,0 +1,7 @@
+
+void osmo_cc_help_screen(void);
+char *osmo_cc_strtok_quotes(const char **text_p);
+int osmo_cc_add_screen(osmo_cc_endpoint_t *ep, const char *text);
+void osmo_cc_flush_screen(osmo_cc_screen_list_t *list);
+osmo_cc_msg_t *osmo_cc_screen_msg(osmo_cc_endpoint_t *ep, osmo_cc_msg_t *old_msg, int in, const char **routing_p);
+
diff --git a/src/libosmocc/sdp.c b/src/libosmocc/sdp.c
new file mode 100644
index 0000000..3fba8af
--- /dev/null
+++ b/src/libosmocc/sdp.c
@@ -0,0 +1,539 @@
+/* Session Description Protocol parsing and generator
+ * This shall be simple and is incomplete.
+ *
+ * (C) 2019 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <errno.h>
+#include "../libdebug/debug.h"
+#include "../libtimer/timer.h"
+#include "endpoint.h"
+#include "sdp.h"
+
+#define strncat_printf(sdp, fmt, arg...) \
+	{ \
+		snprintf(sdp + strlen(sdp), sizeof(sdp) - strlen(sdp), fmt, ## arg); \
+		sdp[sizeof(sdp) - 1] = '\0'; \
+	}
+
+/* generate SDP from session structure */
+char *osmo_cc_session_gensdp(osmo_cc_session_t *session)
+{
+	/* calc max size of SDP: quick an dirty (close to max UDP payload size) */
+	static char sdp[65000];
+	const char *username, *sess_id, *sess_version, *nettype, *addrtype, *unicast_address;
+	const char *session_name;
+	int individual_connection_data = 1; /* in case there is no media, there is no connection data */
+	int individual_send_receive = 1; /* in case there is no media, there is no send/receive attribute */
+	struct osmo_cc_session_media *media;
+	struct osmo_cc_session_codec *codec;
+
+	sdp[0] = 0;
+
+	/* Version */
+	strncat_printf(sdp, "v=0\r\n");
+
+	/* Origin */
+	username = session->origin_local.username;
+	sess_id = session->origin_local.sess_id;
+	sess_version = session->origin_local.sess_version;
+	nettype = session->origin_local.nettype;
+	addrtype = session->origin_local.addrtype;
+	unicast_address = session->origin_local.unicast_address;
+	strncat_printf(sdp, "o=%s %s %s %s %s %s\r\n", username, sess_id, sess_version, nettype, addrtype, unicast_address);
+
+	/* Session */
+	session_name = session->name;
+	strncat_printf(sdp, "s=%s\r\n", session_name);
+
+	/* Connection Data (if all media have the same data) */
+	if (session->media_list) {
+		osmo_cc_session_for_each_media(session->media_list->next, media) {
+			if (session->media_list->connection_data_local.nettype != media->connection_data_local.nettype)
+				break;
+			if (session->media_list->connection_data_local.addrtype != media->connection_data_local.addrtype)
+				break;
+			if (!!strcmp(session->media_list->connection_data_local.address, media->connection_data_local.address))
+				break;
+		}
+		if (!media)
+			individual_connection_data = 0;
+	}
+	if (!individual_connection_data)
+		strncat_printf(sdp, "c=%s %s %s\r\n", osmo_cc_session_nettype2string(session->media_list->connection_data_local.nettype), osmo_cc_session_addrtype2string(session->media_list->connection_data_local.addrtype), session->media_list->connection_data_local.address);
+
+	/* timestamp */
+	strncat_printf(sdp, "t=0 0\r\n");
+
+	/* sendonly /recvonly (if all media have the same data) */
+	if (session->media_list) {
+		osmo_cc_session_for_each_media(session->media_list->next, media) {
+			if (session->media_list->send != media->send)
+				break;
+			if (session->media_list->receive != media->receive)
+				break;
+		}
+		if (!media)
+			individual_send_receive = 0;
+	}
+	if (!individual_send_receive) {
+		if (session->media_list->send && !session->media_list->receive)
+			strncat_printf(sdp, "a=sendonly\r\n");
+		if (!session->media_list->send && session->media_list->receive)
+			strncat_printf(sdp, "a=recvonly\r\n");
+		if (!session->media_list->send && !session->media_list->receive)
+			strncat_printf(sdp, "a=inactive\r\n");
+	}
+
+	/* media */
+	osmo_cc_session_for_each_media(session->media_list, media) {
+		strncat_printf(sdp, "m=%s %u %s",
+			osmo_cc_session_media_type2string(media->description.type) ? : media->description.type_name,
+			media->description.port_local,
+			osmo_cc_session_media_proto2string(media->description.proto) ? : media->description.proto_name);
+		osmo_cc_session_for_each_codec(media->codec_list, codec)
+			strncat_printf(sdp, " %u", codec->payload_type_local);
+		strncat_printf(sdp, "\r\n");
+		/* don't list rtpmap when session was canceled by setting port to 0 */
+		if (media->description.port_local == 0)
+			continue;
+		if (individual_connection_data)
+			strncat_printf(sdp, "c=%s %s %s\r\n", osmo_cc_session_nettype2string(media->connection_data_local.nettype), osmo_cc_session_addrtype2string(media->connection_data_local.addrtype), media->connection_data_local.address);
+		osmo_cc_session_for_each_codec(media->codec_list, codec) {
+			strncat_printf(sdp, "a=rtpmap:%u %s/%d", codec->payload_type_local, codec->payload_name, codec->payload_rate);
+			if (codec->payload_channels >= 2)
+				strncat_printf(sdp, "/%d", codec->payload_channels);
+			strncat_printf(sdp, "\r\n");
+		}
+		if (individual_send_receive) {
+			if (media->send && !media->receive)
+				strncat_printf(sdp, "a=sendonly\r\n");
+			if (!media->send && media->receive)
+				strncat_printf(sdp, "a=recvonly\r\n");
+			if (!media->send && !media->receive)
+				strncat_printf(sdp, "a=inactive\r\n");
+		}
+	}
+
+	/* check for overflow and return */
+	if (strlen(sdp) == sizeof(sdp) - 1) {
+		PDEBUG(DCC, DEBUG_ERROR, "Fatal error: Allocated SDP buffer with %d bytes is too small, please fix!\n", (int)sizeof(sdp));
+		return NULL;
+	}
+	return sdp;
+}
+
+/* seperate a word from string that is delimited with one or more space characters */
+static char *wordsep(char **text_p)
+{
+	char *text = *text_p;
+	static char word[256];
+	int i;
+
+	/* no text */
+	if (text == NULL || *text == '\0')
+		return NULL;
+	/* skip spaces before text */
+	while (*text && *text <= ' ')
+		text++;
+	/* copy content */
+	i = 0;
+	while (*text > ' ' && i < (int)sizeof(word))
+		word[i++] = *text++;
+	word[i] = '\0';
+	/* set next */
+	*text_p = text;
+	return word;
+}
+
+/*
+ * codecs and their default values
+ *
+ * if format is -1, payload type is dynamic
+ * if rate is 0, rate may be any rate
+ */
+struct codec_defaults {
+	int fmt;
+	char *name;
+	uint32_t rate;
+	int channels;
+} codec_defaults[] = {
+	{ 0,	"PCMU",	 	8000,	1 },
+	{ 3,	"GSM",	 	8000,	1 },
+	{ 4,	"G723",	 	8000,	1 },
+	{ 5,	"DVI4",	 	8000,	1 },
+	{ 6,	"DVI4",	 	16000,	1 },
+	{ 7,	"LPC",	 	8000,	1 },
+	{ 8,	"PCMA",	 	8000,	1 },
+	{ 9,	"G722",	 	8000,	1 },
+	{ 10,	"L16",	 	44100,	2 },
+	{ 11,	"L16",	 	44100,	1 },
+	{ 12,	"QCELP", 	8000,	1 },
+	{ 13,	"CN",	 	8000,	1 },
+	{ 14,	"MPA",	 	90000,	1 },
+	{ 15,	"G728",	 	8000,	1 },
+	{ 16,	"DVI4",	 	11025,	1 },
+	{ 17,	"DVI4",	 	22050,	1 },
+	{ 18,	"G729",	 	8000,	1 },
+	{ 25,	"CELB",	 	90000,	0 },
+	{ 26,	"JPEG",	 	90000,	0 },
+	{ 28,	"nv",	 	90000,	0 },
+	{ 31,	"H261",	 	90000,	0 },
+	{ 32,	"MPV",	 	90000,	0 },
+	{ 33,	"MP2T",	 	90000,	0 },
+	{ 34,	"H263",	 	90000,	0 },
+	{ -1, NULL, 0, 0 },
+};
+
+static void complete_codec_by_fmt(uint8_t fmt, const char **name, uint32_t *rate, int *channels)
+{
+	int i;
+
+	for (i = 0; codec_defaults[i].name; i++) {
+		if (codec_defaults[i].fmt == fmt)
+			break;
+	}
+	if (!codec_defaults[i].name)
+		return;
+
+	free((char *)*name);
+	*name = strdup(codec_defaults[i].name);
+	*rate = codec_defaults[i].rate;
+	*channels = codec_defaults[i].channels;
+}
+
+int osmo_cc_payload_type_by_attrs(uint8_t *fmt, const char *name, uint32_t *rate, int *channels)
+{
+	int i;
+
+	for (i = 0; codec_defaults[i].name; i++) {
+		if (!strcmp(codec_defaults[i].name, name)
+		 && (*rate == 0 || codec_defaults[i].rate == *rate)
+		 && (*channels == 0 || codec_defaults[i].channels == *channels))
+			break;
+	}
+	if (!codec_defaults[i].name)
+		return -EINVAL;
+
+	*fmt = codec_defaults[i].fmt;
+	*rate = codec_defaults[i].rate;
+	*channels = codec_defaults[i].channels;
+
+	return 0;
+}
+
+/* parses data and codec list from SDP
+ *
+ * sdp = given SDP text
+ * return: SDP session description structure */
+struct osmo_cc_session *osmo_cc_session_parsesdp(void *priv, const char *_sdp)
+{
+	char buffer[strlen(_sdp) + 1], *sdp = buffer;
+	char *line, *p, *word, *next_word;
+	int line_no = 0;
+	struct osmo_cc_session_connection_data ccd, *cd;
+	int csend = 1, creceive = 1; /* common default */
+	struct osmo_cc_session *session = NULL;
+	struct osmo_cc_session_media *media = NULL;
+	struct osmo_cc_session_codec *codec = NULL;
+
+	/* prepare data */
+	strcpy(sdp, _sdp);
+	memset(&ccd, 0, sizeof(ccd));
+
+	/* create SDP session description */
