Create new 'gprs-sgsn' branch on top of 'gprs-conf'

This branch contains the partial SGSN/GGSN implementation that
was originally developed as part of the gprs branch.

2 files changed, 745 insertions, 0 deletions

diff --git a/openbsc/src/gprs_bssgp.c b/openbsc/src/gprs_bssgp.c
new file mode 100644
index 00000000..de57d25d
--- /dev/null
+++ b/openbsc/src/gprs_bssgp.c
@@ -0,0 +1,397 @@
+/* GPRS BSSGP protocol implementation as per 3GPP TS 08.18 */
+
+/* (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 <errno.h>
+#include <sys/types.h>
+
+#include <netinet/in.h>
+
+#include <osmocore/msgb.h>
+#include <osmocore/tlv.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;
+
+/* Chapter 11.3.9 / Table 11.10: Cause coding */
+static const char *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",
+};
+
+static const char *bssgp_cause_str(enum gprs_bssgp_cause cause)
+{
+	if (cause >= ARRAY_SIZE(bssgp_cause_strings))
+		return "undefined";
+
+	if (bssgp_cause_strings[cause])
+		return bssgp_cause_strings[cause];
+
+	return "undefined";
+}
+
+static inline int bssgp_tlv_parse(struct tlv_parsed *tp, u_int8_t *buf, int len)
+{
+	return tlv_parse(tp, &tvlv_att_def, buf, len, 0, 0);
+}
+
+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(u_int8_t pdu_type, u_int16_t bvci, u_int16_t ns_bvci)
+{
+	struct msgb *msg = bssgp_msgb_alloc();
+	struct bssgp_normal_hdr *bgph =
+			(struct bssgp_normal_hdr *) msgb_put(msg, sizeof(*bgph));
+	u_int16_t _bvci;
+
+	bgph->pdu_type = pdu_type;
+	_bvci = htons(bvci);
+	msgb_tvlv_put(msg, BSSGP_IE_BVCI, 2, (u_int8_t *) &_bvci);
+
+	return gprs_ns_sendmsg(NULL, ns_bvci, msg);
+}
+
+/* Chapter 10.4.5: Flow Control BVC ACK */
+static int bssgp_tx_fc_bvc_ack(u_int8_t tag, u_int16_t ns_bvci)
+{
+	struct msgb *msg = bssgp_msgb_alloc();
+	struct bssgp_normal_hdr *bgph =
+			(struct bssgp_normal_hdr *) msgb_put(msg, sizeof(*bgph));
+
+	bgph->pdu_type = BSSGP_PDUT_FLOW_CONTROL_BVC_ACK;
+	msgb_tvlv_put(msg, BSSGP_IE_TAG, 1, &tag);
+
+	return gprs_ns_sendmsg(NULL, ns_bvci, msg);
+}
+
+/* Chapter 10.4.14: Status */
+static int bssgp_tx_status(u_int8_t cause, u_int16_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));
+
+	bgph->pdu_type = BSSGP_PDUT_STATUS;
+	msgb_tvlv_put(msg, BSSGP_IE_CAUSE, 1, &cause);
+	if (bvci) {
+		u_int16_t _bvci = htons(*bvci);
+		msgb_tvlv_put(msg, BSSGP_IE_BVCI, 2, (u_int8_t *) &_bvci);
+	}
+	if (orig_msg)
+		msgb_tvlv_put(msg, BSSGP_IE_PDU_IN_ERROR,
+			      msgb_l3len(orig_msg), orig_msg->l3h);
+
+	return gprs_ns_sendmsg(NULL, 0, msg);
+}
+
+/* Uplink unit-data */
+static int bssgp_rx_ul_ud(struct msgb *msg, u_int16_t bvci)
+{
+	struct bssgp_ud_hdr *budh = (struct bssgp_ud_hdr *) msg->l3h;
+	struct gsm_bts *bts;
+	int data_len = msgb_l3len(msg) - sizeof(*budh);
+	struct tlv_parsed tp;
+	int rc;
+
+	DEBUGP(DGPRS, "BSSGP UL-UD\n");
+
+	msg->tlli = 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;
+
+	/* Determine the BTS based on the Cell ID */
+	bts = gsm48_bts_by_ra_id(bsc_gsmnet,
+				 TLVP_VAL(&tp, BSSGP_IE_CELL_ID),
+				 TLVP_LEN(&tp, BSSGP_IE_CELL_ID));
+	if (bts)
+		msg->trx = bts->c0;
+
+	msg->llch = TLVP_VAL(&tp, BSSGP_IE_LLC_PDU);
+
+	return gprs_llc_rcvmsg(msg, &tp);
+}
+
+static int bssgp_rx_suspend(struct msgb *msg, u_int16_t bvci)
+{
+	struct bssgp_normal_hdr *bgph = (struct bssgp_normal_hdr *) msg->l3h;
+	int data_len = msgb_l3len(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;
+
+	/* SEND SUSPEND_ACK or SUSPEND_NACK */
+	/* FIXME */
+}
+
+static int bssgp_rx_resume(struct msgb *msg, u_int16_t bvci)
+{
