diff --git a/openbsc/src/gprs/Makefile.am b/openbsc/src/gprs/Makefile.am
new file mode 100644
index 0000000..ac177f7
--- /dev/null
+++ b/openbsc/src/gprs/Makefile.am
@@ -0,0 +1,17 @@
+INCLUDES = $(all_includes) -I$(top_srcdir)/include -I$(top_builddir)
+AM_CFLAGS=-Wall $(LIBOSMOCORE_CFLAGS)
+AM_LDFLAGS = $(LIBOSMOCORE_LIBS)
+
+sbin_PROGRAMS = osmo-gbproxy osmo-sgsn
+noinst_LIBRARIES = libsgsn.a
+
+libsgsn_a_SOURCES = gprs_ns.c gprs_bssgp.c gprs_llc.c gsm_04_08_gprs.c \
+		crc24.c gprs_sgsn.c
+
+osmo_gbproxy_SOURCES = gb_proxy.c gb_proxy_main.c gb_proxy_vty.c \
+			gprs_ns.c ../socket.c ../debug.c
+osmo_gbproxy_LDADD = ../libvty.a
+
+osmo_sgsn_SOURCES = sgsn_main.c sgsn_vty.c \
+			../socket.c ../debug.c
+osmo_sgsn_LDADD = ../libvty.a libsgsn.a
diff --git a/openbsc/src/gprs/crc24.c b/openbsc/src/gprs/crc24.c
new file mode 100644
index 0000000..1082120
--- /dev/null
+++ b/openbsc/src/gprs/crc24.c
@@ -0,0 +1,69 @@
+/* GPRS LLC CRC-24 Implementation */
+
+/* (C) 2008-2009 by Harald Welte <laforge@gnumonks.org>
+ *
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <sys/types.h>
+#include <openbsc/crc24.h>
+
+/* CRC24 table - FCS */
+static const u_int32_t tbl_crc24[256] = {
+	0x00000000, 0x00d6a776, 0x00f64557, 0x0020e221, 0x00b78115, 0x00612663, 0x0041c442, 0x00976334,
+	0x00340991, 0x00e2aee7, 0x00c24cc6, 0x0014ebb0, 0x00838884, 0x00552ff2, 0x0075cdd3, 0x00a36aa5,
+	0x00681322, 0x00beb454, 0x009e5675, 0x0048f103, 0x00df9237, 0x00093541, 0x0029d760, 0x00ff7016,
+	0x005c1ab3, 0x008abdc5, 0x00aa5fe4, 0x007cf892, 0x00eb9ba6, 0x003d3cd0, 0x001ddef1, 0x00cb7987,
+	0x00d02644, 0x00068132, 0x00266313, 0x00f0c465, 0x0067a751, 0x00b10027, 0x0091e206, 0x00474570,
+	0x00e42fd5, 0x003288a3, 0x00126a82, 0x00c4cdf4, 0x0053aec0, 0x008509b6, 0x00a5eb97, 0x00734ce1,
+	0x00b83566, 0x006e9210, 0x004e7031, 0x0098d747, 0x000fb473, 0x00d91305, 0x00f9f124, 0x002f5652,
+	0x008c3cf7, 0x005a9b81, 0x007a79a0, 0x00acded6, 0x003bbde2, 0x00ed1a94, 0x00cdf8b5, 0x001b5fc3,
+	0x00fb4733, 0x002de045, 0x000d0264, 0x00dba512, 0x004cc626, 0x009a6150, 0x00ba8371, 0x006c2407,
+	0x00cf4ea2, 0x0019e9d4, 0x00390bf5, 0x00efac83, 0x0078cfb7, 0x00ae68c1, 0x008e8ae0, 0x00582d96,
+	0x00935411, 0x0045f367, 0x00651146, 0x00b3b630, 0x0024d504, 0x00f27272, 0x00d29053, 0x00043725,
+	0x00a75d80, 0x0071faf6, 0x005118d7, 0x0087bfa1, 0x0010dc95, 0x00c67be3, 0x00e699c2, 0x00303eb4,
+	0x002b6177, 0x00fdc601, 0x00dd2420, 0x000b8356, 0x009ce062, 0x004a4714, 0x006aa535, 0x00bc0243,
+	0x001f68e6, 0x00c9cf90, 0x00e92db1, 0x003f8ac7, 0x00a8e9f3, 0x007e4e85, 0x005eaca4, 0x00880bd2,
+	0x00437255, 0x0095d523, 0x00b53702, 0x00639074, 0x00f4f340, 0x00225436, 0x0002b617, 0x00d41161,
+	0x00777bc4, 0x00a1dcb2, 0x00813e93, 0x005799e5, 0x00c0fad1, 0x00165da7, 0x0036bf86, 0x00e018f0,
+	0x00ad85dd, 0x007b22ab, 0x005bc08a, 0x008d67fc, 0x001a04c8, 0x00cca3be, 0x00ec419f, 0x003ae6e9,
+	0x00998c4c, 0x004f2b3a, 0x006fc91b, 0x00b96e6d, 0x002e0d59, 0x00f8aa2f, 0x00d8480e, 0x000eef78,
+	0x00c596ff, 0x00133189, 0x0033d3a8, 0x00e574de, 0x007217ea, 0x00a4b09c, 0x008452bd, 0x0052f5cb,
+	0x00f19f6e, 0x00273818, 0x0007da39, 0x00d17d4f, 0x00461e7b, 0x0090b90d, 0x00b05b2c, 0x0066fc5a,
+	0x007da399, 0x00ab04ef, 0x008be6ce, 0x005d41b8, 0x00ca228c, 0x001c85fa, 0x003c67db, 0x00eac0ad,
+	0x0049aa08, 0x009f0d7e, 0x00bfef5f, 0x00694829, 0x00fe2b1d, 0x00288c6b, 0x00086e4a, 0x00dec93c,
+	0x0015b0bb, 0x00c317cd, 0x00e3f5ec, 0x0035529a, 0x00a231ae, 0x007496d8, 0x005474f9, 0x0082d38f,
+	0x0021b92a, 0x00f71e5c, 0x00d7fc7d, 0x00015b0b, 0x0096383f, 0x00409f49, 0x00607d68, 0x00b6da1e,
+	0x0056c2ee, 0x00806598, 0x00a087b9, 0x007620cf, 0x00e143fb, 0x0037e48d, 0x001706ac, 0x00c1a1da,
+	0x0062cb7f, 0x00b46c09, 0x00948e28, 0x0042295e, 0x00d54a6a, 0x0003ed1c, 0x00230f3d, 0x00f5a84b,
+	0x003ed1cc, 0x00e876ba, 0x00c8949b, 0x001e33ed, 0x008950d9, 0x005ff7af, 0x007f158e, 0x00a9b2f8,
+	0x000ad85d, 0x00dc7f2b, 0x00fc9d0a, 0x002a3a7c, 0x00bd5948, 0x006bfe3e, 0x004b1c1f, 0x009dbb69,
+	0x0086e4aa, 0x005043dc, 0x0070a1fd, 0x00a6068b, 0x003165bf, 0x00e7c2c9, 0x00c720e8, 0x0011879e,
+	0x00b2ed3b, 0x00644a4d, 0x0044a86c, 0x00920f1a, 0x00056c2e, 0x00d3cb58, 0x00f32979, 0x00258e0f,
+	0x00eef788, 0x003850fe, 0x0018b2df, 0x00ce15a9, 0x0059769d, 0x008fd1eb, 0x00af33ca, 0x007994bc,
+	0x00dafe19, 0x000c596f, 0x002cbb4e, 0x00fa1c38, 0x006d7f0c, 0x00bbd87a, 0x009b3a5b, 0x004d9d2d
+};
+
+#define INIT_CRC24	0xffffff
+
+u_int32_t crc24_calc(u_int32_t fcs, u_int8_t *cp, unsigned int len)
+{
+	while (len--)
+		fcs = (fcs >> 8) ^ tbl_crc24[(fcs ^ *cp++) & 0xff];
+	return fcs;
+}
diff --git a/openbsc/src/gprs/gb_proxy.c b/openbsc/src/gprs/gb_proxy.c
new file mode 100644
index 0000000..fe5ad70
--- /dev/null
+++ b/openbsc/src/gprs/gb_proxy.c
@@ -0,0 +1,416 @@
+/* NS-over-IP proxy */
+
+/* (C) 2010 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2010 by On Waves
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <getopt.h>
+#include <errno.h>
+#include <sys/fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#include <osmocore/talloc.h>
+#include <osmocore/select.h>
+
+#include <openbsc/signal.h>
+#include <openbsc/debug.h>
+#include <openbsc/gprs_ns.h>
+#include <openbsc/gprs_bssgp.h>
+#include <openbsc/gb_proxy.h>
+
+struct gbprox_peer {
+	struct llist_head list;
+
+	/* NS-VC over which we send/receive data to this BVC */
+	struct gprs_nsvc *nsvc;
+
+	/* BVCI used for Point-to-Point to this peer */
+	uint16_t bvci;
+
+	/* Routeing Area that this peer is part of (raw 04.08 encoding) */
+	uint8_t ra[6];
+};
+
+/* Linked list of all Gb peers (except SGSN) */
+static LLIST_HEAD(gbprox_bts_peers);
+
+extern struct gprs_ns_inst *gbprox_nsi;
+
+/* Find the gbprox_peer by its BVCI */
+static struct gbprox_peer *peer_by_bvci(uint16_t bvci)
+{
+	struct gbprox_peer *peer;
+	llist_for_each_entry(peer, &gbprox_bts_peers, list) {
+		if (peer->bvci == bvci)
+			return peer;
+	}
+	return NULL;
+}
+
+static struct gbprox_peer *peer_by_nsvc(struct gprs_nsvc *nsvc)
+{
+	struct gbprox_peer *peer;
+	llist_for_each_entry(peer, &gbprox_bts_peers, list) {
+		if (peer->nsvc == nsvc)
+			return peer;
+	}
+	return NULL;
+}
+
+/* look-up a peer by its Routeing Area Code (RAC) */
+static struct gbprox_peer *peer_by_rac(const uint8_t *ra)
+{
+	struct gbprox_peer *peer;
+	llist_for_each_entry(peer, &gbprox_bts_peers, list) {
+		if (!memcmp(&peer->ra, ra, 6))
+			return peer;
+	}
+	return NULL;
+}
+
+/* look-up a peer by its Location Area Code (LAC) */
+static struct gbprox_peer *peer_by_lac(const uint8_t *la)
+{
+	struct gbprox_peer *peer;
+	llist_for_each_entry(peer, &gbprox_bts_peers, list) {
+		if (!memcmp(&peer->ra, la, 5))
+			return peer;
+	}
+	return NULL;
+}
+
+static struct gbprox_peer *peer_alloc(uint16_t bvci)
+{
+	struct gbprox_peer *peer;
+
+	peer = talloc_zero(tall_bsc_ctx, struct gbprox_peer);
+	if (!peer)
+		return NULL;
+
+	peer->bvci = bvci;
+	llist_add(&peer->list, &gbprox_bts_peers);
+
+	return peer;
+}
+
+static void peer_free(struct gbprox_peer *peer)
+{
+	llist_del(&peer->list);
+	talloc_free(peer);
+}
+
+/* strip off the NS header */
+static void strip_ns_hdr(struct msgb *msg)
+{
+	int strip_len = msgb_bssgph(msg) - msg->data;
+	msgb_pull(msg, strip_len);
+}
+
+/* FIXME: this is copy+paste from gprs_bssgp.c */
+static inline struct msgb *bssgp_msgb_alloc(void)
+{
+	return msgb_alloc_headroom(4096, 128, "BSSGP");
+}
+static int bssgp_tx_simple_bvci(uint8_t pdu_type, uint16_t nsei,
+			        uint16_t bvci, uint16_t ns_bvci)
+{
+	struct msgb *msg = bssgp_msgb_alloc();
+	struct bssgp_normal_hdr *bgph =
+			(struct bssgp_normal_hdr *) msgb_put(msg, sizeof(*bgph));
+	uint16_t _bvci;
+
+	msgb_nsei(msg) = nsei;
+	msgb_bvci(msg) = ns_bvci;
+
+	bgph->pdu_type = pdu_type;
+	_bvci = htons(bvci);
+	msgb_tvlv_put(msg, BSSGP_IE_BVCI, 2, (uint8_t *) &_bvci);
+
+	return gprs_ns_sendmsg(gbprox_nsi, msg);
+}
+
+
+/* feed a message down the NS-VC associated with the specified peer */
+static int gbprox_relay2sgsn(struct msgb *msg, uint16_t ns_bvci)
+{
+	DEBUGP(DGPRS, "NSEI=%u proxying to SGSN (NS_BVCI=%u, NSEI=%u)\n",
+		msgb_nsei(msg), ns_bvci, gbcfg.nsip_sgsn_nsei);
+
+	msgb_bvci(msg) = ns_bvci;
+	msgb_nsei(msg) = gbcfg.nsip_sgsn_nsei;
+
+	strip_ns_hdr(msg);
+
+	return gprs_ns_sendmsg(gbprox_nsi, msg);
+}
+
+/* feed a message down the NS-VC associated with the specified peer */
+static int gbprox_relay2peer(struct msgb *msg, struct gbprox_peer *peer,
+			  uint16_t ns_bvci)
+{
+	DEBUGP(DGPRS, "NSEI=%u proxying to BSS (NS_BVCI=%u, NSEI=%u)\n",
+		msgb_nsei(msg), ns_bvci, peer->nsvc->nsei);
+
+	msgb_bvci(msg) = ns_bvci;
+	msgb_nsei(msg) = peer->nsvc->nsei;
+
+	strip_ns_hdr(msg);
+
+	return gprs_ns_sendmsg(gbprox_nsi, msg);
+}
+
+/* Send a message to a peer identified by ptp_bvci but using ns_bvci
+ * in the NS hdr */
+static int gbprox_relay2bvci(struct msgb *msg, uint16_t ptp_bvci,
+			  uint16_t ns_bvci)
+{
+	struct gbprox_peer *peer;
+
+	peer = peer_by_bvci(ptp_bvci);
+	if (!peer) {
+		LOGP(DGPRS, LOGL_ERROR, "Cannot find BSS for BVCI %u\n",
+			ptp_bvci);
+		return -ENOENT;
+	}
+
+	return gbprox_relay2peer(msg, peer, ns_bvci);
+}
+
+/* Receive an incoming signalling message from a BSS-side NS-VC */
+static int gbprox_rx_sig_from_bss(struct msgb *msg, struct gprs_nsvc *nsvc,
+				  uint16_t ns_bvci)
+{
+	struct bssgp_normal_hdr *bgph = (struct bssgp_normal_hdr *) msgb_bssgph(msg);
+	struct tlv_parsed tp;
+	uint8_t pdu_type = bgph->pdu_type;
+	int data_len = msgb_bssgp_len(msg) - sizeof(*bgph);
+	struct gbprox_peer *from_peer;
+	struct gprs_ra_id raid;
+
+	if (ns_bvci != 0) {
+		LOGP(DGPRS, LOGL_NOTICE, "NSEI=%u BVCI %u is not signalling\n",
+			nsvc->nsei, ns_bvci);
+		return -EINVAL;
+	}
+
+	/* we actually should never see those two for BVCI == 0, but double-check
+	 * just to make sure  */
+	if (pdu_type == BSSGP_PDUT_UL_UNITDATA ||
+	    pdu_type == BSSGP_PDUT_DL_UNITDATA) {
+		LOGP(DGPRS, LOGL_NOTICE, "NSEI=%u UNITDATA not allowed in "
+			"signalling\n", nsvc->nsei);
+		return -EINVAL;
+	}
+
+	bssgp_tlv_parse(&tp, bgph->data, data_len);
+
+	switch (pdu_type) {
+	case BSSGP_PDUT_SUSPEND:
+	case BSSGP_PDUT_RESUME:
+		/* We implement RAC snooping during SUSPEND/RESUME, since
+		 * it establishes a relationsip between BVCI/peer and the
+		 * routeing area code.  The snooped information is then
+		 * used for routing the {SUSPEND,RESUME}_[N]ACK back to
+		 * the correct BSSGP */
+		if (!TLVP_PRESENT(&tp, BSSGP_IE_ROUTEING_AREA))
+			goto err_mand_ie;
+		from_peer = peer_by_nsvc(nsvc);
+		if (!from_peer)
+			goto err_no_peer;
+		memcpy(&from_peer->ra, TLVP_VAL(&tp, BSSGP_IE_ROUTEING_AREA),
+			sizeof(&from_peer->ra));
+		gsm48_parse_ra(&raid, &from_peer->ra);
+		DEBUGP(DGPRS, "NSEI=%u RAC snooping: RAC %u/%u/%u/%u behind BVCI=%u, "
+			"NSVCI=%u\n", nsvc->nsei, raid.mcc, raid.mnc, raid.lac,
+			raid.rac , from_peer->bvci, nsvc->nsvci);
+		/* FIXME: This only supports one BSS per RA */
+		break;
+	case BSSGP_PDUT_BVC_RESET:
+		/* If we receive a BVC reset on the signalling endpoint, we
+		 * don't want the SGSN to reset, as the signalling endpoint
+		 * is common for all point-to-point BVCs (and thus all BTS) */
+		if (TLVP_PRESENT(&tp, BSSGP_IE_BVCI)) {
+			uint16_t bvci = ntohs(*(uint16_t *)TLVP_VAL(&tp, BSSGP_IE_BVCI));
+			if (bvci == 0) {
+				/* FIXME: only do this if SGSN is alive! */
+				LOGP(DGPRS, LOGL_INFO, "NSEI=%u Sending fake "
+					"BVC RESET ACK of BVCI=0\n", nsvc->nsei);
+				return bssgp_tx_simple_bvci(BSSGP_PDUT_BVC_RESET_ACK,
+							    nsvc->nsei, 0, ns_bvci);
+			} else if (!peer_by_bvci(bvci)) {
+				/* if a PTP-BVC is reset, and we don't know that
+				 * PTP-BVCI yet, we should allocate a new peer */
+				LOGP(DGPRS, LOGL_INFO, "Allocationg new peer for "
+				     "BVCI=%u via NSVCI=%u/NSEI=%u\n", bvci,
+				     nsvc->nsvci, nsvc->nsei);
+				from_peer = peer_alloc(bvci);
+				from_peer->nsvc = nsvc;
+			}
+		}
+		break;
+	}
+
+	/* Normally, we can simply pass on all signalling messages from BSS to SGSN */
+	return gbprox_relay2sgsn(msg, ns_bvci);
+err_no_peer:
+err_mand_ie:
+	/* FIXME: do something */
+	;
+}
+
+/* Receive paging request from SGSN, we need to relay to proper BSS */
+static int gbprox_rx_paging(struct msgb *msg, struct tlv_parsed *tp,
+			    struct gprs_nsvc *nsvc, uint16_t ns_bvci)
+{
+	struct gbprox_peer *peer;
+
+	if (TLVP_PRESENT(tp, BSSGP_IE_BVCI)) {
+		uint16_t bvci = ntohs(*(uint16_t *)TLVP_VAL(tp, BSSGP_IE_BVCI));
+		return gbprox_relay2bvci(msg, bvci, ns_bvci);
+	} else if (TLVP_PRESENT(tp, BSSGP_IE_ROUTEING_AREA)) {
+		peer = peer_by_rac(TLVP_VAL(tp, BSSGP_IE_ROUTEING_AREA));
+		return gbprox_relay2peer(msg, peer, ns_bvci);
+	} else if (TLVP_PRESENT(tp, BSSGP_IE_LOCATION_AREA)) {
+		peer = peer_by_lac(TLVP_VAL(tp, BSSGP_IE_LOCATION_AREA));
+		return gbprox_relay2peer(msg, peer, ns_bvci);
+	} else
+		return -EINVAL;
+}
+
+/* Receive an incoming signalling message from the SGSN-side NS-VC */
+static int gbprox_rx_sig_from_sgsn(struct msgb *msg, struct gprs_nsvc *nsvc,
+				   uint16_t ns_bvci)
+{
+	struct bssgp_normal_hdr *bgph = (struct bssgp_normal_hdr *) msgb_bssgph(msg);
+	struct tlv_parsed tp;
+	uint8_t pdu_type = bgph->pdu_type;
+	int data_len = msgb_bssgp_len(msg) - sizeof(*bgph);
+	struct gbprox_peer *peer;
+	uint16_t bvci;
+	int rc = 0;
+
+	if (ns_bvci != 0) {
+		LOGP(DGPRS, LOGL_NOTICE, "NSEI=%u(SGSN) BVCI %u is not "
+			"signalling\n", nsvc->nsei, ns_bvci);
+		return -EINVAL;
+	}
+
+	/* we actually should never see those two for BVCI == 0, but double-check
+	 * just to make sure  */
+	if (pdu_type == BSSGP_PDUT_UL_UNITDATA ||
+	    pdu_type == BSSGP_PDUT_DL_UNITDATA) {
