/* Component implementing a IMS server towards Asterisk's IMS UE
 * (C) 2024 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
 * Author: Pau Espin Pedrol <pespin@sysmocom.de>
 * All rights reserved.
 *
 * Released under the terms of GNU General Public License, Version 2 or
 * (at your option) any later version.
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */
module IMS_ConnectionHandler {

import from TCCEncoding_Functions all;
import from TCCOpenSecurity_Functions all;
import from General_Types all;
import from Osmocom_Types all;
import from Native_Functions all;
import from Misc_Helpers all;

/* the PIPE asp port allows us to interact with ip xfrm via stdin/stdout */
import from PIPEasp_PortType all;
import from PIPEasp_Types all;
import from PIPEasp_Templates all;

import from SDP_Types all;
import from SDP_Templates all;

import from SIP_Emulation all;
import from SIPmsg_Types all;
import from SIP_Templates all;


modulepar {
	charstring mp_ipsec_setup_script_path := "./IMS_ipsec_setup.sh";
}

const integer c_def_expires := 600000; /* 3GPP TS 24.229 5.1.1.2.1 e) */
const charstring c_sip_server_name := "osmo-ttcn3-hacks/0.23";


type port IMSCoord_PT message
{
	inout charstring;
} with { extension "internal" };

const charstring IMS_COORD_CMD_REGISTERED := "IMS_COORD_CMD_REGISTERED";
const charstring IMS_COORD_CMD_START := "IMS_COORD_CMD_START";
const charstring IMS_COORD_CMD_CALL_ESTABLISHED := "IMS_COORD_CMD_CALL_ESTABLISHED";
const charstring IMS_COORD_CMD_HANGUP := "IMS_COORD_CMD_HANGUP";
const charstring IMS_COORD_CMD_CALL_TRYING := "IMS_COORD_CMD_CALL_TRYING";
const charstring IMS_COORD_CMD_CALL_SESSION_PROGRESS := "IMS_COORD_CMD_CALL_SESSION_PROGRESS";

type component IMS_ConnHdlr extends SIP_ConnHdlr {
	var charstring g_name;
	var IMS_ConnHdlrPars g_pars;
	timer g_Tguard;
	var PDU_SIP_Request g_rx_sip_req;
	var PDU_SIP_Response g_rx_sip_resp;

	port IMSCoord_PT COORD;
	port PIPEasp_PT PIPE;
}
type record of IMS_ConnHdlr IMS_ConnHdlrList;

type record IMS_AuthVector {
	OCT16 rand,
	OCT16 autn,
	OCT8 res,
	OCT16 ck,
	OCT16 ik,
	OCT14 auts
}

type record IMS_ConnHdlrSubscrPars {
	charstring remote_sip_host optional,
	uint16_t remote_sip_port optional,
	charstring imsi,
	charstring imei,
	charstring display_name,
	charstring password,
	charstring msisdn,
	boolean support_video,
	boolean support_smsip,
	/* Expected User-Location-Info in P-Access-Network-Info */
	charstring uli_str,
	IMS_AuthVector auth,
	charstring ipsec_auth_key,
	integer ipsec_local_spi_c,
	integer ipsec_local_spi_s,
	integer ipsec_remote_spi_c optional,
	integer ipsec_remote_spi_s optional,
	uint16_t ipsec_remote_port_c optional,
	uint16_t ipsec_remote_port_s optional,
	SipAddr registrar_sip_record,
	CallidString registrar_sip_call_id,
	integer registrar_sip_seq_nr,
	integer registrar_expires,
	SipUrl local_sip_url_ext,
	SipAddr local_sip_record,
	Contact registered_contact optional,
	P_Associated_Uri p_associated_uri,
	IMS_CallPars cp optional
}
type record of IMS_ConnHdlrSubscrPars IMS_ConnHdlrSubscrParsList;


type record IMS_ConnHdlrPars {
	float t_guard,
	charstring realm,
	charstring local_sip_host,
	uint16_t local_sip_port,
	SipUrl registrar_sip_req_uri,
	Via local_via,
	Server server_name,
	IMS_ConnHdlrSubscrPars subscr optional
}
type record of IMS_ConnHdlrPars IMS_ConnHdlrParsList;

type record IMS_CallParsMO {
	/* Whether to COORD.send(IMS_COORD_CMD_CALL_TRYING) when receiving an INVITE from UE. */
	boolean tx_coord_cmd_invite_trying
}
template (value) IMS_CallParsMO t_IMS_CallParsMO := {
	tx_coord_cmd_invite_trying := false
}

type record IMS_CallParsMT {
	/* Whether to COORD.send(IMS_COORD_CMD_CALL_SESSION_PROGRESS) when receiving an 183 Session Progress from UE. */
	boolean tx_coord_cmd_session_progress
}
template (value) IMS_CallParsMT t_IMS_CallParsMT := {
	tx_coord_cmd_session_progress := false
}

type record IMS_CallPars {
	SipAddr calling optional,
	SipAddr called optional,

	From from_addr optional,
	To to_addr optional,

	CallidString sip_call_id,
	integer sip_seq_nr,
	charstring sip_body optional,

	charstring local_rtp_addr,
	uint16_t local_rtp_port,

	boolean support_precondition_ext,
	boolean require_precondition_ext,
	SDP_Message peer_sdp optional,
	IMS_CallParsMO mo,
	IMS_CallParsMT mt
}

template (value) IMS_CallPars t_IMS_CallPars(charstring local_rtp_addr,
					     uint16_t local_rtp_port := 0,
					     template (omit) SipAddr calling := omit,
					     template (omit) SipAddr called := omit) := {
	calling := calling,
	called := called,
	from_addr := omit,
	to_addr := omit,
	sip_call_id := hex2str(f_rnd_hexstring(15)),
	sip_seq_nr := f_sip_rand_seq_nr(),
	sip_body := omit,
	local_rtp_addr := local_rtp_addr,
	local_rtp_port := local_rtp_port,
	support_precondition_ext := true,
	require_precondition_ext := false,
	peer_sdp := omit,
	mo := t_IMS_CallParsMO,
	mt := t_IMS_CallParsMT
}

template (value) IMS_ConnHdlrSubscrPars t_IMS_SubscrPars(charstring local_sip_host,
						   uint16_t local_sip_port,
						   charstring domain,
						   charstring imsi,
						   charstring imei,
						   charstring msisdn := "90828",
						   charstring display_name := "Anonymous",
						   charstring password := "secret",
						   template (omit) IMS_CallPars cp := omit) := {
	remote_sip_host := omit,
	remote_sip_port := omit,
	imsi := imsi,
	imei := imei,
	display_name := f_sip_str_quote(display_name),
	password := password,
	msisdn := msisdn,
	support_video := false,
	support_smsip := false,
	uli_str := "2380100010000101",
	auth := {
		/* The Nonce field is the Base64 encoded version of the RAND value and concatenated with the AUTN: */
		rand := 'd5d5de2bce418d7865ed7fa6956618a2'O,
		autn := 'd42e61db5f15800067393a5b7691a227'O,
		res := '6f2556bbe4366ab1'O,
		ck := '0b389d08c833991734936bec55cac800'O,
		ik := '17141862125bd30c81c4224391a0909a'O,
		/* NOTE: AUTS value randomly crafted. It's fine since it's just forwarded
		 *       AMI -> asterisk -> IMS and we blindly match and accept it. */
		auts := 'd42e61db5f15800067393a5b7691'O
	},
	ipsec_auth_key := "0x17141862125bd30c81c4224391a0909a00000000",
	ipsec_local_spi_c := 4142,
	ipsec_local_spi_s := 4143,
	ipsec_remote_spi_c := omit,
	ipsec_remote_spi_s := omit,
	ipsec_remote_port_c := omit,
	ipsec_remote_port_s := omit,
	registrar_sip_record := ts_SipAddr(ts_HostPort(domain),
					   ts_UserInfo(imsi),
					   f_sip_str_quote(display_name)),
	registrar_sip_call_id := hex2str(f_rnd_hexstring(15)) & "@" & domain,
	registrar_sip_seq_nr := f_sip_rand_seq_nr(),
	registrar_expires := c_def_expires,
	local_sip_url_ext := ts_SipUrl(ts_HostPort(domain, local_sip_port),
				       ts_UserInfo(imsi)),
	local_sip_record := ts_SipAddr(ts_HostPort(domain),
				       ts_UserInfo(imsi)),
	registered_contact := omit,
	p_associated_uri := ts_P_Associated_Uri({}),
	cp := cp
}