+	struct bssgp_normal_hdr *bgph = (struct bssgp_normal_hdr *) msg->l3h;
+	int data_len = msgb_l3len(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;
+
+	/* SEND RESUME_ACK or RESUME_NACK */
+	/* FIXME */
+}
+
+static int bssgp_rx_fc_bvc(struct msgb *msg, struct tlv_parsed *tp,
+			   u_int16_t ns_bvci)
+{
+
+	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);
+
+	/* Send FLOW_CONTROL_BVC_ACK */
+	return bssgp_tx_fc_bvc_ack(*TLVP_VAL(tp, BSSGP_IE_TAG), ns_bvci);
+}
+/* We expect msg->l3h to point to the BSSGP header */
+int gprs_bssgp_rcvmsg(struct msgb *msg, u_int16_t ns_bvci)
+{
+	struct bssgp_normal_hdr *bgph = (struct bssgp_normal_hdr *) msg->l3h;
+	struct tlv_parsed tp;
+	u_int8_t pdu_type = bgph->pdu_type;
+	int data_len = msgb_l3len(msg) - sizeof(*bgph);
+	u_int16_t bvci;
+	int rc = 0;
+
+	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, ns_bvci);
+		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 */
+		break;
+	case BSSGP_PDUT_SUSPEND:
+		/* MS wants to suspend */
+		rc = bssgp_rx_suspend(msg, ns_bvci);
+		break;
+	case BSSGP_PDUT_RESUME:
+		/* MS wants to resume */
+		rc = bssgp_rx_resume(msg, ns_bvci);
+		break;
+	case BSSGP_PDUT_FLUSH_LL:
+		/* BSS informs MS has moved to one cell to other cell */
+		DEBUGP(DGPRS, "BSSGP FLUSH LL\n");
+		/* 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");
+		break;
+	case BSSGP_PDUT_FLOW_CONTROL_BVC:
+		/* BSS informs us of available bandwidth in Gb interface */
+		rc = bssgp_rx_fc_bvc(msg, &tp, ns_bvci);
+		break;
+	case BSSGP_PDUT_FLOW_CONTROL_MS:
+		/* BSS informs us of available bandwidth to one MS */
+		DEBUGP(DGPRS, "BSSGP FC MS\n");
+		/* 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(*(u_int16_t *)TLVP_VAL(&tp, BSSGP_IE_BVCI));
+		DEBUGPC(DGPRS, "BVCI=%u, cause=%s\n", bvci,
+			bssgp_cause_str(*TLVP_VAL(&tp, BSSGP_IE_CAUSE)));
+		rc = bssgp_tx_simple_bvci(BSSGP_PDUT_BVC_BLOCK_ACK,
+					  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(*(u_int16_t *)TLVP_VAL(&tp, BSSGP_IE_BVCI));
+		DEBUGPC(DGPRS, "BVCI=%u\n", bvci);
+		rc = bssgp_tx_simple_bvci(BSSGP_PDUT_BVC_UNBLOCK_ACK,
+					  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;
+		bvci = ntohs(*(u_int16_t *)TLVP_VAL(&tp, BSSGP_IE_BVCI));
+		DEBUGPC(DGPRS, "BVCI=%u, cause=%s\n", bvci,
+			bssgp_cause_str(*TLVP_VAL(&tp, BSSGP_IE_CAUSE)));
+		rc = bssgp_tx_simple_bvci(BSSGP_PDUT_BVC_RESET_ACK,
+					  bvci, ns_bvci);
+		break;
+	case BSSGP_PDUT_STATUS:
+		/* Some exception has occurred */
+	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);
+}
+
+int gprs_bssgp_tx_dl_ud(struct msgb *msg)
+{
+	struct gsm_bts *bts;
+	struct bssgp_ud_hdr *budh;
+	u_int8_t llc_pdu_tlv_hdr_len = 2;
+	u_int8_t *llc_pdu_tlv, *qos_profile;
+	u_int16_t pdu_lifetime = 1000; /* centi-seconds */
+	u_int8_t qos_profile_default[3] = { 0x00, 0x00, 0x21 };
+	u_int16_t msg_len = msg->len;
+
+	if (!msg->trx) {
+		DEBUGP(DGPRS, "Cannot transmit DL-UD without TRX assigned\n");
+		return -EINVAL;
+	}
+
+	bts = msg->trx->bts;
+
+	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, (u_int8_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(msg->tlli);
+	budh->pdu_type = BSSGP_PDUT_DL_UNITDATA;
+
+	return gprs_ns_sendmsg(NULL, bts->gprs.cell.bvci, msg);
+}
diff --git a/openbsc/src/gprs_ns.c b/openbsc/src/gprs_ns.c
new file mode 100644
index 00000000..a686a22a
--- /dev/null
+++ b/openbsc/src/gprs_ns.c
@@ -0,0 +1,348 @@
+/* GPRS Networks Service (NS) messages on the Gb interface
+ * 3GPP TS 08.16 version 8.0.1 Release 1999 / ETSI TS 101 299 V8.0.1 (2002-05) */
+
+/* (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.