+		LOGP(DGPRS, LOGL_NOTICE, "NSEI=%u(SGSN) UNITDATA not allowed in "
+			"signalling\n", nsvc->nsei);
+		return -EINVAL;
+	}
+
+	rc = bssgp_tlv_parse(&tp, bgph->data, data_len);
+
+	switch (pdu_type) {
+	case BSSGP_PDUT_FLUSH_LL:
+	case BSSGP_PDUT_BVC_BLOCK_ACK:
+	case BSSGP_PDUT_BVC_UNBLOCK_ACK:
+	case BSSGP_PDUT_BVC_RESET:
+	case BSSGP_PDUT_BVC_RESET_ACK:
+		/* simple case: BVCI IE is mandatory */
+		if (!TLVP_PRESENT(&tp, BSSGP_IE_BVCI))
+			goto err_mand_ie;
+		bvci = ntohs(*(uint16_t *)TLVP_VAL(&tp, BSSGP_IE_BVCI));
+		rc = gbprox_relay2bvci(msg, bvci, ns_bvci);
+		break;
+	case BSSGP_PDUT_PAGING_PS:
+	case BSSGP_PDUT_PAGING_CS:
+		/* process the paging request (LAC/RAC lookup) */
+		rc = gbprox_rx_paging(msg, &tp, nsvc, ns_bvci);
+		break;
+	case BSSGP_PDUT_STATUS:
+		/* FIXME: Some exception has occurred */
+		LOGP(DGPRS, LOGL_NOTICE,
+			"NSEI=%u(SGSN) STATUS not implemented yet\n", nsvc->nsei);
+		break;
+	/* those only exist in the SGSN -> BSS direction */
+	case BSSGP_PDUT_SUSPEND_ACK:
+	case BSSGP_PDUT_SUSPEND_NACK:
+	case BSSGP_PDUT_RESUME_ACK:
+	case BSSGP_PDUT_RESUME_NACK:
+		/* RAC IE is mandatory */
+		if (!TLVP_PRESENT(&tp, BSSGP_IE_ROUTEING_AREA))
+			goto err_mand_ie;
+		peer = peer_by_rac(TLVP_VAL(&tp, BSSGP_IE_ROUTEING_AREA));
+		if (!peer)
+			goto err_no_peer;
+		rc = gbprox_relay2peer(msg, peer, ns_bvci);
+		break;
+	case BSSGP_PDUT_SGSN_INVOKE_TRACE:
+		LOGP(DGPRS, LOGL_ERROR,
+		     "NSEI=%u(SGSN) INVOKE TRACE not supported\n", nsvc->nsei);
+		break;
+	default:
+		DEBUGP(DGPRS, "BSSGP PDU type 0x%02x unknown\n", pdu_type);
+		break;
+	}
+
+	return rc;
+err_mand_ie:
+	LOGP(DGPRS, LOGL_ERROR, "NSEI=%u(SGSN) missing mandatory IE\n",
+		nsvc->nsei);
+	/* FIXME: this would pull gprs_bssgp.c in, which in turn has dependencies */
+	//return bssgp_tx_status(BSSGP_CAUSE_MISSING_MAND_IE, NULL, msg);
+	return;
+err_no_peer:
+	LOGP(DGPRS, LOGL_ERROR, "NSEI=%u(SGSN) cannot find peer based on RAC\n");
+	/* FIXME */
+	return;
+}
+
+/* Main input function for Gb proxy */
+int gbprox_rcvmsg(struct msgb *msg, struct gprs_nsvc *nsvc, uint16_t ns_bvci)
+{
+	int rc;
+
+	/* Only BVCI=0 messages need special treatment */
+	if (ns_bvci == 0 || ns_bvci == 1) {
+		if (nsvc->remote_end_is_sgsn)
+			rc = gbprox_rx_sig_from_sgsn(msg, nsvc, ns_bvci);
+		else
+			rc = gbprox_rx_sig_from_bss(msg, nsvc, ns_bvci);
+	} else {
+		/* All other BVCI are PTP and thus can be simply forwarded */
+		if (!nsvc->remote_end_is_sgsn) {
+			rc = gbprox_relay2sgsn(msg, ns_bvci);
+		} else {
+			struct gbprox_peer *peer = peer_by_bvci(ns_bvci);
+			if (!peer) {
+				LOGP(DGPRS, LOGL_NOTICE, "Allocationg new peer for "
+				     "BVCI=%u via NSVC=%u/NSEI=%u\n", ns_bvci,
+				     nsvc->nsvci, nsvc->nsei);
+				peer = peer_alloc(ns_bvci);
+				peer->nsvc = nsvc;
+			}
+			rc = gbprox_relay2peer(msg, peer, ns_bvci);
+		}
+	}
+
+	return rc;
+}
diff --git a/openbsc/src/gprs/gb_proxy_main.c b/openbsc/src/gprs/gb_proxy_main.c
new file mode 100644
index 0000000..0054b78
--- /dev/null
+++ b/openbsc/src/gprs/gb_proxy_main.c
@@ -0,0 +1,149 @@
+/* NS-over-IP proxy */
+
+/* (C) 2010 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2010 by On Waves
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <getopt.h>
+#include <errno.h>
+#include <sys/fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#include <osmocore/talloc.h>
+#include <osmocore/select.h>
+
+#include <openbsc/signal.h>
+#include <openbsc/debug.h>
+#include <openbsc/gprs_ns.h>
+#include <openbsc/telnet_interface.h>
+#include <openbsc/vty.h>
+#include <openbsc/gb_proxy.h>
+
+#include "../../bscconfig.h"
+
+/* this is here for the vty... it will never be called */
+void subscr_put() { abort(); }
+
+#define _GNU_SOURCE
+#include <getopt.h>
+
+void *tall_bsc_ctx;
+
+struct gprs_ns_inst *gbprox_nsi;
+
+const char *openbsc_version = "Osmocom NSIP Proxy " PACKAGE_VERSION;
+const char *openbsc_copyright =
+	"Copyright (C) 2010 Harald Welte and On-Waves\n"
+	"Contributions by Daniel Willmann, Jan Lübbe, Stefan Schmidt\n"
+	"Dieter Spaar, Andreas Eversberg, Holger Freyther\n\n"
+	"License GPLv2+: GNU GPL version 2 or later <http://gnu.org/licenses/gpl.html>\n"
+	"This is free software: you are free to change and redistribute it.\n"
+	"There is NO WARRANTY, to the extent permitted by law.\n";
+
+static char *config_file = "osmo_gbproxy.cfg";
+struct gbproxy_config gbcfg;
+
+/* Pointer to the SGSN peer */
+extern struct gbprox_peer *gbprox_peer_sgsn;
+
+/* call-back function for the NS protocol */
+static int proxy_ns_cb(enum gprs_ns_evt event, struct gprs_nsvc *nsvc,
+		      struct msgb *msg, u_int16_t bvci)
+{
+	int rc = 0;
+
+	switch (event) {
+	case GPRS_NS_EVT_UNIT_DATA:
+		rc = gbprox_rcvmsg(msg, nsvc, bvci);
+		break;
+	default:
+		LOGP(DGPRS, LOGL_ERROR, "SGSN: Unknown event %u from NS\n", event);
+		if (msg)
+			talloc_free(msg);
+		rc = -EIO;
+		break;
+	}
+	return rc;
+}
+
+
+int main(int argc, char **argv)
+{
+	struct gsm_network dummy_network;
+	struct log_target *stderr_target;
+	struct sockaddr_in sin;
+	int rc;
+
+	tall_bsc_ctx = talloc_named_const(NULL, 0, "nsip_proxy");
+
+	log_init(&log_info);
+	stderr_target = log_target_create_stderr();
+	log_add_target(stderr_target);
+	log_set_all_filter(stderr_target, 1);
+
+	telnet_init(&dummy_network, 4244);
+	rc = gbproxy_parse_config(config_file, &gbcfg);
+	if (rc < 0) {
+		LOGP(DGPRS, LOGL_FATAL, "Cannot parse config file\n");
+		exit(2);
+	}
+
+	gbprox_nsi = gprs_ns_instantiate(&proxy_ns_cb);
+	if (!gbprox_nsi) {
+		LOGP(DGPRS, LOGL_ERROR, "Unable to instantiate NS\n");
+		exit(1);
+	}
+	gbcfg.nsi = gbprox_nsi;
+	nsip_listen(gbprox_nsi, gbcfg.nsip_listen_port);
+
+	/* 'establish' the outgoing connection to the SGSN */
+	sin.sin_family = AF_INET;
+	sin.sin_port = htons(gbcfg.nsip_sgsn_port);
+	sin.sin_addr.s_addr = htonl(gbcfg.nsip_sgsn_ip);
+	nsip_connect(gbprox_nsi, &sin, gbcfg.nsip_sgsn_nsei,
+			gbcfg.nsip_sgsn_nsvci);
+
+	while (1) {
+		rc = bsc_select_main(0);
+		if (rc < 0)
+			exit(3);
+	}
+
+	exit(0);
+}
+
+struct gsm_network;
+int bsc_vty_init(struct gsm_network *dummy)
+{
+	cmd_init(1);
+	vty_init();
+
+	openbsc_vty_add_cmds();
+        gbproxy_vty_init();
+	return 0;
+}
+
diff --git a/openbsc/src/gprs/gb_proxy_vty.c b/openbsc/src/gprs/gb_proxy_vty.c
new file mode 100644
index 0000000..16f6a1e
--- /dev/null
+++ b/openbsc/src/gprs/gb_proxy_vty.c
@@ -0,0 +1,207 @@
+/*
+ * (C) 2010 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2010 by On-Waves
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#include <osmocore/talloc.h>
+
+#include <openbsc/debug.h>
+#include <openbsc/gb_proxy.h>
+#include <openbsc/gprs_ns.h>
+
+#include <vty/command.h>
+#include <vty/vty.h>
+
+static struct gbproxy_config *g_cfg = NULL;
+
+/*
+ * vty code for mgcp below
+ */
+static struct cmd_node gbproxy_node = {
+	GBPROXY_NODE,
+	"%s(gbproxy)#",
+	1,
+};
+
+static int config_write_gbproxy(struct vty *vty)
+{
+	struct in_addr ia;
+
+	vty_out(vty, "gbproxy%s", VTY_NEWLINE);
+
+	if (g_cfg->nsip_listen_ip) {
+		ia.s_addr = htonl(g_cfg->nsip_listen_ip);
+		vty_out(vty, "  nsip bss local ip %s%s", inet_ntoa(ia),
+			VTY_NEWLINE);
+	}
+	vty_out(vty, "  nsip bss local port %u%s", g_cfg->nsip_listen_port,
+		VTY_NEWLINE);
+	ia.s_addr = htonl(g_cfg->nsip_sgsn_ip);
+	vty_out(vty, "  nsip sgsn remote ip %s%s", inet_ntoa(ia),
+		VTY_NEWLINE);
+	vty_out(vty, "  nsip sgsn remote port %u%s", g_cfg->nsip_sgsn_port,
+		VTY_NEWLINE);
+	vty_out(vty, "  nsip sgsn nsei %u%s", g_cfg->nsip_sgsn_nsei,
+		VTY_NEWLINE);
+	vty_out(vty, "  nsip sgsn nsvci %u%s", g_cfg->nsip_sgsn_nsvci,
+		VTY_NEWLINE);
+
+	return CMD_SUCCESS;
+}
+
+DEFUN(show_gbproxy, show_gbproxy_cmd, "show gbproxy",
+      SHOW_STR "Display information about the Gb proxy")
+{
+	/* FIXME: iterate over list of NS-VC's and display their state */
+	struct gprs_ns_inst *nsi = g_cfg->nsi;
+	struct gprs_nsvc *nsvc;
+
+	llist_for_each_entry(nsvc, &nsi->gprs_nsvcs, list) {
+		vty_out(vty, "NSEI %5u, NS-VC %5u, %s-mode, %s %s%s",
+			nsvc->nsei, nsvc->nsvci,
+			nsvc->remote_end_is_sgsn ? "BSS" : "SGSN",
+			nsvc->state & NSE_S_ALIVE ? "ALIVE" : "DEAD",
+			nsvc->state & NSE_S_BLOCKED ? "BLOCKED" : "UNBLOCKED",
+			VTY_NEWLINE);
+		if (nsvc->nsi->ll == GPRS_NS_LL_UDP)
+			vty_out(vty, "  remote peer %s:%u%s",
+				inet_ntoa(nsvc->ip.bts_addr.sin_addr),
+				ntohs(nsvc->ip.bts_addr.sin_port), VTY_NEWLINE);
+	}
+
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gbproxy,
+      cfg_gbproxy_cmd,
+      "gbproxy",
+      "Configure the Gb proxy")
+{
+	vty->node = GBPROXY_NODE;
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_nsip_bss_local_ip,
+      cfg_nsip_bss_local_ip_cmd,
+      "nsip bss local ip A.B.C.D",
+      "Set the IP address on which we listen for BSS connects")
+{
+	struct in_addr ia;
+
+	inet_aton(argv[0], &ia);
+	g_cfg->nsip_listen_ip = ntohl(ia.s_addr);
+
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_nsip_bss_local_port,
+      cfg_nsip_bss_local_port_cmd,
+      "nsip bss local port <0-65534>",
+      "Set the UDP port on which we listen for BSS connects")
+{
+	unsigned int port = atoi(argv[0]);
+
+	g_cfg->nsip_listen_port = port;
+	return CMD_SUCCESS;
+}
+
+
+DEFUN(cfg_nsip_sgsn_ip,
+      cfg_nsip_sgsn_ip_cmd,
+      "nsip sgsn remote ip A.B.C.D",
+      "Set the IP of the SGSN to which the proxy shall connect")
+{
+	struct in_addr ia;
+
+	inet_aton(argv[0], &ia);
+	g_cfg->nsip_sgsn_ip = ntohl(ia.s_addr);
+
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_nsip_sgsn_port,
+      cfg_nsip_sgsn_port_cmd,
+      "nsip sgsn remote port <0-65534>",
+      "Set the UDP port of the SGSN to which the proxy shall connect")
+{
+	unsigned int port = atoi(argv[0]);
+
+	g_cfg->nsip_sgsn_port = port;
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_nsip_sgsn_nsei,
+      cfg_nsip_sgsn_nsei_cmd,
+      "nsip sgsn nsei <0-65534>",
+      "Set the NSEI to be used in the connection with the SGSN")
+{
+	unsigned int port = atoi(argv[0]);
+
+	g_cfg->nsip_sgsn_nsei = port;
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_nsip_sgsn_nsvci,
+      cfg_nsip_sgsn_nsvci_cmd,
+      "nsip sgsn nsvci <0-65534>",
+      "Set the NSVCI to be used in the connection with the SGSN")
+{
+	unsigned int port = atoi(argv[0]);
+
+	g_cfg->nsip_sgsn_nsvci = port;
+	return CMD_SUCCESS;
+}
+
+
+int gbproxy_vty_init(void)
+{
+	install_element(VIEW_NODE, &show_gbproxy_cmd);
+
+	install_element(CONFIG_NODE, &cfg_gbproxy_cmd);
+	install_node(&gbproxy_node, config_write_gbproxy);
+	install_default(GBPROXY_NODE);
+	install_element(GBPROXY_NODE, &cfg_nsip_bss_local_ip_cmd);
+	install_element(GBPROXY_NODE, &cfg_nsip_bss_local_port_cmd);
+	install_element(GBPROXY_NODE, &cfg_nsip_sgsn_ip_cmd);
+	install_element(GBPROXY_NODE, &cfg_nsip_sgsn_port_cmd);
+	install_element(GBPROXY_NODE, &cfg_nsip_sgsn_nsei_cmd);
+	install_element(GBPROXY_NODE, &cfg_nsip_sgsn_nsvci_cmd);
+
+	return 0;
+}
+
+int gbproxy_parse_config(const char *config_file, struct gbproxy_config *cfg)
+{
+	int rc;
+
+	g_cfg = cfg;
+	rc = vty_read_config_file(config_file);
+	if (rc < 0) {
+		fprintf(stderr, "Failed to parse the config file: '%s'\n", config_file);
+		return rc;
+	}
+
+	return 0;
+}
+
diff --git a/openbsc/src/gprs/gprs_bssgp.c b/openbsc/src/gprs/gprs_bssgp.c
new file mode 100644
index 0000000..554738b
--- /dev/null
+++ b/openbsc/src/gprs/gprs_bssgp.c
@@ -0,0 +1,537 @@
+/* GPRS BSSGP protocol implementation as per 3GPP TS 08.18 */
+
+/* (C) 2009-2010 by Harald Welte <laforge@gnumonks.org>
+ *
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <errno.h>
+#include <stdint.h>
+
+#include <netinet/in.h>
+
+#include <osmocore/msgb.h>
+#include <osmocore/tlv.h>
+#include <osmocore/talloc.h>
+
+#include <openbsc/debug.h>
+#include <openbsc/gsm_data.h>
+#include <openbsc/gsm_04_08_gprs.h>
+#include <openbsc/gprs_bssgp.h>
+#include <openbsc/gprs_llc.h>
+#include <openbsc/gprs_ns.h>
+
+/* global pointer to the gsm network data structure */
+/* FIXME: this must go! */
+extern struct gsm_network *bsc_gsmnet;
+struct gprs_ns_inst *bssgp_nsi;
+
+void *bssgp_tall_ctx = NULL;
+
+/* BSSGP Protocol specific, not implementation specific */
+/* FIXME: This needs to go into libosmocore after finished */
+
+/* Chapter 11.3.9 / Table 11.10: Cause coding */
+static const struct value_string bssgp_cause_strings[] = {
+	{ BSSGP_CAUSE_PROC_OVERLOAD,	"Processor overload" },
+	{ BSSGP_CAUSE_EQUIP_FAIL,	"Equipment Failure" },
+	{ BSSGP_CAUSE_TRASIT_NET_FAIL,	"Transit netowkr service failure" },
+	{ BSSGP_CAUSE_CAPA_GREATER_0KPBS,"Transmission capacity modified" },
+	{ BSSGP_CAUSE_UNKNOWN_MS,	"Unknown MS" },
+	{ BSSGP_CAUSE_UNKNOWN_BVCI,	"Unknown BVCI" },
+	{ BSSGP_CAUSE_CELL_TRAF_CONG,	"Cell traffic congestion" },
+	{ BSSGP_CAUSE_SGSN_CONG,	"SGSN congestion" },
+	{ BSSGP_CAUSE_OML_INTERV,	"O&M intervention" },
+	{ BSSGP_CAUSE_BVCI_BLOCKED,	"BVCI blocked" },
+	{ BSSGP_CAUSE_PFC_CREATE_FAIL,	"PFC create failure" },
+	{ BSSGP_CAUSE_SEM_INCORR_PDU,	"Semantically incorrect PDU" },
+	{ BSSGP_CAUSE_INV_MAND_INF,	"Invalid mandatory information" },
+	{ BSSGP_CAUSE_MISSING_MAND_IE,	"Missing mandatory IE" },
+	{ BSSGP_CAUSE_MISSING_COND_IE,	"Missing conditional IE" },
+	{ BSSGP_CAUSE_UNEXP_COND_IE,	"Unexpected conditional IE" },
+	{ BSSGP_CAUSE_COND_IE_ERR,	"Conditional IE error" },
+	{ BSSGP_CAUSE_PDU_INCOMP_STATE,	"PDU incompatible with protocol state" },
+	{ BSSGP_CAUSE_PROTO_ERR_UNSPEC,	"Protocol error - unspecified" },
+	{ BSSGP_CAUSE_PDU_INCOMP_FEAT, 	"PDU not compatible with feature set" },
+	{ 0, NULL },
+};
+
+const char *bssgp_cause_str(enum gprs_bssgp_cause cause)