template (value) IMS_ConnHdlrPars t_IMS_Pars(charstring local_sip_host,
					uint16_t local_sip_port,
					charstring domain,
					charstring imsi,
					charstring imei,
					template (omit) IMS_CallPars cp := omit) := {
	t_guard := 60.0,
	realm := domain,
	local_sip_host := local_sip_host,
	local_sip_port := local_sip_port,
	registrar_sip_req_uri := valueof(ts_SipUrlHost(domain)),
	local_via := ts_Via_from(ts_HostPort(local_sip_host, local_sip_port)),
	server_name := valueof(ts_Server({c_sip_server_name})),
	subscr := t_IMS_SubscrPars(local_sip_host, local_sip_port,
				   domain := domain, imsi := imsi,
				   imei := imei, cp := cp)
}

private altstep as_Tguard() runs on IMS_ConnHdlr {
	[] g_Tguard.timeout {
		setverdict(fail, "Tguard timeout");
		mtc.stop;
	}
}

type function ims_void_fn(charstring id) runs on IMS_ConnHdlr;
function f_ims_handler_init(ims_void_fn fn, charstring id, IMS_ConnHdlrPars pars)
runs on IMS_ConnHdlr {
	g_name := id;
	g_pars := pars;
	g_Tguard.start(pars.t_guard);
	activate(as_Tguard());

	/* call the user-supied test case function */
	fn.apply(id);
}

altstep as_SIP_fail_req(charstring exp_msg_str := "") runs on IMS_ConnHdlr
{
	var PDU_SIP_Request sip_req;
	[] SIP.receive(PDU_SIP_Request:?) -> value sip_req {
		Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
					log2str(g_name & ": Received unexpected SIP Req message := ", sip_req, "\nvs exp := ", exp_msg_str));
	}
}

altstep as_SIP_fail_resp(charstring exp_msg_str := "") runs on IMS_ConnHdlr
{
	var PDU_SIP_Response sip_resp;
	[] SIP.receive(PDU_SIP_Response:?) -> value sip_resp {
		Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
					log2str(g_name & ": Received unexpected SIP Resp message := ", sip_resp, "\nvs exp := ", exp_msg_str));
	}
}

altstep as_SIP_expect_resp(template (present) PDU_SIP_Response sip_expect, boolean fail_others := true) runs on IMS_ConnHdlr
{
	var charstring sip_expect_str := log2str(sip_expect);
	[] SIP.receive(sip_expect) -> value g_rx_sip_resp;
	[fail_others] as_SIP_fail_resp(sip_expect_str);
	[fail_others] as_SIP_fail_req(sip_expect_str);
}

altstep as_SIP_ignore_resp(template PDU_SIP_Response sip_expect := ?) runs on IMS_ConnHdlr
{
	[] SIP.receive(sip_expect) -> value g_rx_sip_resp {
		log("Ignoring ", g_rx_sip_resp);
		repeat;
	}
}

private function f_nonce_from_rand_autn(octetstring rand, octetstring autn) return charstring {
	var octetstring concat := rand & autn;
	var charstring nonce := enc_MIME_Base64(concat);
	log("rand=", rand, " & autn=",autn, " => nonce=", nonce);
	return nonce;
}

/* HTTP Digest Authentication Using AKA (AKAv1-MD5): RFC 3310 */
function f_tr_Authorization_AKAv1MD5(WwwAuthenticate www_authenticate,
				     charstring username,
				     charstring uri)
return template (present) Authorization {
	var CommaParam_List digestCln;
	var template (present) Authorization authorization;
	var template (present) Credentials cred;
	var template (omit) GenericParam rx_param;

	digestCln := www_authenticate.challenge[0].digestCln;

	var charstring algorithm := f_sip_param_get_value_present_or_fail(digestCln, "algorithm");
	var charstring realm := f_sip_param_get_value_present_or_fail(digestCln, "realm");
	var charstring nonce := f_sip_param_get_value_present_or_fail(digestCln, "nonce");

	var template (present) CommaParam_List digestResponse := superset(
		tr_Param("username", f_sip_str_quote(username)),
		tr_Param("realm", f_sip_str_quote(realm)),
		tr_Param("nonce", f_sip_str_quote(nonce)),
		tr_Param("uri", f_sip_str_quote(uri)),
		tr_Param("response", ?),
		tr_Param("algorithm", algorithm),
		tr_Param("qop", "auth"),
		tr_Param("cnonce", ?),
		tr_Param("nc", ?)
	);
	cred := tr_Credentials_DigestResponse(digestResponse);
	authorization := tr_Authorization(cred);
	return authorization;
}

private function f_ims_validate_Authorization_AKAv1MD5_Response(Authorization authorization, charstring method)
runs on IMS_ConnHdlr {
	f_sip_digest_validate_Authorization_AKAv1MD5(authorization, method, g_pars.subscr.auth.res);
}

/* GSMA IR-92 2.2.1 SIP Registration Procedure */
private function f_ims_validate_register_contact(Contact rx_contact) runs on IMS_ConnHdlr
{
	/* IMS contact shows up like this:
	* Contact: <sip:8adf9f3d-9342-4060-aa4f-a909f37fd6f6@192.168.101.2:5060>;+g.3gpp.accesstype="cellular2";video;audio;+g.3gpp.smsip;+g.3gpp.nw-init-ussi;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel";+sip.instance="<urn:gsma:imei:35589811-338445-0>"
	*/
	if (ischosen(rx_contact.contactBody.wildcard)) {
		Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
			log2str(g_name & ": Received unexpected Contact wildcard := ", rx_contact));
	}
	var ContactAddress_List caddrs := rx_contact.contactBody.contactAddresses;
	if (lengthof(caddrs) == 0) {
		Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
				log2str(g_name & ": Received unexpected empty Contact Address list"));
	}
	for (var integer i := 0; i < lengthof(caddrs); i := i + 1) {
		var ContactAddress caddr := caddrs[i];
		var template (omit) GenericParam param_tpl;
		var boolean rx_supported;
		if (not ispresent(caddr.contactParams)) {
			Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
				log2str(g_name & ": Received unexpected empty Contact attributes (omit)"));
		}
		f_sip_param_match_value_or_fail(caddr.contactParams, "+g.3gpp.icsi-ref", "\"urn\\%3Aurn-7\\%3A3gpp-service.ims.icsi.mmtel\"");
		f_sip_param_match_value_or_fail(caddr.contactParams, "+sip.instance", "\"<urn:gsma:imei:" & g_pars.subscr.imei & ">\"");
		f_sip_param_match_value_or_fail(caddr.contactParams, "audio", omit);

