ASCI: NCH / NOTIFICATION support

This adds very minimalistic support for notification of VBS/VGCS calls.

Minimalistic in that we
* only notify via PCH (not via NCH or FACCH)
* only include notification in otherwise empty PAGING TYPE 1

This means that notification will cease to work once the PCH becomes too
loaded and we never would send otherwise empty PAGING TYPE 1 anymore.

Change-Id: I6f6f72d9a0123cb519b341d72a124aaa2117370e
Requires: libosmocore.git I9586b5cb8514010d9358fcfc97c3d34741294522
Related: OS#5781

include/osmo-bts/Makefile.am

@@ -32,5 +32,6 @@ noinst_HEADERS = \
 	dtx_dl_amr_fsm.h \
 	ta_control.h \
 	nm_common_fsm.h \
+	notification.h \
 	osmux.h \
 	$(NULL)

include/osmo-bts/bts.h

@@ -290,6 +290,11 @@ struct gsm_bts {
 		bool pni;		/* Primary Notification Identifier */
 	} etws;
 
+	/* Advanced Speech Call Items (VBS/VGCS) + NCH related bits */
+	struct {
+		struct llist_head notifications;
+	} asci;
+
 	struct paging_state *paging_state;
 	struct llist_head bsc_oml_hosts;
 	unsigned int rtp_jitter_buf_ms;

include/osmo-bts/notification.h

@@ -0,0 +1,57 @@
+/* Maintain and generate ASCI notifications */
+
+/*
+ * (C) 2023 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ *
+ * SPDX-License-Identifier: AGPL-3.0+
+ *
+ * Author: Harald Welte
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+/* one [concurrent] ASCI (VBS/VGCS) notification */
+struct asci_notification {
+	struct llist_head list;	/* linked to bts->asci.notifications */
+
+	/* Group call reference (TS 24.008 10.5.1.9 "Descriptive group or broadcast call reference") */
+	uint8_t group_call_ref[5];
+
+	/* Group Channel Description (TS 44.018 10.5.2.14b) */
+	struct {
+		bool present;
+		uint8_t value[255];
+		uint8_t len;
+	} chan_desc;
+
+	/* NCH DRX Information (TS 48.058 9.3.47) */
+	struct {
+		bool present;
+		struct rsl_ie_nch_drx_info value;
+	} nch_drx_info;
+};
+
+int bts_asci_notification_add(struct gsm_bts *bts, const uint8_t *group_call_ref, const uint8_t *chan_desc,
+			      uint8_t chan_desc_len, const struct rsl_ie_nch_drx_info *nch_drx_info);
+
+int bts_asci_notification_del(struct gsm_bts *bts, const uint8_t *group_call_ref);
+
+int bts_asci_notification_reset(struct gsm_bts *bts);
+
+const struct asci_notification *bts_asci_notification_get_next(struct gsm_bts *bts);
+
+void append_group_call_information(struct bitvec *bv, const uint8_t *gcr, const uint8_t *ch_desc, uint8_t ch_desc_len);

src/common/Makefile.am

@@ -67,6 +67,7 @@ libbts_a_SOURCES = \
 	nm_gprs_nse_fsm.c \
 	nm_gprs_nsvc_fsm.c \
 	nm_radio_carrier_fsm.c \
+	notification.c \
 	probes.d \
 	$(NULL)
 

src/common/bts.c

@@ -400,6 +400,8 @@ int bts_init(struct gsm_bts *bts)
 	bts->smscb_queue_tgt_len = 2;
 	bts->smscb_queue_hyst = 2;
 
+	INIT_LLIST_HEAD(&bts->asci.notifications);
+
 	INIT_LLIST_HEAD(&bts->bsc_oml_hosts);
 
 	/* register DTX DL FSM */

src/common/nm_bts_fsm.c

@@ -36,6 +36,7 @@
 #include <osmo-bts/nm_common_fsm.h>
 #include <osmo-bts/phy_link.h>
 #include <osmo-bts/cbch.h>
+#include <osmo-bts/notification.h>
 
 #define X(s) (1 << (s))
 
