[handover] Implement handover control logic

Code to implement handover control logic.  A yet-to-be-implemented
handover algorithm will call bsc_handover_start(old_lchan, new_bts)
to start the handover process.

1 files changed, 251 insertions, 0 deletions

diff --git a/openbsc/src/handover_logic.c b/openbsc/src/handover_logic.c
new file mode 100644
index 000000000..d4a888487
--- /dev/null
+++ b/openbsc/src/handover_logic.c
@@ -0,0 +1,251 @@
+/* Handover Logic for Inter-BTS (Intra-BSC) Handover.  This does not
+ * actually implement the handover algorithm/decision, but executes a
+ * handover decision */
+
+/* (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 <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <time.h>
+#include <netinet/in.h>
+
+#include <openbsc/msgb.h>
+#include <openbsc/debug.h>
+#include <openbsc/gsm_data.h>
+#include <openbsc/gsm_utils.h>
+#include <openbsc/gsm_subscriber.h>
+#include <openbsc/gsm_04_08.h>
+#include <openbsc/abis_rsl.h>
+#include <openbsc/chan_alloc.h>
+#include <openbsc/signal.h>
+#include <openbsc/talloc.h>
+#include <openbsc/transaction.h>
+
+struct bsc_handover {
+	struct llist_head list;
+
+	struct gsm_lchan *old_lchan;
+	struct gsm_lchan *new_lchan;
+
+	struct timer_list T3103;
+
+	u_int8_t ho_ref;
+};
+
+static LLIST_HEAD(bsc_handovers);
+
+static struct bsc_handover *bsc_ho_by_new_lchan(struct gsm_lchan *new_lchan)
+{
+	struct bsc_handover *ho;
+
+	llist_for_each_entry(ho, &bsc_handovers, list) {
+		if (ho->new_lchan == new_lchan)
+			return ho;
+	}
+
+	return NULL;
+}
+
+static struct bsc_handover *bsc_ho_by_old_lchan(struct gsm_lchan *old_lchan)
+{
+	struct bsc_handover *ho;
+
+	llist_for_each_entry(ho, &bsc_handovers, list) {
+		if (ho->old_lchan == old_lchan)
+			return ho;
+	}
+
+	return NULL;
+}
+
+/* Hand over the specified logical channel to the specified new BTS.
+ * This is the main entry point for the actual handover algorithm,
+ * after it has decided it wants to initiate HO to a specific BTS */
+int bsc_handover_start(struct gsm_lchan *old_lchan, struct gsm_bts *bts)
+{
+	struct gsm_lchan *new_lchan;
+	struct bsc_handover *ho;
+	int rc;
+
+	new_lchan = lchan_alloc(bts, old_lchan->type);
+	if (!new_lchan)
+		return -ENOSPC;
+
+	ho = talloc_zero(NULL, struct bsc_handover);
+	if (!ho) {
+		lchan_free(new_lchan);
+		return -ENOMEM;
+	}
+	ho->old_lchan = old_lchan;
+	ho->new_lchan = new_lchan;
+
+	/* FIXME: do we have a better idea of the timing advance? */
+	rc = rsl_chan_activate_lchan(new_lchan, RSL_ACT_INTER_ASYNC, 0);
+	if (rc < 0) {
+		talloc_free(ho);
+		lchan_free(new_lchan);
+		return rc;
+	}
+
+	llist_add(&ho->list, &bsc_handovers);
+	/* we continue in the SS_LCHAN handler / ho_chan_activ_ack */
+
+	return 0;
+}
+
+/* T3103 expired: Handover has failed without HO COMPLETE or HO FAIL */
+static void ho_T3103_cb(void *_ho)
+{
+	struct bsc_handover *ho = _ho;