		/* Check video support */
		param_tpl := f_sip_param_find(caddr.contactParams, "video");
		rx_supported := not istemplatekind(param_tpl, "omit");
		if (rx_supported) {
			/* This attribute never has a value: */
			if (not istemplatekind(param_tpl.paramValue, "omit")) {
				Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
					log2str(g_name & ": Received Contact with 'video' attribute containing a value := ", rx_contact));
			}
			if (not g_pars.subscr.support_video) {
				Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
					log2str(g_name & ": Received Contact with unexpected 'video' attribute := ", rx_contact));
			}
		} else if (g_pars.subscr.support_video) {
			Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
				log2str(g_name & ": Received Contact with missing 'video' attribute := ", rx_contact));
		}

		/* Check smsip support */
		param_tpl := f_sip_param_find(caddr.contactParams, "+g.3gpp.smsip");
		rx_supported := not istemplatekind(param_tpl, "omit");
		if (rx_supported) {
			/* This attribute never has a value: */
			if (not istemplatekind(param_tpl.paramValue, "omit")) {
				Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
					log2str(g_name & ": Received Contact with '+g.3gpp.smsip' attribute containing a value := ", rx_contact));
			}
			if (not g_pars.subscr.support_smsip) {
				Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
					log2str(g_name & ": Received Contact with unexpected '+g.3gpp.smsip' attribute := ", rx_contact));
			}
		} else if (g_pars.subscr.support_smsip) {
			Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
				log2str(g_name & ": Received Contact with missing '+g.3gpp.smsip' attribute := ", rx_contact));
		}
	}

}

/* Validate P-Access-Network-Info: RFC7315 6.4 */
private function f_ims_validate_register_P_Access_Network_info(PDU_SIP_Request req,
							       boolean exp_present := true) runs on IMS_ConnHdlr

{
	if (not exp_present) {
		if (ispresent(g_rx_sip_req.msgHeader.p_access_network_info)) {
			Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
						log2str(g_name & ": Received unexpected [rfc7315 6.4] P-Access-Info := ",
						g_rx_sip_req.msgHeader.p_access_network_info));
		}
		return;
	}

	/* exp_present: */
	var template (present) P_Access_Network_Info expl_tmpl :=
		tr_P_Access_Network_Info({ tr_Access_net_spec_EUTRAN(g_pars.subscr.uli_str) });

	if (not ispresent(g_rx_sip_req.msgHeader.p_access_network_info)) {
		Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
					log2str(g_name & ": Received no P-Access-Info vs exp := ",
					expl_tmpl));
	}
	if (not match(g_rx_sip_req.msgHeader.p_access_network_info, expl_tmpl)) {
				Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
							log2str(g_name & ": Received unexpected P-Access-Info := ",
							g_rx_sip_req.msgHeader.p_access_network_info,
							"\nvs exp := ", expl_tmpl));
	}
}

/* GSMA IR.92 2.2.4 Call Establishment and Termination */
private function f_ims_validate_INVITE_Contact(Contact rx_contact) runs on IMS_ConnHdlr
{
	/* INVITE Contact header shows up like this:
	* Contact: <sip:e05d8e82-8565-47b5-aca5-5f6b9164b074@192.168.101.2:44823>;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel";audio;+g.3gpp.mid-call;+g.3gpp.srvcc-alerting;+g.3gpp.ps2cs-srvcc-orig-pre-alerting
	*/
	if (ischosen(rx_contact.contactBody.wildcard)) {
		Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
			log2str(g_name & ": Received unexpected Contact wildcard := ", rx_contact));
	}
	var ContactAddress_List caddrs := rx_contact.contactBody.contactAddresses;
	if (lengthof(caddrs) == 0) {
		Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
				log2str(g_name & ": Received unexpected empty Contact Address list"));
	}
	for (var integer i := 0; i < lengthof(caddrs); i := i + 1) {
		var ContactAddress caddr := caddrs[i];
		if (not ispresent(caddr.contactParams)) {
			Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
				log2str(g_name & ": Received unexpected empty Contact attributes (omit)"));
		}
		/* GSMA FCM.01 3.2.3.3: "The INVITE request contains Within the Contact header [...] the IMS
		 * Communication Service Identifier's (ICSI) for IMS Multimedia Telephony" */
		f_sip_param_match_value_or_fail(caddr.contactParams, "+g.3gpp.icsi-ref", "\"urn\\%3Aurn-7\\%3A3gpp-service.ims.icsi.mmtel\"");
		/* "The UE must include the audio media feature tag, as defined in IETF RFC 3840,
		 * in the Contact header field of the SIP INVITE request, and in the Contact header
		 * field of the SIP response to the SIP INVITE request" */
		f_sip_param_match_value_or_fail(caddr.contactParams, "audio", omit);
	}
}

/* Validate P-Preferred-Service: GSMA FCM.01 3.2.3.3 */
private function f_ims_validate_invite_P_Preferred_Service(PDU_SIP_Request req,
							   boolean exp_present := true) runs on IMS_ConnHdlr

{
	if (not exp_present) {
		if (ispresent(g_rx_sip_req.msgHeader.p_preferred_service)) {
			Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
						log2str(g_name & ": Received unexpected [rfc6050] P-Preferred-Service := ",
						g_rx_sip_req.msgHeader.p_preferred_service));
		}
		return;
	}

	/* exp_present: */
	var template (present) P_Preferred_Service expl_tmpl :=
		tr_P_Preferred_Service({ "urn:urn-7:3gpp-service.ims.icsi.mmtel" });

	if (not ispresent(g_rx_sip_req.msgHeader.p_preferred_service)) {
		Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
					log2str(g_name & ": Received no P-Access-Info vs exp := ",
					expl_tmpl));
	}
	if (not match(g_rx_sip_req.msgHeader.p_preferred_service, expl_tmpl)) {
				Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
							log2str(g_name & ": Received unexpected P-Preferred-Service := ",
							g_rx_sip_req.msgHeader.p_preferred_service,
							"\nvs exp := ", expl_tmpl));
	}
}

/* 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;
	for (var integer i := 0; i < lengthof(security_client.sec_mechanism_list); i := i + 1) {
		var Security_mechanism sec_mec := security_client.sec_mechanism_list[i];
		if (sec_mec.mechanism_name != "ipsec-3gpp") {
			log("Skipping Security Mechansim: ", sec_mec.mechanism_name);
			continue;
		}
		var SemicolonParam_List sec_pars := sec_mec.mechanism_params;
		var charstring par_val;
		par_val := f_sip_param_get_value_present_or_fail(sec_pars, "alg");
		if (par_val != "hmac-sha-1-96") {
			log("Skipping Security Mechansim Algo: ", par_val);
			continue;
		}
		par_val := f_sip_param_get_value_present_or_fail(sec_pars, "spi-c");
		g_pars.subscr.ipsec_remote_spi_c := str2int(par_val);
		par_val := f_sip_param_get_value_present_or_fail(sec_pars, "spi-s");
		g_pars.subscr.ipsec_remote_spi_s := str2int(par_val);
		par_val := f_sip_param_get_value_present_or_fail(sec_pars, "port-c");
		g_pars.subscr.ipsec_remote_port_c := str2int(par_val);
		par_val := f_sip_param_get_value_present_or_fail(sec_pars, "port-s");
		g_pars.subscr.ipsec_remote_port_s := str2int(par_val);
		found := true;
		break;
	}

	if (not found) {
		Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
					log2str(g_name & "alg=hmac-sha-1-96 not found: ", security_client));
	}

	log("ipsec: remote_spi_c=", g_pars.subscr.ipsec_remote_spi_c, " remote_spi_s=", g_pars.subscr.ipsec_remote_spi_s,
	    "local_spi_c=", g_pars.subscr.ipsec_local_spi_c, " local_spi_s=", g_pars.subscr.ipsec_local_spi_s);
}

private function f_ims_parse_register_contact(Contact contact) runs on IMS_ConnHdlr
{
	var HostPort hp := valueof(contact.contactBody.contactAddresses[0].addressField.nameAddr.addrSpec.hostPort);