+	session = osmo_cc_new_session(priv, NULL, NULL, NULL, osmo_cc_session_nettype_inet, osmo_cc_session_addrtype_ipv4, "127.0.0.1", NULL, 0); // values will be replaced by local definitions during negotiation
+
+	/* check every line of SDP and parse its data */
+	while(*sdp) {
+		if ((p = strchr(sdp, '\r'))) {
+			*p++ = '\0';
+			if (*p == '\n')
+				p++;
+			line = sdp;
+			sdp = p;
+		} else if ((p = strchr(sdp, '\n'))) {
+			*p++ = '\0';
+			line = sdp;
+			sdp = p;
+		} else {
+			line = sdp;
+			sdp = strchr(sdp, '\0');
+		}
+		next_word = line + 2;
+		line_no++;
+
+		if (line[0] == '\0')
+			continue;
+
+		if (line[1] != '=') {
+			PDEBUG(DCC, DEBUG_NOTICE, "SDP line %d = '%s' is garbage, expecting '=' as second character.\n", line_no, line);
+			continue;
+		}
+
+		switch(line[0]) {
+		case 'v':
+			PDEBUG(DCC, DEBUG_DEBUG, " -> Version: %s\n", next_word);
+			if (atoi(next_word) != 0) {
+				PDEBUG(DCC, DEBUG_NOTICE, "SDP line %d = '%s' describes unsupported version.\n", line_no, line);
+				osmo_cc_free_session(session);
+				return NULL;
+			}
+			break;
+		case 'o':
+			PDEBUG(DCC, DEBUG_DEBUG, " -> Originator: %s\n", next_word);
+			/* Originator */
+			word = wordsep(&next_word);
+			if (!word)
+				break;
+			free((char *)session->origin_remote.username); // if already set
+			session->origin_remote.username = strdup(word);
+			word = wordsep(&next_word);
+			if (!word)
+				break;
+			free((char *)session->origin_remote.sess_id); // if already set
+			session->origin_remote.sess_id = strdup(word);
+			word = wordsep(&next_word);
+			if (!word)
+				break;
+			free((char *)session->origin_remote.sess_version); // if already set
+			session->origin_remote.sess_version = strdup(word);
+			word = wordsep(&next_word);
+			if (!word)
+				break;
+			free((char *)session->origin_remote.nettype); // if already set
+			session->origin_remote.nettype = strdup(word);
+			word = wordsep(&next_word);
+			if (!word)
+				break;
+			free((char *)session->origin_remote.addrtype); // if already set
+			session->origin_remote.addrtype = strdup(word);
+			word = wordsep(&next_word);
+			if (!word)
+				break;
+			free((char *)session->origin_remote.unicast_address); // if already set
+			session->origin_remote.unicast_address = strdup(word);
+			break;
+		case 's':
+			/* Session Name */
+			PDEBUG(DCC, DEBUG_DEBUG, " -> Session Name: %s\n", next_word);
+			free((char *)session->name); // if already set
+			session->name = strdup(next_word);
+			break;
+		case 'c': /* Connection Data */
+			PDEBUG(DCC, DEBUG_DEBUG, " -> Connection Data: %s\n", next_word);
+			if (media)
+				cd = &media->connection_data_remote;
+			else
+				cd = &ccd;
+			/* network type */
+			if (!(word = wordsep(&next_word)))
+				break;
+			if (!strcmp(word, "IN"))
+				cd->nettype = osmo_cc_session_nettype_inet;
+			else {
+				PDEBUG(DCC, DEBUG_NOTICE, "Unsupported network type '%s' in SDP line %d = '%s'\n", word, line_no, line);
+				break;
+			}
+			/* address type */
+			if (!(word = wordsep(&next_word)))
+				break;
+			if (!strcmp(word, "IP4")) {
+				cd->addrtype = osmo_cc_session_addrtype_ipv4;
+				PDEBUG(DCC, DEBUG_DEBUG, " -> Address Type = IPv4\n");
+			} else
+			if (!strcmp(word, "IP6")) {
+				cd->addrtype = osmo_cc_session_addrtype_ipv6;
+				PDEBUG(DCC, DEBUG_DEBUG, " -> Address Type = IPv6\n");
+			} else {
+				PDEBUG(DCC, DEBUG_NOTICE, "Unsupported address type '%s' in SDP line %d = '%s'\n", word, line_no, line);
+				break;
+			}
+			/* connection address */
+			if (!(word = wordsep(&next_word)))
+				break;
+			if ((p = strchr(word, '/')))
+				*p++ = '\0';
+			free((char *)cd->address); // in case of multiple lines of 'c'
+			cd->address = strdup(word);
+			PDEBUG(DCC, DEBUG_DEBUG, " -> Address = %s\n", word);
+			break;
+		case 'm': /* Media Description */
+			PDEBUG(DCC, DEBUG_DEBUG, " -> Media Description: %s\n", next_word);
+			/* add media description */
+			media = osmo_cc_add_media(session, 0, 0, NULL, 0, 0, 0, csend, creceive, NULL, 0);
+			/* copy common connection data from common connection, if exists */
+			cd = &media->connection_data_remote;
+			memcpy(cd, &ccd, sizeof(*cd));
+			/* media type */
+			if (!(word = wordsep(&next_word)))
+				break;
+			if (!strcmp(word, "audio"))
+				media->description.type = osmo_cc_session_media_type_audio;
+			else
+			if (!strcmp(word, "video"))
+				media->description.type = osmo_cc_session_media_type_video;
+			else {
+				media->description.type = osmo_cc_session_media_type_unknown;
+				media->description.type_name = strdup(word);
+				PDEBUG(DCC, DEBUG_DEBUG, "Unsupported media type in SDP line %d = '%s'\n", line_no, line);
+			}
+			/* port */
+			if (!(word = wordsep(&next_word)))
+				break;
+			media->description.port_remote = atoi(word);
+			/* proto */
+			if (!(word = wordsep(&next_word)))
+				break;
+			if (!strcmp(word, "RTP/AVP"))
+				media->description.proto = osmo_cc_session_media_proto_rtp;
+			else {
+				media->description.proto = osmo_cc_session_media_proto_unknown;
+				media->description.proto_name = strdup(word);
+				PDEBUG(DCC, DEBUG_NOTICE, "Unsupported protocol type in SDP line %d = '%s'\n", line_no, line);
+				break;
+			}
+			/* create codec description for each codec and link */
+			while ((word = wordsep(&next_word))) {
+				/* create codec */
+				codec = osmo_cc_add_codec(media, NULL, 0, 1, NULL, NULL, 0);
+				/* fmt */
+				codec->payload_type_remote = atoi(word);
+				complete_codec_by_fmt(codec->payload_type_remote, &codec->payload_name, &codec->payload_rate, &codec->payload_channels);
+				PDEBUG(DCC, DEBUG_DEBUG, " -> payload type = %d\n", codec->payload_type_remote);
+				if (codec->payload_name)
+					PDEBUG(DCC, DEBUG_DEBUG, " -> payload name = %s\n", codec->payload_name);
+				if (codec->payload_rate)
+					PDEBUG(DCC, DEBUG_DEBUG, " -> payload rate = %d\n", codec->payload_rate);
+				if (codec->payload_channels)
+					PDEBUG(DCC, DEBUG_DEBUG, " -> payload channels = %d\n", codec->payload_channels);
+			}
+			break;
+		case 'a':
+			PDEBUG(DCC, DEBUG_DEBUG, " -> Attribute: %s\n", next_word);
+			word = wordsep(&next_word);
+			if (!strcmp(word, "sendrecv")) {
+				if (media) {
+					media->receive = 1;
+					media->send = 1;
+				} else {
+					creceive = 1;
+					csend = 1;
+				}
+				break;
+			} else
+			if (!strcmp(word, "recvonly")) {
+				if (media) {
+					media->receive = 1;
+					media->send = 0;
+				} else {
+					creceive = 1;
+					csend = 0;
+				}
+				break;
+			} else
+			if (!strcmp(word, "sendonly")) {
+				if (media) {
+					media->receive = 0;
+					media->send = 1;
+				} else {
+					creceive = 0;
+					csend = 1;
+				}
+				break;
+			} else
+			if (!strcmp(word, "inactive")) {
+				if (media) {
+					media->receive = 0;
+					media->send = 0;
+				} else {
+					creceive = 0;
+					csend = 0;
+				}
+				break;
+			} else
+			if (!media) {
+				PDEBUG(DCC, DEBUG_NOTICE, "Attribute without previously defined media in SDP line %d = '%s'\n", line_no, line);
+				break;
+			}
+			if (!strncmp(word, "rtpmap:", 7)) {
+				int fmt = atoi(word + 7);
+				osmo_cc_session_for_each_codec(media->codec_list, codec) {
+					if (codec->payload_type_remote == fmt)
+						break;
+				}
+				if (!codec) {
+					PDEBUG(DCC, DEBUG_NOTICE, "Attribute without previously defined codec in SDP line %d = '%s'\n", line_no, line);
+					break;
+				}
+				PDEBUG(DCC, DEBUG_DEBUG, " -> (rtpmap) payload type = %d\n", codec->payload_type_remote);
+				if (!(word = wordsep(&next_word)))
+					break;
+				if ((p = strchr(word, '/')))
+					*p++ = '\0';
+				free((char *)codec->payload_name); // in case it is already set above
+				codec->payload_name = strdup(word);
+				PDEBUG(DCC, DEBUG_DEBUG, " -> (rtpmap) payload name = %s\n", codec->payload_name);
+				if (!(word = p))
+					break;
+				if ((p = strchr(word, '/')))
+					*p++ = '\0';
+				codec->payload_rate = atoi(word);
+				PDEBUG(DCC, DEBUG_DEBUG, " -> (rtpmap) payload rate = %d\n", codec->payload_rate);
+				if (!(word = p)) {
+					/* if no channel is given and no default was specified, we must set 1 channel */
+					if (!codec->payload_channels)
+						codec->payload_channels = 1;
+					break;
+				}
+				codec->payload_channels = atoi(word);
+				PDEBUG(DCC, DEBUG_DEBUG, " -> (rtpmap) payload channels = %d\n", codec->payload_channels);
+			}
+			break;
+		}
+	}
+
+	/* if something is incomplete, abort here */
+	if (osmo_cc_session_check(session, 1)) {
+		PDEBUG(DCC, DEBUG_NOTICE, "Parsing SDP failed.\n");
+		osmo_cc_free_session(session);
+		return NULL;
+	}
+
+	return session;
+}
+
+void osmo_cc_debug_sdp(const char *_sdp)
+{
+	const unsigned char *sdp = (const unsigned char *)_sdp;
+	char text[256];
+	int i;
