assignment_fsm: fix channel allocator preferences

When the MSC allocates a channel through the ASSIGNMENT REQUEST, it may
ask for a TCH/H and a TCH/F at the same time and tell which of the two
types it prefers.

The process of channel allocation currently selects, based on the BTS,
MSC and MS capabilites exactly one apropriate codec/rate (e.g. TCH/H)
and then tries to allocate it. If that allocation fails, there is no way
to try the second choice and the assignment fails.

For example: The MSC asks for TCH/F and TCH/H, prefering TCH/F, then the
channel allocator will try TCH/F and if it fails (all TCH/F are
currently in use), then TCH/H is never tried.

Since the BSC currently only trys the first best codec/rate that is
supported it also ignores the preference.

Lets fix those problems by including the preference information and both
possible codec/rate settings into the channel allocation decision.

Change-Id: I5239e05c1cfbcb8af28f43373a58fa6c2d216c51
Related: OS#3503

1 files changed, 107 insertions, 26 deletions

diff --git a/src/osmo-bsc/osmo_bsc_bssap.c b/src/osmo-bsc/osmo_bsc_bssap.c
index ab7f79ce1..85aab22d2 100644
--- a/src/osmo-bsc/osmo_bsc_bssap.c
+++ b/src/osmo-bsc/osmo_bsc_bssap.c
@@ -616,6 +616,101 @@ static int bssmap_handle_lcls_connect_ctrl(struct gsm_subscriber_connection *con
 	return 0;
 }
 
+/* Select a prefered and an alternative codec rate depending on the available
+ * capabilities. This decision does not include the actual channel load yet,
+ * this is also the reason why the result is a prefered and an alternate
+ * setting. The final decision is made in assignment_fsm.c when the actual
+ * lchan is requested. The preferred lchan will be requested first. If we
+ * find an alternate setting here, this one will be tried secondly if our
+ * primary coice fails. */
+static int select_codecs(struct assignment_request *req, struct gsm0808_channel_type *ct,
+			 struct gsm_subscriber_connection *conn)
+{
+	int rc;
+	struct bsc_msc_data *msc;
+
+	msc = conn->sccp.msc;
+	req->ch_mode_rate_alt_present = false;
+
+	switch (ct->ch_rate_type) {
+	case GSM0808_SPEECH_FULL_BM:
+		rc = match_codec_pref(&req->ch_mode_rate_pref, ct, &conn->codec_list, msc, conn_get_bts(conn),
+				      RATE_PREF_FR);
+		break;
+	case GSM0808_SPEECH_HALF_LM:
+		rc = match_codec_pref(&req->ch_mode_rate_pref, ct, &conn->codec_list, msc, conn_get_bts(conn),
+				      RATE_PREF_HR);
+		break;
+	case GSM0808_SPEECH_PERM:
+	case GSM0808_SPEECH_PERM_NO_CHANGE:
+	case GSM0808_SPEECH_FULL_PREF_NO_CHANGE:
+	case GSM0808_SPEECH_FULL_PREF:
+		rc = match_codec_pref(&req->ch_mode_rate_pref, ct, &conn->codec_list, msc, conn_get_bts(conn),
+				      RATE_PREF_FR);
+		if (rc < 0) {
+			rc = match_codec_pref(&req->ch_mode_rate_pref, ct, &conn->codec_list, msc, conn_get_bts(conn),
+					      RATE_PREF_HR);
+			break;
+		}
+		rc = match_codec_pref(&req->ch_mode_rate_alt, ct, &conn->codec_list, msc, conn_get_bts(conn),
+				      RATE_PREF_HR);
+		if (rc == 0)
+			req->ch_mode_rate_alt_present = true;
+		rc = 0;
+		break;
+	case GSM0808_SPEECH_HALF_PREF_NO_CHANGE:
+	case GSM0808_SPEECH_HALF_PREF:
+		rc = match_codec_pref(&req->ch_mode_rate_pref, ct, &conn->codec_list, msc, conn_get_bts(conn),
+				      RATE_PREF_HR);
+
+		if (rc < 0) {
+			rc = match_codec_pref(&req->ch_mode_rate_pref, ct, &conn->codec_list, msc, conn_get_bts(conn),
+					      RATE_PREF_FR);
+			break;
+		}
+		rc = match_codec_pref(&req->ch_mode_rate_alt, ct, &conn->codec_list, msc, conn_get_bts(conn),
+				      RATE_PREF_FR);
+		if (rc == 0)
+			req->ch_mode_rate_alt_present = true;
+		rc = 0;
+		break;
+	default:
+		rc = -EINVAL;
+		break;
+	}
+
+	if (rc < 0) {
+		LOGP(DMSC, LOGL_ERROR, "No supported audio type found for channel_type ="
+		     " { ch_indctr=0x%x, ch_rate_type=0x%x, perm_spch=[%s] }\n",
+		     ct->ch_indctr, ct->ch_rate_type, osmo_hexdump(ct->perm_spch, ct->perm_spch_len));
+		/* TODO: actually output codec names, e.g. implement
+		 * gsm0808_permitted_speech_names[] and iterate perm_spch. */
+		return -EINVAL;
+	}
+
+	if (req->ch_mode_rate_alt_present) {
+		DEBUGP(DMSC, "Found matching audio type (preferred): %s %s for channel_type ="
+		       " { ch_indctr=0x%x, ch_rate_type=0x%x, perm_spch=[ %s] }\n",
+		       req->ch_mode_rate_pref.full_rate ? "full rate" : "half rate",
+		       get_value_string(gsm48_chan_mode_names, req->ch_mode_rate_pref.chan_mode),
+		       ct->ch_indctr, ct->ch_rate_type, osmo_hexdump(ct->perm_spch, ct->perm_spch_len));
+		DEBUGP(DMSC, "Found matching audio type (alternative): %s %s for channel_type ="
+		       " { ch_indctr=0x%x, ch_rate_type=0x%x, perm_spch=[ %s] }\n",
+		       req->ch_mode_rate_alt.full_rate ? "full rate" : "half rate",
+		       get_value_string(gsm48_chan_mode_names, req->ch_mode_rate_alt.chan_mode),
+		       ct->ch_indctr, ct->ch_rate_type, osmo_hexdump(ct->perm_spch, ct->perm_spch_len));
+	} else {
+		DEBUGP(DMSC, "Found matching audio type: %s %s for channel_type ="
+		       " { ch_indctr=0x%x, ch_rate_type=0x%x, perm_spch=[ %s] }\n",
+		       req->ch_mode_rate_pref.full_rate ? "full rate" : "half rate",
+		       get_value_string(gsm48_chan_mode_names, req->ch_mode_rate_pref.chan_mode),
+		       ct->ch_indctr, ct->ch_rate_type, osmo_hexdump(ct->perm_spch, ct->perm_spch_len));
+
+	}
+
+	return 0;
+}
+
 /*
  * Handle the assignment request message.
  *
@@ -625,18 +720,15 @@ static int bssmap_handle_assignm_req(struct gsm_subscriber_connection *conn,
 				     struct msgb *msg, unsigned int length)
 {
 	struct msgb *resp;
-	struct bsc_msc_data *msc;
 	struct tlv_parsed tp;
 	uint16_t cic = 0;
-	enum gsm48_chan_mode chan_mode = GSM48_CMODE_SIGN;
-	bool full_rate = false;
-	uint16_t s15_s0 = 0;
 	bool aoip = false;
 	struct sockaddr_storage rtp_addr;
 	struct gsm0808_channel_type ct;
 	uint8_t cause;
 	int rc;
 	struct assignment_request req = {};
+	struct channel_mode_and_rate ch_mode_rate_pref = {};
 