	g_pars.subscr.remote_sip_host := hp.host;
	if (ispresent(hp.portField)) {
		g_pars.subscr.remote_sip_port := hp.portField;
	} else {
		g_pars.subscr.remote_sip_port := 5060;
	}
}

private function f_IMS_exec_sync(charstring cmdline, template (present) integer rc := 0)
		runs on IMS_ConnHdlr return ASP_PResult {
	var ASP_PResult res;

	map(self:PIPE, system:PIPE);
	res := f_PIPEasp_exec_sync_PResult(PIPE, cmdline, tr_PResult(?, ?, rc));
	unmap(self:PIPE, system:PIPE);

	return res;
}

private function f_ims_setup_ipsec() runs on IMS_ConnHdlr
{
	var ASP_PResult res;

	var charstring cmd := mp_ipsec_setup_script_path & " " &
		g_pars.local_sip_host & " " &
		int2str(g_pars.local_sip_port) & " " & int2str(g_pars.subscr.ipsec_local_spi_c) & " " &
		int2str(g_pars.local_sip_port) & " " & int2str(g_pars.subscr.ipsec_local_spi_s) & " " &
		g_pars.subscr.remote_sip_host & " " &
		int2str(g_pars.subscr.ipsec_remote_port_c) & " " & int2str(g_pars.subscr.ipsec_remote_spi_c) & " " &
		int2str(g_pars.subscr.ipsec_remote_port_s) & " " & int2str(g_pars.subscr.ipsec_remote_spi_s) & " " &
		g_pars.subscr.ipsec_auth_key;

	res := f_IMS_exec_sync(cmd);

	/* Debug applied rules: */
	/*
	res := f_IMS_exec_sync("ip xfrm state");
	log("ip-xfrm-state Result-Stdout: " & res.stdout);

	res := f_IMS_exec_sync("ip xfrm policy");
	log("ip-xfrm-policy Result-Stdout: " & res.stdout);
	*/
}

private function f_tr_Via_response(Via via_req) return template (present) Via {
	template (present) SemicolonParam_List via_resp_params := ?;

	/*via_resp_params := {
		{ id := "rport", paramValue := int2str(g_pars.subscr.remote_sip_port.subscr.remote_sip_port) },
		{ id := "received", paramValue := g_pars.subscr.remote_sip_host }
	}; */
	return 	tr_Via_from(via_req.viaBody[0].sentBy,
			    via_req.viaBody[0].sentProtocol.transport,
			    via_resp_params);
}

private function f_tr_From(template (value) SipAddr from_req) return template (present) SipAddr {
	return tr_SipAddr_from_val(from_req);
}

private altstep as_SIP_expect_req(template (present) PDU_SIP_Request sip_expect, boolean fail_others := true) runs on IMS_ConnHdlr
{
	var charstring sip_expect_str := log2str(sip_expect);
	[] SIP.receive(sip_expect) -> value g_rx_sip_req;
	[fail_others] as_SIP_fail_req(sip_expect_str);
	[fail_others] as_SIP_fail_resp(sip_expect_str);
}

type enumerated IMS_gen_sdp_state {
	IMS_GEN_SDP_None,
	IMS_GEN_SDP_MO_INVITE,
	IMS_GEN_SDP_MO_UPDATE,
	IMS_GEN_SDP_MT_Session_Progress,
	IMS_GEN_SDP_MT_UPDATE_200OK
}

private function f_gen_sdp(IMS_gen_sdp_state st := IMS_GEN_SDP_None) runs on IMS_ConnHdlr return charstring {
	var charstring sdp :=
		"v=0\r\n" &
		"o=0502 2390 1824 IN IP4 " & g_pars.subscr.cp.local_rtp_addr & "\r\n" &
		"s=Talk\r\n" &
		"c=IN IP4 " & g_pars.subscr.cp.local_rtp_addr & "\r\n" &
		"t=0 0\r\n" &
		"a=rtcp-xr:rcvr-rtt=all:10000 stat-summary=loss,dup,jitt,TTL voip-metrics\r\n" &
		"a=record:off\r\n" &
		"m=audio " & int2str(g_pars.subscr.cp.local_rtp_port) & " RTP/AVP 8 96 97 98 0 18 99 100 101\r\n" &
		"a=rtpmap:8 PCMA/8000\r\n" &
		"a=rtpmap:96 opus/48000/2\r\n" &
		"a=fmtp:96 useinbandfec=1\r\n" &
		"a=rtpmap:97 speex/16000\r\n" &
		"a=fmtp:97 vbr=on\r\n" &
		"a=rtpmap:98 speex/8000\r\n" &
		"a=fmtp:98 vbr=on\r\n" &
		"a=fmtp:18 annexb=yes\r\n" &
		"a=rtpmap:99 telephone-event/48000\r\n" &
		"a=rtpmap:100 telephone-event/16000\r\n" &
		"a=rtpmap:101 telephone-event/8000\r\n" &
		"a=rtcp:" & int2str(g_pars.subscr.cp.local_rtp_port + 1) & "\r\n" &
		"a=rtcp-fb:* trr-int 1000\r\n" &
		"a=rtcp-fb:* ccm tmmbr\r\n";
	select (st) {
	case (IMS_GEN_SDP_None) {
	}
	case (IMS_GEN_SDP_MO_INVITE) {
		sdp := sdp &
			"a=curr:qos local none\r\n" &
			"a=curr:qos remote none\r\n" &
			"a=des:qos mandatory local sendrecv\r\n" &
			"a=des:qos optional remote sendrecv\r\n";
	}
	case (IMS_GEN_SDP_MO_UPDATE) {
		sdp := sdp &
			"a=curr:qos local sendrecv\r\n" &
			"a=curr:qos remote none\r\n" &
			"a=des:qos mandatory local sendrecv\r\n" &
			"a=des:qos mandatory remote sendrecv\r\n";
	}
	case (IMS_GEN_SDP_MT_Session_Progress) {
		sdp := sdp &
			"a=curr:qos local none\r\n" &
			"a=curr:qos remote none\r\n" &
			"a=des:qos mandatory local sendrecv\r\n" &
			"a=des:qos mandatory remote sendrecv\r\n" &
			"a=conf:qos remote sendrecv\r\n";
	}
	case (IMS_GEN_SDP_MT_UPDATE_200OK) {
		sdp := sdp &
			"a=curr:qos local sendrecv\r\n" &
			"a=curr:qos remote sendrecv\r\n" &
			"a=des:qos mandatory local sendrecv\r\n" &
			"a=des:qos mandatory remote sendrecv\r\n";
	}
	}
	return sdp;
}

private function f_gen_Security_server() runs on IMS_ConnHdlr return Security_server {
		var template (value) Security_server security_server;
		/* Security-Server: ipsec-3gpp;q=0.1;prot=esp;mod=trans;spi-c=4096;spi-s=4097;port-c=5104;port-s=6104;alg=hmac-sha-1-96;ealg=null */
		var template (value) SemicolonParam_List sec_params := {
			ts_Param("q", "0.1"),
			ts_Param("prot", "esp"),
			ts_Param("mod", "trans"),
			ts_Param("spi-c", int2str(g_pars.subscr.ipsec_local_spi_c)),
			ts_Param("spi-s", int2str(g_pars.subscr.ipsec_local_spi_s)),
			ts_Param("port-c", int2str(g_pars.local_sip_port)),
			ts_Param("port-s", int2str(g_pars.local_sip_port)),
			ts_Param("alg", "hmac-sha-1-96"),
			ts_Param("ealg", "null")
		};
		security_server := ts_Security_server({
			ts_Security_mechanism("ipsec-3gpp", sec_params)
		});
		return valueof(security_server);
}