@@ -64,6 +65,7 @@ static void st_op_disabled_notinstalled_on_enter(struct osmo_fsm_inst *fi, uint3
 	bts->bsic = 0xff; /* invalid value */
 	TALLOC_FREE(bts->mo.nm_attr);
 	bts_cbch_reset(bts);
+	bts_asci_notification_reset(bts);
 	if (bts->c0_power_red_db > 0)
 		bts_set_c0_pwr_red(bts, 0);
 

src/common/notification.c

@@ -0,0 +1,155 @@
+/* Maintain and generate ASCI notifications */
+
+/*
+ * (C) 2023 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ *
+ * SPDX-License-Identifier: AGPL-3.0+
+ *
+ * Author: Harald Welte
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <errno.h>
+
+#include <osmocom/core/bitvec.h>
+#include <osmocom/core/linuxlist.h>
+#include <osmocom/gsm/protocol/gsm_08_58.h>
+
+#include <osmo-bts/bts.h>
+#include <osmo-bts/logging.h>
+#include <osmo-bts/notification.h>
+
+static struct asci_notification *bts_asci_notification_find(struct gsm_bts *bts, const uint8_t *group_call_ref)
+{
+	struct asci_notification *n;
+	llist_for_each_entry(n, &bts->asci.notifications, list) {
+		if (!memcmp(n->group_call_ref, group_call_ref, sizeof(n->group_call_ref)))
+			return n;
+	}
+	return NULL;
+}
+
+int bts_asci_notification_add(struct gsm_bts *bts, const uint8_t *group_call_ref, const uint8_t *chan_desc,
+			      uint8_t chan_desc_len, const struct rsl_ie_nch_drx_info *nch_drx_info)
+{
+	struct asci_notification *n;
+
+	if (bts_asci_notification_find(bts, group_call_ref))
+		return -EEXIST;
+
+	n = talloc_zero(bts, struct asci_notification);
+	if (!n)
+		return -ENOMEM;
+
+	memcpy(n->group_call_ref, group_call_ref, sizeof(n->group_call_ref));
+	if (chan_desc && chan_desc_len) {
+		n->chan_desc.present = true;
+		n->chan_desc.len = chan_desc_len;
+		memcpy(&n->chan_desc.value, chan_desc, chan_desc_len);
+	}
+	if (nch_drx_info) {
+		n->nch_drx_info.present = true;
+		n->nch_drx_info.value = *nch_drx_info;
+	}
+
+	LOGP(DASCI, LOGL_INFO, "Added ASCI Notification for group call reference %s\n",
+	     osmo_hexdump_nospc(n->group_call_ref, ARRAY_SIZE(n->group_call_ref)));
+
+	/* add at beginning of "queue" to make sure a new call is notified first */
+	llist_add(&n->list, &bts->asci.notifications);
+
+	return 0;
+}
+
+int bts_asci_notification_del(struct gsm_bts *bts, const uint8_t *group_call_ref)
+{
+	struct asci_notification *n = bts_asci_notification_find(bts, group_call_ref);
+	if (!n)
+		return -ENODEV;
+
+	LOGP(DASCI, LOGL_INFO, "Deleting ASCI Notification for group call reference %s\n",
+	     osmo_hexdump_nospc(n->group_call_ref, ARRAY_SIZE(n->group_call_ref)));
+
+	llist_del(&n->list);
+	talloc_free(n);
+
+	return 0;
+}
+
+int bts_asci_notification_reset(struct gsm_bts *bts)
+{
+	struct asci_notification *n, *n2;
+
+	LOGP(DASCI, LOGL_INFO, "Deleting all %u ASCI Notifications of BTS\n",
+	     llist_count(&bts->asci.notifications));
+
+	llist_for_each_entry_safe(n, n2, &bts->asci.notifications, list) {
+		llist_del(&n->list);
+		talloc_free(n);
+	}
+	return 0;
+}
+
+const struct asci_notification *bts_asci_notification_get_next(struct gsm_bts *bts)
+{
+	struct asci_notification *n;
+
+	n = llist_first_entry_or_null(&bts->asci.notifications, struct asci_notification, list);
+	if (!n)
+		return NULL;
+
+	/* move to end of list to iterate over them */
+	llist_del(&n->list);
+	llist_add_tail(&n->list, &bts->asci.notifications);
+
+	return n;
+}
+
+
+/*! append a "Group Call Information" CSN.1 structure to the caller-provided bit-vector.
+ *  \param[out] bv caller-provided output bit-vector
+ *  \param[in] gcr 5-byte group call reference
+ *  \param[in] ch_desc optional group channel description (may be NULL)
+ *  \param[in] ch_desc_len length of group channel description (in bytes) */
+void append_group_call_information(struct bitvec *bv, const uint8_t *gcr, const uint8_t *ch_desc, uint8_t ch_desc_len)
+{
+	/* spec reference: TS 44.018 Section 9.1.21a */
+
+	/* <Group Call Reference : bit(36)> */
+	struct bitvec *gcr_bv = bitvec_alloc(5*8, NULL);
+	OSMO_ASSERT(gcr_bv);
+	bitvec_unpack(gcr_bv, gcr);
+	for (unsigned int i = 0; i < 36; i++)
+		bitvec_set_bit(bv, bitvec_get_bit_pos(gcr_bv, i));
+
+	/* Group Channel Description */
+	if (ch_desc && ch_desc_len) {
+		struct bitvec *chd_bv = bitvec_alloc(ch_desc_len*8, NULL);
+		OSMO_ASSERT(chd_bv);
+		bitvec_unpack(chd_bv, ch_desc);
+		bitvec_set_bit(bv, 1);
+		/* <Channel Description : bit(24)> */
+		for (unsigned int i = 0; i < ch_desc_len * 8; i++)
+			bitvec_set_bit(bv, bitvec_get_bit_pos(chd_bv, i));
+		bitvec_free(chd_bv);
+		/* FIXME: hopping */
+		bitvec_set_bit(bv, 0);
+	} else {
+		bitvec_set_bit(bv, 0);
+	}
+
+	bitvec_free(gcr_bv);
+}