+
+	while (*sdp) {
+		for (i = 0; *sdp > 0 && *sdp >= 32 && i < (int)sizeof(text) - 1; i++)
+			text[i] = *sdp++;
+		text[i] = '\0';
+		PDEBUG(DCC, DEBUG_DEBUG, " | %s\n", text);
+		while (*sdp > 0 && *sdp < 32)
+			sdp++;
+	}
+}
+
diff --git a/src/libosmocc/sdp.h b/src/libosmocc/sdp.h
new file mode 100644
index 0000000..4aa6f60
--- /dev/null
+++ b/src/libosmocc/sdp.h
@@ -0,0 +1,6 @@
+
+char *osmo_cc_session_gensdp(struct osmo_cc_session *session);
+struct osmo_cc_session *osmo_cc_session_parsesdp(void *priv, const char *_sdp);
+int osmo_cc_payload_type_by_attrs(uint8_t *fmt, const char *name, uint32_t *rate, int *channels);
+void osmo_cc_debug_sdp(const char *sdp);
+
diff --git a/src/libosmocc/session.c b/src/libosmocc/session.c
new file mode 100644
index 0000000..72e805a
--- /dev/null
+++ b/src/libosmocc/session.c
@@ -0,0 +1,639 @@
+/* Osmo-CC: Media Session handling
+ *
+ * (C) 2016 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <sys/time.h>
+#include <inttypes.h>
+#include "../libtimer/timer.h"
+#include "../libdebug/debug.h"
+#include "endpoint.h"
+
+#define NTP_OFFSET      2208988800
+
+enum osmo_cc_session_nettype default_nettype = osmo_cc_session_nettype_inet;
+enum osmo_cc_session_addrtype default_addrtype = osmo_cc_session_addrtype_ipv4;
+const char *default_unicast_address = "127.0.0.1";
+
+void osmo_cc_set_local_peer(enum osmo_cc_session_nettype nettype, enum osmo_cc_session_addrtype addrtype, const char *address)
+{
+	default_nettype = nettype;
+	default_addrtype = addrtype;
+	default_unicast_address = strdup(address);
+}
+
+osmo_cc_session_t *osmo_cc_new_session(void *priv, const char *username, const char *sess_id, const char *sess_version, enum osmo_cc_session_nettype nettype, enum osmo_cc_session_addrtype addrtype, const char *unicast_address, const char *session_name, int debug)
+{
+	osmo_cc_session_t *session;
+
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, "Creating session structure.\n");
+
+	session = calloc(1, sizeof(*session));
+	if (!session) {
+		PDEBUG(DCC, DEBUG_ERROR, "No mem!\n");
+		abort();
+	}
+	session->priv = priv;
+	if (username) {
+		int i;
+		for (i = 0; username[i]; i++) {
+			if ((uint8_t)username[i] < 33) {
+				PDEBUG(DCC, DEBUG_ERROR, "Fatal error: SDP's originator (username) uses invalid characters, please fix!\n");
+				abort();
+			}
+		}
+		session->origin_local.username = strdup(username);
+	}
+	if (!username)
+		session->origin_local.username = strdup("-");
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> user name = %s\n", session->origin_local.username);
+	if (sess_id)
+		session->origin_local.sess_id = strdup(sess_id);
+	if (sess_version)
+		session->origin_local.sess_version = strdup(sess_version);
+	if (!sess_id || !sess_version) {
+		struct timeval tv;
+		char ntp_timestamp[32];
+		/* get time NTP format time stamp (time since 1900) */
+		gettimeofday(&tv, NULL);
+		sprintf(ntp_timestamp, "%" PRIu64, (uint64_t)tv.tv_sec + NTP_OFFSET);
+		if (!sess_id)
+			session->origin_local.sess_id = strdup(ntp_timestamp);
+		if (!sess_version)
+			session->origin_local.sess_version = strdup(ntp_timestamp);
+	}
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> session ID = %s\n", session->origin_local.sess_id);
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> session version = %s\n", session->origin_local.sess_version);
+	if (nettype)
+		session->origin_local.nettype = strdup(osmo_cc_session_nettype2string(nettype));
+	else
+		session->origin_local.nettype = strdup(osmo_cc_session_nettype2string(default_nettype));
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> network type = %s\n", session->origin_local.nettype);
+	if (addrtype)
+		session->origin_local.addrtype = strdup(osmo_cc_session_addrtype2string(addrtype));
+	else
+		session->origin_local.addrtype = strdup(osmo_cc_session_addrtype2string(default_addrtype));
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> address type = %s\n", session->origin_local.addrtype);
+	if (unicast_address)
+		session->origin_local.unicast_address = strdup(unicast_address);
+	else
+		session->origin_local.unicast_address = strdup(default_unicast_address);
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> unicast address = %s\n", session->origin_local.unicast_address);
+	if (session_name)
+		session->name = strdup(session_name);
+	if (!session_name)
+		session->name = strdup("-");
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> session name = %s\n", session->name);
+
+	return session;
+}
+
+void osmo_cc_free_session(osmo_cc_session_t *session)
+{
+	PDEBUG(DCC, DEBUG_DEBUG, "Free session structure.\n");
+
+	free((char *)session->origin_local.username);
+	free((char *)session->origin_local.sess_id);
+	free((char *)session->origin_local.sess_version);
+	free((char *)session->origin_local.nettype);
+	free((char *)session->origin_local.addrtype);
+	free((char *)session->origin_local.unicast_address);
+	free((char *)session->origin_remote.username);
+	free((char *)session->origin_remote.sess_id);
+	free((char *)session->origin_remote.sess_version);
+	free((char *)session->origin_remote.nettype);
+	free((char *)session->origin_remote.addrtype);
+	free((char *)session->origin_remote.unicast_address);
+	free((char *)session->name);
+	while (session->media_list)
+		osmo_cc_free_media(session->media_list);
+	free(session);
+}
+
+osmo_cc_session_media_t *osmo_cc_add_media(osmo_cc_session_t *session, enum osmo_cc_session_nettype nettype, enum osmo_cc_session_addrtype addrtype, const char *address, enum osmo_cc_session_media_type type, uint16_t port, enum osmo_cc_session_media_proto proto, int send, int receive, void (*receiver)(struct osmo_cc_session_codec *codec, uint16_t sequence_number, uint32_t timestamp, uint8_t *data, int len), int debug)
+{
+	osmo_cc_session_media_t *media, **mediap;
+
+	media = calloc(1, sizeof(*media));
+	if (!media) {
+		PDEBUG(DCC, DEBUG_ERROR, "No mem!\n");
+		abort();
+	}
+	media->session = session;
+	if (nettype)
+		media->connection_data_local.nettype = nettype;
+	else
+		media->connection_data_local.nettype = default_nettype;
+	if (addrtype)
+		media->connection_data_local.addrtype = addrtype;
+	else
+		media->connection_data_local.addrtype = default_addrtype;
+	if (address)
+		media->connection_data_local.address = strdup(address);
+	else
+		media->connection_data_local.address = strdup(default_unicast_address);
+	media->description.type = type;
+	media->description.port_local = port;
+	media->description.proto = proto;
+	media->send = send;
+	media->receive = receive;
+	media->receiver = receiver;
+	media->tx_sequence = random();
+	media->tx_timestamp = random();
+	mediap = &media->session->media_list;
+	while (*mediap)
+		mediap = &((*mediap)->next);
+	*mediap = media;
+
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, "Adding session media.\n");
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> network type = %s\n", osmo_cc_session_nettype2string(media->connection_data_local.nettype));
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> address type = %s\n", osmo_cc_session_addrtype2string(media->connection_data_local.addrtype));
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> address = %s\n", media->connection_data_local.address);
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> media type = %s\n", osmo_cc_session_media_type2string(media->description.type));
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> media port = %d\n", media->description.port_local);
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> media proto = %s\n", osmo_cc_session_media_proto2string(media->description.proto));
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, "Opening and binding media port %d\n", media->description.port_local);
+
+	return media;
+}
+
+void osmo_cc_free_media(osmo_cc_session_media_t *media)
+{
+	osmo_cc_session_media_t **mediap;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Free session media.\n");
+
+	osmo_cc_rtp_close(media);
+	free((char *)media->connection_data_local.nettype_name);
+	free((char *)media->connection_data_local.addrtype_name);
+	free((char *)media->connection_data_local.address);
+	free((char *)media->connection_data_remote.nettype_name);
+	free((char *)media->connection_data_remote.addrtype_name);
+	free((char *)media->connection_data_remote.address);
+	while (media->codec_list)
+		osmo_cc_free_codec(media->codec_list);
+	mediap = &media->session->media_list;
+	while (*mediap != media)
+		mediap = &((*mediap)->next);
+	*mediap = media->next;
+	free(media);
+}
+