private function f_gen_WwwAuthenticate() runs on IMS_ConnHdlr return WwwAuthenticate {
	var template (value) WwwAuthenticate wwwAuthenticate;
	var template (value) CommaParam_List digestCln;
	digestCln := {
		ts_Param("realm", f_sip_str_quote(g_pars.realm)),
		ts_Param("qop", f_sip_str_quote("auth")),
		ts_Param("algorithm", "AKAv1-MD5"),
		ts_Param("nonce", f_sip_str_quote(f_nonce_from_rand_autn(g_pars.subscr.auth.rand,
									 g_pars.subscr.auth.autn)))
		/* "opaque not needed in IMS "*/
	};
	wwwAuthenticate := ts_WwwAuthenticate( { ts_Challenge_digestCln(digestCln) } );
	return valueof(wwwAuthenticate);
}

type enumerated IMS_register_early_return {
	IMS_REG_EARLY_RET_BEFORE_None,
	IMS_REG_EARLY_RET_BEFORE_Initial_100Trying,
	IMS_REG_EARLY_RET_BEFORE_Initial_401Unauthorized,
	IMS_REG_EARLY_RET_BEFORE_Resync_401Unauthorized,
	IMS_REG_EARLY_RET_BEFORE_Protected_100Trying,
	IMS_REG_EARLY_RET_BEFORE_Protected_200OK
}

/* Peer is issuing 1st register, accept it: */
altstep as_IMS_register(boolean exp_auth_resync := false,
			IMS_register_early_return early_ret := IMS_REG_EARLY_RET_BEFORE_None,
			boolean fail_others := true) runs on IMS_ConnHdlr
{
	var template (present) PDU_SIP_Request exp_req :=
		tr_SIP_REGISTER(g_pars.registrar_sip_req_uri,
				?,
				tr_From(),
				tr_To(),
				tr_Via_from(?),
				expires := tr_Expires(int2str(c_def_expires)),
				require := tr_Require(superset("sec-agree")),
				security_client := tr_Security_client(superset(tr_Security_mechanism("ipsec-3gpp",
												     superset(tr_Param("alg","hmac-sha-1-96"))))),
				supported := tr_Supported(superset("path", "sec-agree")));
	var charstring sip_expect_str := log2str(exp_req);

	[] SIP.receive(exp_req) -> value g_rx_sip_req {
		var template (value) PDU_SIP_Response tx_resp;
		var Via via;
		var CallidString sip_call_id;
		var template (value) From from_addr;
		var template (value) To to_addr;
		var WwwAuthenticate wwwAuthenticate;
		var Security_server security_server;
		var template (value) Require require := ts_Require({"sec-agree"});
		var template (value) Supported supported := ts_Supported({"sec-agree"});
		var integer sip_seq_nr;

		if (early_ret == IMS_REG_EARLY_RET_BEFORE_Initial_100Trying) {
			return; /* Done */
		}

		sip_call_id := g_rx_sip_req.msgHeader.callId.callid;
		via := g_rx_sip_req.msgHeader.via;
		via.viaBody[0].viaParams := f_sip_param_set(via.viaBody[0].viaParams, "rport", "1234"); /* TODO: set remote src port of the REGISTER */
		from_addr := g_rx_sip_req.msgHeader.fromField;
		to_addr := g_rx_sip_req.msgHeader.toField;
		sip_seq_nr := g_rx_sip_req.msgHeader.cSeq.seqNumber;

		/* Tx 100 Tyring */
		tx_resp := ts_SIP_Response_Trying(sip_call_id,
					from_addr,
					to_addr,
					via,
					sip_seq_nr,
					"REGISTER",
					allow := omit,
					server := g_pars.server_name,
					userAgent := omit);
		SIP.send(tx_resp);

		/* Validate P-Access-Network-Info: rfc7315 6.4:
		 * "3GPP will use the P-Access-Network-Info header field to
		 * carry relatively sensitive information like the cell ID.  Therefore,
		 * the information MUST NOT be sent outside of the 3GPP domain.""
		 * [...] "the sensitive information carried in the
		 * P-Access-Network-Info header field MUST NOT be sent in any initial
		 * unauthenticated and unprotected requests (e.g., REGISTER)."
		 */
		f_ims_validate_register_P_Access_Network_info(g_rx_sip_req, exp_present := false);

		f_ims_validate_register_contact(g_rx_sip_req.msgHeader.contact);
		f_ims_parse_register_contact(g_rx_sip_req.msgHeader.contact);
		f_ims_parse_security_client(g_rx_sip_req.msgHeader.security_client);

		if (early_ret == IMS_REG_EARLY_RET_BEFORE_Initial_401Unauthorized) {
			return; /* Done */
		}

		if (not exp_auth_resync) {
			/* Delay ipsec setup in ip xfrm, since there will be another
			* 1st REGISTER with potentially new ports coming in later. */
			f_ims_setup_ipsec();
		}

		to_addr.toParams := f_sip_param_set(to_addr.toParams, "tag", f_sip_rand_tag());
		wwwAuthenticate := f_gen_WwwAuthenticate();
		security_server := f_gen_Security_server();

		/* Tx 401 Unauthorized */
		tx_resp := ts_SIP_Response_Unauthorized(sip_call_id,
					from_addr,
					to_addr,
					via,
					wwwAuthenticate,
					sip_seq_nr,
					"REGISTER",
					p_associated_uri := g_pars.subscr.p_associated_uri,
					security_server := security_server,
					server := g_pars.server_name,
					supported := supported,
					userAgent := omit);
		SIP.send(tx_resp);

		if (exp_auth_resync) {
			/* Now we should receive a new non-protected REGISTER
			 * with Authoritzation containing auts in base64: */
			var template (present) Authorization authorization :=
				f_tr_Authorization_AKAv1MD5(wwwAuthenticate,
							    g_pars.subscr.imsi & "@" & g_pars.realm,
							    f_sip_SipUrl_to_str(g_pars.registrar_sip_req_uri));
			exp_req :=
			tr_SIP_REGISTER(g_pars.registrar_sip_req_uri,
					?,
					tr_From(),
					tr_To(),
					tr_Via_from(f_tr_HostPort(via.viaBody[0].sentBy.host, via.viaBody[0].sentBy.portField)),
					authorization := authorization);
			SIP.receive(exp_req) -> value g_rx_sip_req;

			if (early_ret == IMS_REG_EARLY_RET_BEFORE_Resync_401Unauthorized) {
				return; /* Done */
			}

			via := g_rx_sip_req.msgHeader.via;
			from_addr := g_rx_sip_req.msgHeader.fromField;
			to_addr := g_rx_sip_req.msgHeader.toField;
			sip_seq_nr := g_rx_sip_req.msgHeader.cSeq.seqNumber;

			/* Tx 100 Tyring */
			tx_resp := ts_SIP_Response_Trying(sip_call_id,
						from_addr,
						to_addr,
						via,
						sip_seq_nr,
						"REGISTER",
						allow := omit,
						server := g_pars.server_name,
						userAgent := omit);
			SIP.send(tx_resp);

			f_sip_param_match_value_or_fail(g_rx_sip_req.msgHeader.authorization.body.digestResponse,
							"auts", f_sip_str_quote(enc_MIME_Base64(g_pars.subscr.auth.auts)));
			f_ims_validate_register_P_Access_Network_info(g_rx_sip_req, exp_present := false);
			f_ims_validate_register_contact(g_rx_sip_req.msgHeader.contact);
			f_ims_parse_register_contact(g_rx_sip_req.msgHeader.contact);
			f_ims_parse_security_client(g_rx_sip_req.msgHeader.security_client);
			f_ims_setup_ipsec();

			security_server := f_gen_Security_server();