src/common/paging.c

@@ -43,6 +43,7 @@
 #include <osmo-bts/paging.h>
 #include <osmo-bts/signal.h>
 #include <osmo-bts/pcu_if.h>
+#include <osmo-bts/notification.h>
 
 #define MAX_PAGING_BLOCKS_CCCH	9
 #define MAX_BS_PA_MFRMS		9
@@ -366,7 +367,8 @@ static void append_etws_prim_notif(struct bitvec *bv, bool is_first, uint8_t pag
 }
 
 /* 3GPP TS 44.018 10.5.2.23 append P1 Rest Octets to given bit-vector */
-static void append_p1_rest_octets(struct bitvec *bv, const struct p1_rest_octets *p1ro)
+static void append_p1_rest_octets(struct bitvec *bv, const struct p1_rest_octets *p1ro,
+				  const struct asci_notification *notif)
 {
 	/* Paging 1 RO (at least 10 bits before ETWS struct) */
 	if (p1ro->nln_pch.present) {
@@ -378,7 +380,14 @@ static void append_p1_rest_octets(struct bitvec *bv, const struct p1_rest_octets
 	}
 	bitvec_set_bit(bv, L);		/* no Priority1 */
 	bitvec_set_bit(bv, L);		/* no Priority2 */
-	bitvec_set_bit(bv, L);		/* no Group Call Info */
+	if (notif) {
+		bitvec_set_bit(bv, H);		/* Group Call Info */
+		append_group_call_information(bv, notif->group_call_ref,
+					      notif->chan_desc.present ? notif->chan_desc.value : NULL,
+					      notif->chan_desc.len);
+	} else {
+		bitvec_set_bit(bv, L);		/* no Group Call Info */
+	}
 	if (p1ro->packet_page_ind[0])
 		bitvec_set_bit(bv, H);		/* Packet Page Indication 1 */
 	else
@@ -405,7 +414,8 @@ static void append_p1_rest_octets(struct bitvec *bv, const struct p1_rest_octets
 
 static int fill_paging_type_1(uint8_t *out_buf, const uint8_t *identity1_lv,
 				uint8_t chan1, const uint8_t *identity2_lv,
-				uint8_t chan2, const struct p1_rest_octets *p1ro)
+				uint8_t chan2, const struct p1_rest_octets *p1ro,
+				const struct asci_notification *notif)
 {
 	struct gsm48_paging1 *pt1 = (struct gsm48_paging1 *) out_buf;
 	unsigned int ro_len;
@@ -436,7 +446,7 @@ static int fill_paging_type_1(uint8_t *out_buf, const uint8_t *identity1_lv,
 			.data = cur,
 		};
 
