SNDCP: add V.42bis data compression functionality

 - Add compression control for V.42bis Add code to handle compression
   (gprs_sndcp_dcomp.c/h)
 - Add Adjustments in SNDCP
 - Add VTY commands

Change-Id: I6d36cbdf2f5c5f83ca9ba57c70452f02b8582e7e

3 files changed, 63 insertions, 0 deletions

diff --git a/openbsc/include/openbsc/Makefile.am b/openbsc/include/openbsc/Makefile.am
index 3014d5fa1..c6a01499f 100644
--- a/openbsc/include/openbsc/Makefile.am
+++ b/openbsc/include/openbsc/Makefile.am
@@ -26,6 +26,7 @@ noinst_HEADERS = \
 	gprs_sgsn.h \
 	gprs_sndcp.h \
 	gprs_sndcp_comp.h \
+	gprs_sndcp_dcomp.h \
 	gprs_sndcp_pcomp.h \
 	gprs_sndcp_xid.h \
 	gprs_utils.h \
diff --git a/openbsc/include/openbsc/gprs_sndcp_dcomp.h b/openbsc/include/openbsc/gprs_sndcp_dcomp.h
new file mode 100644
index 000000000..a76b4a4b3
--- /dev/null
+++ b/openbsc/include/openbsc/gprs_sndcp_dcomp.h
@@ -0,0 +1,53 @@
+/* GPRS SNDCP data compression handler */
+
+/* (C) 2016 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ *
+ * Author: Philipp Maier
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <osmocom/core/linuxlist.h>
+#include <openbsc/gprs_sndcp_comp.h>
+
+/* Note: The decompressed packet may have a maximum size of:
+ * Return value * MAX_DATADECOMPR_FAC */
+#define MAX_DATADECOMPR_FAC 10
+
+/* Note: In unacknowledged mode (SN_UNITDATA), the comression state is reset
+ * for every NPDU. The compressor needs a reasonably large payload to operate
+ * effectively (yield positive compression gain). For packets shorter than 100
+ * byte, no positive compression gain can be expected so we will skip the
+ * compression for short packets. */
+#define MIN_COMPR_PAYLOAD 100
+
+/* Initalize data compression */
+int gprs_sndcp_dcomp_init(const void *ctx, struct gprs_sndcp_comp *comp_entity,
+			  const struct gprs_sndcp_comp_field *comp_field);
+
+/* Terminate data compression */
+void gprs_sndcp_dcomp_term(struct gprs_sndcp_comp *comp_entity);
+
+/* Expand packet */
+int gprs_sndcp_dcomp_expand(uint8_t *data, unsigned int len, uint8_t pcomp,
+			    const struct llist_head *comp_entities);
+
+/* Compress packet */
+int gprs_sndcp_dcomp_compress(uint8_t *data, unsigned int len, uint8_t *pcomp,
+			      const struct llist_head *comp_entities,
+			      uint8_t nsapi);
diff --git a/openbsc/include/openbsc/sgsn.h b/openbsc/include/openbsc/sgsn.h
index 9537c0afc..786e2b240 100644
--- a/openbsc/include/openbsc/sgsn.h
+++ b/openbsc/include/openbsc/sgsn.h
@@ -100,6 +100,15 @@ struct sgsn_config {
 		int passive;
 		int s01;
 	} pcomp_rfc1144;
+
+	/* V.42vis data compression */
+	struct {
+		int active;
+		int passive;
+		int p0;
+		int p1;
+		int p2;
+	} dcomp_v42bis;
 };
 
 struct sgsn_instance {