			/* Tx again 401 Unauthorized, this time our AMI interface will accept it: */
			tx_resp := ts_SIP_Response_Unauthorized(sip_call_id,
						from_addr,
						to_addr,
						via,
						wwwAuthenticate,
						sip_seq_nr,
						"REGISTER",
						p_associated_uri := g_pars.subscr.p_associated_uri,
						security_server := security_server,
						server := g_pars.server_name,
						supported := supported,
						userAgent := omit);
			SIP.send(tx_resp);
		}

		/* Now we should receive a new REGISTER over ipsec: */
		as_IMS_2nd_register(wwwAuthenticate, early_ret := early_ret);
	}
	[fail_others] as_SIP_fail_resp(sip_expect_str);
	[fail_others] as_SIP_fail_req(sip_expect_str);

}

/* Peer is issuing 2nd register, accept it: */
altstep as_IMS_2nd_register(WwwAuthenticate wwwAuthenticate,
			    IMS_register_early_return early_ret := IMS_REG_EARLY_RET_BEFORE_None,
			    boolean fail_others := true) runs on IMS_ConnHdlr
{
	var template (present) Authorization authorization :=
		f_tr_Authorization_AKAv1MD5(wwwAuthenticate,
					    g_pars.subscr.imsi & "@" & g_pars.realm,
					    f_sip_SipUrl_to_str(g_pars.registrar_sip_req_uri));
	var template (present) PDU_SIP_Request exp_req :=
		tr_SIP_REGISTER(g_pars.registrar_sip_req_uri,
				?,
				tr_From(),
				tr_To(),
				tr_Via_from(f_tr_HostPort(g_pars.subscr.remote_sip_host, g_pars.subscr.ipsec_remote_port_s)),
				authorization := authorization);
	var charstring sip_expect_str := log2str(exp_req);

	[] SIP.receive(exp_req) -> value g_rx_sip_req {
		var template (value) PDU_SIP_Response tx_resp;
		var Via via;
		var Contact contact;
		var CallidString sip_call_id;
		var template (value) From from_addr;
		var template (value) To to_addr;
		var template (value) Require require := ts_Require({"sec-agree"});
		var template (value) Supported supported := ts_Supported({"sec-agree"});
		var integer sip_seq_nr;

		if (early_ret == IMS_REG_EARLY_RET_BEFORE_Protected_100Trying) {
			return; /* Done */
		}

		sip_call_id := g_rx_sip_req.msgHeader.callId.callid;
		via := g_rx_sip_req.msgHeader.via;
		from_addr := g_rx_sip_req.msgHeader.fromField;
		to_addr := g_rx_sip_req.msgHeader.toField;
		sip_seq_nr := g_rx_sip_req.msgHeader.cSeq.seqNumber;

		/* Tx 100 Trying */
		tx_resp := ts_SIP_Response_Trying(sip_call_id,
					from_addr,
					to_addr,
					via,
					sip_seq_nr,
					"REGISTER",
					allow := omit,
					server := g_pars.server_name,
					userAgent := omit);
		SIP.send(tx_resp);

		/* Validate Digest Response: */
		f_ims_validate_Authorization_AKAv1MD5_Response(g_rx_sip_req.msgHeader.authorization, "REGISTER");

		/* Validate P-Access-Network-Info: */
		f_ims_validate_register_P_Access_Network_info(g_rx_sip_req, exp_present := true);

		if (early_ret == IMS_REG_EARLY_RET_BEFORE_Protected_200OK) {
			return; /* Done */
		}

		g_pars.subscr.p_associated_uri := valueof(ts_P_Associated_Uri({
				ts_P_Assoc_uri_spec(ts_NameAddr(ts_SipUrl(ts_HostPort(g_pars.realm),
									  ts_UserInfo(g_pars.subscr.msisdn),
									  scheme := "sip"))),
				ts_P_Assoc_uri_spec(ts_NameAddr(ts_SipUrl(ts_HostPort(g_pars.subscr.msisdn),
									  omit,
									  scheme := "tel"))),
				ts_P_Assoc_uri_spec(g_rx_sip_req.msgHeader.toField.addressField.nameAddr)
			}));

		contact := g_rx_sip_req.msgHeader.contact;
		f_ims_validate_register_contact(contact);
		f_ims_parse_register_contact(contact);
		g_pars.subscr.registered_contact := contact;
		/* Set expires= to configured value: RFC3261 10.3 8) */
		for (var integer i := 0; i < lengthof(contact.contactBody.contactAddresses); i := i + 1) {
			contact.contactBody.contactAddresses[i].contactParams :=
				valueof({ ts_Param("expires", int2str(g_pars.subscr.registrar_expires)) });
		}

		/* Tx 200 OK */
		to_addr.toParams := f_sip_param_set(to_addr.toParams, "tag", f_sip_rand_tag());
		tx_resp := ts_SIP_Response(sip_call_id,
			from_addr,
			to_addr,
			"REGISTER", 200,
			sip_seq_nr,
			"OK",
			via,
			contact := contact,
			p_associated_uri := g_pars.subscr.p_associated_uri,
			require := require,
			server := g_pars.server_name,
			supported := supported,
			userAgent := omit);
		SIP.send(tx_resp);
	}
	[fail_others] as_SIP_fail_resp(sip_expect_str);
	[fail_others] as_SIP_fail_req(sip_expect_str);
}

/* Peer wants to unregister, accept it: */
altstep as_IMS_unregister(boolean fail_others := true) runs on IMS_ConnHdlr
{
	var template (present) PDU_SIP_Request exp_req :=
		tr_SIP_REGISTER(g_pars.registrar_sip_req_uri,
				?,
				tr_From(),
				tr_To(),
				tr_Via_from(f_tr_HostPort(g_pars.subscr.remote_sip_host, g_pars.subscr.ipsec_remote_port_s)),
				expires := tr_Expires(int2str(0)),
				require := tr_Require(superset("sec-agree")),
				security_client := tr_Security_client(superset(tr_Security_mechanism("ipsec-3gpp",
												     superset(tr_Param("alg","hmac-sha-1-96"))))),
				supported := tr_Supported(superset("path", "sec-agree")));
	var charstring sip_expect_str := log2str(exp_req);

	[] SIP.receive(exp_req) -> value g_rx_sip_req {
		var template (value) PDU_SIP_Response tx_resp;
		var Via via;
		var CallidString sip_call_id;
		var Contact contact;
		var template (value) From from_addr;
		var template (value) To to_addr;
		var template (value) CommaParam_List digestCln ;
		var template (value) WwwAuthenticate wwwAuthenticate;
		var template (value) Security_server security_server;
		var template (value) Require require := ts_Require({"sec-agree"});
		var template (value) Supported supported := ts_Supported({"sec-agree"});
		var template (present) Authorization authorization;
		var integer sip_seq_nr;

		sip_call_id := g_rx_sip_req.msgHeader.callId.callid;
		via := g_rx_sip_req.msgHeader.via;
		via.viaBody[0].viaParams := f_sip_param_set(via.viaBody[0].viaParams, "rport", "1234"); /* TODO: set remote src port of the REGISTER */
		from_addr := g_rx_sip_req.msgHeader.fromField;
		to_addr := g_rx_sip_req.msgHeader.toField;
		sip_seq_nr := g_rx_sip_req.msgHeader.cSeq.seqNumber;

		contact := g_rx_sip_req.msgHeader.contact;
		f_ims_validate_register_contact(contact);

		/* 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,
					to_addr,
					via,
					sip_seq_nr,
					"REGISTER",
					allow := omit,
					server := g_pars.server_name,
					userAgent := omit);
		SIP.send(tx_resp);