+{
+	return get_value_string(bssgp_cause_strings, cause);
+}
+
+
+/* Our actual implementation */
+
+#define BVC_F_BLOCKED	0x0001
+
+/* The per-BTS context that we keep on the SGSN side of the BSSGP link */
+struct bssgp_bts_ctx {
+	struct llist_head list;
+
+	/* parsed RA ID and Cell ID of the remote BTS */
+	struct gprs_ra_id ra_id;
+	uint16_t cell_id;
+
+	/* NSEI and BVCI of underlying Gb link.  Together they
+	 * uniquely identify a link to a BTS (5.4.4) */
+	uint16_t bvci;
+	uint16_t nsei;
+
+	uint32_t bvc_state;
+
+	/* we might want to add this as a shortcut later, avoiding the NSVC
+	 * lookup for every packet, similar to a routing cache */
+	//struct gprs_nsvc *nsvc;
+};
+LLIST_HEAD(bts_ctxts);
+
+/* Find a BTS Context based on parsed RA ID and Cell ID */
+struct bssgp_bts_ctx *btsctx_by_raid_cid(const struct gprs_ra_id *raid, uint16_t cid)
+{
+	struct bssgp_bts_ctx *bctx;
+
+	llist_for_each_entry(bctx, &bts_ctxts, list) {
+		if (!memcmp(&bctx->ra_id, raid, sizeof(bctx->ra_id)) &&
+		    bctx->cell_id == cid)
+			return bctx;
+	}
+	return NULL;
+}
+
+/* Find a BTS context based on BVCI+NSEI tuple */
+struct bssgp_bts_ctx *btsctx_by_bvci_nsei(uint16_t bvci, uint16_t nsei)
+{
+	struct bssgp_bts_ctx *bctx;
+
+	llist_for_each_entry(bctx, &bts_ctxts, list) {
+		if (bctx->nsei == nsei && bctx->bvci == bvci)
+			return bctx;
+	}
+	return NULL;
+}
+
+struct bssgp_btx_ctx *btsctx_alloc(uint16_t bvci, uint16_t nsei)
+{
+	struct bssgp_bts_ctx *ctx;
+
+	ctx = talloc_zero(bssgp_tall_ctx, struct bssgp_bts_ctx);
+	if (!ctx)
+		return NULL;
+	ctx->bvci = bvci;
+	ctx->nsei = nsei;
+	llist_add(&ctx->list, &bts_ctxts);
+
+	return ctx;
+}
+
+static inline struct msgb *bssgp_msgb_alloc(void)
+{
+	return msgb_alloc_headroom(4096, 128, "BSSGP");
+}
+
+/* Transmit a simple response such as BLOCK/UNBLOCK/RESET ACK/NACK */
+static int bssgp_tx_simple_bvci(uint8_t pdu_type, uint16_t nsei,
+			        uint16_t bvci, uint16_t ns_bvci)
+{
+	struct msgb *msg = bssgp_msgb_alloc();
+	struct bssgp_normal_hdr *bgph =
+			(struct bssgp_normal_hdr *) msgb_put(msg, sizeof(*bgph));
+	uint16_t _bvci;
+
+	msgb_nsei(msg) = nsei;
+	msgb_bvci(msg) = ns_bvci;
+
+	bgph->pdu_type = pdu_type;
+	_bvci = htons(bvci);
+	msgb_tvlv_put(msg, BSSGP_IE_BVCI, 2, (uint8_t *) &_bvci);
+
+	return gprs_ns_sendmsg(bssgp_nsi, msg);
+}
+
+/* Chapter 10.4.5: Flow Control BVC ACK */
+static int bssgp_tx_fc_bvc_ack(uint16_t nsei, uint8_t tag, uint16_t ns_bvci)
+{
+	struct msgb *msg = bssgp_msgb_alloc();
+	struct bssgp_normal_hdr *bgph =
+			(struct bssgp_normal_hdr *) msgb_put(msg, sizeof(*bgph));
+
+	msgb_nsei(msg) = nsei;
+	msgb_bvci(msg) = ns_bvci;
+
+	bgph->pdu_type = BSSGP_PDUT_FLOW_CONTROL_BVC_ACK;
+	msgb_tvlv_put(msg, BSSGP_IE_TAG, 1, &tag);
+
+	return gprs_ns_sendmsg(bssgp_nsi, msg);
+}
+
+/* Chapter 10.4.14: Status */
+int bssgp_tx_status(uint8_t cause, uint16_t *bvci, struct msgb *orig_msg)
+{
+	struct msgb *msg = bssgp_msgb_alloc();
+	struct bssgp_normal_hdr *bgph =
+			(struct bssgp_normal_hdr *) msgb_put(msg, sizeof(*bgph));
+
+	DEBUGPC(DGPRS, "BSSGP: TX STATUS, cause=%s\n", bssgp_cause_str(cause));
+	msgb_nsei(msg) = msgb_nsei(orig_msg);
+	msgb_bvci(msg) = 0;
+
+	bgph->pdu_type = BSSGP_PDUT_STATUS;
+	msgb_tvlv_put(msg, BSSGP_IE_CAUSE, 1, &cause);
+	if (bvci) {
+		uint16_t _bvci = htons(*bvci);
+		msgb_tvlv_put(msg, BSSGP_IE_BVCI, 2, (uint8_t *) &_bvci);
+	}
+	if (orig_msg)
+		msgb_tvlv_put(msg, BSSGP_IE_PDU_IN_ERROR,
+			      msgb_bssgp_len(orig_msg), msgb_bssgph(orig_msg));
+
+	return gprs_ns_sendmsg(bssgp_nsi, msg);
+}
+
+uint16_t bssgp_parse_cell_id(struct gprs_ra_id *raid, const uint8_t *buf)
+{
+	/* 6 octets RAC */
+	gsm48_parse_ra(raid, buf);
+	/* 2 octets CID */
+	return ntohs(*(uint16_t *) (buf+6));
+}
+
+/* Chapter 8.4 BVC-Reset Procedure */
+static int bssgp_rx_bvc_reset(struct msgb *msg, struct tlv_parsed *tp,	
+			      uint16_t ns_bvci)
+{
+	struct bssgp_bts_ctx *bctx;
+	uint16_t nsei = msgb_nsei(msg);
+	uint16_t bvci;
+	int rc;
+
+	bvci = ntohs(*(uint16_t *)TLVP_VAL(tp, BSSGP_IE_BVCI));
+	DEBUGPC(DGPRS, "BVCI=%u, cause=%s\n", bvci,
+		bssgp_cause_str(*TLVP_VAL(tp, BSSGP_IE_CAUSE)));
+
+	/* look-up or create the BTS context for this BVC */
+	bctx = btsctx_by_bvci_nsei(bvci, nsei);
+	if (!bctx)
+		bctx = btsctx_alloc(bvci, nsei);
+
+	/* When we receive a BVC-RESET PDU (at least of a PTP BVCI), the BSS
+	 * informs us about its RAC + Cell ID, so we can create a mapping */
+	if (bvci != 0 && bvci != 1) {
+		if (!TLVP_PRESENT(tp, BSSGP_IE_CELL_ID)) {
+			LOGP(DGPRS, LOGL_ERROR, "BSSGP RESET BVCI=%u "
+				"missing mandatory IE\n", bvci);
+			return -EINVAL;
+		}
+		/* actually extract RAC / CID */
+		bctx->cell_id = bssgp_parse_cell_id(&bctx->ra_id,
+						TLVP_VAL(tp, BSSGP_IE_CELL_ID));
+		LOGP(DGPRS, LOGL_NOTICE, "Cell %u-%u-%u-%u CI %u on BVCI %u\n",
+			bctx->ra_id.mcc, bctx->ra_id.mnc, bctx->ra_id.lac,
+			bctx->ra_id.rac, bctx->cell_id, bvci);
+	}
+
+	/* Acknowledge the RESET to the BTS */
+	rc = bssgp_tx_simple_bvci(BSSGP_PDUT_BVC_RESET_ACK,
+				  nsei, bvci, ns_bvci);
+	return 0;
+}
+
+/* Uplink unit-data */
+static int bssgp_rx_ul_ud(struct msgb *msg)
+{
+	struct bssgp_ud_hdr *budh = (struct bssgp_ud_hdr *) msgb_bssgph(msg);
+	int data_len = msgb_bssgp_len(msg) - sizeof(*budh);
+	struct tlv_parsed tp;
+	int rc;
+
+	DEBUGP(DGPRS, "BSSGP UL-UD\n");
+
+	/* extract TLLI and parse TLV IEs */
+	msgb_tlli(msg) = ntohl(budh->tlli);
+	rc = bssgp_tlv_parse(&tp, budh->data, data_len);
+
+	/* Cell ID and LLC_PDU are the only mandatory IE */
+	if (!TLVP_PRESENT(&tp, BSSGP_IE_CELL_ID) ||
+	    !TLVP_PRESENT(&tp, BSSGP_IE_LLC_PDU))
+		return -EIO;
+
+	/* FIXME: lookup bssgp_bts_ctx based on BVCI + NSEI */
+
+	/* store pointer to LLC header and CELL ID in msgb->cb */
+	msgb_llch(msg) = TLVP_VAL(&tp, BSSGP_IE_LLC_PDU);
+	msgb_bcid(msg) = TLVP_VAL(&tp, BSSGP_IE_CELL_ID);
+
+	return gprs_llc_rcvmsg(msg, &tp);
+}
+
+static int bssgp_rx_suspend(struct msgb *msg)
+{
+	struct bssgp_normal_hdr *bgph =
+			(struct bssgp_normal_hdr *) msgb_bssgph(msg);
+	int data_len = msgb_bssgp_len(msg) - sizeof(*bgph);
+	struct tlv_parsed tp;
+	int rc;
+
+	DEBUGP(DGPRS, "BSSGP SUSPEND\n");
+
+	rc = bssgp_tlv_parse(&tp, bgph->data, data_len);
+	if (rc < 0)
+		return rc;
+
+	if (!TLVP_PRESENT(&tp, BSSGP_IE_TLLI) ||
+	    !TLVP_PRESENT(&tp, BSSGP_IE_ROUTEING_AREA))
+		return -EIO;
+
+	/* FIXME: pass the SUSPEND request to GMM */
+	/* SEND SUSPEND_ACK or SUSPEND_NACK */
+}
+
+static int bssgp_rx_resume(struct msgb *msg)
+{
+	struct bssgp_normal_hdr *bgph =
+			(struct bssgp_normal_hdr *) msgb_bssgph(msg);
+	int data_len = msgb_bssgp_len(msg) - sizeof(*bgph);
+	struct tlv_parsed tp;
+	int rc;
+
+	DEBUGP(DGPRS, "BSSGP RESUME\n");
+
+	rc = bssgp_tlv_parse(&tp, bgph->data, data_len);
+	if (rc < 0)
+		return rc;
+
+	if (!TLVP_PRESENT(&tp, BSSGP_IE_TLLI) ||
+	    !TLVP_PRESENT(&tp, BSSGP_IE_ROUTEING_AREA) ||
+	    !TLVP_PRESENT(&tp, BSSGP_IE_SUSPEND_REF_NR))
+		return -EIO;
+
+	/* FIXME: pass the RESUME request to GMM */
+	/* SEND RESUME_ACK or RESUME_NACK */
+}
+
+static int bssgp_rx_fc_bvc(struct msgb *msg, struct tlv_parsed *tp)
+{
+
+	DEBUGP(DGPRS, "BSSGP FC BVC\n");
+
+	if (!TLVP_PRESENT(tp, BSSGP_IE_TAG) ||
+	    !TLVP_PRESENT(tp, BSSGP_IE_BVC_BUCKET_SIZE) ||
+	    !TLVP_PRESENT(tp, BSSGP_IE_BUCKET_LEAK_RATE) ||
+	    !TLVP_PRESENT(tp, BSSGP_IE_BMAX_DEFAULT_MS) ||
+	    !TLVP_PRESENT(tp, BSSGP_IE_R_DEFAULT_MS))
+		return bssgp_tx_status(BSSGP_CAUSE_MISSING_MAND_IE, NULL, msg);
+
+	/* FIXME: actually implement flow control */
+
+	/* Send FLOW_CONTROL_BVC_ACK */
+	return bssgp_tx_fc_bvc_ack(msgb_nsei(msg), *TLVP_VAL(tp, BSSGP_IE_TAG),
+				   msgb_bvci(msg));
+}
+
+/* We expect msgb_bssgph() to point to the BSSGP header */
+int gprs_bssgp_rcvmsg(struct msgb *msg)
+{
+	struct bssgp_normal_hdr *bgph =
+			(struct bssgp_normal_hdr *) msgb_bssgph(msg);
+	struct tlv_parsed tp;
+	uint8_t pdu_type = bgph->pdu_type;
+	int data_len = msgb_bssgp_len(msg) - sizeof(*bgph);
+	uint16_t bvci;	/* PTP BVCI */
+	uint16_t ns_bvci = msgb_bvci(msg);
+	int rc = 0;
+
+	/* Identifiers from DOWN: NSEI, BVCI (both in msg->cb) */
+
+	/* UNITDATA BSSGP headers have TLLI in front */
+	if (pdu_type != BSSGP_PDUT_UL_UNITDATA &&
+	    pdu_type != BSSGP_PDUT_DL_UNITDATA)
+		rc = bssgp_tlv_parse(&tp, bgph->data, data_len);
+
+	switch (pdu_type) {
+	case BSSGP_PDUT_UL_UNITDATA:
+		/* some LLC data from the MS */
+		rc = bssgp_rx_ul_ud(msg);
+		break;
+	case BSSGP_PDUT_RA_CAPABILITY:
+		/* BSS requests RA capability or IMSI */
+		DEBUGP(DGPRS, "BSSGP RA CAPABILITY UPDATE\n");
+		/* FIXME: send RA_CAPA_UPDATE_ACK */
+		break;
+	case BSSGP_PDUT_RADIO_STATUS:
+		DEBUGP(DGPRS, "BSSGP RADIO STATUS\n");
+		/* BSS informs us of some exception */
+		/* FIXME: notify GMM */
+		break;
+	case BSSGP_PDUT_SUSPEND:
+		/* MS wants to suspend */
+		rc = bssgp_rx_suspend(msg);
+		break;
+	case BSSGP_PDUT_RESUME:
+		/* MS wants to resume */
+		rc = bssgp_rx_resume(msg);
+		break;
+	case BSSGP_PDUT_FLUSH_LL:
+		/* BSS informs MS has moved to one cell to other cell */
+		DEBUGP(DGPRS, "BSSGP FLUSH LL\n");
+		/* FIXME: notify GMM */
+		/* Send FLUSH_LL_ACK */
+		break;
+	case BSSGP_PDUT_LLC_DISCARD:
+		/* BSS informs that some LLC PDU's have been discarded */
+		DEBUGP(DGPRS, "BSSGP LLC DISCARDED\n");
+		/* FIXME: notify GMM */
+		break;
+	case BSSGP_PDUT_FLOW_CONTROL_BVC:
+		/* BSS informs us of available bandwidth in Gb interface */
+		rc = bssgp_rx_fc_bvc(msg, &tp);
+		break;
+	case BSSGP_PDUT_FLOW_CONTROL_MS:
+		/* BSS informs us of available bandwidth to one MS */
+		DEBUGP(DGPRS, "BSSGP FC MS\n");
+		/* FIXME: actually implement flow control */
+		/* FIXME: Send FLOW_CONTROL_MS_ACK */
+		break;
+	case BSSGP_PDUT_BVC_BLOCK:
+		/* BSS tells us that BVC shall be blocked */
+		DEBUGP(DGPRS, "BSSGP BVC BLOCK ");
+		if (!TLVP_PRESENT(&tp, BSSGP_IE_BVCI) ||
+		    !TLVP_PRESENT(&tp, BSSGP_IE_CAUSE))
+			goto err_mand_ie;
+		bvci = ntohs(*(uint16_t *)TLVP_VAL(&tp, BSSGP_IE_BVCI));
+		DEBUGPC(DGPRS, "BVCI=%u, cause=%s\n", bvci,
+			bssgp_cause_str(*TLVP_VAL(&tp, BSSGP_IE_CAUSE)));
+		/* We always acknowledge the BLOCKing */
+		rc = bssgp_tx_simple_bvci(BSSGP_PDUT_BVC_BLOCK_ACK,
+					  msgb_nsei(msg), bvci, ns_bvci);
+		break;
+	case BSSGP_PDUT_BVC_UNBLOCK:
+		/* BSS tells us that BVC shall be unblocked */
+		DEBUGP(DGPRS, "BSSGP BVC UNBLOCK ");
+		if (!TLVP_PRESENT(&tp, BSSGP_IE_BVCI))
+			goto err_mand_ie;
+		bvci = ntohs(*(uint16_t *)TLVP_VAL(&tp, BSSGP_IE_BVCI));
+		DEBUGPC(DGPRS, "BVCI=%u\n", bvci);
+		/* We always acknowledge the unBLOCKing */
+		rc = bssgp_tx_simple_bvci(BSSGP_PDUT_BVC_UNBLOCK_ACK,
+					  msgb_nsei(msg), bvci, ns_bvci);
+		break;
+	case BSSGP_PDUT_BVC_RESET:
+		/* BSS tells us that BVC init is required */
+		DEBUGP(DGPRS, "BSSGP BVC RESET ");
+		if (!TLVP_PRESENT(&tp, BSSGP_IE_BVCI) ||
+		    !TLVP_PRESENT(&tp, BSSGP_IE_CAUSE))
+			goto err_mand_ie;
+		rc = bssgp_rx_bvc_reset(msg, &tp, ns_bvci);
+		break;
+	case BSSGP_PDUT_STATUS:
+		/* Some exception has occurred */
+		/* FIXME: notify GMM */
+	case BSSGP_PDUT_DOWNLOAD_BSS_PFC:
+	case BSSGP_PDUT_CREATE_BSS_PFC_ACK:
+	case BSSGP_PDUT_CREATE_BSS_PFC_NACK:
+	case BSSGP_PDUT_MODIFY_BSS_PFC:
+	case BSSGP_PDUT_DELETE_BSS_PFC_ACK:
+		DEBUGP(DGPRS, "BSSGP PDU type 0x%02x not [yet] implemented\n",
+			pdu_type);
+		break;
+	/* those only exist in the SGSN -> BSS direction */
+	case BSSGP_PDUT_DL_UNITDATA:
+	case BSSGP_PDUT_PAGING_PS:
+	case BSSGP_PDUT_PAGING_CS:
+	case BSSGP_PDUT_RA_CAPA_UPDATE_ACK:
+	case BSSGP_PDUT_SUSPEND_ACK:
+	case BSSGP_PDUT_SUSPEND_NACK:
+	case BSSGP_PDUT_RESUME_ACK:
+	case BSSGP_PDUT_RESUME_NACK:
+	case BSSGP_PDUT_FLUSH_LL_ACK:
+	case BSSGP_PDUT_FLOW_CONTROL_BVC_ACK:
+	case BSSGP_PDUT_FLOW_CONTROL_MS_ACK:
+	case BSSGP_PDUT_BVC_BLOCK_ACK:
+	case BSSGP_PDUT_BVC_UNBLOCK_ACK:
+	case BSSGP_PDUT_SGSN_INVOKE_TRACE:
+		DEBUGP(DGPRS, "BSSGP PDU type 0x%02x only exists in DL\n",
+			pdu_type);
+		rc = -EINVAL;
+		break;
+	default:
+		DEBUGP(DGPRS, "BSSGP PDU type 0x%02x unknown\n", pdu_type);
+		break;
+	}
+
+	return rc;
+err_mand_ie:
+	return bssgp_tx_status(BSSGP_CAUSE_MISSING_MAND_IE, NULL, msg);
+}
+
+/* Entry function from upper level (LLC), asking us to transmit a BSSGP PDU
+ * to a remote MS (identified by TLLI) at a BTS identified by its BVCI and NSEI */
+int gprs_bssgp_tx_dl_ud(struct msgb *msg)
+{
+	struct bssgp_bts_ctx *bctx;
+	struct bssgp_ud_hdr *budh;
+	uint8_t llc_pdu_tlv_hdr_len = 2;
+	uint8_t *llc_pdu_tlv, *qos_profile;
+	uint16_t pdu_lifetime = 1000; /* centi-seconds */
+	uint8_t qos_profile_default[3] = { 0x00, 0x00, 0x21 };
+	uint16_t msg_len = msg->len;
+	uint16_t bvci = msgb_bvci(msg);
+	uint16_t nsei = msgb_nsei(msg);
+
+	/* Identifiers from UP: TLLI, BVCI, NSEI (all in msgb->cb) */
+	if (bvci < 2) {
+		LOGP(DGPRS, LOGL_ERROR, "Cannot send DL-UD to BVCI %u\n",
+			bvci);
+		return -EINVAL;
+	}
+
+	bctx = btsctx_by_bvci_nsei(bvci, nsei);
+	if (!bctx)
+		bctx = btsctx_alloc(bvci, nsei);
+
+	if (msg->len > TVLV_MAX_ONEBYTE)
+		llc_pdu_tlv_hdr_len += 1;
+
+	/* prepend the tag and length of the LLC-PDU TLV */
+	llc_pdu_tlv = msgb_push(msg, llc_pdu_tlv_hdr_len);
+	llc_pdu_tlv[0] = BSSGP_IE_LLC_PDU;
+	if (llc_pdu_tlv_hdr_len > 2) {
+		llc_pdu_tlv[1] = msg_len >> 8;
+		llc_pdu_tlv[2] = msg_len & 0xff;
+	} else {
+		llc_pdu_tlv[1] = msg_len & 0x3f;
+		llc_pdu_tlv[1] |= 0x80;
+	}
+
+	/* FIXME: optional elements */
+
+	/* prepend the pdu lifetime */
+	pdu_lifetime = htons(pdu_lifetime);
+	msgb_tvlv_push(msg, BSSGP_IE_PDU_LIFETIME, 2, (uint8_t *)&pdu_lifetime);
+
+	/* prepend the QoS profile, TLLI and pdu type */
