cosmetic tweaks in msc_a_up_call_assignment_complete()neels/dev

Move the CSD check upwards, out of the middle of codecs stuff.

Improve the comments.

Change-Id: I1c13fd8aec5b43b0ccc78d80c1bee28504510051

1 files changed, 20 insertions, 15 deletions

diff --git a/src/libmsc/msc_a.c b/src/libmsc/msc_a.c
index b4776a025..b37c34f21 100644
--- a/src/libmsc/msc_a.c
+++ b/src/libmsc/msc_a.c
@@ -1461,18 +1461,32 @@ static void msc_a_up_call_assignment_complete(struct msc_a *msc_a, const struct
 
 	if (codec_if_known) {
 		const struct codec_mapping *codec_cn;
-		/* For 2G:
-		 * - The Assignment Complete has returned a specific codec (e.g. FR3 for AMR FR).
-		 * - Set this codec at the MGW endpoint facing the RAN.
-		 * - Also set this codec at the MGW endpoint facing the CN -- we require an exact match on both call
-		 *   legs.
+
+		/* Check for unexpected codec with CSD */
+		if (cc_trans->bearer_cap.transfer == GSM48_BCAP_ITCAP_UNR_DIG_INF &&
+		    codec_if_known->type != GSM0808_SCT_CSD) {
+			LOG_TRANS(cc_trans, LOGL_ERROR, "Unexpected codec in Assignment Complete for CSD: %s\n",
+				  gsm0808_speech_codec_type_name(codec_if_known->type));
+			call_leg_release(msc_a->cc.call_leg);
+			return;
+		}
+
+		/*
+		 * The Assignment Complete has returned a specific codec in codec_if_known.
+		 *
+		 * For 2G:
+		 * - Set this codec at the MGW endpoint on both the RAN and the CN sides.
 		 *   - TODO: be aware of transcoding that the MGW is capable of, e.g. AMR octet-aligned to AMR
 		 *     bandwidth-efficient...
 		 *
+		 *   RAN <--CODEC--> MGW <--CODEC--> CN
+		 *
 		 * For 3G:
 		 * - ran_infra->force_mgw_codecs_to_ran sets VND.3GPP.IUFP as single codec at the MGW towards RAN.
-		 * - ran_msg_iu.c always returns FR3 (AMR FR) for the assigned codec. Set that at the MGW towards CN.
+		 * - Iu always returns FR3 (AMR FR) in codec_if_known. Set that at the MGW towards CN.
 		 * - So the MGW decapsulates IuUP <-> AMR
+		 *
+		 *   RAN <--IuFP--> MGW <--CODEC=AMR--> CN
 		 */
 		codec_cn = codec_mapping_by_gsm0808_speech_codec_type(codec_if_known->type);
 		/* TODO: use codec_mapping_by_gsm0808_speech_codec() to also match on codec_if_known->cfg */
@@ -1483,15 +1497,6 @@ static void msc_a_up_call_assignment_complete(struct msc_a *msc_a, const struct
 			return;
 		}
 
-		/* Check for unexpected codec with CSD */
-		if (cc_trans->bearer_cap.transfer == GSM48_BCAP_ITCAP_UNR_DIG_INF &&
-		    codec_if_known->type != GSM0808_SCT_CSD) {
-			LOG_TRANS(cc_trans, LOGL_ERROR, "Unexpected codec in Assignment Complete for CSD: %s\n",
-				  gsm0808_speech_codec_type_name(codec_if_known->type));
-			call_leg_release(msc_a->cc.call_leg);
-			return;
-		}
-
 		/* Update RAN-side endpoint CI from Assignment result -- unless it is forced by the ran_infra, in which
 		 * case it remains unchanged as passed to the earlier call of call_leg_ensure_ci(). */
 		if (msc_a->c.ran->force_mgw_codecs_to_ran.count == 0)