+osmo_cc_session_codec_t *osmo_cc_add_codec(osmo_cc_session_media_t *media, const char *payload_name, uint32_t payload_rate, int payload_channels, void (*encoder)(uint8_t *src_data, int src_len, uint8_t **dst_data, int *dst_len), void (*decoder)(uint8_t *src_data, int src_len, uint8_t **dst_data, int *dst_len), int debug)
+{
+	osmo_cc_session_codec_t *codec, **codecp;
+	int rc;
+
+	codec = calloc(1, sizeof(*codec));
+	if (!codec) {
+		PDEBUG(DCC, DEBUG_ERROR, "No mem!\n");
+		abort();
+	}
+	codec->media = media;
+	if (payload_name) {
+		codec->payload_name = strdup(payload_name);
+		codec->payload_rate = payload_rate;
+		codec->payload_channels = payload_channels;
+		rc = osmo_cc_payload_type_by_attrs(&codec->payload_type_local, payload_name, &payload_rate, &payload_channels);
+		if (rc < 0) {
+			/* hunt for next free dynamic payload type */
+			uint8_t fmt = 96;
+			osmo_cc_session_codec_t *c;
+			osmo_cc_session_for_each_codec(media->codec_list, c) {
+				if (c->payload_type_local >= fmt)
+					fmt = c->payload_type_local + 1;
+			}
+			codec->payload_type_local = fmt;
+		}
+	}
+	codec->encoder = encoder;
+	codec->decoder = decoder;
+	codecp = &codec->media->codec_list;
+	while (*codecp)
+		codecp = &((*codecp)->next);
+	*codecp = codec;
+
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, "Adding session codec.\n");
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> payload type = %d\n", codec->payload_type_local);
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> payload name = %s\n", codec->payload_name);
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> payload rate = %d\n", codec->payload_rate);
+	if (debug) PDEBUG(DCC, DEBUG_DEBUG, " -> payload channels = %d\n", codec->payload_channels);
+
+	return codec;
+}
+
+void osmo_cc_free_codec(osmo_cc_session_codec_t *codec)
+{
+	osmo_cc_session_codec_t **codecp;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Free session codec.\n");
+
+	free((char *)codec->payload_name);
+	codecp = &codec->media->codec_list;
+	while (*codecp != codec)
+		codecp = &((*codecp)->next);
+	*codecp = codec->next;
+	free(codec);
+}
+
+int osmo_cc_session_check(osmo_cc_session_t *session, int remote)
+{
+	struct osmo_cc_session_origin *orig;
+	struct osmo_cc_session_media *media;
+	struct osmo_cc_session_connection_data *cd;
+	struct osmo_cc_session_media_description *md;
+	struct osmo_cc_session_codec *codec;
+	int i, j;
+
+	if (remote)
+		orig = &session->origin_remote;
+	else
+		orig = &session->origin_local;
+	if (!orig->username
+	 || !orig->sess_id
+	 || !orig->sess_version
+	 || !orig->nettype
+	 || !orig->addrtype
+	 || !orig->unicast_address) {
+		PDEBUG(DCC, DEBUG_NOTICE, "Missing data in session origin\n");
+		return -EINVAL;
+	}
+	if (!session->name) {
+		PDEBUG(DCC, DEBUG_NOTICE, "Missing data in session origin\n");
+		return -EINVAL;
+	}
+	if (!session->media_list) {
+		PDEBUG(DCC, DEBUG_NOTICE, "Missing media session\n");
+		return -EINVAL;
+	}
+	i = 0;
+	osmo_cc_session_for_each_media(session->media_list, media) {
+		i++;
+		if (remote)
+			cd = &media->connection_data_remote;
+		else
+			cd = &media->connection_data_local;
+		if (!cd->nettype && !cd->nettype_name) {
+			PDEBUG(DCC, DEBUG_NOTICE, "Session with media #%d is missing connection network type\n", i);
+			return -EINVAL;
+		}
+		if (!cd->addrtype && !cd->addrtype_name) {
+			PDEBUG(DCC, DEBUG_NOTICE, "Session with media #%d is missing connection address type\n", i);
+			return -EINVAL;
+		}
+		if (!cd->address) {
+			PDEBUG(DCC, DEBUG_NOTICE, "Session with media #%d is missing connection address\n", i);
+			return -EINVAL;
+		}
+		md = &media->description;
+		if (!md->type && !md->type_name) {
+			PDEBUG(DCC, DEBUG_NOTICE, "Session with media #%d is missing media type\n", i);
+			return -EINVAL;
+		}
+		if (!md->proto && !md->proto_name) {
+			PDEBUG(DCC, DEBUG_NOTICE, "Session with media #%d is missing protocol\n", i);
+			return -EINVAL;
+		}
+		j = 0;
+		osmo_cc_session_for_each_codec(media->codec_list, codec) {
+			j++;
+			if (!codec->payload_name) {
+				PDEBUG(DCC, DEBUG_NOTICE, "Session with media #%d, codec #%d is missing name\n", i, j);
+				return -EINVAL;
+			}
+			if (!codec->payload_rate) {
+				PDEBUG(DCC, DEBUG_NOTICE, "Session with media #%d, codec #%d is missing rate\n", i, j);
+				return -EINVAL;
+			}
+			if (!codec->payload_channels) {
+				PDEBUG(DCC, DEBUG_NOTICE, "Session with media #%d, codec #%d is missing channel count\n", i, j);
+				return -EINVAL;
+			}
+		}
+	}
+
+	return 0;
+}
+
+/* check session description and generate SDP */
+const char *osmo_cc_session_send_offer(osmo_cc_session_t *session)
+{
+	const char *sdp;
+	int rc;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Generating session offer and opening RTP stream.\n");
+
+	rc = osmo_cc_session_check(session, 0);
+	if (rc < 0) {
+		PDEBUG(DCC, DEBUG_ERROR, "Please fix!\n");
+		abort();
+	}
+
+	sdp = osmo_cc_session_gensdp(session);
+	osmo_cc_debug_sdp(sdp);
+
+	return sdp;
+}
+
+osmo_cc_session_t *osmo_cc_session_receive_offer(void *priv, const char *sdp)
+{
+	osmo_cc_session_t *session;
+	int rc;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Parsing session offer.\n");
+
+	osmo_cc_debug_sdp(sdp);
+	session = osmo_cc_session_parsesdp(priv, sdp);
+	if (!session)
+		return NULL;
+
+	rc = osmo_cc_session_check(session, 0);
+	if (rc < 0) {
+		osmo_cc_free_session(session);
+		return NULL;
+	}
+
+	return session;
+}
+
+void osmo_cc_session_accept_media(osmo_cc_session_media_t *media, enum osmo_cc_session_nettype nettype, enum osmo_cc_session_addrtype addrtype, const char *address, int send, int receive, void (*receiver)(struct osmo_cc_session_codec *codec, uint16_t sequence_number, uint32_t timestamp, uint8_t *data, int len))
+{
+	media->accepted = 1;
+	if (nettype)
+		media->connection_data_local.nettype = nettype;
+	else
+		media->connection_data_local.nettype = default_nettype;
+	if (addrtype)
+		media->connection_data_local.addrtype = addrtype;
+	else
+		media->connection_data_local.addrtype = default_addrtype;
+	free((char *)media->connection_data_local.address);
+	if (address)
+		media->connection_data_local.address = strdup(address);
+	else
+		media->connection_data_local.address = strdup(default_unicast_address);
+	media->send = send;
+	media->receive = receive;
+	media->receiver = receiver;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Accepting session media.\n");
+	PDEBUG(DCC, DEBUG_DEBUG, " -> network type = %s\n", osmo_cc_session_nettype2string(media->connection_data_local.nettype));
+	PDEBUG(DCC, DEBUG_DEBUG, " -> address type = %s\n", osmo_cc_session_addrtype2string(media->connection_data_local.addrtype));
+	PDEBUG(DCC, DEBUG_DEBUG, " -> address = %s\n", media->connection_data_local.address);
+}
+
+
+void osmo_cc_session_accept_codec(osmo_cc_session_codec_t *codec, void (*encoder)(uint8_t *src_data, int src_len, uint8_t **dst_data, int *dst_len), void (*decoder)(uint8_t *src_data, int src_len, uint8_t **dst_data, int *dst_len))
+{
+	codec->accepted = 1;
+	codec->encoder = encoder;
+	codec->decoder = decoder;
+	/* when we accept a codec, we just use the same payload type as the remote */
+	codec->payload_type_local = codec->payload_type_remote;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Accepting session codec.\n");
+	PDEBUG(DCC, DEBUG_DEBUG, " -> payload type = %d\n", codec->payload_type_local);
+	PDEBUG(DCC, DEBUG_DEBUG, " -> payload name = %s\n", codec->payload_name);
+	PDEBUG(DCC, DEBUG_DEBUG, " -> payload rate = %d\n", codec->payload_rate);
+	PDEBUG(DCC, DEBUG_DEBUG, " -> payload channels = %d\n", codec->payload_channels);
+}
+
+/* remove codecs/media that have not been accepted and generate SDP */
+const char *osmo_cc_session_send_answer(osmo_cc_session_t *session)
+{
+	osmo_cc_session_media_t *media;
+	osmo_cc_session_codec_t *codec, **codec_p;
+	const char *sdp;
+	int rc;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Generating session answer.\n");
+
+	/* loop all media */
+	osmo_cc_session_for_each_media(session->media_list, media) {
+		/* remove unaccepted codecs */
+		codec_p = &media->codec_list;
+		codec = *codec_p;
+		while (codec) {
+			if (!codec->accepted) {
+				osmo_cc_free_codec(codec);
+				codec = *codec_p;
+				continue;
+			}
+			codec_p = &codec->next;
+			codec = *codec_p;
+		}
+		/* mark media as unused, if no codec or not accepted */
+		if (!media->accepted || !media->codec_list)
+			media->description.port_local = 0;
+	}
+
+	rc = osmo_cc_session_check(session, 0);
+	if (rc < 0) {
+		PDEBUG(DCC, DEBUG_ERROR, "Please fix!\n");
+		abort();
+	}
+
+	sdp = osmo_cc_session_gensdp(session);
+	osmo_cc_debug_sdp(sdp);
+
+	return sdp;
+}
+
+/* Apply remote session description to local session description.