+	budh = (struct bssgp_ud_hdr *) msgb_push(msg, sizeof(*budh));
+	memcpy(budh->qos_profile, qos_profile_default, sizeof(qos_profile_default));
+	budh->tlli = htonl(msgb_tlli(msg));
+	budh->pdu_type = BSSGP_PDUT_DL_UNITDATA;
+
+	/* Identifiers down: BVCI, NSEI (in msgb->cb) */
+
+	return gprs_ns_sendmsg(bssgp_nsi, msg);
+}
diff --git a/openbsc/src/gprs/gprs_llc.c b/openbsc/src/gprs/gprs_llc.c
new file mode 100644
index 0000000..9c75a3d
--- /dev/null
+++ b/openbsc/src/gprs/gprs_llc.c
@@ -0,0 +1,549 @@
+/* GPRS LLC protocol implementation as per 3GPP TS 04.64 */
+
+/* (C) 2009-2010 by Harald Welte <laforge@gnumonks.org>
+ *
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <errno.h>
+#include <stdint.h>
+
+#include <osmocore/msgb.h>
+#include <osmocore/linuxlist.h>
+#include <osmocore/timer.h>
+#include <osmocore/talloc.h>
+
+#include <openbsc/gsm_data.h>
+#include <openbsc/debug.h>
+#include <openbsc/gprs_bssgp.h>
+#include <openbsc/gprs_llc.h>
+#include <openbsc/crc24.h>
+
+/* Section 4.5.2 Logical Link States + Annex C.2 */
+enum gprs_llc_ll_state {
+	GPRS_LLS_UNASSIGNED	= 1,	/* No TLLI yet */
+	GPRS_LLS_ASSIGNED_ADM	= 2,	/* TLLI assigned */
+	GPRS_LLS_LOCAL_EST	= 3,	/* Local Establishment */
+	GPRS_LLS_REMOTE_EST	= 4,	/* Remote Establishment */
+	GPRS_LLS_ABM		= 5,
+	GPRS_LLS_LOCAL_REL	= 6,	/* Local Release */
+	GPRS_LLS_TIMER_REC 	= 7,	/* Timer Recovery */
+};
+
+/* Section 4.7.1: Logical Link Entity: One per DLCI (TLLI + SAPI) */
+struct gprs_llc_lle {
+	struct llist_head list;
+	struct timer_list t200;
+	struct timer_list t201;	/* wait for acknowledgement */
+
+	enum gprs_llc_ll_state state;
+
+	uint32_t tlli;
+	uint32_t sapi;
+
+	uint8_t v_sent;
+	uint8_t v_ack;
+	uint8_t v_recv;
+
+	unsigned int n200;
+	unsigned int retrans_ctr;
+
+	/* over which BSSGP BTS ctx do we need to transmit */
+	uint16_t bvci;
+	uint16_t nsei;
+};
+
+static LLIST_HEAD(gprs_llc_lles);
+void *llc_tall_ctx;
+
+/* lookup LLC Entity based on DLCI (TLLI+SAPI tuple) */
+static struct gprs_llc_lle *lle_by_tlli_sapi(uint32_t tlli, uint32_t sapi)
+{
+	struct gprs_llc_lle *lle;
+
+	llist_for_each_entry(lle, &gprs_llc_lles, list) {
+		if (lle->tlli == tlli && lle->sapi == sapi)
+			return lle;
+	}
+	return NULL;
+}
+
+static struct gprs_llc_lle *lle_alloc(uint32_t tlli, uint32_t sapi)
+{
+	struct gprs_llc_lle *lle;
+
+	lle = talloc_zero(llc_tall_ctx, struct gprs_llc_lle);
+	if (!lle)
+		return NULL;
+
+	lle->tlli = tlli;
+	lle->sapi = sapi;
+	lle->state = GPRS_LLS_UNASSIGNED;
+	llist_add(&lle->list, &gprs_llc_lles);
+
+	return lle;
+}
+
+enum gprs_llc_cmd {
+	GPRS_LLC_NULL,
+	GPRS_LLC_RR,
+	GPRS_LLC_ACK,
+	GPRS_LLC_RNR,
+	GPRS_LLC_SACK,
+	GPRS_LLC_DM,
+	GPRS_LLC_DISC,
+	GPRS_LLC_UA,
+	GPRS_LLC_SABM,
+	GPRS_LLC_FRMR,
+	GPRS_LLC_XID,
+};
+
+struct gprs_llc_hdr_parsed {
+	uint8_t sapi;
+	uint8_t is_cmd:1,
+		 ack_req:1,
+		 is_encrypted:1;
+	uint32_t seq_rx;
+	uint32_t seq_tx;
+	uint32_t fcs;
+	uint32_t fcs_calc;
+	uint8_t *data;
+	uint16_t data_len;
+	enum gprs_llc_cmd cmd;
+};
+
+#define LLC_ALLOC_SIZE 16384
+#define UI_HDR_LEN	3
+#define N202		4
+#define CRC24_LENGTH	3
+
+static int gprs_llc_fcs(uint8_t *data, unsigned int len)
+{
+	uint32_t fcs_calc;
+
+	fcs_calc = crc24_calc(INIT_CRC24, data, len);
+	fcs_calc = ~fcs_calc;
+	fcs_calc &= 0xffffff;
+
+	return fcs_calc;
+}
+
+static void t200_expired(void *data)
+{
+	struct gprs_llc_lle *lle = data;
+
+	/* 8.5.1.3: Expiry of T200 */
+
+	if (lle->retrans_ctr >= lle->n200) {
+		/* FIXME: LLGM-STATUS-IND, LL-RELEASE-IND/CNF */
+		lle->state = GPRS_LLS_ASSIGNED_ADM;
+	}
+
+	switch (lle->state) {
+	case GPRS_LLS_LOCAL_EST:
+		/* retransmit SABM */
+		/* re-start T200 */
+		lle->retrans_ctr++;
+		break;
+	case GPRS_LLS_LOCAL_REL:
+		/* retransmit DISC */
+		/* re-start T200 */
+		lle->retrans_ctr++;
+		break;
+	}
+
+}
+
+static void t201_expired(void *data)
+{
+	struct gprs_llc_lle *lle = data;
+
+	if (lle->retrans_ctr < lle->n200) {
+		/* transmit apropriate supervisory frame (8.6.4.1) */
+		/* set timer T201 */
+		lle->retrans_ctr++;
+	}
+}
+
+int gprs_llc_tx_u(struct msgb *msg, uint8_t sapi, int command,
+		  enum gprs_llc_u_cmd u_cmd, int pf_bit)
+{
+	uint8_t *fcs, *llch;
+	uint8_t addr, ctrl;
+	uint32_t fcs_calc;
+
+	/* Identifiers from UP: (TLLI, SAPI) + (BVCI, NSEI) */
+
+	/* Address Field */
+	addr = sapi & 0xf;
+	if (command)
+		addr |= 0x40;
+
+	/* 6.3 Figure 8 */
+	ctrl = 0xe0 | u_cmd;
+	if (pf_bit)
+		ctrl |= 0x10;
+
+	/* prepend LLC UI header */
+	llch = msgb_push(msg, 2);
+	llch[0] = addr;
+	llch[1] = ctrl;
+
+	/* append FCS to end of frame */
+	fcs = msgb_put(msg, 3);
+	fcs_calc = gprs_llc_fcs(llch, fcs - llch);
+	fcs[0] = fcs_calc & 0xff;
+	fcs[1] = (fcs_calc >> 8) & 0xff;
+	fcs[2] = (fcs_calc >> 16) & 0xff;
+
+	/* Identifiers passed down: (BVCI, NSEI) */
+
+	return gprs_bssgp_tx_dl_ud(msg);
+}
+
+/* Send XID response to LLE */
+static int gprs_llc_tx_xid(struct gprs_llc_lle *lle, struct msgb *msg)
+{
+	/* copy identifiers from LLE to ensure lower layers can route */
+	msgb_tlli(msg) = lle->tlli;
+	msgb_bvci(msg) = lle->bvci;
+	msgb_nsei(msg) = lle->nsei;
+
+	return gprs_llc_tx_u(msg, lle->sapi, 0, GPRS_LLC_U_XID, 1);
+}
+
+/* Transmit a UI frame over the given SAPI */
+int gprs_llc_tx_ui(struct msgb *msg, uint8_t sapi, int command)
+{
+	struct gprs_llc_lle *lle;
+	uint8_t *fcs, *llch;
+	uint8_t addr, ctrl[2];
+	uint32_t fcs_calc;
+	uint16_t nu = 0;
+
+	/* Identifiers from UP: (TLLI, SAPI) + (BVCI, NSEI) */
+
+	/* look-up or create the LL Entity for this (TLLI, SAPI) tuple */
+	lle = lle_by_tlli_sapi(msgb_tlli(msg), sapi);
+	if (!lle)
+		lle = lle_alloc(msgb_tlli(msg), sapi);
+	/* Update LLE's (BVCI, NSEI) tuple */
+	lle->bvci = msgb_bvci(msg);
+	lle->nsei = msgb_nsei(msg);
+
+	/* Address Field */
+	addr = sapi & 0xf;
+	if (command)
+		addr |= 0x40;
+
+	/* Control Field */
+	ctrl[0] = 0xc0;
+	ctrl[0] |= nu >> 6;
+	ctrl[1] = (nu << 2) & 0xfc;
+	ctrl[1] |= 0x01; /* Protected Mode */
+
+	/* prepend LLC UI header */
+	llch = msgb_push(msg, 3);
+	llch[0] = addr;
+	llch[1] = ctrl[0];
+	llch[2] = ctrl[1];
+
+	/* append FCS to end of frame */
+	fcs = msgb_put(msg, 3);
+	fcs_calc = gprs_llc_fcs(llch, fcs - llch);
+	fcs[0] = fcs_calc & 0xff;
+	fcs[1] = (fcs_calc >> 8) & 0xff;
+	fcs[2] = (fcs_calc >> 16) & 0xff;
+
+	/* Identifiers passed down: (BVCI, NSEI) */
+
+	return gprs_bssgp_tx_dl_ud(msg);
+}
+
+static int gprs_llc_hdr_dump(struct gprs_llc_hdr_parsed *gph)
+{
+	DEBUGP(DGPRS, "LLC SAPI=%u %c %c FCS=0x%06x(%s) ",
+		gph->sapi, gph->is_cmd ? 'C' : 'R', gph->ack_req ? 'A' : ' ',
+		gph->fcs, gph->fcs_calc == gph->fcs ? "correct" : "WRONG");
+
+	if (gph->cmd)
+		DEBUGPC(DGPRS, "CMD=%u ", gph->cmd);
+
+	if (gph->data)
+		DEBUGPC(DGPRS, "DATA ");
+
+	DEBUGPC(DGPRS, "\n");
+}
+static int gprs_llc_hdr_rx(struct gprs_llc_hdr_parsed *gph,
+			   struct gprs_llc_lle *lle)
+{
+	switch (gph->cmd) {
+	case GPRS_LLC_SABM: /* Section 6.4.1.1 */
+		lle->v_sent = lle->v_ack = lle->v_recv = 0;
+		if (lle->state == GPRS_LLS_ASSIGNED_ADM) {
+			/* start re-establishment (8.7.1) */
+		}
+		lle->state = GPRS_LLS_REMOTE_EST;
+		/* FIXME: Send UA */
+		lle->state = GPRS_LLS_ABM;
+		/* FIXME: process data */
+		break;
+	case GPRS_LLC_DISC: /* Section 6.4.1.2 */
+		/* FIXME: Send UA */
+		/* terminate ABM */
+		lle->state = GPRS_LLS_ASSIGNED_ADM;
+		break;
+	case GPRS_LLC_UA: /* Section 6.4.1.3 */
+		if (lle->state == GPRS_LLS_LOCAL_EST)
+			lle->state = GPRS_LLS_ABM;
+		break;
+	case GPRS_LLC_DM: /* Section 6.4.1.4: ABM cannot be performed */
+		if (lle->state == GPRS_LLS_LOCAL_EST)
+			lle->state = GPRS_LLS_ASSIGNED_ADM;
+		break;
+	case GPRS_LLC_FRMR: /* Section 6.4.1.5 */
+		break;
+	case GPRS_LLC_XID: /* Section 6.4.1.6 */
+		/* FIXME: implement XID negotiation using SNDCP */
+		{
+			struct msgb *resp;
+			uint8_t *xid;
+			resp = msgb_alloc_headroom(4096, 1024, "LLC_XID");
+			xid = msgb_put(resp, gph->data_len);
+			memcpy(xid, gph->data, gph->data_len);
+			gprs_llc_tx_xid(lle, resp);
+		}
+		break;
+	}
+
+	return 0;
+}
+
+/* parse a GPRS LLC header, also check for invalid frames */
+static int gprs_llc_hdr_parse(struct gprs_llc_hdr_parsed *ghp,
+			      const uint8_t *llc_hdr, int len)
+{
+	uint8_t *ctrl = llc_hdr+1;
+	int is_sack = 0;
+	unsigned int crc_length;
+	uint32_t fcs_calc;
+
+	if (len <= CRC24_LENGTH)
+		return -EIO;
+
+	crc_length = len - CRC24_LENGTH;
+
+	ghp->ack_req = 0;
+
+	/* Section 5.5: FCS */
+	ghp->fcs = *(llc_hdr + len - 3);
+	ghp->fcs |= *(llc_hdr + len - 2) << 8;
+	ghp->fcs |= *(llc_hdr + len - 1) << 16;
+
+	/* Section 6.2.1: invalid PD field */
+	if (llc_hdr[0] & 0x80)
+		return -EIO;
+
+	/* This only works for the MS->SGSN direction */
+	if (llc_hdr[0] & 0x40)
+		ghp->is_cmd = 0;
+	else
+		ghp->is_cmd = 1;
+
+	ghp->sapi = llc_hdr[0] & 0xf;
+
+	/* Section 6.2.3: check for reserved SAPI */
+	switch (ghp->sapi) {
+	case 0:
+	case 4:
+	case 6:
+	case 0xa:
+	case 0xc:
+	case 0xd:
+	case 0xf:
+		return -EINVAL;
+	}
+
+	if ((ctrl[0] & 0x80) == 0) {
+		/* I (Information transfer + Supervisory) format */
+		uint8_t k;
+
+		ghp->data = ctrl + 3;
+
+		if (ctrl[0] & 0x40)
+			ghp->ack_req = 1;
+
+		ghp->seq_tx  = (ctrl[0] & 0x1f) << 4;
+		ghp->seq_tx |= (ctrl[1] >> 4);
+
+		ghp->seq_rx  = (ctrl[1] & 0x7) << 6;
+		ghp->seq_rx |= (ctrl[2] >> 2);
+
+		switch (ctrl[2] & 0x03) {
+		case 0:
+			ghp->cmd = GPRS_LLC_RR;
+			break;
+		case 1:
+			ghp->cmd = GPRS_LLC_ACK;
+			break;
+		case 2:
+			ghp->cmd = GPRS_LLC_RNR;
+			break;
+		case 3:
+			ghp->cmd = GPRS_LLC_SACK;
+			k = ctrl[3] & 0x1f;
+			ghp->data += 1 + k;
+			break;
+		}
+		ghp->data_len = (llc_hdr + len - 3) - ghp->data;
+	} else if ((ctrl[0] & 0xc0) == 0x80) {
+		/* S (Supervisory) format */
+		ghp->data = NULL;
+		ghp->data_len = 0;
+
+		if (ctrl[0] & 0x20)
+			ghp->ack_req = 1;
+		ghp->seq_rx  = (ctrl[0] & 0x7) << 6;
+		ghp->seq_rx |= (ctrl[1] >> 2);
+
+		switch (ctrl[1] & 0x03) {
+		case 0:
+			ghp->cmd = GPRS_LLC_RR;
+			break;
+		case 1:
+			ghp->cmd = GPRS_LLC_ACK;
+			break;
+		case 2:
+			ghp->cmd = GPRS_LLC_RNR;
+			break;
+		case 3:
+			ghp->cmd = GPRS_LLC_SACK;
+			break;
+		}
+	} else if ((ctrl[0] & 0xe0) == 0xc0) {
+		/* UI (Unconfirmed Inforamtion) format */
+		ghp->data = ctrl + 2;
+		ghp->data_len = (llc_hdr + len - 3) - ghp->data;
+
+		ghp->seq_tx  = (ctrl[0] & 0x7) << 6;
+		ghp->seq_tx |= (ctrl[1] >> 2);
+		if (ctrl[1] & 0x02) {
+			ghp->is_encrypted = 1;
+			/* FIXME: encryption */
+		}
+		if (ctrl[1] & 0x01) {
+			/* FCS over hdr + all inf fields */
+		} else {
+			/* FCS over hdr + N202 octets (4) */
+			if (crc_length > UI_HDR_LEN + N202)
+				crc_length = UI_HDR_LEN + N202;
+		}
+	} else {
+		/* U (Unnumbered) format: 1 1 1 P/F M4 M3 M2 M1 */
+		ghp->data = NULL;
+		ghp->data_len = 0;
+
+		switch (ctrl[0] & 0xf) {
+		case GPRS_LLC_U_NULL_CMD:
+			ghp->cmd = GPRS_LLC_NULL;
+			break;
+		case GPRS_LLC_U_DM_RESP:
+			ghp->cmd = GPRS_LLC_DM;
+			break;
+		case GPRS_LLC_U_DISC_CMD:
+			ghp->cmd = GPRS_LLC_DISC;
+			break;
+		case GPRS_LLC_U_UA_RESP:
+			ghp->cmd = GPRS_LLC_UA;
+			break;
+		case GPRS_LLC_U_SABM_CMD:
+			ghp->cmd = GPRS_LLC_SABM;
+			break;
+		case GPRS_LLC_U_FRMR_RESP:
+			ghp->cmd = GPRS_LLC_FRMR;
+			break;
+		case GPRS_LLC_U_XID:
+			ghp->cmd = GPRS_LLC_XID;
+			ghp->data = ctrl + 1;
+			ghp->data_len = (llc_hdr + len - 3) - ghp->data;
+			break;
+		default:
+			return -EIO;
+		}
+	}
+
+	/* calculate what FCS we expect */
+	ghp->fcs_calc = gprs_llc_fcs(llc_hdr, crc_length);
+
+	/* FIXME: parse sack frame */
+}
+
+/* receive an incoming LLC PDU (BSSGP-UL-UNITDATA-IND, 7.2.4.2) */
+int gprs_llc_rcvmsg(struct msgb *msg, struct tlv_parsed *tv)
+{
+	struct bssgp_ud_hdr *udh = (struct bssgp_ud_hdr *) msgb_bssgph(msg);
+	struct gprs_llc_hdr *lh = msgb_llch(msg);
+	struct gprs_llc_hdr_parsed llhp;
+	struct gprs_llc_lle *lle;
+	int rc = 0;
+
+	/* Identifiers from DOWN: NSEI, BVCI, TLLI */
+
+	rc = gprs_llc_hdr_parse(&llhp, lh, TLVP_LEN(tv, BSSGP_IE_LLC_PDU));
+	/* FIXME */
+
+	gprs_llc_hdr_dump(&llhp);
+
+	/* find the LLC Entity for this TLLI+SAPI tuple */
+	lle = lle_by_tlli_sapi(msgb_tlli(msg), llhp.sapi);
+	/* allocate a new LLE if needed */
+	if (!lle)
+		lle = lle_alloc(msgb_tlli(msg), llhp.sapi);
+
+	/* Update LLE's (BVCI, NSEI) tuple */
+	lle->bvci = msgb_bvci(msg);
+	lle->nsei = msgb_nsei(msg);
+
+	rc = gprs_llc_hdr_rx(&llhp, lle);
+	/* FIXME */
+
+	if (llhp.data) {
+		msgb_gmmh(msg) = llhp.data;
+		switch (llhp.sapi) {
+		case GPRS_SAPI_GMM:
+			rc = gsm0408_gprs_rcvmsg(msg);
+			break;
+		case GPRS_SAPI_TOM2:
+		case GPRS_SAPI_TOM8:
+			/* FIXME */
+		case GPRS_SAPI_SNDCP3:
+		case GPRS_SAPI_SNDCP5:
+		case GPRS_SAPI_SNDCP9:
+		case GPRS_SAPI_SNDCP11:
+			/* FIXME */
+		case GPRS_SAPI_SMS:
+			/* FIXME */
+		default:
+			LOGP(DGPRS, LOGL_NOTICE, "Unsupported SAPI %u\n", llhp.sapi);
+			rc = -EINVAL;
+			break;
+		}
+	}
+
+	return rc;
+}
diff --git a/openbsc/src/gprs/gprs_ns.c b/openbsc/src/gprs/gprs_ns.c
new file mode 100644
index 0000000..3d9bb89
--- /dev/null
+++ b/openbsc/src/gprs/gprs_ns.c
@@ -0,0 +1,644 @@
+/* GPRS Networks Service (NS) messages on the Gb interfacebvci = msgb_bvci(msg);
+ * 3GPP TS 08.16 version 8.0.1 Release 1999 / ETSI TS 101 299 V8.0.1 (2002-05) */
+
+/* (C) 2009-2010 by Harald Welte <laforge@gnumonks.org>
+ *
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+/* Some introduction into NS:  NS is used typically on top of frame relay,
+ * but in the ip.access world it is encapsulated in UDP packets.  It serves
+ * as an intermediate shim betwen BSSGP and the underlying medium.  It doesn't
+ * do much, apart from providing congestion notification and status indication.
