diff --git a/bsc/BSC_Tests.ttcn b/bsc/BSC_Tests.ttcn
index f40b19e..aa627b7 100644
--- a/bsc/BSC_Tests.ttcn
+++ b/bsc/BSC_Tests.ttcn
@@ -1852,6 +1852,7 @@
 private function f_tc_assignment_csd(charstring id) runs on MSC_ConnHdlr {
 	var template PDU_BSSAP exp_compl := f_gen_exp_compl();
 	var PDU_BSSAP ass_cmd := f_gen_ass_req();
+	var SDP_FIELD_PayloadType pt_csd := PT_CSD;
 
 	ass_cmd.pdu.bssmap.assignmentRequest.channelType := valueof(ts_BSSMAP_IE_ChannelTypeCSD);
 	ass_cmd.pdu.bssmap.assignmentRequest.codecList := valueof(ts_BSSMAP_IE_CodecList({ts_CodecCSData}));
@@ -1859,6 +1860,11 @@
 	ass_cmd.pdu.bssmap.assignmentRequest.channelType.speechId_DataIndicator := GSM0808_DATA_RATE_TRANSP_4k8;
 
 	f_establish_fully(ass_cmd, exp_compl);
+
+	if (g_media.bts.rtp_pt != enum2int(pt_csd)) {
+		Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail, log2str("unexpected RTP payload type: ", g_media.bts.rtp_pt));
+	}
+
 	f_perform_clear();
 }
 testcase TC_assignment_csd() runs on test_CT {
diff --git a/bsc/MSC_ConnectionHandler.ttcn b/bsc/MSC_ConnectionHandler.ttcn
index b3e6af6..fa7cd84 100644
--- a/bsc/MSC_ConnectionHandler.ttcn
+++ b/bsc/MSC_ConnectionHandler.ttcn
@@ -198,6 +198,28 @@
 	return -1;
 }
 
+/* Verify that CSD CRCX/MDCX has the RSL_IE_IPAC_RTP_CSD_FMT IE, and that
+ * inside it the D value is set to RSL_IPA_RTP_CSD_TRAU_BTS. */
+private function f_ipacc_crcx_mdcx_check_rtp_pt_csd(RSL_Message rsl) runs on MSC_ConnHdlr {
+	var SDP_FIELD_PayloadType pt_csd := PT_CSD;
+	var RSL_IE_Body ie;
+
+	if (g_media.bts.rtp_pt != enum2int(pt_csd)) {
+		return;
+	}
+
+	if (f_rsl_find_ie(rsl, RSL_IE_IPAC_RTP_CSD_FMT, ie)) {
+		if (ie.ipa_rtp_csd_fmt.d != RSL_IPA_RTP_CSD_TRAU_BTS) {
+			Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
+						"Rx unexpected IPAC CRCX for CSD with RTP_CSD_FMT IE");
+		}
+		return;
+	}
+
+	Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
+				"Rx unexpected IPAC CRCX for CSD without RTP_CSD_FMT IE");
+}
+
 /* altstep for handling of IPACC media related commands. Activated by as_Media() to test
  * RSL level media handling */
 altstep as_Media_ipacc(RSL_DCHAN_PT rsl_pt := RSL, RSL_DCHAN_PT rsl_pt_ho_target := RSL1) runs on MSC_ConnHdlr {
@@ -224,6 +246,7 @@
 			g_media.bts.local_osmux_cid := omit;
 			g_media.bts.remote_osmux_cid := omit;
 		}
+		f_ipacc_crcx_mdcx_check_rtp_pt_csd(rsl);
 		rsl_pt.send(ts_RSL_IPA_CRCX_ACK(g_chan_nr, g_media.bts.conn_id,
 						f_inet_addr(g_media.bts.bts.host),
 						g_media.bts.bts.port_nr,
@@ -262,6 +285,7 @@
 			g_media.bts.local_osmux_cid := omit;
 			g_media.bts.remote_osmux_cid := omit;
 		}
+		f_ipacc_crcx_mdcx_check_rtp_pt_csd(rsl);
 		rsl_pt.send(ts_RSL_IPA_MDCX_ACK(g_chan_nr, g_media.bts.conn_id,
 						f_inet_addr(g_media.bts.peer.host),
 						g_media.bts.peer.port_nr,
diff --git a/library/MGCP_Types.ttcn b/library/MGCP_Types.ttcn
index 01d4d3a..da1b7f6 100644
--- a/library/MGCP_Types.ttcn
+++ b/library/MGCP_Types.ttcn
@@ -128,7 +128,8 @@
 		PT_GSMEFR(110),
 		PT_GSMHR(111),
 		PT_AMR(112),
-		PT_AMRWB(113)
+		PT_AMRWB(113),
+		PT_CSD(120)
 	}
 
 } with { encode "TEXT" }
diff --git a/library/RSL_Types.ttcn b/library/RSL_Types.ttcn
index fff87f2..0f03c87 100644
--- a/library/RSL_Types.ttcn
+++ b/library/RSL_Types.ttcn
@@ -945,6 +945,25 @@
 		RSL_IPA_Codec		codec
 	}
 
+	type enumerated RSL_IPA_RTP_CSD_FMT_D {
+		RSL_IPA_RTP_CSD_EXT_TRAU	('0000'B),
+		RSL_IPA_RTP_CSD_NON_TRAU	('0001'B),
+		RSL_IPA_RTP_CSD_TRAU_BTS	('0010'B),
+		RSL_IPA_RTP_CSD_IWF_FREE	('0011'B)
+	} with { variant "FIELDLENGTH(4)" }
+
+	type enumerated RSL_IPA_RTP_CSD_FMT_IR {
+		RSL_IPA_RTP_CSD_8k	('0000'B),
+		RSL_IPA_RTP_CSD_16k	('0001'B),
+		RSL_IPA_RTP_CSD_32k	('0010'B),
+		RSL_IPA_RTP_CSD_64	('0011'B)
+	} with { variant "FIELDLENGTH(4)" }
+
+	type record RSL_IE_IPA_RTP_CSD_FMT {
+		RSL_IPA_RTP_CSD_FMT_IR	ir,
+		RSL_IPA_RTP_CSD_FMT_D	d
+	}
+
 	/* 9.3.20 */
 	type enumerated RSL_IE_ReleaseMode {
 		RSL_REL_MODE_NORMAL	('00'B),
@@ -1076,6 +1095,7 @@
 		uint8_t			ipa_rtp_pt2,
 		RSL_IE_IPA_ConnectionStats ipa_stats,
 		RSL_IE_IPA_SpeechMode	ipa_speech_mode,
+		RSL_IE_IPA_RTP_CSD_FMT	ipa_rtp_csd_fmt,
 
 		RSL_IE_OSMO_TrainingSequence osmo_training_sequence,
 		RSL_IE_OSMO_RepAcchCap	rep_acch_cap,
@@ -1142,6 +1162,7 @@
 					ipa_rtp_pt2, iei = RSL_IE_IPAC_RTP_PAYLOAD2;
 					ipa_stats, iei = RSL_IE_IPAC_CONN_STAT;
 					ipa_speech_mode, iei = RSL_IE_IPAC_SPEECH_MODE;
+					ipa_rtp_csd_fmt, iei = RSL_IE_IPAC_RTP_CSD_FMT;
 
 					osmo_training_sequence, iei = RSL_IE_OSMO_TRAINING_SEQUENCE;
 					rep_acch_cap, iei = RSL_IE_OSMO_REP_ACCH_CAP;