-		append_p1_rest_octets(&bv, p1ro);
+		append_p1_rest_octets(&bv, p1ro, notif);
 	}
 
 	return GSM_MACBLOCK_LEN;
@@ -582,6 +592,7 @@ static void build_p1_rest_octets(struct p1_rest_octets *p1ro, struct gsm_bts *bt
 int paging_gen_msg(struct paging_state *ps, uint8_t *out_buf, struct gsm_time *gt,
 		   int *is_empty)
 {
+	const struct asci_notification *notif;
 	struct llist_head *group_q;
 	struct gsm_bts *bts = ps->bts;
 	int group;
@@ -607,12 +618,16 @@ int paging_gen_msg(struct paging_state *ps, uint8_t *out_buf, struct gsm_time *g
 	if (ps->bts->etws.prim_notif) {
 		struct p1_rest_octets p1ro;
 		build_p1_rest_octets(&p1ro, bts);
-		len = fill_paging_type_1(out_buf, empty_id_lv, 0, NULL, 0, &p1ro);
+		/* we intentioanally don't try to add notifications here, as ETWS is more critical */
+		len = fill_paging_type_1(out_buf, empty_id_lv, 0, NULL, 0, &p1ro, NULL);
 	} else if (llist_empty(group_q)) {
 		/* There is nobody to be paged, send Type1 with two empty ID */
 		//DEBUGP(DPAG, "Tx PAGING TYPE 1 (empty)\n");
-		len = fill_paging_type_1(out_buf, empty_id_lv, 0,
-					 NULL, 0, NULL);
+		/* for now, we only send VGCS/VBS notfication if we have nothing else to page;
+		 * this is the safe choice.  For other situations with mobile identities in the
+		 * paging type 1, we'd need to check if there's sufficient space in the rest octets. */
+		notif = bts_asci_notification_get_next(bts);
+		len = fill_paging_type_1(out_buf, empty_id_lv, 0, NULL, 0, NULL, notif);
 		*is_empty = 1;
 	} else {
 		struct paging_record *pr[4];
@@ -688,19 +703,21 @@ int paging_gen_msg(struct paging_state *ps, uint8_t *out_buf, struct gsm_time *g
 			}
 		} else if (num_pr == 1) {
 			DEBUGP(DPAG, "Tx PAGING TYPE 1 (1 xMSI,1 empty)\n");
+			/* TODO: check if we can include an ASCI notification */
 			len = fill_paging_type_1(out_buf,
 						 pr[0]->u.normal.identity_lv,
 						 pr[0]->u.normal.chan_needed,
-						 NULL, 0, NULL);
+						 NULL, 0, NULL, NULL);
 		} else {
 			/* 2 (any type) or
 			 * 3 or 4, of which only 2 will be sent */
 			DEBUGP(DPAG, "Tx PAGING TYPE 1 (2 xMSI)\n");
+			/* TODO: check if we can include an ASCI notification */
 			len = fill_paging_type_1(out_buf,
 						 pr[0]->u.normal.identity_lv,
 						 pr[0]->u.normal.chan_needed,
 						 pr[1]->u.normal.identity_lv,
-						 pr[1]->u.normal.chan_needed, NULL);
+						 pr[1]->u.normal.chan_needed, NULL, NULL);
 			if (num_pr >= 3) {
 				/* re-add #4 for next time */
 				llist_add(&pr[2]->list, group_q);

src/common/rsl.c

@@ -56,6 +56,7 @@
 #include <osmo-bts/l1sap.h>
 #include <osmo-bts/bts_model.h>
 #include <osmo-bts/pcuif_proto.h>
+#include <osmo-bts/notification.h>
 
 //#define FAKE_CIPH_MODE_COMPL
 
@@ -775,6 +776,52 @@ static int rsl_rx_sms_bcast_cmd(struct gsm_bts_trx *trx, struct msgb *msg)
 	return 0;
 }
 