+ *
+ * Terms:
+ * 	NS		Network Service
+ *	NSVC		NS Virtual Connection
+ *	NSEI		NS Entity Identifier
+ *	NSVL		NS Virtual Link
+ *	NSVLI		NS Virtual Link Identifier
+ *	BVC		BSSGP Virtual Connection
+ *	BVCI		BSSGP Virtual Connection Identifier
+ *	NSVCG		NS Virtual Connection Goup
+ *	Blocked		NS-VC cannot be used for user traffic
+ *	Alive		Ability of a NS-VC to provide communication
+ *
+ *  There can be multiple BSSGP virtual connections over one (group of) NSVC's.  BSSGP will
+ * therefore identify the BSSGP virtual connection by a BVCI passed down to NS.
+ * NS then has to firgure out which NSVC's are responsible for this BVCI.
+ * Those mappings are administratively configured.
+ */
+
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdint.h>
+
+#include <arpa/inet.h>
+
+#include <openbsc/gsm_data.h>
+#include <osmocore/msgb.h>
+#include <osmocore/tlv.h>
+#include <osmocore/talloc.h>
+#include <osmocore/select.h>
+#include <openbsc/debug.h>
+#include <openbsc/gprs_ns.h>
+#include <openbsc/gprs_bssgp.h>
+
+#define NS_ALLOC_SIZE	1024
+
+static const struct tlv_definition ns_att_tlvdef = {
+	.def = {
+		[NS_IE_CAUSE]	= { TLV_TYPE_TvLV, 0 },
+		[NS_IE_VCI]	= { TLV_TYPE_TvLV, 0 },
+		[NS_IE_PDU]	= { TLV_TYPE_TvLV, 0 },
+		[NS_IE_BVCI]	= { TLV_TYPE_TvLV, 0 },
+		[NS_IE_NSEI]	= { TLV_TYPE_TvLV, 0 },
+	},
+};
+
+/* Lookup struct gprs_nsvc based on NSVCI */
+static struct gprs_nsvc *nsvc_by_nsvci(struct gprs_ns_inst *nsi,
+					uint16_t nsvci)
+{
+	struct gprs_nsvc *nsvc;
+	llist_for_each_entry(nsvc, &nsi->gprs_nsvcs, list) {
+		if (nsvc->nsvci == nsvci)
+			return nsvc;
+	}
+	return NULL;
+}
+
+/* Lookup struct gprs_nsvc based on NSVCI */
+static struct gprs_nsvc *nsvc_by_nsei(struct gprs_ns_inst *nsi,
+					uint16_t nsei)
+{
+	struct gprs_nsvc *nsvc;
+	llist_for_each_entry(nsvc, &nsi->gprs_nsvcs, list) {
+		if (nsvc->nsei == nsei)
+			return nsvc;
+	}
+	return NULL;
+}
+
+
+/* Lookup struct gprs_nsvc based on remote peer socket addr */
+static struct gprs_nsvc *nsvc_by_rem_addr(struct gprs_ns_inst *nsi,
+					  struct sockaddr_in *sin)
+{
+	struct gprs_nsvc *nsvc;
+	llist_for_each_entry(nsvc, &nsi->gprs_nsvcs, list) {
+		if (!memcmp(&nsvc->ip.bts_addr, sin, sizeof(*sin)))
+			return nsvc;
+	}
+	return NULL;
+}
+
+static void gprs_ns_timer_cb(void *data);
+
+static struct gprs_nsvc *nsvc_create(struct gprs_ns_inst *nsi, uint16_t nsvci)
+{
+	struct gprs_nsvc *nsvc;
+
+	nsvc = talloc_zero(nsi, struct gprs_nsvc);
+	nsvc->nsvci = nsvci;
+	/* before RESET procedure: BLOCKED and DEAD */
+	nsvc->state = NSE_S_BLOCKED;
+	nsvc->nsi = nsi;
+	nsvc->timer.cb = gprs_ns_timer_cb;
+	nsvc->timer.data = nsvc;
+
+	llist_add(&nsvc->list, &nsi->gprs_nsvcs);
+
+	return nsvc;
+}
+
+/* Section 10.3.2, Table 13 */
+static const struct value_string ns_cause_str[] = {
+	{ NS_CAUSE_TRANSIT_FAIL,	"Transit network failure" },
+	{ NS_CAUSE_OM_INTERVENTION, 	"O&M intervention" },
+	{ NS_CAUSE_EQUIP_FAIL,		"Equipment failure" },
+	{ NS_CAUSE_NSVC_BLOCKED,	"NS-VC blocked" },
+	{ NS_CAUSE_NSVC_UNKNOWN,	"NS-VC unknown" },
+	{ NS_CAUSE_BVCI_UNKNOWN,	"BVCI unknown" },
+	{ NS_CAUSE_SEM_INCORR_PDU,	"Semantically incorrect PDU" },
+	{ NS_CAUSE_PDU_INCOMP_PSTATE,	"PDU not compatible with protocol state" },
+	{ NS_CAUSE_PROTO_ERR_UNSPEC,	"Protocol error, unspecified" },
+	{ NS_CAUSE_INVAL_ESSENT_IE,	"Invalid essential IE" },
+	{ NS_CAUSE_MISSING_ESSENT_IE,	"Missing essential IE" },
+	{ 0, NULL }
+};
+
+const char *gprs_ns_cause_str(enum ns_cause cause)
+{
+	return get_value_string(ns_cause_str, cause);
+}
+
+static int nsip_sendmsg(struct gprs_nsvc *nsvc, struct msgb *msg);
+
+static int gprs_ns_tx(struct gprs_nsvc *nsvc, struct msgb *msg)
+{
+	int ret;
+
+	switch (nsvc->nsi->ll) {
+	case GPRS_NS_LL_UDP:
+		ret = nsip_sendmsg(nsvc, msg);
+		break;
+	default:
+		LOGP(DGPRS, LOGL_ERROR, "unsupported NS linklayer %u\n", nsvc->nsi->ll);
+		msgb_free(msg);
+		ret = -EIO;
+		break;
+	}
+	return ret;
+}
+
+static int gprs_ns_tx_simple(struct gprs_nsvc *nsvc, uint8_t pdu_type)
+{
+	struct msgb *msg = msgb_alloc(NS_ALLOC_SIZE, "GPRS/NS");
+	struct gprs_ns_hdr *nsh;
+
+	if (!msg)
+		return -ENOMEM;
+
+	nsh = (struct gprs_ns_hdr *) msgb_put(msg, sizeof(*nsh));
+
+	nsh->pdu_type = pdu_type;
+
+	return gprs_ns_tx(nsvc, msg);
+}
+
+static int gprs_ns_tx_reset(struct gprs_nsvc *nsvc, uint8_t cause)
+{
+	struct msgb *msg = msgb_alloc(NS_ALLOC_SIZE, "GPRS/NS");
+	struct gprs_ns_hdr *nsh;
+	uint16_t nsvci = htons(nsvc->nsvci);
+	uint16_t nsei = htons(nsvc->nsei);
+
+	if (!msg)
+		return -ENOMEM;
+
+	nsh = (struct gprs_ns_hdr *) msgb_put(msg, sizeof(*nsh));
+	nsh->pdu_type = NS_PDUT_RESET;
+
+	msgb_tvlv_put(msg, NS_IE_CAUSE, 1, &cause);
+	msgb_tvlv_put(msg, NS_IE_VCI, 2, (uint8_t *) &nsvci);
+	msgb_tvlv_put(msg, NS_IE_NSEI, 2, (uint8_t *) &nsei);
+
+	return gprs_ns_tx(nsvc, msg);
+
+}
+
+#define NS_ALIVE_RETRIES  10	/* after 3 failed retransmit we declare BTS as dead */
+
+static const uint8_t timer_mode_tout[_NSVC_TIMER_NR] = {
+	[NSVC_TIMER_TNS_RESET]	= 60,
+	[NSVC_TIMER_TNS_ALIVE]	= 3,
+	[NSVC_TIMER_TNS_TEST]	= 30,
+};
+
+static void nsvc_start_timer(struct gprs_nsvc *nsvc, enum nsvc_timer_mode mode)
+{
+	nsvc->alive_retries = 0;
+
+	if (bsc_timer_pending(&nsvc->timer))
+		bsc_del_timer(&nsvc->timer);
+
+	nsvc->timer_mode = mode;
+	bsc_schedule_timer(&nsvc->timer, timer_mode_tout[mode], 0);
+}
+
+static void gprs_ns_timer_cb(void *data)
+{
+	struct gprs_nsvc *nsvc = data;
+
+	switch (nsvc->timer_mode) {
+	case NSVC_TIMER_TNS_ALIVE:
+		/* Tns-alive case: we expired without response ! */
+		nsvc->alive_retries++;
+		if (nsvc->alive_retries > NS_ALIVE_RETRIES) {
+			/* mark as dead and blocked */
+			nsvc->state = NSE_S_BLOCKED;
+			DEBUGP(DGPRS, "NSEI=%u Tns-alive expired more then "
+				"%u times, blocking NS-VC\n", nsvc->nsei,
+				NS_ALIVE_RETRIES);
+			/* FIXME: inform higher layers */
+			return;
+		}
+		nsvc_start_timer(nsvc, NSVC_TIMER_TNS_ALIVE);
+		break;
+	case NSVC_TIMER_TNS_TEST:
+		/* Tns-test case: send NS-ALIVE PDU */
+		gprs_ns_tx_simple(nsvc, NS_PDUT_ALIVE);
+		/* start Tns-alive timer */
+		nsvc_start_timer(nsvc, NSVC_TIMER_TNS_ALIVE);
+		break;
+	case NSVC_TIMER_TNS_RESET:
+		/* Chapter 7.3: Re-send the RESET */
+		gprs_ns_tx_reset(nsvc, NS_CAUSE_OM_INTERVENTION);
+		nsvc_start_timer(nsvc, NSVC_TIMER_TNS_RESET);
+		break;
+	}
+}
+
+/* Section 9.2.6 */
+static int gprs_ns_tx_reset_ack(struct gprs_nsvc *nsvc)
+{
+	struct msgb *msg = msgb_alloc(NS_ALLOC_SIZE, "GPRS/NS");
+	struct gprs_ns_hdr *nsh;
+	uint16_t nsvci, nsei;
+
+	if (!msg)
+		return -ENOMEM;
+
+	nsvci = htons(nsvc->nsvci);
+	nsei = htons(nsvc->nsei);
+
+	nsh = (struct gprs_ns_hdr *) msgb_put(msg, sizeof(*nsh));
+
+	nsh->pdu_type = NS_PDUT_RESET_ACK;
+
+	DEBUGP(DGPRS, "NSEI=%u Tx NS RESET ACK (NSVCI=%u)\n",
+		nsvc->nsei, nsvc->nsvci);
+
+	msgb_tvlv_put(msg, NS_IE_VCI, 2, (uint8_t *)&nsvci);
+	msgb_tvlv_put(msg, NS_IE_NSEI, 2, (uint8_t *)&nsei);
+
+	return gprs_ns_tx(nsvc, msg);
+}
+
+/* Section 9.2.10: transmit side / NS-UNITDATA-REQUEST primitive */
+int gprs_ns_sendmsg(struct gprs_ns_inst *nsi, struct msgb *msg)
+{
+	struct gprs_nsvc *nsvc;
+	struct gprs_ns_hdr *nsh;
+	uint16_t bvci = msgb_bvci(msg);
+
+	nsvc = nsvc_by_nsei(nsi, msgb_nsei(msg));
+	if (!nsvc) {
+		LOGP(DGPRS, LOGL_ERROR, "Unable to resolve NSEI %u "
+			"to NS-VC!\n", msgb_nsei(msg));
+		return -EINVAL;
+	}
+
+	if (!(nsvc->state & NSE_S_ALIVE)) {
+		LOGP(DGPRS, LOGL_ERROR, "NSEI=%u is not alive, cannot send\n",
+			nsvc->nsei);
+		return -EBUSY;
+	}
+	if (nsvc->state & NSE_S_BLOCKED) {
+		LOGP(DGPRS, LOGL_ERROR, "NSEI=%u is blocked, cannot send\n",
+			nsvc->nsei);
+		return -EBUSY;
+	}
+
+	nsh = (struct gprs_ns_hdr *) msgb_push(msg, sizeof(*nsh) + 3);
+	if (!nsh) {
+		LOGP(DGPRS, LOGL_ERROR, "Not enough headroom for NS header\n");
+		return -EIO;
+	}
+
+	nsh->pdu_type = NS_PDUT_UNITDATA;
+	/* spare octet in data[0] */
+	nsh->data[1] = bvci >> 8;
+	nsh->data[2] = bvci & 0xff;
+
+	return gprs_ns_tx(nsvc, msg);
+}
+
+/* Section 9.2.10: receive side */
+static int gprs_ns_rx_unitdata(struct gprs_nsvc *nsvc, struct msgb *msg)
+{
+	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *)msg->l2h;
+	uint16_t bvci;
+
+	/* spare octet in data[0] */
+	bvci = nsh->data[1] << 8 | nsh->data[2];
+	msgb_bssgph(msg) = &nsh->data[3];
+	msgb_bvci(msg) = bvci;
+
+	/* call upper layer (BSSGP) */
+	return nsvc->nsi->cb(GPRS_NS_EVT_UNIT_DATA, nsvc, msg, bvci);
+}
+
+/* Section 9.2.7 */
+static int gprs_ns_rx_status(struct gprs_nsvc *nsvc, struct msgb *msg)
+{
+	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *) msg->l2h;
+	struct tlv_parsed tp;
+	uint8_t cause;
+	int rc;
+
+	DEBUGP(DGPRS, "NSEI=%u NS STATUS ", nsvc->nsei);
+
+	rc = tlv_parse(&tp, &ns_att_tlvdef, nsh->data, msgb_l2len(msg), 0, 0);
+
+	if (!TLVP_PRESENT(&tp, NS_IE_CAUSE)) {
+		DEBUGPC(DGPRS, "missing cause IE\n");
+		return -EINVAL;
+	}
+
+	cause = *TLVP_VAL(&tp, NS_IE_CAUSE);
+	DEBUGPC(DGPRS, "cause=%s\n", gprs_ns_cause_str(cause));
+
+	return 0;
+}
+
+/* Section 7.3 */
+static int gprs_ns_rx_reset(struct gprs_nsvc *nsvc, struct msgb *msg)
+{
+	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *) msg->l2h;
+	struct tlv_parsed tp;
+	uint8_t *cause;
+	uint16_t *nsvci, *nsei;
+	int rc;
+
+	rc = tlv_parse(&tp, &ns_att_tlvdef, nsh->data, msgb_l2len(msg), 0, 0);
+
+	if (!TLVP_PRESENT(&tp, NS_IE_CAUSE) ||
+	    !TLVP_PRESENT(&tp, NS_IE_VCI) ||
+	    !TLVP_PRESENT(&tp, NS_IE_NSEI)) {
+		/* FIXME: respond with NS_CAUSE_MISSING_ESSENT_IE */
+		LOGP(DGPRS, LOGL_ERROR, "NS RESET Missing mandatory IE\n");
+		return -EINVAL;
+	}
+
+	cause = (uint8_t *) TLVP_VAL(&tp, NS_IE_CAUSE);
+	nsvci = (uint16_t *) TLVP_VAL(&tp, NS_IE_VCI);
+	nsei = (uint16_t *) TLVP_VAL(&tp, NS_IE_NSEI);
+
+	DEBUGP(DGPRS, "NSEI=%u NS RESET (NSVCI=%u, cause=%s)\n",
+		nsvc->nsvci, nsvc->nsei, gprs_ns_cause_str(*cause));
+
+	nsvc->state = NSE_S_BLOCKED | NSE_S_ALIVE;
+	nsvc->nsei = ntohs(*nsei);
+	nsvc->nsvci = ntohs(*nsvci);
+
+	/* mark the NS-VC as blocked and alive */
+	/* start the test procedure */
+	nsvc_start_timer(nsvc, NSVC_TIMER_TNS_ALIVE);
+
+	return gprs_ns_tx_reset_ack(nsvc);
+}
+
+/* main entry point, here incoming NS frames enter */
+int gprs_ns_rcvmsg(struct gprs_ns_inst *nsi, struct msgb *msg,
+		   struct sockaddr_in *saddr)
+{
+	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *) msg->l2h;
+	struct gprs_nsvc *nsvc;
+	int rc = 0;
+
+	/* look up the NSVC based on source address */
+	nsvc = nsvc_by_rem_addr(nsi, saddr);
+	if (!nsvc) {
+		/* Only the RESET procedure creates a new NSVC */
+		if (nsh->pdu_type != NS_PDUT_RESET) {
+			LOGP(DGPRS, LOGL_INFO, "Ignoring NS PDU type 0x%0x "
+				"from %s for non-existing NS-VC\n",
+				nsh->pdu_type, inet_ntoa(saddr->sin_addr));
+			//gprs_ns_tx_reset(nsvc, NS_CAUSE_NSVC_UNKNOWN);
+			return -EIO;
+		}
+		LOGP(DGPRS, LOGL_INFO, "Creating NS-VC for BSS at %s:%u\n",
+			inet_ntoa(saddr->sin_addr), ntohs(saddr->sin_port));
+		nsvc = nsvc_create(nsi, 0xffff);
+		nsvc->ip.bts_addr = *saddr;
+	} else
+		msgb_nsei(msg) = nsvc->nsei;
+
+	switch (nsh->pdu_type) {
+	case NS_PDUT_ALIVE:
+		/* remote end inquires whether we're still alive,
+		 * we need to respond with ALIVE_ACK */
+		rc = gprs_ns_tx_simple(nsvc, NS_PDUT_ALIVE_ACK);
+		break;
+	case NS_PDUT_ALIVE_ACK:
+		/* stop Tns-alive */
+		bsc_del_timer(&nsvc->timer);
+		/* start Tns-test */
+		nsvc_start_timer(nsvc, NSVC_TIMER_TNS_TEST);
+		if (nsvc->remote_end_is_sgsn) {
+			/* FIXME: this should be one level higher */
+			if (nsvc->state & NSE_S_BLOCKED)
+				rc = gprs_ns_tx_simple(nsvc, NS_PDUT_UNBLOCK);
+		}
+		break;
+	case NS_PDUT_UNITDATA:
+		/* actual user data */
+		rc = gprs_ns_rx_unitdata(nsvc, msg);
+		break;
+	case NS_PDUT_STATUS:
+		rc = gprs_ns_rx_status(nsvc, msg);
+		break;
+	case NS_PDUT_RESET:
+		rc = gprs_ns_rx_reset(nsvc, msg);
+		break;
+	case NS_PDUT_RESET_ACK:
+		DEBUGP(DGPRS, "NSEI=%u Rx NS RESET ACK\n", nsvc->nsei);
+		/* mark remote NS-VC as blocked + active */
+		nsvc->remote_state = NSE_S_BLOCKED | NSE_S_ALIVE;
+		if (nsvc->remote_end_is_sgsn) {
+			/* stop RESET timer */
+			bsc_del_timer(&nsvc->timer);
+			/* send ALIVE PDU */
+			rc = gprs_ns_tx_simple(nsvc, NS_PDUT_ALIVE);
+			nsvc_start_timer(nsvc, NSVC_TIMER_TNS_ALIVE);
+			/* mark local state as BLOCKED + ALIVE */
+			nsvc->state = NSE_S_BLOCKED | NSE_S_ALIVE;