		/* Change all Contact parameters to expires=0: */
		for (var integer i := 0; i < lengthof(contact.contactBody.contactAddresses); i := i + 1) {
			contact.contactBody.contactAddresses[i].contactParams := valueof({ ts_Param("expires", "0") });
		}
		g_pars.subscr.registered_contact := omit;
		/* Tx 200 OK */
		to_addr.toParams := f_sip_param_set(to_addr.toParams, "tag", f_sip_rand_tag());
		tx_resp := ts_SIP_Response(sip_call_id,
			from_addr,
			to_addr,
			"REGISTER", 200,
			sip_seq_nr,
			"OK",
			via,
			contact := contact,
			p_associated_uri := g_pars.subscr.p_associated_uri,
			require := require,
			server := g_pars.server_name,
			supported := supported,
			userAgent := omit);
		SIP.send(tx_resp);
	}
	[fail_others] as_SIP_fail_resp(sip_expect_str);
	[fail_others] as_SIP_fail_req(sip_expect_str);
}

/* IMS Core starts a call towards the peer: 3GPP TS 24.229 5.1.3.1 */
function f_IMS_mt_call_setup() runs on IMS_ConnHdlr
{
	var template (value) PDU_SIP_Request req;
	var template (present) PDU_SIP_Response exp;
	var template (present) From from_addr_exp;
	var template (present) To to_addr_exp;
	var Via via;
	var template (omit) Require require := omit;
	var template (omit) Supported supported := omit;
	var charstring tx_sdp;
	var default d_trying, d_ringing;
	var charstring branch_value;
	var Contact calling_contact;

	/* RFC 3261 8.1.1.3 From */
	g_pars.subscr.cp.from_addr := valueof(ts_From(g_pars.subscr.cp.calling.addr, g_pars.subscr.cp.calling.params));
	g_pars.subscr.cp.from_addr.fromParams := f_sip_param_set(g_pars.subscr.cp.from_addr.fromParams, "tag", f_sip_rand_tag());
	g_pars.subscr.cp.to_addr := valueof(ts_To(g_pars.subscr.cp.called.addr, g_pars.subscr.cp.called.params));
	from_addr_exp := tr_From(tr_Addr_Union_from_val(g_pars.subscr.cp.from_addr.addressField), *);
	to_addr_exp := tr_To(tr_Addr_Union_from_val(g_pars.subscr.cp.to_addr.addressField), *);
	branch_value := f_sip_gen_branch(f_sip_Addr_Union_to_str(g_pars.subscr.cp.from_addr.addressField),
					 f_sip_Addr_Union_to_str(valueof(g_pars.subscr.cp.to_addr.addressField)),
					 g_pars.subscr.cp.sip_call_id,
					 g_pars.subscr.cp.sip_seq_nr);
	via := g_pars.local_via;
	via.viaBody[0].viaParams := f_sip_param_set(via.viaBody[0].viaParams, "branch", branch_value);

	calling_contact := valueof(ts_Contact({
					ts_ContactAddress(g_pars.subscr.cp.calling.addr, omit)
				}));

	if (g_pars.subscr.cp.support_precondition_ext) {
		/* indicate the support for "reliable provisional response"
		 * and "preconditions mechanism" */
		supported := ts_Supported({ "100rel", "precondition" });
		tx_sdp := f_gen_sdp(IMS_GEN_SDP_MO_INVITE);
	} else {
		/* Don't add any preconditions to SDP: */
		tx_sdp := f_gen_sdp(IMS_GEN_SDP_None);
	}

	req := ts_SIP_INVITE(g_pars.subscr.cp.sip_call_id,
			     g_pars.subscr.cp.from_addr,
			     g_pars.subscr.cp.to_addr,
			     via,
			     calling_contact,
			     g_pars.subscr.cp.sip_seq_nr,
			     supported := supported,
			     body := tx_sdp);

	SIP.send(req);

	/* Conditionally match and accept 100 Trying. */
	exp := tr_SIP_Response_Trying(g_pars.subscr.cp.sip_call_id,
			from_addr_exp,
			to_addr_exp,
			f_tr_Via_response(via),
			g_pars.subscr.cp.sip_seq_nr, "INVITE");
	d_trying := activate(as_SIP_ignore_resp(exp));

	if (g_pars.subscr.cp.require_precondition_ext) {
		var template (present) SDP_attribute_list preconds;
		/* Rx 183 Session Progress */
		exp := tr_SIP_Response_SessionProgress(
				g_pars.subscr.cp.sip_call_id,
				from_addr_exp,
				to_addr_exp,
				f_tr_Via_response(via),
				g_pars.subscr.cp.sip_seq_nr, "INVITE",
				require := tr_Require(superset("100rel", "precondition")),
				rseq := tr_RSeq(?));
		alt {
		[] SIP.receive(exp) -> value g_rx_sip_resp;
		[] SIP.receive(tr_SIP_Response_Ringing(?, ?, ?)) -> value g_rx_sip_resp {
			Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
						log2str(g_name & ": Expected 183 Session Progress instead of 180 Ringing: ",
							g_rx_sip_resp));
			}
		}

		/* Validate SDP in Session Progress contains the preconditions:
		 * a=curr:qos local none
		 * a=curr:qos remote none
		 * a=des:qos mandatory local sendrecv
		 * a=des:qos mandatory remote sendrecv
		 * a=conf:qos remote sendrecv
		*/
		preconds := superset(
			tr_SDP_curr(c_SDP_PRECON_STATUS_TYPE_local,  c_SDP_PRECON_DIR_TAG_none),
			tr_SDP_curr(c_SDP_PRECON_STATUS_TYPE_remote, c_SDP_PRECON_DIR_TAG_none),
			tr_SDP_des(c_SDP_PRECON_STRENGTH_TAG_mandatory, c_SDP_PRECON_STATUS_TYPE_local, c_SDP_PRECON_DIR_TAG_sendrecv),
			tr_SDP_des(c_SDP_PRECON_STRENGTH_TAG_mandatory,  c_SDP_PRECON_STATUS_TYPE_remote, c_SDP_PRECON_DIR_TAG_sendrecv),
			tr_SDP_conf(c_SDP_PRECON_STATUS_TYPE_remote,  c_SDP_PRECON_DIR_TAG_sendrecv));
		if (not ispresent(g_pars.subscr.cp.peer_sdp.attributes) or
			not match(g_pars.subscr.cp.peer_sdp.attributes, preconds)) {
			Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
						log2str(g_name & ": Unexpected precondition attrs in Session Progress : ",
							g_pars.subscr.cp.peer_sdp.attributes));
		}

		/* Tx PRACK */
		req := ts_SIP_PRACK(g_pars.subscr.cp.to_addr.addressField.nameAddr.addrSpec,
				    g_pars.subscr.cp.sip_call_id,
				    g_pars.subscr.cp.from_addr,
				    g_pars.subscr.cp.to_addr,
				    via,
				    g_rx_sip_resp.msgHeader.cSeq.seqNumber + 1,
				    rack := ts_RAck(g_rx_sip_resp.msgHeader.rseq.response_num,
						    g_rx_sip_resp.msgHeader.cSeq.seqNumber,
						    "INVITE"),
				    body := omit);
		SIP.send(req);

		if (g_pars.subscr.cp.mt.tx_coord_cmd_session_progress) {
			/* Signal used to inform that Dedicated bearer can be established: */
			COORD.send(IMS_COORD_CMD_CALL_SESSION_PROGRESS);
		}

		/* Rx 200 OK (PRACK) */
		exp := tr_SIP_Response(g_pars.subscr.cp.sip_call_id,
				       from_addr_exp,
				       to_addr_exp,
				       f_tr_Via_response(via),
				       omit,
				       "PRACK", 200,
				       g_rx_sip_resp.msgHeader.cSeq.seqNumber + 1, "OK",
				       body := omit);
		as_SIP_expect_resp(exp, fail_others := false);