+ * If remote media's port is 0, remove from local session description.
+ * If codecs in the remote session description are missing, remove from local session description.
+ */
+static int osmo_cc_session_negotiate(osmo_cc_session_t *session_local, struct osmo_cc_session *session_remote)
+{
+	osmo_cc_session_media_t *media_local, *media_remote, **media_local_p;
+	osmo_cc_session_codec_t *codec_local, *codec_remote, **codec_local_p;
+	int rc;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Negotiating session.\n");
+
+	/* copy remote session infromation */
+	session_local->origin_remote.username = strdup(session_remote->origin_remote.username);
+	session_local->origin_remote.sess_id = strdup(session_remote->origin_remote.sess_id);
+	session_local->origin_remote.sess_version = strdup(session_remote->origin_remote.sess_version);
+	session_local->origin_remote.nettype = strdup(session_remote->origin_remote.nettype);
+	session_local->origin_remote.addrtype = strdup(session_remote->origin_remote.addrtype);
+	session_local->origin_remote.unicast_address = strdup(session_remote->origin_remote.unicast_address);
+
+	/* loop all media */
+	for (media_local = session_local->media_list, media_remote = session_remote->media_list; media_local && media_remote; media_local = media_local->next, media_remote = media_remote->next) {
+		/* copy remote media information */
+		media_local->connection_data_remote.nettype = media_remote->connection_data_remote.nettype;
+		if (media_remote->connection_data_remote.nettype_name)
+			media_local->connection_data_remote.nettype_name = strdup(media_remote->connection_data_remote.nettype_name);
+		media_local->connection_data_remote.addrtype = media_remote->connection_data_remote.addrtype;
+		if (media_remote->connection_data_remote.addrtype_name)
+			media_local->connection_data_remote.addrtype_name = strdup(media_remote->connection_data_remote.addrtype_name);
+		if (media_remote->connection_data_remote.address)
+			media_local->connection_data_remote.address = strdup(media_remote->connection_data_remote.address);
+		media_local->description.port_remote = media_remote->description.port_remote;
+		media_local->send = media_remote->send;
+		media_local->receive = media_remote->receive;
+		/* loop all codecs and remove if they are not found in local session description */
+		codec_local_p = &media_local->codec_list;
+		codec_local = *codec_local_p;
+		while (codec_local) {
+			/* search for equal codec, payload type may differe for each direction */
+			osmo_cc_session_for_each_codec(media_remote->codec_list, codec_remote) {
+				if (!strcmp(codec_local->payload_name, codec_remote->payload_name)
+				 && codec_local->payload_rate == codec_remote->payload_rate
+				 && codec_local->payload_channels == codec_remote->payload_channels)
+					break;
+			}
+			if (!codec_remote) {
+				osmo_cc_free_codec(codec_local);
+				codec_local = *codec_local_p;
+				continue;
+			}
+			/* copy remote codec information */
+			codec_local->payload_type_remote = codec_remote->payload_type_remote;
+			codec_local_p = &codec_local->next;
+			codec_local = *codec_local_p;
+		}
+	}
+	if (media_local) {
+		PDEBUG(DCC, DEBUG_NOTICE, "Negotiation failed, because remote endpoint returns less media streams than we offered.\n");
+		return -EINVAL;
+	}
+	if (media_remote) {
+		PDEBUG(DCC, DEBUG_NOTICE, "Negotiation failed, because remote endpoint returns more media streams than we offered.\n");
+		return -EINVAL;
+	}
+
+	/* remove media with port == 0 or no codec at all */
+	media_local_p = &session_local->media_list;
+	media_local = *media_local_p;
+	while (media_local) {
+		if (media_local->description.port_remote == 0 || !media_local->codec_list) {
+			osmo_cc_free_media(media_local);
+			media_local = *media_local_p;
+			continue;
+		}
+		media_local_p = &media_local->next;
+		media_local = *media_local_p;
+	}	
+
+	rc = osmo_cc_session_check(session_local, 1);
+	if (rc < 0)
+		return rc;
+
+	return 0;
+}
+
+int osmo_cc_session_receive_answer(osmo_cc_session_t *session, const char *sdp)
+{
+	osmo_cc_session_t *session_remote;
+	int rc;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Parsing session answer.\n");
+
+	osmo_cc_debug_sdp(sdp);
+	session_remote = osmo_cc_session_parsesdp(NULL, sdp);
+	if (!session_remote)
+		return -EINVAL;
+
+	rc = osmo_cc_session_check(session_remote, 1);
+	if (rc < 0) {
+		osmo_cc_free_session(session_remote);
+		return rc;
+	}
+	rc = osmo_cc_session_negotiate(session, session_remote);
+	if (rc < 0) {
+		osmo_cc_free_session(session_remote);
+		return rc;
+	}
+	osmo_cc_free_session(session_remote);
+
+	return 0;
+}
+
+const char *osmo_cc_session_nettype2string(enum osmo_cc_session_nettype nettype)
+{
+	switch (nettype) {
+	case osmo_cc_session_nettype_inet:
+		return "IN";
+	default:
+		return NULL;
+	}
+}
+
+const char *osmo_cc_session_addrtype2string(enum osmo_cc_session_addrtype addrtype)
+{
+	switch (addrtype) {
+	case osmo_cc_session_addrtype_ipv4:
+		return "IP4";
+	case osmo_cc_session_addrtype_ipv6:
+		return "IP6";
+	default:
+		return NULL;
+	}
+}
+
+const char *osmo_cc_session_media_type2string(enum osmo_cc_session_media_type media_type)
+{
+	switch (media_type) {
+	case osmo_cc_session_media_type_audio:
+		return "audio";
+	case osmo_cc_session_media_type_video:
+		return "video";
+	default:
+		return NULL;
+	}
+}
+
+const char *osmo_cc_session_media_proto2string(enum osmo_cc_session_media_proto media_proto)
+{
+	switch (media_proto) {
+	case osmo_cc_session_media_proto_rtp:
+		return "RTP/AVP";
+	default:
+		return NULL;
+	}
+}
+
+int osmo_cc_session_if_codec(osmo_cc_session_codec_t *codec, const char *name, uint32_t rate, int channels)
+{
+	return (!strcmp(codec->payload_name, name)
+	     && codec->payload_rate == rate
+	     && codec->payload_channels == channels);
+}
+
+int osmo_cc_session_handle(osmo_cc_session_t *session)
+{
+	osmo_cc_session_media_t *media;
+	int w = 0, rc;
+
+	osmo_cc_session_for_each_media(session->media_list, media) {
+		do {
+			rc = osmo_cc_rtp_receive(media);
+			if (rc >= 0)
+				w = 1;
+		} while (rc >= 0);
+	}
+
+	return w;
+}
+
diff --git a/src/libosmocc/session.h b/src/libosmocc/session.h
new file mode 100644
index 0000000..cab8fea
--- /dev/null
+++ b/src/libosmocc/session.h
@@ -0,0 +1,119 @@
+
+/* session description, global part: */
+
+typedef struct osmo_cc_session_origin {
+	const char *username;
+	const char *sess_id;
+	const char *sess_version;
+	const char *nettype;
+	const char *addrtype;
+	const char *unicast_address;
+} osmo_cc_session_origin_t;
+
+/* session instance */
+typedef struct osmo_cc_session {