+
+	lchan_free(ho->new_lchan);
+	llist_del(&ho->list);
+	talloc_free(ho);
+}
+
+/* RSL has acknowledged activation of the new lchan */
+static int ho_chan_activ_ack(struct gsm_lchan *new_lchan)
+{
+	struct bsc_handover *ho;
+	int rc;
+
+	ho = bsc_ho_by_new_lchan(new_lchan);
+	if (!ho)
+		return -ENODEV;
+
+	/* we can now send the 04.08 HANDOVER COMMAND to the MS
+	 * using the old lchan */
+
+	rc = gsm48_send_ho_cmd(ho->old_lchan, new_lchan, 0);
+
+	/* start T3103.  We can continue either with T3103 expiration,
+	 * 04.08 HANDOVER COMPLETE or 04.08 HANDOVER FAIL */
+	ho->T3103.cb = ho_T3103_cb;
+	bsc_schedule_timer(&ho->T3103, 10, 0);
+
+	return 0;
+}
+
+/* RSL has not acknowledged activation of the new lchan */
+static int ho_chan_activ_nack(struct gsm_lchan *new_lchan)
+{
+	struct bsc_handover *ho;
+
+	ho = bsc_ho_by_new_lchan(new_lchan);
+	if (!ho)
+		return -ENODEV;
+
+	llist_del(&ho->list);
+	talloc_free(ho);
+
+	/* FIXME: maybe we should try to allocate a new LCHAN here? */
+
+	return 0;
+}
+
+/* GSM 04.08 HANDOVER COMPLETE has been received on new channel */
+static int ho_gsm48_ho_compl(struct gsm_lchan *new_lchan)
+{
+	struct bsc_handover *ho;
+
+	ho = bsc_ho_by_new_lchan(new_lchan);
+	if (!ho)
+		return -ENODEV;
+
+	bsc_del_timer(&ho->T3103);
+	llist_del(&ho->list);
+
+	/* do something to re-route the actual speech frames ! */
+	//tch_remap(ho->old_lchan, ho->new_lchan);
+
+	/* release old lchan */
+	put_lchan(ho->old_lchan);
+
+	talloc_free(ho);
+
+	return 0;
+}
+
+/* GSM 04.08 HANDOVER FAIL has been received */
+static int ho_gsm48_ho_fail(struct gsm_lchan *old_lchan)
+{
+	struct bsc_handover *ho;
+
+	ho = bsc_ho_by_old_lchan(old_lchan);
+	if (!ho)
+		return -ENODEV;
+
+	bsc_del_timer(&ho->T3103);
+	llist_del(&ho->list);
+	put_lchan(ho->new_lchan);
+	talloc_free(ho);
+
+	return 0;
+}
+
+/* GSM 08.58 HANDOVER DETECT has been received */
+static int ho_rsl_detect(struct gsm_lchan *new_lchan)
+{
+	struct bsc_handover *ho;
+
+	ho = bsc_ho_by_old_lchan(new_lchan);
+	if (!ho)
+		return -ENODEV;
+
+	/* FIXME: do we actually want to do something here ? */
+
+	return 0;
+}
+
+static int ho_logic_sig_cb(unsigned int subsys, unsigned int signal,
+			   void *handler_data, void *signal_data)
+{
+	struct gsm_lchan *lchan;
+
+	switch (subsys) {
+	case SS_LCHAN:
+		lchan = signal_data;
+		switch (signal) {
+		case S_LCHAN_ACTIVATE_ACK:
+			return ho_chan_activ_ack(lchan);
+		case S_LCHAN_ACTIVATE_NACK:
+			return ho_chan_activ_nack(lchan);
+		case S_LCHAN_HANDOVER_DETECT:
+			return ho_rsl_detect(lchan);
+		case S_LCHAN_HANDOVER_COMPL:
+			return ho_gsm48_ho_compl(lchan);
+		case S_LCHAN_HANDOVER_FAIL:
+			return ho_gsm48_ho_fail(lchan);
+		}
+		break;
+	default:
+		break;
+	}
+
+	return 0;
+}
+
+static __attribute__((constructor)) void on_dso_load_ho_logic(void)
+{
+	register_signal_handler(SS_LCHAN, ho_logic_sig_cb, NULL);
+}