+ *
+ */
+
+/* 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 <sys/types.h>
+
+#include <arpa/inet.h>
+
+#include <openbsc/gsm_data.h>
+#include <osmocore/msgb.h>
+#include <osmocore/tlv.h>
+#include <osmocore/talloc.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 },
+	},
+};
+
+#define NSE_S_BLOCKED	0x0001
+#define NSE_S_ALIVE	0x0002
+
+struct gprs_nsvc {
+	struct llist_head list;
+
+	u_int16_t nsei;		/* end-to-end significance */
+	u_int16_t nsvci;	/* uniquely identifies NS-VC at SGSN */
+
+	u_int32_t state;
+
+	struct timer_list alive_timer;
+	int timer_is_tns_alive;
+	int alive_retries;
+};
+
+/* FIXME: dynamically search for the matching NSVC */
+static struct gprs_nsvc dummy_nsvc = { .state = NSE_S_BLOCKED | NSE_S_ALIVE };
+
+/* Section 10.3.2, Table 13 */
+static const char *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",
+};
+
+static const char *gprs_ns_cause_str(enum ns_cause cause)
+{
+	if (cause >= ARRAY_SIZE(ns_cause_str))
+		return "undefined";
+
+	if (ns_cause_str[cause])
+		return ns_cause_str[cause];
+
+	return "undefined";
+}
+
+static int gprs_ns_tx(struct msgb *msg)
+{
+	return ipac_gprs_send(msg);
+}
+
+static int gprs_ns_tx_simple(struct gprs_ns_link *link, u_int8_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(msg);
+}
+
+#define NS_TIMER_ALIVE	3, 0 	/* after 3 seconds without response, we retry */
+#define NS_TIMER_TEST	30, 0	/* every 10 seconds we check if the BTS is still alive */
+#define NS_ALIVE_RETRIES  10	/* after 3 failed retransmit we declare BTS as dead */
+
+static void gprs_ns_alive_cb(void *data)
+{
+	struct gprs_nsvc *nsvc = data;
+
+	if (nsvc->timer_is_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, "Tns-alive more then %u retries, "
+				" blocking NS-VC\n", NS_ALIVE_RETRIES);
+			/* FIXME: inform higher layers */
+			return;
+		}
+	} else {
+		/* Tns-test case: send NS-ALIVE PDU */
+		gprs_ns_tx_simple(NULL, NS_PDUT_ALIVE);
+		/* start Tns-alive timer */
+		nsvc->timer_is_tns_alive = 1;
+	}
+	bsc_schedule_timer(&nsvc->alive_timer, NS_TIMER_ALIVE);
+}
+
+/* Section 9.2.6 */
+static int gprs_ns_tx_reset_ack(u_int16_t nsvci, u_int16_t nsei)
+{
+	struct msgb *msg = msgb_alloc(NS_ALLOC_SIZE, "GPRS/NS");
+	struct gprs_ns_hdr *nsh;
+
+	if (!msg)
+		return -ENOMEM;
+
+	nsvci = htons(nsvci);
+	nsei = htons(nsei);
+
+	nsh = (struct gprs_ns_hdr *) msgb_put(msg, sizeof(*nsh));
+
+	nsh->pdu_type = NS_PDUT_RESET_ACK;
+
+	msgb_tvlv_put(msg, NS_IE_VCI, 2, (u_int8_t *)&nsvci);
+	msgb_tvlv_put(msg, NS_IE_NSEI, 2, (u_int8_t *)&nsei);
+
+	return gprs_ns_tx(msg);
+}
+
+/* Section 9.2.10: transmit side */
+int gprs_ns_sendmsg(struct gprs_ns_link *link, u_int16_t bvci,
+		    struct msgb *msg)
+{
+	struct gprs_ns_hdr *nsh;
+
+	nsh = (struct gprs_ns_hdr *) msgb_push(msg, sizeof(*nsh) + 3);
+	if (!nsh) {
+		DEBUGP(DGPRS, "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(msg);
+}
+
+/* Section 9.2.10: receive side */
+static int gprs_ns_rx_unitdata(struct msgb *msg)
+{