+/* 8.5.10 NOTIFICATION COMMAND */
+static int rsl_rx_notification_cmd(struct gsm_bts_trx *trx, struct msgb *msg)
+{
+	struct abis_rsl_cchan_hdr *cch = msgb_l2(msg);
+	struct tlv_parsed tp;
+	uint8_t command_indicator;
+	int rc;
+
+	if (rsl_tlv_parse(&tp, msgb_l3(msg), msgb_l3len(msg)) < 0) {
+		LOGPTRX(trx, DRSL, LOGL_ERROR, "%s(): rsl_tlv_parse() failed\n", __func__);
+		return rsl_tx_error_report(trx, RSL_ERR_PROTO, &cch->chan_nr, NULL, msg);
+	}
+
+	if (cch->chan_nr != RSL_CHAN_PCH_AGCH) {
+		LOGPTRX(trx, DRSL, LOGL_ERROR, "%s(): chan nr is not Downlink CCCH\n", __func__);
+		return rsl_tx_error_report(trx, RSL_ERR_IE_CONTENT, &cch->chan_nr, NULL, msg);
+	}
+
+	if (!TLVP_PRES_LEN(&tp, RSL_IE_CMD_INDICATOR, 1))
+		return rsl_tx_error_report(trx, RSL_ERR_MAND_IE_ERROR, &cch->chan_nr, NULL, msg);
+	command_indicator = *TLVP_VAL(&tp, RSL_IE_CMD_INDICATOR);
+
+	switch (command_indicator) {
+	case RSL_CMD_INDICATOR_START:
+		/* we need at least a Group Call Reference to start notification */
+		if (!TLVP_PRES_LEN(&tp, RSL_IE_GROUP_CALL_REF, 5))
+			return rsl_tx_error_report(trx, RSL_ERR_OPT_IE_ERROR, &cch->chan_nr, NULL, msg);
+		rc = bts_asci_notification_add(trx->bts, TLVP_VAL(&tp, RSL_IE_GROUP_CALL_REF),
+					       TLVP_VAL(&tp, RSL_IE_CHAN_DESC), TLVP_LEN(&tp, RSL_IE_CHAN_DESC),
+					       (struct rsl_ie_nch_drx_info *) TLVP_VAL(&tp, RSL_IE_NCH_DRX_INFO));
+		break;
+	case RSL_CMD_INDICATOR_STOP:
+		if (!TLVP_PRES_LEN(&tp, RSL_IE_GROUP_CALL_REF, 5)) {
+			/* interpret this as stopping of all notification */
+			rc = bts_asci_notification_reset(trx->bts);
+		} else {
+			rc = bts_asci_notification_del(trx->bts, TLVP_VAL(&tp, RSL_IE_GROUP_CALL_REF));
+		}
+		break;
+	default:
+		return rsl_tx_error_report(trx, RSL_ERR_IE_CONTENT, &cch->chan_nr, NULL, msg);
+	}
+
+	return rc;
+}
+
 /* OSMO_ETWS_CMD - proprietary extension as TS 48.058 has no standardized way to do this :( */
 static int rsl_rx_osmo_etws_cmd(struct gsm_bts_trx *trx, struct msgb *msg)
 {
@@ -3680,8 +3727,10 @@ static int rsl_rx_cchan(struct gsm_bts_trx *trx, struct msgb *msg)
 	case RSL_MT_SMS_BC_CMD:
 		ret = rsl_rx_sms_bcast_cmd(trx, msg);
 		break;
-	case RSL_MT_SMS_BC_REQ:
 	case RSL_MT_NOT_CMD:
+		ret = rsl_rx_notification_cmd(trx, msg);
+		break;
+	case RSL_MT_SMS_BC_REQ:
 		LOGPLCHAN(msg->lchan, DRSL, LOGL_NOTICE, "unimplemented RSL cchan msg_type %s\n",
 			  rsl_msg_name(cch->c.msg_type));
 		rsl_tx_error_report(trx, RSL_ERR_MSG_TYPE, &cch->chan_nr, NULL, msg);