+	void *priv;
+	osmo_cc_session_origin_t origin_local, origin_remote;
+	const char *name;
+	struct osmo_cc_session_media *media_list;
+} osmo_cc_session_t;
+
+/* connection description: */
+
+enum osmo_cc_session_nettype {
+	osmo_cc_session_nettype_unknown = 0,
+	osmo_cc_session_nettype_inet,
+};
+
+enum osmo_cc_session_addrtype {
+	osmo_cc_session_addrtype_unknown = 0,
+	osmo_cc_session_addrtype_ipv4,
+	osmo_cc_session_addrtype_ipv6,
+};
+
+typedef struct osmo_cc_session_connection_data {
+	enum osmo_cc_session_nettype nettype;
+	const char *nettype_name;
+	enum osmo_cc_session_addrtype addrtype;
+	const char *addrtype_name;
+	const char *address;
+} osmo_cc_session_connection_data_t;
+
+/* one media of session description: */
+
+enum osmo_cc_session_media_type {
+	osmo_cc_session_media_type_unknown,
+	osmo_cc_session_media_type_audio,
+	osmo_cc_session_media_type_video,
+};
+
+enum osmo_cc_session_media_proto {
+	osmo_cc_session_media_proto_unknown,
+	osmo_cc_session_media_proto_rtp,
+};
+
+typedef struct osmo_cc_session_media_description {
+	enum osmo_cc_session_media_type type;
+	const char *type_name;
+	uint16_t port_local, port_remote;
+	enum osmo_cc_session_media_proto proto;
+	const char *proto_name;
+} osmo_cc_session_media_description_t;
+
+/* media entry */
+typedef struct osmo_cc_session_media {
+	struct osmo_cc_session_media *next;
+	osmo_cc_session_t *session;
+	osmo_cc_session_media_description_t description;
+	osmo_cc_session_connection_data_t connection_data_local, connection_data_remote;
+	struct osmo_cc_session_codec *codec_list;
+	int send, receive;
+	void (*receiver)(struct osmo_cc_session_codec *codec, uint16_t sequence_number, uint32_t timestamp, uint8_t *data, int len);
+	int rtp_socket;
+	int rtcp_socket;
+	uint32_t rtp_ssrc;
+	uint16_t tx_sequence, rx_sequence;
+	uint32_t tx_timestamp, rx_timestamp;
+	int accepted;
+} osmo_cc_session_media_t;
+
+/* codec entry */
+typedef struct osmo_cc_session_codec {
+	struct osmo_cc_session_codec *next;
+	osmo_cc_session_media_t *media;
+	uint8_t payload_type_local, payload_type_remote; /* local = towards local, remote = toward remote */
+	const char *payload_name;
+	uint32_t payload_rate;
+	int payload_channels;
+	void (*encoder)(uint8_t *src_data, int src_len, uint8_t **dst_data, int *dst_len);
+	void (*decoder)(uint8_t *src_data, int src_len, uint8_t **dst_data, int *dst_len);
+	int accepted;
+} osmo_cc_session_codec_t;
+
+#define osmo_cc_session_for_each_media(head, m) \
+	for (m = (head); m; m = m->next)
+
+#define osmo_cc_session_for_each_codec(head, c) \
+	for (c = (head); c; c = c->next)
+
+void osmo_cc_set_local_peer(enum osmo_cc_session_nettype nettype, enum osmo_cc_session_addrtype addrtype, const char *address);
+osmo_cc_session_t *osmo_cc_new_session(void *priv, const char *username, const char *sess_id, const char *sess_version, enum osmo_cc_session_nettype nettype, enum osmo_cc_session_addrtype addrtype, const char *unicast_address, const char *session_name, int debug);
+void osmo_cc_free_session(osmo_cc_session_t *session);
+osmo_cc_session_media_t *osmo_cc_add_media(osmo_cc_session_t *session, enum osmo_cc_session_nettype nettype, enum osmo_cc_session_addrtype addrtype, const char *address, enum osmo_cc_session_media_type type, uint16_t port, enum osmo_cc_session_media_proto proto, int send, int receive, void (*receiver)(struct osmo_cc_session_codec *codec, uint16_t sequence_number, uint32_t timestamp, uint8_t *data, int len), int debug);
+void osmo_cc_free_media(osmo_cc_session_media_t *media);
+osmo_cc_session_codec_t *osmo_cc_add_codec(osmo_cc_session_media_t *media, const char *playload_name, uint32_t playload_rate, int playload_channels, void (*encoder)(uint8_t *src_data, int src_len, uint8_t **dst_data, int *dst_len), void (*decoder)(uint8_t *src_data, int src_len, uint8_t **dst_data, int *dst_len), int debug);
+void osmo_cc_free_codec(osmo_cc_session_codec_t *codec);
+int osmo_cc_session_check(struct osmo_cc_session *session, int remote);
+const char *osmo_cc_session_send_offer(osmo_cc_session_t *session);
+osmo_cc_session_t *osmo_cc_session_receive_offer(void *priv, const char *sdp);
+void osmo_cc_session_accept_media(osmo_cc_session_media_t *media, enum osmo_cc_session_nettype nettype, enum osmo_cc_session_addrtype addrtype, const char *address, int send, int receive, void (*receiver)(struct osmo_cc_session_codec *codec, uint16_t sequence_number, uint32_t timestamp, uint8_t *data, int len));
+void osmo_cc_session_accept_codec(osmo_cc_session_codec_t *codec, void (*encoder)(uint8_t *src_data, int src_len, uint8_t **dst_data, int *dst_len), void (*decoder)(uint8_t *src_data, int src_len, uint8_t **dst_data, int *dst_len));
+const char *osmo_cc_session_send_answer(osmo_cc_session_t *session);
+int osmo_cc_session_receive_answer(osmo_cc_session_t *session, const char *sdp);
+const char *osmo_cc_session_nettype2string(enum osmo_cc_session_nettype nettype);
+const char *osmo_cc_session_addrtype2string(enum osmo_cc_session_addrtype addrtype);
+const char *osmo_cc_session_media_type2string(enum osmo_cc_session_media_type media_type);
+const char *osmo_cc_session_media_proto2string(enum osmo_cc_session_media_proto media_proto);
+int osmo_cc_session_if_codec(osmo_cc_session_codec_t *codec, const char *name, uint32_t rate, int channels);
+int osmo_cc_session_handle(osmo_cc_session_t *session);
+
diff --git a/src/libosmocc/socket.c b/src/libosmocc/socket.c
new file mode 100644
index 0000000..d4eb12e
--- /dev/null
+++ b/src/libosmocc/socket.c
@@ -0,0 +1,583 @@
+/* Osmo-CC: Socket handling
+ *
+ * (C) 2016 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <string.h>
+#include <errno.h>
+#include <sys/socket.h>
+#include <netdb.h>
+#include "../libdebug/debug.h"
+#include "../libtimer/timer.h"
+#include "message.h"
+#include "cause.h"
+#include "socket.h"
+
+static const char version_string[] = OSMO_CC_VERSION;
+
+static int _getaddrinfo(const char *host, uint16_t port, struct addrinfo **result)
+{
+	char portstr[8];
+	struct addrinfo hints;
+	int rc;
+
+	sprintf(portstr, "%d", port);
+
+	/* bind socket */
+	memset(&hints, 0, sizeof(struct addrinfo));
+	hints.ai_family = AF_UNSPEC;
+	hints.ai_socktype = SOCK_STREAM;
+	hints.ai_flags = AI_PASSIVE;
+	hints.ai_protocol = 0;
+	hints.ai_canonname = NULL;
+	hints.ai_addr = NULL;
+	hints.ai_next = NULL;
+
+	rc = getaddrinfo(host, portstr, &hints, result);
+	if (rc < 0) {
+		PDEBUG(DCC, DEBUG_ERROR, "Failed to create socket for host '%s', port '%d': %s.\n", host, port, gai_strerror(rc));
+		return rc;
+	}
+	return rc;
+}
+
+/* send a reject message toward CC process.