+		}
+		break;
+	case NS_PDUT_UNBLOCK:
+		/* Section 7.2: unblocking procedure */
+		DEBUGP(DGPRS, "NSEI=%u Rx NS UNBLOCK\n", nsvc->nsei);
+		nsvc->state &= ~NSE_S_BLOCKED;
+		rc = gprs_ns_tx_simple(nsvc, NS_PDUT_UNBLOCK_ACK);
+		break;
+	case NS_PDUT_UNBLOCK_ACK:
+		DEBUGP(DGPRS, "NSEI=%u Rx NS UNBLOCK ACK\n", nsvc->nsei);
+		/* mark remote NS-VC as unblocked + active */
+		nsvc->remote_state = NSE_S_ALIVE;
+		if (nsvc->remote_end_is_sgsn)
+			nsvc->state = NSE_S_ALIVE;
+		break;
+	case NS_PDUT_BLOCK:
+		DEBUGP(DGPRS, "NSEI=%u Rx NS BLOCK\n", nsvc->nsei);
+		nsvc->state |= NSE_S_BLOCKED;
+		rc = gprs_ns_tx_simple(nsvc, NS_PDUT_UNBLOCK_ACK);
+		break;
+	case NS_PDUT_BLOCK_ACK:
+		DEBUGP(DGPRS, "NSEI=%u Rx NS BLOCK ACK\n", nsvc->nsei);
+		/* mark remote NS-VC as blocked + active */
+		nsvc->remote_state = NSE_S_BLOCKED | NSE_S_ALIVE;
+		break;
+	default:
+		DEBUGP(DGPRS, "NSEI=%u Rx Unknown NS PDU type 0x%02x\n",
+			nsvc->nsei, nsh->pdu_type);
+		rc = -EINVAL;
+		break;
+	}
+	return rc;
+}
+
+struct gprs_ns_inst *gprs_ns_instantiate(gprs_ns_cb_t *cb)
+{
+	struct gprs_ns_inst *nsi = talloc_zero(tall_bsc_ctx, struct gprs_ns_inst);
+
+	nsi->cb = cb;
+	INIT_LLIST_HEAD(&nsi->gprs_nsvcs);
+
+	return nsi;
+}
+
+void gprs_ns_destroy(struct gprs_ns_inst *nsi)
+{
+	/* FIXME: clear all timers */
+
+	/* recursively free the NSI and all its NSVCs */
+	talloc_free(nsi);
+}
+
+
+/* NS-over-IP code, according to 3GPP TS 48.016 Chapter 6.2
+ * We don't support Size Procedure, Configuration Procedure, ChangeWeight Procedure */
+
+/* Read a single NS-over-IP message */
+static struct msgb *read_nsip_msg(struct bsc_fd *bfd, int *error,
+				  struct sockaddr_in *saddr)
+{
+	struct msgb *msg = msgb_alloc(NS_ALLOC_SIZE, "Abis/IP/GPRS-NS");
+	int ret = 0;
+	socklen_t saddr_len = sizeof(*saddr);
+
+	if (!msg) {
+		*error = -ENOMEM;
+		return NULL;
+	}
+
+	ret = recvfrom(bfd->fd, msg->data, NS_ALLOC_SIZE, 0,
+			(struct sockaddr *)saddr, &saddr_len);
+	if (ret < 0) {
+		LOGP(DGPRS, LOGL_ERROR, "recv error %s during NSIP recv\n",
+			strerror(errno));
+		msgb_free(msg);
+		*error = ret;
+		return NULL;
+	} else if (ret == 0) {
+		msgb_free(msg);
+		*error = ret;
+		return NULL;
+	}
+
+	msg->l2h = msg->data;
+	msgb_put(msg, ret);
+
+	return msg;
+}
+
+static int handle_nsip_read(struct bsc_fd *bfd)
+{
+	int error;
+	struct sockaddr_in saddr;
+	struct gprs_ns_inst *nsi = bfd->data;
+	struct msgb *msg = read_nsip_msg(bfd, &error, &saddr);
+
+	if (!msg)
+		return error;
+
+	return gprs_ns_rcvmsg(nsi, msg, &saddr);
+}
+
+static int handle_nsip_write(struct bsc_fd *bfd)
+{
+	/* FIXME: actually send the data here instead of nsip_sendmsg() */
+	return -EIO;
+}
+
+int nsip_sendmsg(struct gprs_nsvc *nsvc, struct msgb *msg)
+{
+	int rc;
+	struct gprs_ns_inst *nsi = nsvc->nsi;
+	struct sockaddr_in *daddr = &nsvc->ip.bts_addr;
+
+	rc = sendto(nsi->nsip.fd.fd, msg->data, msg->len, 0,
+		  (struct sockaddr *)daddr, sizeof(*daddr));
+
+	talloc_free(msg);
+
+	return rc;
+}
+
+/* UDP Port 23000 carries the LLC-in-BSSGP-in-NS protocol stack */
+static int nsip_fd_cb(struct bsc_fd *bfd, unsigned int what)
+{
+	int rc = 0;
+
+	if (what & BSC_FD_READ)
+		rc = handle_nsip_read(bfd);
+	if (what & BSC_FD_WRITE)
+		rc = handle_nsip_write(bfd);
+
+	return rc;
+}
+
+
+/* FIXME: this is currently in input/ipaccess.c */
+extern int make_sock(struct bsc_fd *bfd, int proto, uint16_t port,
+		     int (*cb)(struct bsc_fd *fd, unsigned int what));
+
+/* Listen for incoming GPRS packets */
+int nsip_listen(struct gprs_ns_inst *nsi, uint16_t udp_port)
+{
+	int ret;
+
+	ret = make_sock(&nsi->nsip.fd, IPPROTO_UDP, udp_port, nsip_fd_cb);
+	if (ret < 0)
+		return ret;
+
+	nsi->ll = GPRS_NS_LL_UDP;
+	nsi->nsip.fd.data = nsi;
+
+	return ret;
+}
+
+/* Establish a connection (from the BSS) to the SGSN */
+struct gprs_nsvc *nsip_connect(struct gprs_ns_inst *nsi,
+				struct sockaddr_in *dest, uint16_t nsei,
+				uint16_t nsvci)
+{
+	struct gprs_nsvc *nsvc;
+
+	nsvc = nsvc_by_rem_addr(nsi, dest);
+	if (!nsvc) {
+		nsvc = nsvc_create(nsi, nsvci);
+		nsvc->ip.bts_addr = *dest;
+	}
+	nsvc->nsei = nsei;
+	nsvc->nsvci = nsvci;
+	nsvc->remote_end_is_sgsn = 1;
+
+	/* Initiate a RESET procedure */
+	if (gprs_ns_tx_reset(nsvc, NS_CAUSE_OM_INTERVENTION) < 0) {
+		LOGP(DGPRS, LOGL_ERROR, "NSEI=%u, error resetting NS-VC\n",
+			nsei);
+	}
+	/* run a timer and re-transmit the reset request? */
+	nsvc_start_timer(nsvc, NSVC_TIMER_TNS_RESET);
+
+	return nsvc;
+}
diff --git a/openbsc/src/gprs/gprs_sgsn.c b/openbsc/src/gprs/gprs_sgsn.c
new file mode 100644
index 0000000..ba46719
--- /dev/null
+++ b/openbsc/src/gprs/gprs_sgsn.c
@@ -0,0 +1,96 @@
+/* GPRS SGSN functionality */
+
+/* (C) 2009 by Harald Welte <laforge@gnumonks.org>
+ *
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <stdint.h>
+
+#include <osmocore/linuxlist.h>
+#include <osmocore/talloc.h>
+#include <osmocore/timer.h>
+#include <openbsc/gsm_subscriber.h>
+#include <openbsc/debug.h>
+#include <openbsc/gprs_sgsn.h>
+#include <openbsc/gprs_ns.h>
+#include <openbsc/gprs_bssgp.h>
+
+static LLIST_HEAD(sgsn_mm_ctxts);
+
+static int ra_id_equals(const struct gprs_ra_id *id1,
+			const struct gprs_ra_id *id2)
+{
+	return (id1->mcc == id2->mcc && id1->mnc == id2->mnc &&
+		id1->lac == id2->lac && id1->rac == id2->rac);
+}
+
+/* look-up a SGSN MM context based on TLLI + RAI */
+struct sgsn_mm_ctx *sgsn_mm_ctx_by_tlli(uint32_t tlli,
+					const struct gprs_ra_id *raid)
+{
+	struct sgsn_mm_ctx *ctx;
+
+	llist_for_each_entry(ctx, &sgsn_mm_ctxts, list) {
+		if (tlli == ctx->tlli &&
+		    ra_id_equals(raid, &ctx->ra))
+			return ctx;
+	}
+	return NULL;
+}
+
+struct sgsn_mm_ctx *sgsn_mm_ctx_by_ptmsi(uint32_t p_tmsi)
+{
+	struct sgsn_mm_ctx *ctx;
+
+	llist_for_each_entry(ctx, &sgsn_mm_ctxts, list) {
+		if (p_tmsi == ctx->p_tmsi)
+			return ctx;
+	}
+	return NULL;
+}
+
+struct sgsn_mm_ctx *sgsn_mm_ctx_by_imsi(const char *imsi)
+{
+	struct sgsn_mm_ctx *ctx;
+
+	llist_for_each_entry(ctx, &sgsn_mm_ctxts, list) {
+		if (!strcmp(imsi, ctx->imsi))
+			return ctx;
+	}
+	return NULL;
+
+}
+
+/* Allocate a new SGSN MM context */
+struct sgsn_mm_ctx *sgsn_mm_ctx_alloc(uint32_t tlli,
+					const struct gprs_ra_id *raid)
+{
+	struct sgsn_mm_ctx *ctx = talloc_zero(NULL, struct sgsn_mm_ctx);
+
+	if (!ctx)
+		return NULL;
+
+	memcpy(&ctx->ra, raid, sizeof(ctx->ra));
+	ctx->tlli = tlli;
+	ctx->mm_state = GMM_DEREGISTERED;
+
+	llist_add(&ctx->list, &sgsn_mm_ctxts);
+
+	return ctx;
+}
diff --git a/openbsc/src/gprs/gprs_sndcp.c b/openbsc/src/gprs/gprs_sndcp.c
new file mode 100644
index 0000000..0d1a390
--- /dev/null
+++ b/openbsc/src/gprs/gprs_sndcp.c
@@ -0,0 +1,70 @@
+/* GPRS SNDCP protocol implementation as per 3GPP TS 04.65 */
+
+/* (C) 2010 by Harald Welte <laforge@gnumonks.org>
+ *
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <errno.h>
+#include <stdint.h>
+
+#include <osmocore/msgb.h>
+#include <osmocore/linuxlist.h>
+#include <osmocore/timer.h>
+#include <osmocore/talloc.h>
+
+#include <openbsc/gsm_data.h>
+#include <openbsc/debug.h>
+#include <openbsc/gprs_bssgp.h>
+#include <openbsc/gprs_llc.h>
+
+/* Chapter 7.2: SN-PDU Formats */
+struct sndcp_common_hdr {
+	/* octet 1 */
+	uint8_t nsapi:4;
+	uint8_t more:1;
+	uint8_t type:1;
+	uint8_t first:1;
+	uint8_t spare:1;
+	/* octet 2 */
+	uint8_t pcomp;
+	uint8_t dcomp;
+};
+
+struct sndcp_udata_hdr {
+	/* octet 3 */
+	uint8_t npdu_high:4;
+	uint8_t seg_nr:4;
+	/* octet 4 */
+	uint8_t npdu_low;
+};
+
+/* Entry point for the LL-UNITDATA.indication */
+int sndcp_unitdata_ind(struct msgb *msg, uint8_t sapi, uint8_t *hdr, uint8_t len)
+{
+	struct sndcp_udata_hdr *suh;
+	uint16_t npdu;
+
+	if (suh->type == 0) {
+		LOGP(DGPRS, LOGL_ERROR, "SN-DATA PDU at unitdata_ind() function\n");
+		return -EINVAL;
+	}
+
+	npdu = (suh->npdu_high << 8) | suh->npdu_low;
+}
+
diff --git a/openbsc/src/gprs/gsm_04_08_gprs.c b/openbsc/src/gprs/gsm_04_08_gprs.c
new file mode 100644
index 0000000..4a42113
--- /dev/null
+++ b/openbsc/src/gprs/gsm_04_08_gprs.c
@@ -0,0 +1,762 @@
+/* GSM Mobile Radio Interface Layer 3 messages on the A-bis interface
+ * 3GPP TS 04.08 version 7.21.0 Release 1998 / ETSI TS 100 940 V7.21.0 */
+
+/* (C) 2009-2010 by Harald Welte <laforge@gnumonks.org>
+ *
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <errno.h>
+
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#include <openbsc/db.h>
+#include <osmocore/msgb.h>
+#include <osmocore/tlv.h>
+#include <osmocore/gsm_utils.h>
+#include <osmocore/signal.h>
+#include <osmocore/talloc.h>
+
+#include <openbsc/debug.h>
+#include <openbsc/gsm_data.h>
+#include <openbsc/gsm_subscriber.h>
+#include <openbsc/gsm_04_08.h>
+#include <openbsc/gsm_04_08_gprs.h>
+#include <openbsc/paging.h>
+#include <openbsc/transaction.h>
+#include <openbsc/gprs_bssgp.h>
+#include <openbsc/gprs_llc.h>
+#include <openbsc/gprs_sgsn.h>
+
+/* 10.5.5.14 GPRS MM Cause / Table 10.5.147 */
+struct value_string gmm_cause_names[] = {
+	/* FIXME */
+	{ GMM_CAUSE_SEM_INCORR_MSG, "Semantically incorrect message" },
+	{ GMM_CAUSE_INV_MAND_INFO, "Invalid mandatory information" },
+	{ GMM_CAUSE_MSGT_NOTEXIST_NOTIMPL,
+			"Message type non-existant or not implemented" },
+	{ GMM_CAUSE_MSGT_INCOMP_P_STATE,
+			"Message type not compatible with protocol state" },
+	{ GMM_CAUSE_IE_NOTEXIST_NOTIMPL,
+			"Information element non-existent or not implemented" },
+	{ GMM_CAUSE_COND_IE_ERR, "Conditional IE error" },
+	{ GMM_CAUSE_MSG_INCOMP_P_STATE,
+				"Message not compatible with protocol state " },
+	{ GMM_CAUSE_PROTO_ERR_UNSPEC, "Protocol error, unspecified" },
+	{ 0, NULL }
+};
+
+/* 10.5.6.6 SM Cause / Table 10.5.157 */
+struct value_string gsm_cause_names[] = {
+	{ GSM_CAUSE_INSUFF_RSRC, "Insufficient resources" },
+	{ GSM_CAUSE_MISSING_APN, "Missing or unknown APN" },
+	{ GSM_CAUSE_UNKNOWN_PDP, "Unknown PDP address or PDP type" },
+	{ GSM_CAUSE_AUTH_FAILED, "User Authentication failed" },
+	{ GSM_CAUSE_ACT_REJ_GGSN, "Activation rejected by GGSN" },
+	{ GSM_CAUSE_ACT_REJ_UNSPEC, "Activation rejected, unspecified" },
+	{ GSM_CAUSE_SERV_OPT_NOTSUPP, "Service option not supported" },
+	{ GSM_CAUSE_REQ_SERV_OPT_NOTSUB,
+				"Requested service option not subscribed" },
+	{ GSM_CAUSE_SERV_OPT_TEMP_OOO,
+				"Service option temporarily out of order" },
+	{ GSM_CAUSE_NSAPI_IN_USE, "NSAPI already used" },
+	{ GSM_CAUSE_DEACT_REGULAR, "Regular deactivation" },
+	{ GSM_CAUSE_QOS_NOT_ACCEPTED, "QoS not accepted" },
+	{ GSM_CAUSE_NET_FAIL, "Network Failure" },
+	{ GSM_CAUSE_REACT_RQD, "Reactivation required" },
+	{ GSM_CAUSE_FEATURE_NOTSUPP, "Feature not supported " },
+	{ GSM_CAUSE_INVALID_TRANS_ID, "Invalid transaction identifier" },
+	{ GSM_CAUSE_SEM_INCORR_MSG, "Semantically incorrect message" },
+	{ GSM_CAUSE_INV_MAND_INFO, "Invalid mandatory information" },
+	{ GSM_CAUSE_MSGT_NOTEXIST_NOTIMPL,
+			"Message type non-existant or not implemented" },
+	{ GSM_CAUSE_MSGT_INCOMP_P_STATE,
+			"Message type not compatible with protocol state" },
+	{ GSM_CAUSE_IE_NOTEXIST_NOTIMPL,
+			"Information element non-existent or not implemented" },
+	{ GSM_CAUSE_COND_IE_ERR, "Conditional IE error" },
+	{ GSM_CAUSE_MSG_INCOMP_P_STATE,
+				"Message not compatible with protocol state " },
+	{ GSM_CAUSE_PROTO_ERR_UNSPEC, "Protocol error, unspecified" },
+	{ 0, NULL }
+};
+
+static const char *att_name(uint8_t type)
+{
+	switch (type) {
+	case GPRS_ATT_T_ATTACH:
+		return "GPRS attach";
+	case GPRS_ATT_T_ATT_WHILE_IMSI:
+		return "GPRS attach while IMSI attached";
+	case GPRS_ATT_T_COMBINED:
+		return "Combined GPRS/IMSI attach";
+	default:
+		return "unknown";
+	}
+}
+
+static const char *upd_name(uint8_t type)
+{
+	switch (type) {
+	case GPRS_UPD_T_RA:
+		return "RA updating";
+	case GPRS_UPD_T_RA_LA:
+		return "combined RA/LA updating";
+	case GPRS_UPD_T_RA_LA_IMSI_ATT:
+		return "combined RA/LA updating + IMSI attach";
+	case GPRS_UPD_T_PERIODIC:
+		return "periodic updating";
+	}
+	return "unknown";
+}
+
+/* Send a message through the underlying layer */
+static int gsm48_gmm_sendmsg(struct msgb *msg, int command)
+{
+	/* caller needs to provide TLLI, BVCI and NSEI */
+	return gprs_llc_tx_ui(msg, GPRS_SAPI_GMM, command);
+}
+
+/* copy identifiers from old message to new message, this
+ * is required so lower layers can route it correctly */