+	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *)msg->l2h;
+	u_int16_t bvci;
+
+	/* spare octet in data[0] */
+	bvci = nsh->data[1] << 8 | nsh->data[2];
+	msg->l3h = &nsh->data[3];
+
+	/* call upper layer (BSSGP) */
+	return gprs_bssgp_rcvmsg(msg, bvci);
+}
+
+/* Section 9.2.7 */
+static int gprs_ns_rx_status(struct msgb *msg)
+{
+	struct gprs_ns_hdr *nsh = msg->l2h;
+	struct tlv_parsed tp;
+	u_int8_t cause;
+	int rc;
+
+	DEBUGP(DGPRS, "NS STATUS ");
+
+	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 msgb *msg)
+{
+	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *) msg->l2h;
+	struct gprs_nsvc *nsvc = &dummy_nsvc;
+	struct tlv_parsed tp;
+	u_int8_t *cause;
+	u_int16_t *nsvci, *nsei;
+	int rc;
+
+	DEBUGP(DGPRS, "NS RESET ");
+
+	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 */
+		DEBUGPC(DGPRS, "Missing mandatory IE\n");
+		return -EINVAL;
+	}
+
+	cause = (u_int8_t *) TLVP_VAL(&tp, NS_IE_CAUSE);
+	nsvci = (u_int16_t *) TLVP_VAL(&tp, NS_IE_VCI);
+	nsei = (u_int16_t *) TLVP_VAL(&tp, NS_IE_NSEI);
+
+	*nsvci = ntohs(*nsvci);
+	*nsei = ntohs(*nsei);
+
+	DEBUGPC(DGPRS, "cause=%s, NSVCI=%u, NSEI=%u\n",
+		gprs_ns_cause_str(*cause), *nsvci, *nsei);
+
+	/* mark the NS-VC as blocked and alive */
+	nsvc->state = NSE_S_BLOCKED | NSE_S_ALIVE;
+	nsvc->nsei = *nsei;
+	nsvc->nsvci = *nsvci;
+
+	/* start the test procedure */
+	nsvc->alive_timer.cb = gprs_ns_alive_cb;
+	nsvc->alive_timer.data = nsvc;
+	bsc_schedule_timer(&nsvc->alive_timer, NS_TIMER_ALIVE);
+
+	return gprs_ns_tx_reset_ack(*nsvci, *nsei);
+}
+
+/* main entry point, here incoming NS frames enter */
+int gprs_ns_rcvmsg(struct msgb *msg)
+{
+	struct gprs_ns_hdr *nsh = (struct gprs_ns_hdr *) msg->l2h;
+	struct gprs_nsvc *nsvc = &dummy_nsvc;
+	int rc = 0;
+
+	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(NULL, NS_PDUT_ALIVE_ACK);
+		break;
+	case NS_PDUT_ALIVE_ACK:
+		/* stop Tns-alive */
+		bsc_del_timer(&nsvc->alive_timer);
+		/* start Tns-test */
+		nsvc->timer_is_tns_alive = 0;
+		bsc_schedule_timer(&nsvc->alive_timer, NS_TIMER_TEST);
+		break;
+	case NS_PDUT_UNITDATA:
+		/* actual user data */
+		rc = gprs_ns_rx_unitdata(msg);
+		break;
+	case NS_PDUT_STATUS:
+		rc = gprs_ns_rx_status(msg);
+		break;
+	case NS_PDUT_RESET:
+		rc = gprs_ns_rx_reset(msg);
+		break;
+	case NS_PDUT_RESET_ACK:
+		/* FIXME: mark remote NS-VC as blocked + active */
+		break;
+	case NS_PDUT_UNBLOCK:
+		/* Section 7.2: unblocking procedure */
+		DEBUGP(DGPRS, "NS UNBLOCK\n");
+		nsvc->state &= ~NSE_S_BLOCKED;
+		rc = gprs_ns_tx_simple(NULL, NS_PDUT_UNBLOCK_ACK);
+		break;
+	case NS_PDUT_UNBLOCK_ACK:
+		/* FIXME: mark remote NS-VC as unblocked + active */
+		break;
+	case NS_PDUT_BLOCK:
+		DEBUGP(DGPRS, "NS BLOCK\n");
+		nsvc->state |= NSE_S_BLOCKED;
+		rc = gprs_ns_tx_simple(NULL, NS_PDUT_UNBLOCK_ACK);
+		break;
+	case NS_PDUT_BLOCK_ACK:
+		/* FIXME: mark remote NS-VC as blocked + active */
+		break;
+	default:
+		DEBUGP(DGPRS, "Unknown NS PDU type 0x%02x\n", nsh->pdu_type);
+		rc = -EINVAL;
+		break;
+	}
+	return rc;
+}
+