+ * the CC process will change the reject message to a release message when not in INIT_IN state
+ */
+static void rej_msg(osmo_cc_socket_t *os, uint32_t callref, uint8_t socket_cause, uint8_t isdn_cause, uint16_t sip_cause)
+{
+	osmo_cc_msg_t *msg;
+
+	/* create message */
+	msg = osmo_cc_new_msg(OSMO_CC_MSG_REJ_REQ);
+	if (!msg)
+		abort();
+
+	/* add cause */
+	osmo_cc_add_ie_cause(msg, os->location, isdn_cause, sip_cause, socket_cause);
+	osmo_cc_convert_cause_msg(msg);
+
+	/* message down */
+	os->recv_msg_cb(os->priv, callref, msg);
+}
+
+void tx_keepalive_timeout(struct timer *timer)
+{
+	osmo_cc_conn_t *conn = (osmo_cc_conn_t *)timer->priv;
+	osmo_cc_msg_t *msg;
+
+	/* send keepalive message */ 
+	msg = osmo_cc_new_msg(OSMO_CC_MSG_DUMMY_REQ);
+	osmo_cc_msg_list_enqueue(&conn->os->write_list, msg, conn->callref);
+	timer_start(&conn->tx_keepalive_timer, OSMO_CC_SOCKET_TX_KEEPALIVE);
+}
+
+static void close_conn(osmo_cc_conn_t *conn, uint8_t socket_cause);
+
+void rx_keepalive_timeout(struct timer *timer)
+{
+	osmo_cc_conn_t *conn = (osmo_cc_conn_t *)timer->priv;
+
+	PDEBUG(DCC, DEBUG_ERROR, "OsmoCC-Socket failed due to timeout.\n");
+	close_conn(conn, OSMO_CC_SOCKET_CAUSE_TIMEOUT);
+}
+
+/* create socket process and bind socket */
+int osmo_cc_open_socket(osmo_cc_socket_t *os, const char *host, uint16_t port, void *priv, void (*recv_msg_cb)(void *priv, uint32_t callref, osmo_cc_msg_t *msg), uint8_t location)
+{
+	int try = 0, auto_port = 0;
+	struct addrinfo *result, *rp;
+	int rc, sock, flags;
+
+	memset(os, 0, sizeof(*os));
+
+try_again:
+	/* check for given port, if NULL, autoselect port */
+	if (!port || auto_port) {
+		port = OSMO_CC_DEFAULT_PORT + try;
+		try++;
+		auto_port = 1;
+	}
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Create socket for host %s port %d.\n", host, port);
+
+	rc = _getaddrinfo(host, port, &result);
+	if (rc < 0)
+		return rc;
+	for (rp = result; rp; rp = rp->ai_next) {
+		int on = 1;
+		sock = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
+		if (sock < 0)
+			continue;
+		setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (unsigned char *)&on, sizeof(on));
+		rc = bind(sock, rp->ai_addr, rp->ai_addrlen);
+		if (rc == 0)
+			break;
+		close(sock);
+	}
+	freeaddrinfo(result);
+	if (rp == NULL) {
+		if (auto_port && port < OSMO_CC_DEFAULT_PORT_MAX) {
+			PDEBUG(DCC, DEBUG_DEBUG, "Failed to bind host %s port %d, trying again.\n", host, port);
+			goto try_again;
+		}
+		PDEBUG(DCC, DEBUG_ERROR, "Failed to bind given host %s port %d.\n", host, port);
+		return -EIO;
+	}
+
+	/* listen to socket */
+	rc = listen(sock, 10);
+	if (rc < 0) {
+		PDEBUG(DCC, DEBUG_ERROR, "Failed to listen on socket.\n");
+		return rc;
+	}
+
+	/* set nonblocking io */
+	flags = fcntl(sock, F_GETFL);
+	flags |= O_NONBLOCK;
+	fcntl(sock, F_SETFL, flags);
+
+	os->socket = sock;
+	os->recv_msg_cb = recv_msg_cb;
+	os->priv = priv;
+	os->location = location;
+
+	return port;
+}
+
+/* create a connection */
+static osmo_cc_conn_t *open_conn(osmo_cc_socket_t *os, int sock, uint32_t callref, int read_setup)
+{
+	osmo_cc_conn_t *conn, **connp;
+
+	/* create connection */
+	conn = calloc(1, sizeof(*conn));
+	if (!conn) {
+		PDEBUG(DCC, DEBUG_ERROR, "No mem!\n");
+		abort();
+	}
+	conn->os = os;
+	conn->socket = sock;
+	conn->read_version = 1;
+	conn->write_version = 1;
+	conn->read_setup = read_setup;
+	if (callref)
+		conn->callref = callref;
+	else
+		conn->callref = osmo_cc_new_callref();
+
+	timer_init(&conn->tx_keepalive_timer, tx_keepalive_timeout, conn);
+	timer_init(&conn->rx_keepalive_timer, rx_keepalive_timeout, conn);
+	timer_start(&conn->tx_keepalive_timer, OSMO_CC_SOCKET_TX_KEEPALIVE);
+	timer_start(&conn->rx_keepalive_timer, OSMO_CC_SOCKET_RX_KEEPALIVE);
+
+	PDEBUG(DCC, DEBUG_DEBUG, "New socket connection (callref %d).\n", conn->callref);
+
+	/* attach to list */
+	connp = &os->conn_list;
+	while (*connp)
+		connp = &((*connp)->next);
+	*connp = conn;
+
+	return conn;
+}
+
+/* remove a connection */
+static void close_conn(osmo_cc_conn_t *conn, uint8_t socket_cause)
+{
+	osmo_cc_conn_t **connp;
+	osmo_cc_msg_list_t *ml;
+
+	/* detach connection first, to prevent a destruction during message handling (double free) */
+	connp = &conn->os->conn_list;
+	while (*connp != conn)
+		connp = &((*connp)->next);
+	*connp = conn->next;
+	/* send reject message, if socket_cause is set */
+	if (socket_cause && !conn->read_setup) {
+		/* receive a release or reject (depending on state), but only if we sent a setup */
+		rej_msg(conn->os, conn->callref, socket_cause, 0, 0);
+	}
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Destroy socket connection (callref %d).\n", conn->callref);
+
+	/* close socket */
+	if (conn->socket)
+		close(conn->socket);
+	/* free partly received message */
+	if (conn->read_msg)
+		osmo_cc_free_msg(conn->read_msg);
+	/* free send queue */
+	while ((ml = conn->write_list)) {
+		osmo_cc_free_msg(ml->msg);
+		conn->write_list = ml->next;
+		free(ml);
+	}
+	/* free timers */
+	timer_exit(&conn->tx_keepalive_timer);
+	timer_exit(&conn->rx_keepalive_timer);
+	/* free connection (already detached above) */
+	free(conn);
+}
+
+/* close socket and remove */
+void osmo_cc_close_socket(osmo_cc_socket_t *os)
+{
+	osmo_cc_msg_list_t *ml;
+
+	PDEBUG(DCC, DEBUG_DEBUG, "Destroy socket.\n");
+
+	/* free all connections */
+	while (os->conn_list)
+		close_conn(os->conn_list, 0);
+	/* close socket */
+	if (os->socket > 0) {
+		close(os->socket);
+		os->socket = 0;
+	}
+	/* free send queue */
+	while ((ml = os->write_list)) {
+		osmo_cc_free_msg(ml->msg);
+		os->write_list = ml->next;
+		free(ml);
+	}
+}
+
+/* send message to send_queue of sock instance */
+int osmo_cc_sock_send_msg(osmo_cc_socket_t *os, uint32_t callref, osmo_cc_msg_t *msg, const char *host, uint16_t port)
+{
+	osmo_cc_msg_list_t *ml;
+
+	/* turn _IND into _REQ and _CNF into _RSP */
+	msg->type &= ~1;
+
+	/* create list entry */
+	ml = osmo_cc_msg_list_enqueue(&os->write_list, msg, callref);
+	if (host)
+		strncpy(ml->host, host, sizeof(ml->host) - 1);
+	ml->port = port;
+
+	return 0;
+}
+
+/* receive message
+ * return 1 if work was done.
+ */
+static int receive_conn(osmo_cc_conn_t *conn)
+{
+	uint8_t socket_cause = OSMO_CC_SOCKET_CAUSE_BROKEN_PIPE;
+	int rc;
+	osmo_cc_msg_t *msg;
+	uint8_t msg_type;
+	int len;
+	int work = 0;
+
+	/* get version from remote */
+	if (conn->read_version) {
+		rc = recv(conn->socket, conn->read_version_string + conn->read_version_pos, strlen(version_string) - conn->read_version_pos, 0);
+		if (rc < 0 && errno == EAGAIN)
+			return work;
+		work = 1;
+		if (rc <= 0) {
+			goto close;
+		}
+		conn->read_version_pos += rc;
+		if (conn->read_version_pos == strlen(version_string)) {
+			conn->read_version = 0;
+			if (!!memcmp(conn->read_version_string, version_string, strlen(version_string) - 1)) {
+				PDEBUG(DCC, DEBUG_NOTICE, "Remote does not seem to be an Osmo-CC socket, rejecting!\n");
+				socket_cause = OSMO_CC_SOCKET_CAUSE_FAILED;
+				goto close;
+			}
+			if (conn->read_version_string[strlen(version_string) - 1] != version_string[strlen(version_string) - 1]) {
+				PDEBUG(DCC, DEBUG_NOTICE, "Remote Osmo-CC socket has wrong version (local=%s, remote=%s), rejecting!\n", version_string, conn->read_version_string);
+				socket_cause = OSMO_CC_SOCKET_CAUSE_VERSION_MISMATCH;
+				goto close;
+			}
+		} else
+			return work;
+	}
+
+try_next_message:
+	/* read message header from remote */
+	if (!conn->read_msg) {
+		rc = recv(conn->socket, ((uint8_t *)&conn->read_hdr) + conn->read_pos, sizeof(conn->read_hdr) - conn->read_pos, 0);
+		if (rc < 0 && errno == EAGAIN)
+			return work;
+		work = 1;
+		if (rc <= 0) {
+			goto close;
+		}
+		conn->read_pos += rc;
+		if (conn->read_pos == sizeof(conn->read_hdr)) {
+			conn->read_msg = osmo_cc_new_msg(conn->read_hdr.type);
+			if (!conn->read_msg)
+				abort();
+			conn->read_msg->length_networkorder = conn->read_hdr.length_networkorder;
+			/* prepare for reading message */
+			conn->read_pos = 0;
+		} else
+			return work;
+	}
+
+	/* read message data from remote */
+	msg = conn->read_msg;
+	len = ntohs(msg->length_networkorder);
+	if (len == 0)
+		goto empty_message;
+	rc = recv(conn->socket, msg->data + conn->read_pos, len - conn->read_pos, 0);
+	if (rc < 0 && errno == EAGAIN)
+		return work;
+	work = 1;
+	if (rc <= 0) {
+		goto close;
+	}
+	conn->read_pos += rc;
+	if (conn->read_pos == len) {
+empty_message:
+		/* start RX keepalive timeer, if not already */
+		timer_start(&conn->rx_keepalive_timer, OSMO_CC_SOCKET_RX_KEEPALIVE);
+		/* we got our setup message, so we clear the flag */
+		conn->read_setup = 0;
+		/* prepare for reading header */
+		conn->read_pos = 0;
+		/* detach message first, because the connection might be destroyed during message handling */
+		msg_type = conn->read_msg->type;
+		conn->read_msg = NULL;
+		/* drop dummy or forward message */
+		if (msg_type == OSMO_CC_MSG_DUMMY_REQ)
+			osmo_cc_free_msg(msg);
+		else
+			conn->os->recv_msg_cb(conn->os->priv, conn->callref, msg);
+		if (msg_type == OSMO_CC_MSG_REL_REQ || msg_type == OSMO_CC_MSG_REJ_REQ) {
+			PDEBUG(DCC, DEBUG_DEBUG, "closing socket because we received a release or reject message.\n");
+			close_conn(conn, 0);
+			return 1; /* conn removed */
+		}
+		goto try_next_message;
+	}
+	return work;
+
+close:
+	PDEBUG(DCC, DEBUG_ERROR, "OsmoCC-Socket failed, socket cause %d.\n", socket_cause);
+	close_conn(conn, socket_cause);
+	return work; /* conn removed */
+}
+
+/* transmit message
+ * return 1 if work was done.