+static void gmm_copy_id(struct msgb *msg, const struct msgb *old)
+{
+	msgb_tlli(msg) = msgb_tlli(old);
+	msgb_bvci(msg) = msgb_bvci(old);
+	msgb_nsei(msg) = msgb_nsei(old);
+}
+
+static struct gsm48_qos default_qos = {
+	.delay_class = 4,	/* best effort */
+	.reliab_class = GSM48_QOS_RC_LLC_UN_RLC_ACK_DATA_PROT,
+	.peak_tput = GSM48_QOS_PEAK_TPUT_32000bps,
+	.preced_class = GSM48_QOS_PC_NORMAL,
+	.mean_tput = GSM48_QOS_MEAN_TPUT_BEST_EFFORT,
+	.traf_class = GSM48_QOS_TC_INTERACTIVE,
+	.deliv_order = GSM48_QOS_DO_UNORDERED,
+	.deliv_err_sdu = GSM48_QOS_ERRSDU_YES,
+	.max_sdu_size = GSM48_QOS_MAXSDU_1520,
+	.max_bitrate_up = GSM48_QOS_MBRATE_63k,
+	.max_bitrate_down = GSM48_QOS_MBRATE_63k,
+	.resid_ber = GSM48_QOS_RBER_5e_2,
+	.sdu_err_ratio = GSM48_QOS_SERR_1e_2,
+	.handling_prio = 3,
+	.xfer_delay = 0x10,	/* 200ms */
+	.guar_bitrate_up = GSM48_QOS_MBRATE_0k,
+	.guar_bitrate_down = GSM48_QOS_MBRATE_0k,
+	.sig_ind = 0,	/* not optimised for signalling */
+	.max_bitrate_down_ext = 0,	/* use octet 9 */
+	.guar_bitrate_down_ext = 0,	/* use octet 13 */
+};
+
+/* Chapter 9.4.2: Attach accept */
+static int gsm48_tx_gmm_att_ack(struct msgb *old_msg)
+{
+	struct msgb *msg = gsm48_msgb_alloc();
+	struct gsm48_hdr *gh;
+	struct gsm48_attach_ack *aa;
+	struct gprs_ra_id ra_id;
+
+	DEBUGP(DMM, "<- GPRS ATTACH ACCEPT\n");
+
+	gmm_copy_id(msg, old_msg);
+
+	gh = (struct gsm48_hdr *) msgb_put(msg, sizeof(*gh));
+	gh->proto_discr = GSM48_PDISC_MM_GPRS;
+	gh->msg_type = GSM48_MT_GMM_ATTACH_ACK;
+
+	aa = (struct gsm48_attach_ack *) msgb_put(msg, sizeof(*aa));
+	aa->force_stby = 0;	/* not indicated */
+	aa->att_result = 1;	/* GPRS only */
+	aa->ra_upd_timer = GPRS_TMR_MINUTE | 10;
+	aa->radio_prio = 4;	/* lowest */
+	bssgp_parse_cell_id(&ra_id, msgb_bcid(old_msg));
+	gsm48_construct_ra(aa->ra_id.digits, &ra_id);
+
+	/* Option: P-TMSI signature, allocated P-TMSI, MS ID, ... */
+	return gsm48_gmm_sendmsg(msg, 0);
+}
+
+/* Chapter 9.4.5: Attach reject */
+static int gsm48_tx_gmm_att_rej(struct msgb *old_msg, uint8_t gmm_cause)
+{
+	struct msgb *msg = gsm48_msgb_alloc();
+	struct gsm48_hdr *gh;
+
+	DEBUGP(DMM, "<- GPRS ATTACH REJECT\n");
+
+	gmm_copy_id(msg, old_msg);
+
+	gh = (struct gsm48_hdr *) msgb_put(msg, sizeof(*gh) + 1);
+	gh->proto_discr = GSM48_PDISC_MM_GPRS;
+	gh->msg_type = GSM48_MT_GMM_ATTACH_REJ;
+	gh->data[0] = gmm_cause;
+
+	return gsm48_gmm_sendmsg(msg, 0);
+}
+
+/* Transmit Chapter 9.4.12 Identity Request */
+static int gsm48_tx_gmm_id_req(struct msgb *old_msg, uint8_t id_type)
+{
+	struct msgb *msg = gsm48_msgb_alloc();
+	struct gsm48_hdr *gh;
+
+	DEBUGP(DMM, "-> GPRS IDENTITY REQUEST: mi_type=%02x\n", id_type);
+
+	gmm_copy_id(msg, old_msg);
+
+	gh = (struct gsm48_hdr *) msgb_put(msg, sizeof(*gh) + 1);
+	gh->proto_discr = GSM48_PDISC_MM_GPRS;
+	gh->msg_type = GSM48_MT_GMM_ID_REQ;
+	/* 10.5.5.9 ID type 2 + identity type and 10.5.5.7 'force to standby' IE */
+	gh->data[0] = id_type & 0xf;
+
+	return gsm48_gmm_sendmsg(msg, 0);
+}
+
+/* Check if we can already authorize a subscriber */
+static int gsm48_gmm_authorize(struct sgsn_mm_ctx *ctx, struct msgb *msg)
+{
+	if (strlen(ctx->imei) && strlen(ctx->imsi)) {
+		ctx->mm_state = GMM_REGISTERED_NORMAL;
+		return gsm48_tx_gmm_att_ack(msg);
+	} 
+	if (!strlen(ctx->imei))
+		return gsm48_tx_gmm_id_req(msg, GSM_MI_TYPE_IMEI);
+
+	if (!strlen(ctx->imsi))
+		return gsm48_tx_gmm_id_req(msg, GSM_MI_TYPE_IMSI);
+
+	return 0;
+}
+
+/* Parse Chapter 9.4.13 Identity Response */
+static int gsm48_rx_gmm_id_resp(struct msgb *msg)
+{
+	struct gsm48_hdr *gh = (struct gsm48_hdr *) msgb_gmmh(msg);
+	uint8_t mi_type = gh->data[1] & GSM_MI_TYPE_MASK;
+	char mi_string[GSM48_MI_SIZE];
+	struct gprs_ra_id ra_id;
+	struct sgsn_mm_ctx *ctx;
+
+	gsm48_mi_to_string(mi_string, sizeof(mi_string), &gh->data[1], gh->data[0]);
+	DEBUGP(DMM, "GMM IDENTITY RESPONSE: mi_type=0x%02x MI(%s) ",
+		mi_type, mi_string);
+
+	bssgp_parse_cell_id(&ra_id, msgb_bcid(msg));
+	ctx = sgsn_mm_ctx_by_tlli(msgb_tlli(msg), &ra_id);
+	if (!ctx) {
+		DEBUGP(DMM, "from unknown TLLI 0x%08x?!?\n", msgb_tlli(msg));
+		return -EINVAL;
+	}
+
+	switch (mi_type) {
+	case GSM_MI_TYPE_IMSI:
+		/* we already have a mm context with current TLLI, but no
+		 * P-TMSI / IMSI yet.  What we now need to do is to fill
+		 * this initial context with data from the HLR */
+		strncpy(ctx->imsi, mi_string, sizeof(ctx->imei));
+		break;
+	case GSM_MI_TYPE_IMEI:
+		strncpy(ctx->imei, mi_string, sizeof(ctx->imei));
+		break;
+	case GSM_MI_TYPE_IMEISV:
+		break;
+	}
+
+	DEBUGPC(DMM, "\n");
+	/* Check if we can let the mobile station enter */
+	return gsm48_gmm_authorize(ctx, msg);
+}
+
+static void attach_rej_cb(void *data)
+{
+	struct sgsn_mm_ctx *ctx = data;
+
+	/* FIXME: determine through which BTS/TRX to send this */
+	//gsm48_tx_gmm_att_rej(ctx->tlli, GMM_CAUSE_MS_ID_NOT_DERIVED);
+	ctx->mm_state = GMM_DEREGISTERED;
+	/* FIXME: release the context */
+}
+
+static void schedule_reject(struct sgsn_mm_ctx *ctx)
+{
+	ctx->T = 3370;
+	ctx->timer.cb = attach_rej_cb;
+	ctx->timer.data = ctx;
+	bsc_schedule_timer(&ctx->timer, 6, 0);
+}
+
+/* Section 9.4.1 Attach request */
+static int gsm48_rx_gmm_att_req(struct msgb *msg)
+{
+	struct gsm48_hdr *gh = (struct gsm48_hdr *) msgb_gmmh(msg);
+	uint8_t *cur = gh->data, *msnc, *mi, *old_ra_info;
+	uint8_t msnc_len, att_type, mi_len, mi_type;
+	uint16_t drx_par;
+	uint32_t tmsi;
+	char mi_string[GSM48_MI_SIZE];
+	struct gprs_ra_id ra_id;
+	uint16_t cid;
+	struct sgsn_mm_ctx *ctx;
+
+	DEBUGP(DMM, "GMM ATTACH REQUEST ");
+
+	/* As per TS 04.08 Chapter 4.7.1.4, the attach request arrives either
+	 * with a foreign TLLI (P-TMSI that was allocated to the MS before),
+	 * or with random TLLI. */
+
+	cid = bssgp_parse_cell_id(&ra_id, msgb_bcid(msg));
+
+	/* MS network capability 10.5.5.12 */
+	msnc_len = *cur++;
+	msnc = cur;
+	if (msnc_len > 2)
+		goto err_inval;
+	cur += msnc_len;
+
+	/* aTTACH Type 10.5.5.2 */
+	att_type = *cur++ & 0x0f;
+
+	/* DRX parameter 10.5.5.6 */
+	drx_par = *cur++;
+	drx_par |= *cur++ << 8;
+
+	/* Mobile Identity (P-TMSI or IMSI) 10.5.1.4 */
+	mi_len = *cur++;
+	mi = cur;
+	if (mi_len > 8)
+		goto err_inval;
+	mi_type = *mi & GSM_MI_TYPE_MASK;
+	cur += mi_len;
+
+	gsm48_mi_to_string(mi_string, sizeof(mi_string), mi, mi_len);
+
+	DEBUGPC(DMM, "MI(%s) type=\"%s\" ", mi_string, att_name(att_type));
+
+	/* Old routing area identification 10.5.5.15 */
+	old_ra_info = cur;
+	cur += 6;
+
+	/* MS Radio Access Capability 10.5.5.12a */
+
+	/* Optional: Old P-TMSI Signature, Requested READY timer, TMSI Status */
+
+	switch (mi_type) {
+	case GSM_MI_TYPE_IMSI:
+		/* Try to find MM context based on IMSI */
+		ctx = sgsn_mm_ctx_by_imsi(mi_string);
+		if (!ctx) {
+#if 0
+			return gsm48_tx_gmm_att_rej(msg, GMM_CAUSE_IMSI_UNKNOWN);
+#else
+			/* As a temorary hack, we simply assume that the IMSI exists */
+			ctx = sgsn_mm_ctx_alloc(0, &ra_id);
+			if (!ctx)
+				return gsm48_tx_gmm_att_rej(msg, GMM_CAUSE_NET_FAIL);
+			strncpy(ctx->imsi, mi_string, sizeof(ctx->imsi));
+#endif
+		}
+		/* FIXME: Start some timer */
+		ctx->mm_state = GMM_COMMON_PROC_INIT;
+		ctx->tlli = msgb_tlli(msg);
+		break;
+	case GSM_MI_TYPE_TMSI:
+		tmsi = strtoul(mi_string, NULL, 10);
+		/* Try to find MM context based on P-TMSI */
+		ctx = sgsn_mm_ctx_by_ptmsi(tmsi);
+		if (!ctx) {
+			ctx = sgsn_mm_ctx_alloc(msgb_tlli(msg), &ra_id);
+			/* FIXME: Start some timer */
+			ctx->mm_state = GMM_COMMON_PROC_INIT;
+			ctx->tlli = msgb_tlli(msg);
+		}
+		break;
+	default:
+		return 0;
+	}
+	/* Update MM Context with currient RA and Cell ID */
+	ctx->ra = ra_id;
+	ctx->cell_id = cid;
+
+	/* FIXME: allocate a new P-TMSI (+ P-TMSI signature) */
+	/* FIXME: update the TLLI with the new local TLLI based on the P-TMSI */
+
+	DEBUGPC(DMM, "\n");
+
+	return ctx ? gsm48_gmm_authorize(ctx, msg) : 0;
+
+err_inval:
+	DEBUGPC(DMM, "\n");
+	return gsm48_tx_gmm_att_rej(msg, GMM_CAUSE_SEM_INCORR_MSG);
+}
+
+/* Chapter 9.4.15: Routing area update accept */
+static int gsm48_tx_gmm_ra_upd_ack(struct msgb *old_msg)
+{
+	struct msgb *msg = gsm48_msgb_alloc();
+	struct gsm48_hdr *gh;
+	struct gsm48_ra_upd_ack *rua;
+	struct gprs_ra_id ra_id;
+
+	DEBUGP(DMM, "<- ROUTING AREA UPDATE ACCEPT\n");
+
+	gmm_copy_id(msg, old_msg);
+
+	gh = (struct gsm48_hdr *) msgb_put(msg, sizeof(*gh));
+	gh->proto_discr = GSM48_PDISC_MM_GPRS;
+	gh->msg_type = GSM48_MT_GMM_RA_UPD_ACK;
+
+	rua = (struct gsm48_ra_upd_ack *) msgb_put(msg, sizeof(*rua));
+	rua->force_stby = 0;	/* not indicated */
+	rua->upd_result = 0;	/* RA updated */
+	rua->ra_upd_timer = GPRS_TMR_MINUTE | 10;
+
+	bssgp_parse_cell_id(&ra_id, msgb_bcid(old_msg));
+	gsm48_construct_ra(rua->ra_id.digits, &ra_id);
+
+	/* Option: P-TMSI signature, allocated P-TMSI, MS ID, ... */
+	return gsm48_gmm_sendmsg(msg, 0);
+}
+
+/* Chapter 9.4.17: Routing area update reject */
+static int gsm48_tx_gmm_ra_upd_rej(struct msgb *old_msg, uint8_t cause)
+{
+	struct msgb *msg = gsm48_msgb_alloc();
+	struct gsm48_hdr *gh;
+
+	DEBUGP(DMM, "<- ROUTING AREA UPDATE REJECT\n");
+
+	gmm_copy_id(msg, old_msg);
+
+	gh = (struct gsm48_hdr *) msgb_put(msg, sizeof(*gh) + 2);
+	gh->proto_discr = GSM48_PDISC_MM_GPRS;
+	gh->msg_type = GSM48_MT_GMM_RA_UPD_REJ;
+	gh->data[0] = cause;
+	gh->data[1] = 0; /* ? */
+
+	/* Option: P-TMSI signature, allocated P-TMSI, MS ID, ... */
+	return gsm48_gmm_sendmsg(msg, 0);
+}
+
+/* Chapter 9.4.14: Routing area update request */
+static int gsm48_rx_gmm_ra_upd_req(struct msgb *msg)
+{
+	struct gsm48_hdr *gh = (struct gsm48_hdr *) msgb_gmmh(msg);
+	struct sgsn_mm_ctx *mmctx;
+	uint8_t *cur = gh->data;
+	struct gprs_ra_id old_ra_id;
+	uint8_t upd_type;
+
+	/* Update Type 10.5.5.18 */
+	upd_type = *cur++ & 0x0f;
+
+	DEBUGP(DMM, "GMM RA UPDATE REQUEST type=\"%s\" ", upd_name(upd_type));
+
+	/* Old routing area identification 10.5.5.15 */
+	gsm48_parse_ra(&old_ra_id, cur);
+	cur += 6;
+
+	/* MS Radio Access Capability 10.5.5.12a */
+
+	/* Optional: Old P-TMSI Signature, Requested READY timer, TMSI Status,
+	 * DRX parameter, MS network capability */
+
+	switch (upd_type) {
+	case GPRS_UPD_T_RA_LA:
+	case GPRS_UPD_T_RA_LA_IMSI_ATT:
+		DEBUGPC(DMM, " unsupported in Mode III, is your SI13 corrupt?\n");
+		return gsm48_tx_gmm_ra_upd_rej(msg, GMM_CAUSE_PROTO_ERR_UNSPEC);
+		break;
+	case GPRS_UPD_T_RA:
+	case GPRS_UPD_T_PERIODIC:
+		break;
+	}
+
+	/* Look-up the MM context based on old RA-ID and TLLI */
+	mmctx = sgsn_mm_ctx_by_tlli(msgb_tlli(msg), &old_ra_id);
+	if (!mmctx || mmctx->mm_state == GMM_DEREGISTERED) {
+		/* The MS has to perform GPRS attach */
+		DEBUGPC(DMM, " REJECT\n");
+		return gsm48_tx_gmm_ra_upd_rej(msg, GMM_CAUSE_IMPL_DETACHED);
+	}
+
+	/* Update the MM context with the new RA-ID */
+	bssgp_parse_cell_id(&mmctx->ra, msgb_bcid(msg));
+	/* Update the MM context with the new TLLI */
+	mmctx->tlli = msgb_tlli(msg);
+	/* FIXME: Update the MM context with the MS radio acc capabilities */
+	/* FIXME: Update the MM context with the MS network capabilities */
+
+	DEBUGPC(DMM, " ACCEPT\n");
+	return gsm48_tx_gmm_ra_upd_ack(msg);
+}
+
+static int gsm48_rx_gmm_status(struct msgb *msg)
+{
+	struct gsm48_hdr *gh = msgb_l3(msg);
+
+	DEBUGP(DMM, "GPRS MM STATUS (cause: %s)\n",
+		get_value_string(gmm_cause_names, gh->data[0]));
+
+	return 0;
+}
+
+/* GPRS Mobility Management */
+static int gsm0408_rcv_gmm(struct msgb *msg)
+{
+	struct gsm48_hdr *gh = (struct gsm48_hdr *) msgb_gmmh(msg);
+	int rc;
+
+	switch (gh->msg_type) {
+	case GSM48_MT_GMM_RA_UPD_REQ:
+		rc = gsm48_rx_gmm_ra_upd_req(msg);
+		break;
+	case GSM48_MT_GMM_ATTACH_REQ:
+		rc = gsm48_rx_gmm_att_req(msg);
+		break;
+	case GSM48_MT_GMM_ID_RESP:
+		rc = gsm48_rx_gmm_id_resp(msg);
+		break;
+	case GSM48_MT_GMM_STATUS:
+		rc = gsm48_rx_gmm_status(msg);
+		break;
+	case GSM48_MT_GMM_RA_UPD_COMPL:
+		/* only in case SGSN offered new P-TMSI */
+	case GSM48_MT_GMM_ATTACH_COMPL:
+		/* only in case SGSN offered new P-TMSI */
+	case GSM48_MT_GMM_DETACH_REQ:
+	case GSM48_MT_GMM_PTMSI_REALL_COMPL:
+	case GSM48_MT_GMM_AUTH_CIPH_RESP:
+		DEBUGP(DMM, "Unimplemented GSM 04.08 GMM msg type 0x%02x\n",
+			gh->msg_type);
+		break;
+	default:
+		DEBUGP(DMM, "Unknown GSM 04.08 GMM msg type 0x%02x\n",
+			gh->msg_type);
+		break;
+	}
+
+	return rc;
+}
+