 	if (!conn) {
 		LOGP(DMSC, LOGL_ERROR,
@@ -644,7 +736,6 @@ static int bssmap_handle_assignm_req(struct gsm_subscriber_connection *conn,
 		return -1;
 	}
 
-	msc = conn->sccp.msc;
 	aoip = gscon_is_aoip(conn);
 
 	tlv_parse(&tp, gsm0808_att_tlvdef(), msg->l4h + 1, length - 1, 0, 0);
@@ -732,33 +823,19 @@ static int bssmap_handle_assignm_req(struct gsm_subscriber_connection *conn,
 			goto reject;
 		}
 
+		req = (struct assignment_request){
+			.aoip = aoip,
+			.msc_assigned_cic = cic,
+		};
+
 		/* Match codec information from the assignment command against the
 		 * local preferences of the BSC and BTS */
-		rc = match_codec_pref(&chan_mode, &full_rate, &s15_s0, &ct, &conn->codec_list,
-				      msc, conn_get_bts(conn));
+		rc = select_codecs(&req, &ct, conn);
 		if (rc < 0) {
-			LOGP(DMSC, LOGL_ERROR, "No supported audio type found for channel_type ="
-			     " { ch_indctr=0x%x, ch_rate_type=0x%x, perm_spch=[ %s] }\n",
-			     ct.ch_indctr, ct.ch_rate_type, osmo_hexdump(ct.perm_spch, ct.perm_spch_len));
-			/* TODO: actually output codec names, e.g. implement
-			 * gsm0808_permitted_speech_names[] and iterate perm_spch. */
 			cause = GSM0808_CAUSE_REQ_CODEC_TYPE_OR_CONFIG_UNAVAIL;
 			goto reject;
 		}
 
-		DEBUGP(DMSC, "Found matching audio type: %s %s for channel_type ="
-		       " { ch_indctr=0x%x, ch_rate_type=0x%x, perm_spch=[ %s] }\n",
-		       full_rate? "full rate" : "half rate",
-		       get_value_string(gsm48_chan_mode_names, chan_mode),
-		       ct.ch_indctr, ct.ch_rate_type, osmo_hexdump(ct.perm_spch, ct.perm_spch_len));
-
-		req = (struct assignment_request){
-			.aoip = aoip,
-			.msc_assigned_cic = cic,
-			.chan_mode = chan_mode,
-			.full_rate = full_rate,
-			.s15_s0 = s15_s0
-		};
 		if (aoip) {
 			unsigned int rc = osmo_sockaddr_to_str_and_uint(req.msc_rtp_addr,
 									sizeof(req.msc_rtp_addr),
@@ -772,9 +849,13 @@ static int bssmap_handle_assignm_req(struct gsm_subscriber_connection *conn,
 		}
 		break;
 	case GSM0808_CHAN_SIGN:
+		ch_mode_rate_pref = (struct channel_mode_and_rate) {
+			.chan_mode = GSM48_CMODE_SIGN,
+		};
+
 		req = (struct assignment_request){
 			.aoip = aoip,
-			.chan_mode = chan_mode,
+			.ch_mode_rate_pref = ch_mode_rate_pref,
 		};
 		break;
 	default: