diff --git a/asterisk/IMS_ConnectionHandler.ttcn b/asterisk/IMS_ConnectionHandler.ttcn
index 7819e62..1eae16d 100644
--- a/asterisk/IMS_ConnectionHandler.ttcn
+++ b/asterisk/IMS_ConnectionHandler.ttcn
@@ -697,9 +697,15 @@
 		contact := g_rx_sip_req.msgHeader.contact;
 		f_ims_validate_register_contact(contact);
 
-		/* Validate P-Access-Network-Info: */
+		/* Validate P-Access-Network-Info: 3GPP TS 24.229 5.1.2A.1.1
+		 * "If available to the UE (as defined in the access technology specific annexes for each access technology), the UE shall
+		 * insert a P-Access-Network-Info header field into any request for a dialog, any subsequent request (except CANCEL
+		 * requests) or response (except CANCEL responses) within a dialog or any request for a standalone method (see
+		 * subclause 7.2A.4). Insertion of the P-Access-Network-Info header field into the ACK request is optional."
+		 */
 		f_ims_validate_register_P_Access_Network_info(g_rx_sip_req, exp_present := true);
 
+
 		/* Tx 100 Tyring */
 		tx_resp := ts_SIP_Response_Trying(sip_call_id,
 					from_addr,
@@ -772,6 +778,8 @@
 		f_ConnHdlr_parse_initial_SIP_INVITE(g_rx_sip_req);
 		via := g_rx_sip_req.msgHeader.via;
 
+		f_ims_validate_register_P_Access_Network_info(g_rx_sip_req, exp_present := true);
+
 
 		/* Tx 180 Ringing */
 		tx_resp := ts_SIP_Response_Ringing(g_pars.subscr.cp.sip_call_id,