+static void msgb_put_pdp_addr_ipv4(struct msgb *msg, uint32_t ipaddr)
+{
+	uint8_t v[6];
+
+	v[0] = PDP_TYPE_ORG_IETF;
+	v[1] = PDP_TYPE_N_IETF_IPv4;
+	*(uint32_t *)(v+2) = htonl(ipaddr);
+
+	msgb_tlv_put(msg, GSM48_IE_GSM_PDP_ADDR, sizeof(v), v);
+}
+
+static void msgb_put_pdp_addr_ppp(struct msgb *msg)
+{
+	uint8_t v[2];
+
+	v[0] = PDP_TYPE_ORG_ETSI;
+	v[1] = PDP_TYPE_N_ETSI_PPP;
+
+	msgb_tlv_put(msg, GSM48_IE_GSM_PDP_ADDR, sizeof(v), v);
+}
+
+/* Section 9.5.2: Ativate PDP Context Accept */
+static int gsm48_tx_gsm_act_pdp_acc(struct msgb *old_msg, struct gsm48_act_pdp_ctx_req *req)
+{
+	struct gsm48_hdr *old_gh = (struct gsm48_hdr *) msgb_gmmh(old_msg);
+	struct msgb *msg = gsm48_msgb_alloc();
+	struct gsm48_act_pdp_ctx_ack *act_ack;
+	struct gsm48_hdr *gh;
+	uint8_t transaction_id = ((old_gh->proto_discr >> 4) ^ 0x8); /* flip */
+
+	DEBUGP(DMM, "<- ACTIVATE PDP CONTEXT ACK\n");
+
+	gmm_copy_id(msg, old_msg);
+
+	gh = (struct gsm48_hdr *) msgb_put(msg, sizeof(*gh));
+	gh->proto_discr = GSM48_PDISC_SM_GPRS | (transaction_id << 4);
+	gh->msg_type = GSM48_MT_GSM_ACT_PDP_ACK;
+
+	/* Negotiated LLC SAPI */
+	msgb_v_put(msg, req->req_llc_sapi);
+	/* copy QoS parameters from original request */
+	msgb_lv_put(msg, sizeof(default_qos), (uint8_t *)&default_qos);
+	/* Radio priority 10.5.7.2 */
+	msgb_v_put(msg, 4);
+	/* PDP address */
+	msgb_put_pdp_addr_ipv4(msg, 0x01020304);
+	/* Optional: Protocol configuration options */
+	/* Optional: Packet Flow Identifier */
+
+	return gsm48_gmm_sendmsg(msg, 0);
+}
+
+/* Section 9.5.9: Deactivate PDP Context Accept */
+static int gsm48_tx_gsm_deact_pdp_acc(struct msgb *old_msg)
+{
+	struct gsm48_hdr *old_gh = (struct gsm48_hdr *) msgb_gmmh(old_msg);
+	struct msgb *msg = gsm48_msgb_alloc();
+	struct gsm48_hdr *gh;
+	uint8_t transaction_id = ((old_gh->proto_discr >> 4) ^ 0x8); /* flip */
+
+	DEBUGP(DMM, "<- DEACTIVATE PDP CONTEXT ACK\n");
+
+	gmm_copy_id(msg, old_msg);
+
+	gh = (struct gsm48_hdr *) msgb_put(msg, sizeof(*gh));
+	gh->proto_discr = GSM48_PDISC_SM_GPRS | (transaction_id << 4);
+	gh->msg_type = GSM48_MT_GSM_DEACT_PDP_ACK;
+
+	return gsm48_gmm_sendmsg(msg, 0);
+}
+
+/* Section 9.5.1: Activate PDP Context Request */
+static int gsm48_rx_gsm_act_pdp_req(struct msgb *msg)
+{
+	struct gsm48_hdr *gh = (struct gsm48_hdr *) msgb_gmmh(msg);
+	struct gsm48_act_pdp_ctx_req *act_req = (struct gsm48_act_pdp_ctx_req *) gh->data;
+	uint8_t *pdp_addr_lv = act_req->data;
+	uint8_t req_qos_len, req_pdpa_len;
+	uint8_t *req_qos, *req_pdpa;
+	struct tlv_parsed tp;
+
+	DEBUGP(DMM, "ACTIVATE PDP CONTEXT REQ: ");
+	req_qos_len = act_req->data[0];
+	req_qos = act_req->data + 1;	/* 10.5.6.5 */
+	req_pdpa_len = act_req->data[1 + req_qos_len];
+	req_pdpa = act_req->data + 1 + req_qos_len + 1;	/* 10.5.6.4 */
+
+	switch (req_pdpa[0] & 0xf) {
+	case 0x0:
+		DEBUGPC(DMM, "ETSI ");
+		break;
+	case 0x1:
+		DEBUGPC(DMM, "IETF ");
+		break;
+	case 0xf:
+		DEBUGPC(DMM, "Empty ");
+		break;
+	}
+
+	switch (req_pdpa[1]) {
+	case 0x21:
+		DEBUGPC(DMM, "IPv4 ");
+		if (req_pdpa_len >= 6) {
+			struct in_addr ia;
+			ia.s_addr = ntohl(*((uint32_t *) (req_pdpa+2)));
+			DEBUGPC(DMM, "%s ", inet_ntoa(ia));
+		}
+		break;
+	case 0x57:
+		DEBUGPC(DMM, "IPv6 ");
+		if (req_pdpa_len >= 18) {
+			/* FIXME: print IPv6 address */
+		}
+		break;
+	default:	
+		DEBUGPC(DMM, "0x%02x ", req_pdpa[1]);
+		break;
+	}
+
+	/* FIXME: parse TLV for AP name and protocol config options */
+	if (TLVP_PRESENT(&tp, GSM48_IE_GSM_APN)) {}
+	if (TLVP_PRESENT(&tp, GSM48_IE_GSM_PROTO_CONF_OPT)) {}
+
+	return gsm48_tx_gsm_act_pdp_acc(msg, act_req);
+}
+
+/* Section 9.5.8: Deactivate PDP Context Request */
+static int gsm48_rx_gsm_deact_pdp_req(struct msgb *msg)
+{
+	struct gsm48_hdr *gh = (struct gsm48_hdr *) msgb_gmmh(msg);
+
+	DEBUGP(DMM, "DEACTIVATE PDP CONTEXT REQ (cause: %s)\n",
+		get_value_string(gsm_cause_names, gh->data[0]));
+
+	return gsm48_tx_gsm_deact_pdp_acc(msg);
+}
+
+static int gsm48_rx_gsm_status(struct msgb *msg)
+{
+	struct gsm48_hdr *gh = msgb_l3(msg);
+
+	DEBUGP(DMM, "GPRS SM STATUS (cause: %s)\n",
+		get_value_string(gsm_cause_names, gh->data[0]));
+
+	return 0;
+}
+
+/* GPRS Session Management */
+static int gsm0408_rcv_gsm(struct msgb *msg)
+{
+	struct gsm48_hdr *gh = (struct gsm48_hdr *) msgb_gmmh(msg);
+	int rc;
+
+	switch (gh->msg_type) {
+	case GSM48_MT_GSM_ACT_PDP_REQ:
+		rc = gsm48_rx_gsm_act_pdp_req(msg);
+		break;
+	case GSM48_MT_GSM_DEACT_PDP_REQ:
+		rc = gsm48_rx_gsm_deact_pdp_req(msg);
+	case GSM48_MT_GSM_STATUS:
+		rc = gsm48_rx_gsm_status(msg);
+		break;
+	case GSM48_MT_GSM_REQ_PDP_ACT_REJ:
+	case GSM48_MT_GSM_ACT_AA_PDP_REQ:
+	case GSM48_MT_GSM_DEACT_AA_PDP_REQ:
+		DEBUGP(DMM, "Unimplemented GSM 04.08 GSM msg type 0x%02x\n",
+			gh->msg_type);
+		break;
+	default:
+		DEBUGP(DMM, "Unknown GSM 04.08 GSM msg type 0x%02x\n",
+			gh->msg_type);
+		break;
+
+	}
+
+	return rc;
+}
+
+/* Main entry point for incoming 04.08 GPRS messages */
+int gsm0408_gprs_rcvmsg(struct msgb *msg)
+{
+	struct gsm48_hdr *gh = (struct gsm48_hdr *) msgb_gmmh(msg);
+	uint8_t pdisc = gh->proto_discr & 0x0f;
+	int rc = -EINVAL;
+
+	switch (pdisc) {
+	case GSM48_PDISC_MM_GPRS:
+		rc = gsm0408_rcv_gmm(msg);
+		break;
+	case GSM48_PDISC_SM_GPRS:
+		rc = gsm0408_rcv_gsm(msg);
+		break;
+	default:
+		DEBUGP(DMM, "Unknown GSM 04.08 discriminator 0x%02x\n",
+			pdisc);
+		break;
+	}
+
+	return rc;
+}
diff --git a/openbsc/src/gprs/osmo_gbproxy.cfg b/openbsc/src/gprs/osmo_gbproxy.cfg
new file mode 100644
index 0000000..f2ef141
--- /dev/null
+++ b/openbsc/src/gprs/osmo_gbproxy.cfg
@@ -0,0 +1,13 @@
+!
+! OpenBSC configuration saved from vty
+!   !
+!
+line vty
+ no login
+!
+gbproxy
+  nsip bss local port 23000
+  nsip sgsn remote ip 192.168.100.239
+  nsip sgsn remote port 23000
+  nsip sgsn nsei 1
+  nsip sgsn nsvci 11
diff --git a/openbsc/src/gprs/osmo_sgsn.cfg b/openbsc/src/gprs/osmo_sgsn.cfg
new file mode 100644
index 0000000..f39e853
--- /dev/null
+++ b/openbsc/src/gprs/osmo_sgsn.cfg
@@ -0,0 +1,9 @@
+!
+! OpenBSC configuration saved from vty
+!   !
+!
+line vty
+ no login
+!
+sgsn
+  nsip local port 23000
diff --git a/openbsc/src/gprs/sgsn_main.c b/openbsc/src/gprs/sgsn_main.c
new file mode 100644
index 0000000..15f760d
--- /dev/null
+++ b/openbsc/src/gprs/sgsn_main.c
@@ -0,0 +1,143 @@
+/* GPRS SGSN Implementation */
+
+/* (C) 2010 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2010 by On Waves
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <getopt.h>
+#include <errno.h>
+#include <sys/fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#include <osmocore/talloc.h>
+#include <osmocore/select.h>
+
+#include <openbsc/signal.h>
+#include <openbsc/debug.h>
+#include <openbsc/telnet_interface.h>
+#include <openbsc/vty.h>
+#include <openbsc/sgsn.h>
+#include <openbsc/gprs_ns.h>
+#include <openbsc/gprs_bssgp.h>
+
+#include "../../bscconfig.h"
+
+/* this is here for the vty... it will never be called */
+void subscr_put() { abort(); }
+
+#define _GNU_SOURCE
+#include <getopt.h>
+
+void *tall_bsc_ctx;
+
+struct gprs_ns_inst *sgsn_nsi;
+
+const char *openbsc_version = "Osmocom NSIP Proxy " PACKAGE_VERSION;
+const char *openbsc_copyright =
+	"Copyright (C) 2010 Harald Welte and On-Waves\n"
+	"Contributions by Daniel Willmann, Jan Lübbe, Stefan Schmidt\n"
+	"Dieter Spaar, Andreas Eversberg, Holger Freyther\n\n"
+	"License GPLv2+: GNU GPL version 2 or later <http://gnu.org/licenses/gpl.html>\n"
+	"This is free software: you are free to change and redistribute it.\n"
+	"There is NO WARRANTY, to the extent permitted by law.\n";
+
+static char *config_file = "osmo_sgsn.cfg";
+static struct sgsn_config sgcfg;
+
+/* call-back function for the NS protocol */
+static int sgsn_ns_cb(enum gprs_ns_evt event, struct gprs_nsvc *nsvc,
+		      struct msgb *msg, u_int16_t bvci)
+{
+	int rc = 0;
+
+	switch (event) {
+	case GPRS_NS_EVT_UNIT_DATA:
+		/* hand the message into the BSSGP implementation */
+		rc = gprs_bssgp_rcvmsg(msg);
+		break;
+	default:
+		LOGP(DGPRS, LOGL_ERROR, "SGSN: Unknown event %u from NS\n", event);
+		if (msg)
+			talloc_free(msg);
+		rc = -EIO;
+		break;
+	}
+	return rc;
+}
+
+/* NSI that BSSGP uses when transmitting on NS */
+extern struct gprs_ns_inst *bssgp_nsi;
+
+int main(int argc, char **argv)
+{
+	struct gsm_network dummy_network;
+	struct log_target *stderr_target;
+	struct sockaddr_in sin;
+	int rc;
+
+	tall_bsc_ctx = talloc_named_const(NULL, 0, "osmo_sgsn");
+
+	log_init(&log_info);
+	stderr_target = log_target_create_stderr();
+	log_add_target(stderr_target);
+	log_set_all_filter(stderr_target, 1);
+
+	telnet_init(&dummy_network, 4245);
+	rc = sgsn_parse_config(config_file, &sgcfg);
+	if (rc < 0) {
+		LOGP(DGPRS, LOGL_FATAL, "Cannot parse config file\n");
+		exit(2);
+	}
+
+	sgsn_nsi = gprs_ns_instantiate(&sgsn_ns_cb);
+	if (!sgsn_nsi) {
+		LOGP(DGPRS, LOGL_ERROR, "Unable to instantiate NS\n");
+		exit(1);
+	}
+	bssgp_nsi = sgcfg.nsi = sgsn_nsi;
+	nsip_listen(sgsn_nsi, sgcfg.nsip_listen_port);
+
+	while (1) {
+		rc = bsc_select_main(0);
+		if (rc < 0)
+			exit(3);
+	}
+
+	exit(0);
+}
+
+struct gsm_network;
+int bsc_vty_init(struct gsm_network *dummy)
+{
+	cmd_init(1);
+	vty_init();
+
+	openbsc_vty_add_cmds();
+        sgsn_vty_init();
+	return 0;
+}
+
diff --git a/openbsc/src/gprs/sgsn_vty.c b/openbsc/src/gprs/sgsn_vty.c
new file mode 100644
index 0000000..ec18fcb
--- /dev/null
+++ b/openbsc/src/gprs/sgsn_vty.c
@@ -0,0 +1,146 @@
+/*
+ * (C) 2010 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2010 by On-Waves
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#include <osmocore/talloc.h>
+
+#include <openbsc/debug.h>
+#include <openbsc/sgsn.h>
+#include <openbsc/gprs_ns.h>
+
+#include <vty/command.h>
+#include <vty/vty.h>
+
+static struct sgsn_config *g_cfg = NULL;
+
+static struct cmd_node sgsn_node = {
+	SGSN_NODE,
+	"%s(sgsn)#",
+	1,
+};
+
+static int config_write_sgsn(struct vty *vty)
+{
+	struct in_addr ia;
+
+	vty_out(vty, "sgsn%s", VTY_NEWLINE);
+
+	if (g_cfg->nsip_listen_ip) {
+		ia.s_addr = htonl(g_cfg->nsip_listen_ip);
+		vty_out(vty, "  nsip local ip %s%s", inet_ntoa(ia),
+			VTY_NEWLINE);
+	}
+	vty_out(vty, "  nsip local port %u%s", g_cfg->nsip_listen_port,
+		VTY_NEWLINE);
+
+	return CMD_SUCCESS;
+}
+
+DEFUN(show_sgsn, show_sgsn_cmd, "show sgsn",
+      SHOW_STR "Display information about the SGSN")
+{
+	/* FIXME: iterate over list of NS-VC's and display their state */
+	struct gprs_ns_inst *nsi = g_cfg->nsi;
+	struct gprs_nsvc *nsvc;
+
+	llist_for_each_entry(nsvc, &nsi->gprs_nsvcs, list) {
+		vty_out(vty, "NSEI %5u, NS-VC %5u, %s-mode, %s %s%s",
+			nsvc->nsei, nsvc->nsvci,
+			nsvc->remote_end_is_sgsn ? "BSS" : "SGSN",
+			nsvc->state & NSE_S_ALIVE ? "ALIVE" : "DEAD",
+			nsvc->state & NSE_S_BLOCKED ? "BLOCKED" : "UNBLOCKED",
+			VTY_NEWLINE);
+		if (nsvc->nsi->ll == GPRS_NS_LL_UDP)
+			vty_out(vty, "  remote peer %s:%u%s",
+				inet_ntoa(nsvc->ip.bts_addr.sin_addr),
+				ntohs(nsvc->ip.bts_addr.sin_port), VTY_NEWLINE);
+	}
+
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_sgsn,
+      cfg_sgsn_cmd,
+      "sgsn",
+      "Configure the SGSN")
+{
+	vty->node = SGSN_NODE;
+	return CMD_SUCCESS;
+}
+
+
+DEFUN(cfg_nsip_local_ip,
+      cfg_nsip_local_ip_cmd,
+      "nsip local ip A.B.C.D",
+      "Set the IP address on which we listen for BSS connects")
+{
+	struct in_addr ia;
+
+	inet_aton(argv[0], &ia);
+	g_cfg->nsip_listen_ip = ntohl(ia.s_addr);
+
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_nsip_local_port,
+      cfg_nsip_local_port_cmd,
+      "nsip local port <0-65534>",
+      "Set the UDP port on which we listen for BSS connects")
+{
+	unsigned int port = atoi(argv[0]);
+
+	g_cfg->nsip_listen_port = port;
+	return CMD_SUCCESS;
+}
+
+
+
+
+int sgsn_vty_init(void)
+{
+	install_element(VIEW_NODE, &show_sgsn_cmd);
+
+	install_element(CONFIG_NODE, &cfg_sgsn_cmd);
+	install_node(&sgsn_node, config_write_sgsn);
+	install_default(SGSN_NODE);
+	install_element(SGSN_NODE, &cfg_nsip_local_ip_cmd);
+	install_element(SGSN_NODE, &cfg_nsip_local_port_cmd);
+
+	return 0;
+}
+
+int sgsn_parse_config(const char *config_file, struct sgsn_config *cfg)
+{
+	int rc;
+
+	g_cfg = cfg;
+	rc = vty_read_config_file(config_file);
+	if (rc < 0) {
+		fprintf(stderr, "Failed to parse the config file: '%s'\n", config_file);
+		return rc;
+	}
+
+	return 0;
+}