Prepare entry/exit point for MSC -> BSC and MSC -> RNC communication.

Add msc_ifaces.[hc], a_iface.c, with a general msc_tx_dtap() to redirect to
different interfaces depending on the actual subscriber connection.

While iu_tx() is going to be functional fairly soon, the a_tx() is going to be
just a dummy for some time (see comment).

Add via_iface marker to gsm_subscriber_connection with enum values IFACE_A and
IFACE_IU so far.

Add Iu specific fields in a sub-struct: the UE connection pointer and an
indicator for the Integrity Protection status on Iu (to be fully implemented in
later commits).

Add lac member to gsm_subscriber_connection, to allow decoupling from
bts->location_area_code. The conn->lac will actually be set in iu.c in an
upcoming commit ("add iucs.[hc]").

Change-Id: Idf8020a30562426e8f939706bf5c2188d5a09798

3 files changed, 63 insertions, 0 deletions

diff --git a/openbsc/include/openbsc/Makefile.am b/openbsc/include/openbsc/Makefile.am
index 1bec4f8f1..eca23e6fd 100644
--- a/openbsc/include/openbsc/Makefile.am
+++ b/openbsc/include/openbsc/Makefile.am
@@ -49,6 +49,7 @@ noinst_HEADERS = \
 	misdn.h \
 	mncc.h \
 	mncc_int.h \
+	msc_ifaces.h \
 	nat_rewrite_trie.h \
 	network_listen.h \
 	oap.h \
diff --git a/openbsc/include/openbsc/gsm_data.h b/openbsc/include/openbsc/gsm_data.h
index c742a9d33..694ad2381 100644
--- a/openbsc/include/openbsc/gsm_data.h
+++ b/openbsc/include/openbsc/gsm_data.h
@@ -23,6 +23,7 @@
 
 struct mncc_sock_state;
 struct gsm_subscriber_group;
+struct ue_conn_ctx;
 
 #define OBSC_LINKID_CB(__msgb)	(__msgb)->cb[3]
 
@@ -104,6 +105,18 @@ struct neigh_meas_proc {
 	uint8_t last_seen_nr;
 };
 
+enum interface_type {
+	IFACE_UNKNOWN = -1,
+	IFACE_A = 0,        /* A-interface for 2G */
+	IFACE_IU = 1        /* Iu-interface for UMTS aka 3G (IuCS or IuPS) */
+};
+
+enum integrity_protection_state {
+	INTEGRITY_PROTECTION_NONE	= 0,
+	INTEGRITY_PROTECTION_IK		= 1,
+	INTEGRITY_PROTECTION_IK_CK	= 2,
+};
+
 /* active radio connection of a mobile subscriber */
 struct gsm_subscriber_connection {
 	struct llist_head entry;
@@ -146,6 +159,16 @@ struct gsm_subscriber_connection {
 	struct osmo_timer_list T10; /* BSC */
 	struct gsm_lchan *secondary_lchan; /* BSC */
 
+	uint16_t lac;
+
+	/* 2G or 3G? See enum interface_type */
+	int via_iface;
+
+	/* which Iu-CS connection, if any. */
+	struct {
+		struct ue_conn_ctx *ue_ctx;
+		int integrity_protection;
+	} iu;
 };
 
 
diff --git a/openbsc/include/openbsc/msc_ifaces.h b/openbsc/include/openbsc/msc_ifaces.h
new file mode 100644
index 000000000..cd0039c6f
--- /dev/null
+++ b/openbsc/include/openbsc/msc_ifaces.h
@@ -0,0 +1,39 @@
+#pragma once
+
+#include <osmocom/core/msgb.h>
+#include <openbsc/gsm_data.h>
+
+/* These are the interfaces of the MSC layer towards (from?) the BSC and RNC,
+ * i.e. in the direction towards the mobile device (MS aka UE).
+ *
+ * 2G will use the A-interface,
+ * 3G aka UMTS will use the Iu-interface (for the MSC, it's IuCS).
+ *
+ * To allow linking parts of the MSC code without having to include entire
+ * infrastructures of external libraries, the core transmitting and receiving
+ * functions are left unimplemented. For example, a unit test does not need to
+ * link against external ASN1 libraries if it is never going to encode actual
+ * outgoing messages. It is up to each building scope to implement real world
+ * functions or to plug mere dummy implementations.
+ *
+ * For example, msc_tx_dtap(conn, msg), depending on conn->via_iface, will call
+ * either iu_tx() or a_tx() [note: at time of writing, the A-interface is not
+ * yet implemented]. When you try to link against libmsc, you will find that
+ * the compiler complains about an undefined reference to iu_tx(). If you,
+ * however, link against libiu as well as the osmo-iuh libs (etc.), iu_tx() is
+ * available. A unit test may instead simply implement a dummy iu_tx() function
+ * and not link against osmo-iuh.
+ */
+
+/* Each main linkage must implement this function (see comment above). */
+extern int iu_tx(struct msgb *msg, uint8_t sapi);
+
+/* So far this is a dummy implemented in libmsc/a_iface.c. When A-interface
+ * gets implemented, it should be in a separate lib (like libiu), this function
+ * should move there, and the following comment should remain here: "
+ * Each main linkage must implement this function (see comment above).
+ * " */
+extern int a_tx(struct msgb *msg);
+
+int msc_tx_dtap(struct gsm_subscriber_connection *conn,
+		struct msgb *msg);