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fix send_assignment_complete(): proper SCE encoding for CSD

As stated in 3GPP TS 48.008, section 3.2.2.103, coding of the Speech
Codec Element for the CSData Codec Type differs from coding for the
actual speech codecs like FR/HR/AMR/etc.  However, osmo-bsc currently
encodes the "Speech Codec (Choosen)" IE regardless of the channel
mode, be it GSM0808_CHAN_SPEECH or GSM0808_CHAN_DATA.  This causes
failures at the establishment stage of modem-to-modem data calls.

Change-Id: I8b94c0292964f6d5f5ffa98ad8da03728f8bf6a0
Related: OS#6110, OS#4393
---
M src/osmo-bsc/assignment_fsm.c
1 file changed, 55 insertions(+), 19 deletions(-)

diff --git a/src/osmo-bsc/assignment_fsm.c b/src/osmo-bsc/assignment_fsm.c
index 9a53652..5e98a28 100644
--- a/src/osmo-bsc/assignment_fsm.c
+++ b/src/osmo-bsc/assignment_fsm.c
@@ -200,21 +200,26 @@
 		return;
 	}
 
+	if (gscon_is_aoip(conn) && bsc_chan_ind_requires_rtp_stream(conn->assignment.ch_indctr)) {
+		if (!osmo_mgcpc_ep_ci_get_crcx_info_to_sockaddr(conn->user_plane.mgw_endpoint_ci_msc,
+								&addr_local)) {
+			assignment_fail(GSM0808_CAUSE_EQUIPMENT_FAILURE,
+					"Unable to compose RTP address of MGW -> MSC");
+			return;
+		}
+		addr_local_p = &addr_local;
+	}
+
 	/* Generate rtp related fields */
-	if (bsc_chan_ind_requires_rtp_stream(conn->assignment.ch_indctr)) {
+	switch (conn->assignment.ch_indctr) {
+	case GSM0808_CHAN_SPEECH:
 		perm_spch = gsm0808_permitted_speech(lchan->type, lchan->current_ch_mode_rate.chan_mode);
 
-		if (gscon_is_aoip(conn)) {
-			if (!osmo_mgcpc_ep_ci_get_crcx_info_to_sockaddr(conn->user_plane.mgw_endpoint_ci_msc,
-									&addr_local)) {
-				assignment_fail(GSM0808_CAUSE_EQUIPMENT_FAILURE,
-						"Unable to compose RTP address of MGW -> MSC");
-				return;
-			}
-			addr_local_p = &addr_local;
-		}
+		/* below is AoIP specific logic */
+		if (!gscon_is_aoip(conn))
+			break;
 
-		if (gscon_is_aoip(conn) && conn->assignment.req.use_osmux) {
+		if (conn->assignment.req.use_osmux) {
 			if (!osmo_mgcpc_ep_ci_get_crcx_info_to_osmux_cid(conn->user_plane.mgw_endpoint_ci_msc,
 									 &osmux_cid)) {
 				assignment_fail(GSM0808_CAUSE_EQUIPMENT_FAILURE,
@@ -223,14 +228,28 @@
 			}
 		}
 
-		/* Only AoIP networks include a speech codec (chosen) in the
-		 * assignment complete message. */
-		if (gscon_is_aoip(conn)) {
-			/* Extrapolate speech codec from speech mode */
-			gsm0808_speech_codec_from_chan_type(&sc, perm_spch);
-			sc.cfg = conn->lchan->current_ch_mode_rate.s15_s0;
-			sc_ptr = ≻
-		}
+		/* Extrapolate speech codec from speech mode */
+		gsm0808_speech_codec_from_chan_type(&sc, perm_spch);
+		sc.cfg = conn->lchan->current_ch_mode_rate.s15_s0;
+		sc_ptr = ≻
+		break;
+	case GSM0808_CHAN_DATA:
+		/* below is AoIP specific logic */
+		if (!gscon_is_aoip(conn))
+			break;
+
+		/* The coding of Speech Codec Element for the CSData Codec Type
+		 * is defined in 3GPP TS 48.008 section 3.2.2.103 */
+		sc = (struct gsm0808_speech_codec) {
+			.pi = true, /* PI indicates CSDoIP support */
+			.pt = false, /* PT indicates CSDoTDM support */
+			.type = GSM0808_SCT_CSD,
+			.cfg = 0, /* R2/R3 not set (redundancy not supported) */
+		};
+		sc_ptr = ≻
+		break;
+	default:
+		break;
 	}
 
 	resp = gsm0808_create_ass_compl2(lchan->abis_ip.ass_compl.rr_cause,

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