diff --git a/asterisk/IMS_ConnectionHandler.ttcn b/asterisk/IMS_ConnectionHandler.ttcn
index b9a9852..58ca87a 100644
--- a/asterisk/IMS_ConnectionHandler.ttcn
+++ b/asterisk/IMS_ConnectionHandler.ttcn
@@ -463,6 +463,22 @@
 	}
 }
 
+/* GSMA IR.92 2.2.4 Call Establishment and Termination */
+private function f_ims_validate_INVITE_SDP(SDP_Message sdp) runs on IMS_ConnHdlr
+{
+		/* "The UE must indicate in the SDP of the initial INVITE that the audio media
+		 * is send-receive i.e. either by including the direction attribute "a=sendrecv"
+		 * or by omitting the direction attributes. */
+		if (ispresent(sdp.attributes)) {
+			if (match (sdp.attributes, superset(tr_SDP_recvonly)) or
+			    match (sdp.attributes, superset(tr_SDP_sendonly))) {
+				Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
+					log2str(g_name & ": Unexpected SDP direction attribute != sendrecv: ",
+						sdp.attributes));
+			}
+		}
+}
+
 private function f_ims_parse_security_client(Security_client security_client) runs on IMS_ConnHdlr
 {
 	var boolean found := false;
@@ -1326,6 +1342,7 @@
 
 		f_ims_validate_register_P_Access_Network_info(g_rx_sip_req, exp_present := true);
 		f_ims_validate_INVITE_Contact(g_rx_sip_req.msgHeader.contact);
+		f_ims_validate_INVITE_SDP(g_pars.subscr.cp.peer_sdp);
 
 		if (g_pars.subscr.cp.require_precondition_ext and not peer_support_precondition) {
 			Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,