codec_pref: Add Codec List to COMPLETE LAYER 3 INFORMATION

The COMPLETE LAYER 3 INFORMATION message lacks the Codec List (BSS Supported)
information element. This information element is mandatory for networks
that use an IP based user plane (AoIP).

- Add function to generate the speech codec list from the current codec
  settings (Available codecs)
- Generate and embed information element in L3 Compl. message

Depends: libosmocore I4e656731b16621736c7a2f4e64d9ce63b1064e98

Change-Id: Id6f2af3fdab45bf05f06aec03e222734d7a4cf70
Related: OS#3548

2 files changed, 73 insertions, 1 deletions

diff --git a/src/osmo-bsc/codec_pref.c b/src/osmo-bsc/codec_pref.c
index 924f77fe2..c998e6007 100644
--- a/src/osmo-bsc/codec_pref.c
+++ b/src/osmo-bsc/codec_pref.c
@@ -242,3 +242,68 @@ int match_codec_pref(enum gsm48_chan_mode *chan_mode,
 
 	return 0;
 }
+
+/*! Determine the BSS supported speech codec list that is sent to the MSC with
+ * the COMPLETE LAYER 3 INFORMATION message.
+ *  \param[out] scl GSM 08.08 speech codec list with BSS supported codecs.
+ *  \param[in] msc associated msc (current codec settings).
+ *  \param[in] bts associated bts (current codec settings). */
+void gen_bss_supported_codec_list(struct gsm0808_speech_codec_list *scl,
+				  const struct bsc_msc_data *msc, const struct gsm_bts *bts)
+{
+	uint8_t perm_spch;
+	unsigned int i;
+	int rc;
+	uint16_t amr_s15_s0_bts;
+	uint16_t amr_s15_s0_msc;
+	uint16_t amr_s15_s0;
+	const struct gsm48_multi_rate_conf *amr_cfg_bts;
+	const struct gsm48_multi_rate_conf *amr_cfg_msc;
+
+	memset(scl, 0, sizeof(*scl));
+
+	for (i = 0; i < msc->audio_length; i++) {
+
+		/* Pick a permitted speech value from the global codec configuration list */
+		perm_spch = audio_support_to_gsm88(msc->audio_support[i]);
+
+		/* Check this permitted speech value against the BTS specific parameters.
+		 * if the BTS does not support the codec, try the next one */
+		if (!test_codec_support_bts(&bts->codec, perm_spch))
+			continue;
+
+		/* Write item into codec list */
+		rc = gsm0808_speech_codec_from_chan_type(&scl->codec[scl->len], perm_spch);
+		if (rc != 0)
+			continue;
+
+		/* AMR (HR/FR version 3) is the only codec that requires a codec
+		 * configuration (S0-S15). Determine the current configuration and update
+		 * the cfg flag. */
+		if (msc->audio_support[i]->ver == 3) {
+
+			/* First lookup the BTS specific AMR rate configuration. Thsi config
+			 * is set via the VTY for each BTS individually. In cases where no
+			 * configuration is set we will assume a safe default */
+			if (msc->audio_support[i]->hr) {
+				amr_cfg_bts = (struct gsm48_multi_rate_conf *)&bts->mr_half.gsm48_ie;
+				amr_s15_s0_bts = gsm0808_sc_cfg_from_gsm48_mr_cfg(amr_cfg_bts, false);
+			} else {
+				amr_cfg_bts = (struct gsm48_multi_rate_conf *)&bts->mr_full.gsm48_ie;
+				amr_s15_s0_bts = gsm0808_sc_cfg_from_gsm48_mr_cfg(amr_cfg_bts, true);
+			}
+
+			/* At next, lookup the AMR rate configuration that is set for the MSC */
+			amr_cfg_msc = &msc->amr_conf;
+			amr_s15_s0_msc = gsm0808_sc_cfg_from_gsm48_mr_cfg(amr_cfg_msc, true);
+
+			/* Calculate the intersection of the two configurations and update S0-S15
+			 * in the codec list. */
+			amr_s15_s0 = amr_s15_s0_bts & amr_s15_s0_msc;
+			scl->codec[scl->len].cfg = amr_s15_s0;
+		}
+
+		scl->len++;
+	}
+}
+
diff --git a/src/osmo-bsc/gsm_08_08.c b/src/osmo-bsc/gsm_08_08.c
index 0d7cdf0d5..807eb8c44 100644
--- a/src/osmo-bsc/gsm_08_08.c
+++ b/src/osmo-bsc/gsm_08_08.c
@@ -24,6 +24,7 @@
 #include <osmocom/bsc/debug.h>
 #include <osmocom/bsc/paging.h>
 #include <osmocom/bsc/gsm_08_08.h>
+#include <osmocom/bsc/codec_pref.h>
 
 #include <osmocom/bsc/gsm_04_80.h>
 #include <osmocom/bsc/gsm_04_08_rr.h>
@@ -446,6 +447,7 @@ static bool complete_layer3(struct gsm_subscriber_connection *conn,
 	char *imsi = NULL;
 	struct msgb *resp;
 	enum bsc_con ret;
+	struct gsm0808_speech_codec_list scl;
 
 	/* Check the filter */
 	rc = bsc_filter_initial(msc->network->bsc_data, msc, conn, msg,
@@ -491,7 +493,12 @@ static bool complete_layer3(struct gsm_subscriber_connection *conn,
 
 	bsc_scan_bts_msg(conn, msg);
 
-	resp = gsm0808_create_layer3_2(msg, cgi_for_msc(conn->sccp.msc, conn_get_bts(conn)), NULL);
+	if (gscon_is_aoip(conn)) {
+		gen_bss_supported_codec_list(&scl, msc, conn_get_bts(conn));
+		resp = gsm0808_create_layer3_2(msg, cgi_for_msc(conn->sccp.msc, conn_get_bts(conn)), &scl);
+	} else
+		resp = gsm0808_create_layer3_2(msg, cgi_for_msc(conn->sccp.msc, conn_get_bts(conn)), NULL);
+
 	if (!resp) {
 		LOGP(DMSC, LOGL_DEBUG, "Failed to create layer3 message.\n");
 		return false;