+ */
+static int transmit_conn(osmo_cc_conn_t *conn)
+{
+	uint8_t socket_cause = OSMO_CC_SOCKET_CAUSE_BROKEN_PIPE;
+	int rc;
+	osmo_cc_msg_t *msg;
+	int len;
+	osmo_cc_msg_list_t *ml;
+	int work = 0;
+
+	/* send socket version to remote */
+	if (conn->write_version) {
+		rc = write(conn->socket, version_string, strlen(version_string));
+		if (rc < 0 && errno == EAGAIN)
+			return work;
+		work = 1;
+		if (rc <= 0) {
+			goto close;
+		}
+		if (rc != strlen(version_string)) {
+			PDEBUG(DCC, DEBUG_ERROR, "short write, please fix handling!\n");
+			abort();
+		}
+		conn->write_version = 0;
+	}
+
+	/* send message to remote */
+	while (conn->write_list) {
+		timer_stop(&conn->tx_keepalive_timer);
+		msg = conn->write_list->msg;
+		len = sizeof(*msg) + ntohs(msg->length_networkorder);
+		rc = write(conn->socket, msg, len);
+		if (rc < 0 && errno == EAGAIN)
+			return work;
+		work = 1;
+		if (rc <= 0) {
+			goto close;
+		}
+		if (rc != len) {
+			PDEBUG(DCC, DEBUG_ERROR, "short write, please fix handling!\n");
+			abort();
+		}
+		/* close socket after sending release/reject message */
+		if (msg->type == OSMO_CC_MSG_REL_REQ || msg->type == OSMO_CC_MSG_REJ_REQ) {
+			PDEBUG(DCC, DEBUG_DEBUG, "closing socket because we sent a release or reject message.\n");
+			close_conn(conn, 0);
+			return work; /* conn removed */
+		}
+		/* free message after sending */
+		ml = conn->write_list;
+		conn->write_list = ml->next;
+		osmo_cc_free_msg(msg);
+		free(ml);
+	}
+
+	/* start TX keepalive timeer, if not already
+	 * because we stop at every message above, we actually restart the timer here.
+	 * only if there is no message for the amout of time, the timer fires.
+	 */
+	if (!timer_running(&conn->tx_keepalive_timer))
+		timer_start(&conn->tx_keepalive_timer, OSMO_CC_SOCKET_TX_KEEPALIVE);
+
+	return work;
+
+close:
+	PDEBUG(DCC, DEBUG_NOTICE, "OsmoCC-Socket failed.\n");
+	close_conn(conn, socket_cause);
+	return work; /* conn removed */
+}
+
+/* handle all sockets of a socket interface
+ * return 1 if work was done.
+ */
+int osmo_cc_handle_socket(osmo_cc_socket_t *os)
+{
+	struct sockaddr_storage sa;
+	socklen_t slen = sizeof(sa);
+	int sock;
+	osmo_cc_conn_t *conn;
+	osmo_cc_msg_list_t *ml, **mlp;
+	int flags;
+	struct addrinfo *result, *rp;
+	int rc;
+	int work = 0;
+
+	/* handle messages in send queue */
+	while ((ml = os->write_list)) {
+		work = 1;
+		/* detach list entry */
+		os->write_list = ml->next;
+		ml->next = NULL;
+		/* search for socket connection */
+		for (conn = os->conn_list; conn; conn=conn->next) {
+			if (conn->callref == ml->callref)
+				break;
+		}
+		if (conn) {
+			/* attach to list */
+			mlp = &conn->write_list;
+			while (*mlp)
+				mlp = &((*mlp)->next);
+			*mlp = ml;
+			/* done with message */
+			continue;
+		}
+
+		/* reject and release are ignored */
+		if (ml->msg->type == OSMO_CC_MSG_REJ_REQ
+		 || ml->msg->type == OSMO_CC_MSG_REL_REQ) {
+			/* drop message */
+			osmo_cc_free_msg(ml->msg);
+			free(ml);
+			/* done with message */
+			continue;
+		}
+
+		/* reject, if this is not a setup message */
+		if (ml->msg->type != OSMO_CC_MSG_SETUP_REQ
+		 && ml->msg->type != OSMO_CC_MSG_ATTACH_REQ) {
+			PDEBUG(DCC, DEBUG_ERROR, "Message with unknown callref.\n");
+			rej_msg(os, ml->callref, 0, OSMO_CC_ISDN_CAUSE_INVAL_CALLREF, 0);
+			/* drop message */
+			osmo_cc_free_msg(ml->msg);
+			free(ml);
+			/* done with message */
+			continue;
+		}
+		/* connect to remote */
+		rc = _getaddrinfo(ml->host, ml->port, &result);
+		if (rc < 0) {
+			rej_msg(os, ml->callref, OSMO_CC_SOCKET_CAUSE_FAILED, 0, 0);
+			/* drop message */
+			osmo_cc_free_msg(ml->msg);
+			free(ml);
+			/* done with message */
+			continue;
+		}
+		for (rp = result; rp; rp = rp->ai_next) {
+			sock = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
+			if (sock < 0)
+				continue;
+			/* set nonblocking io */
+			flags = fcntl(sock, F_GETFL);
+			flags |= O_NONBLOCK;
+			fcntl(sock, F_SETFL, flags);
+			/* connect */
+			rc = connect(sock, rp->ai_addr, rp->ai_addrlen);
+			if (rc == 0 || errno == EINPROGRESS)
+				break;
+			close(sock);
+		}
+		freeaddrinfo(result);
+		if (rp == NULL) {
+			PDEBUG(DCC, DEBUG_ERROR, "Failed to connect to given host %s port %d.\n", ml->host, ml->port);
+			rej_msg(os, ml->callref, OSMO_CC_SOCKET_CAUSE_FAILED, 0, 0);
+			/* drop message */
+			osmo_cc_free_msg(ml->msg);
+			free(ml);
+			/* done with message */
+			continue;
+		}
+		/* create connection */
+		conn = open_conn(os, sock, ml->callref, 0);
+		/* attach to list */
+		conn->write_list = ml;
+		/* done with (setup) message */
+	}
+
+	/* handle new socket connection */
+	while ((sock = accept(os->socket, (struct sockaddr *)&sa, &slen)) > 0) {
+		work = 1;
+		/* set nonblocking io */
+		flags = fcntl(sock, F_GETFL);
+		flags |= O_NONBLOCK;
+		fcntl(sock, F_SETFL, flags);
+		/* create connection */
+		open_conn(os, sock, 0, 1);
+	}
+
+	/* start with list after each read/write, because while handling (the message), one or more connections may be destroyed */
+	for (conn = os->conn_list; conn; conn=conn->next) {
+		/* check for rx */
+		work = receive_conn(conn);
+		/* if "change" is set, connection list might have changed, so we restart processing the list */
+		if (work)
+			break;
+		/* check for tx */
+		work = transmit_conn(conn);
+		/* if "change" is set, connection list might have changed, so we restart processing the list */
+		if (work)
+			break;
+	}
+
+	return work;
+}
+
diff --git a/src/libosmocc/socket.h b/src/libosmocc/socket.h
new file mode 100644
index 0000000..a0f96ed
--- /dev/null
+++ b/src/libosmocc/socket.h
@@ -0,0 +1,44 @@
+#ifndef OSMO_CC_SOCKET_H
+#define OSMO_CC_SOCKET_H
+
+#define OSMO_CC_DEFAULT_PORT		4200
+#define OSMO_CC_DEFAULT_PORT_MAX	4299
+
+#define OSMO_CC_SOCKET_TX_KEEPALIVE	10.0
+#define OSMO_CC_SOCKET_RX_KEEPALIVE	20.0
+
+struct osmo_cc_socket;
+
+typedef struct osmo_cc_conn {
+	struct osmo_cc_conn	*next;
+	struct osmo_cc_socket	*os;
+	int			socket;
+	uint32_t		callref;
+	int			read_setup;
+	int			read_version;
+	char			read_version_string[sizeof(OSMO_CC_VERSION)]; /* must include 0-termination */
+	int			read_version_pos;
+	int			write_version;
+	osmo_cc_msg_t		read_hdr;
+	osmo_cc_msg_t		*read_msg;
+	int			read_pos;
+	osmo_cc_msg_list_t	*write_list;
+	struct timer		tx_keepalive_timer;
+	struct timer		rx_keepalive_timer;
+} osmo_cc_conn_t;
+
+typedef struct osmo_cc_socket {
+	int			socket;
+	osmo_cc_conn_t		*conn_list;
+	osmo_cc_msg_list_t	*write_list;
+	void (*recv_msg_cb)(void *priv, uint32_t callref, osmo_cc_msg_t *msg);
+	void *priv;
+	uint8_t			location;
+} osmo_cc_socket_t;
+
+int osmo_cc_open_socket(osmo_cc_socket_t *os, const char *host, uint16_t port, void *priv, void (*recv_msg_cb)(void *priv, uint32_t callref, osmo_cc_msg_t *msg), uint8_t location);
+void osmo_cc_close_socket(osmo_cc_socket_t *os);
+int osmo_cc_sock_send_msg(osmo_cc_socket_t *os, uint32_t callref, osmo_cc_msg_t *msg, const char *host, uint16_t port);
+int osmo_cc_handle_socket(osmo_cc_socket_t *os);
+
+#endif /* OSMO_CC_SOCKET_H */