		/* Tx UPDATE */
		tx_sdp := f_gen_sdp(IMS_GEN_SDP_MO_UPDATE);
		req := ts_SIP_UPDATE(g_pars.subscr.cp.to_addr.addressField.nameAddr.addrSpec,
				     g_pars.subscr.cp.sip_call_id,
				     g_pars.subscr.cp.from_addr,
				     g_pars.subscr.cp.to_addr,
				     via,
				     g_rx_sip_resp.msgHeader.cSeq.seqNumber + 1,
				     contact := calling_contact,
				     require := ts_Require({"sec-agree", "precondition"}),
				     body := tx_sdp);
		SIP.send(req);

		/* Rx 200 OK (UPDATE) */
		exp := tr_SIP_Response(g_pars.subscr.cp.sip_call_id,
				       from_addr_exp,
				       to_addr_exp,
				       f_tr_Via_response(via),
				       omit,
				       "UPDATE", 200,
				       g_rx_sip_resp.msgHeader.cSeq.seqNumber + 1, "OK",
				       body := ?);
		as_SIP_expect_resp(exp, fail_others := false);

		/* Validate SDP in 200 OK (UPDATE) contains the preconditions:
		 * a=curr:qos local sendrecv
		 * a=curr:qos remote sendrecv
		 * a=des:qos mandatory local sendrecv
		 * a=des:qos mandatory remote sendrecv
		*/
		preconds := superset(
			tr_SDP_curr(c_SDP_PRECON_STATUS_TYPE_local,  c_SDP_PRECON_DIR_TAG_sendrecv),
			tr_SDP_curr(c_SDP_PRECON_STATUS_TYPE_remote, c_SDP_PRECON_DIR_TAG_sendrecv),
			tr_SDP_des(c_SDP_PRECON_STRENGTH_TAG_mandatory, c_SDP_PRECON_STATUS_TYPE_local, c_SDP_PRECON_DIR_TAG_sendrecv),
			tr_SDP_des(c_SDP_PRECON_STRENGTH_TAG_mandatory,  c_SDP_PRECON_STATUS_TYPE_remote, c_SDP_PRECON_DIR_TAG_sendrecv));
		if (not ispresent(g_pars.subscr.cp.peer_sdp.attributes) or
			not match(g_pars.subscr.cp.peer_sdp.attributes, preconds)) {
			Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
						log2str(g_name & ": Unexpected precondition attrs in 200 OK (UPDATE): ",
							g_pars.subscr.cp.peer_sdp.attributes));
		}

		g_pars.subscr.cp.sip_seq_nr := g_rx_sip_resp.msgHeader.cSeq.seqNumber + 1;
	}

	/* Conditionally match and accept 180 Ringing */
	exp := tr_SIP_Response_Ringing(g_pars.subscr.cp.sip_call_id,
			from_addr_exp,
			to_addr_exp,
			f_tr_Via_response(via),
			g_pars.subscr.cp.sip_seq_nr, "INVITE");
	d_ringing := activate(as_SIP_ignore_resp(exp));

	/* Wait for 200 OK (INVITE) answer */
	exp := tr_SIP_Response(
			g_pars.subscr.cp.sip_call_id,
			from_addr_exp,
			to_addr_exp,
			f_tr_Via_response(via),
			*,
			"INVITE", 200,
			g_pars.subscr.cp.sip_seq_nr, "OK",
			body := *);
	as_SIP_expect_resp(exp, fail_others := false);

	deactivate(d_trying);
	deactivate(d_ringing);

	/* Make sure "audio" tag set in Contact header */
	f_ims_validate_INVITE_Contact(g_rx_sip_resp.msgHeader.contact);

	/* Update To with the tags received from peer: */
	g_pars.subscr.cp.to_addr := g_rx_sip_resp.msgHeader.toField;

	/* Transmit ACK */
	g_pars.subscr.cp.sip_seq_nr := g_pars.subscr.cp.sip_seq_nr + 1;
	req := ts_SIP_ACK(g_pars.subscr.cp.sip_call_id,
			  g_pars.subscr.cp.from_addr,
			  g_pars.subscr.cp.to_addr,
			  via,
			  g_pars.subscr.cp.sip_seq_nr,
			  omit);
	SIP.send(req);
	g_pars.subscr.cp.sip_seq_nr := g_pars.subscr.cp.sip_seq_nr + 1;
}

/* Tx BYE: */
function f_IMS_do_call_hangup() runs on IMS_ConnHdlr
{
	var template (value) PDU_SIP_Request req;
	var template (present) PDU_SIP_Response exp_resp;
	var Via via;
	var charstring branch_value;

	branch_value := f_sip_gen_branch(f_sip_Addr_Union_to_str(g_pars.subscr.cp.from_addr.addressField),
					 f_sip_Addr_Union_to_str(valueof(g_pars.subscr.cp.to_addr.addressField)),
					 g_pars.subscr.cp.sip_call_id,
					 g_pars.subscr.cp.sip_seq_nr);

	via := g_pars.local_via;
	via.viaBody[0].viaParams := f_sip_param_set(via.viaBody[0].viaParams, "branch", branch_value);

	/* Transmit ACK */
	req := ts_SIP_BYE(g_pars.subscr.cp.sip_call_id,
			  g_pars.subscr.cp.from_addr,
			  g_pars.subscr.cp.to_addr,
			  via,
			  g_pars.subscr.cp.sip_seq_nr,
			  omit);
	SIP.send(req);

	/* Wait for OK answer */
	exp_resp := tr_SIP_Response(
			g_pars.subscr.cp.sip_call_id,
			g_pars.subscr.cp.from_addr,
			tr_To(tr_Addr_Union_from_val(g_pars.subscr.cp.to_addr.addressField), *),
			f_tr_Via_response(via),
			*,
			"BYE", 200,
			g_pars.subscr.cp.sip_seq_nr, "OK");
	as_SIP_expect_resp(exp_resp);

	g_pars.subscr.cp.sip_seq_nr := g_pars.subscr.cp.sip_seq_nr + 1;
}

private function f_ConnHdlr_parse_initial_SIP_INVITE(PDU_SIP_Request rx_sip_req) runs on IMS_ConnHdlr
{
	f_SDP_decodeMessage(rx_sip_req.messageBody, g_pars.subscr.cp.peer_sdp);
	log("Rx Initial MO INVITE decoded SDP: ", g_pars.subscr.cp.peer_sdp);

	/* Obtain params: */
	g_pars.subscr.cp.sip_call_id := rx_sip_req.msgHeader.callId.callid;
	g_pars.subscr.cp.from_addr := rx_sip_req.msgHeader.fromField;
	g_pars.subscr.cp.to_addr := rx_sip_req.msgHeader.toField;
	g_pars.subscr.cp.to_addr.toParams := f_sip_param_set(g_pars.subscr.cp.to_addr.toParams, "tag", f_sip_rand_tag());
	g_pars.subscr.cp.sip_seq_nr := rx_sip_req.msgHeader.cSeq.seqNumber;
}

/* Peer is calling us, accept it: */
altstep as_IMS_mo_call_accept(boolean exp_update_to_direct_rtp := false,
			      boolean fail_others := true) runs on IMS_ConnHdlr
{
	var template (present) PDU_SIP_Request exp_req :=
		tr_SIP_INVITE(f_tr_SipUrl_opt_defport(ts_SipUrl_from_Addr_Union(g_pars.subscr.cp.called.addr)),
			      ?,
			      tr_From(tr_Addr_Union_from_val(g_pars.subscr.cp.calling.addr), *),
			      tr_To(tr_Addr_Union_from_val(g_pars.subscr.cp.called.addr), *),
			      tr_Via_from(f_tr_HostPort(g_pars.subscr.remote_sip_host, g_pars.subscr.ipsec_remote_port_s)),
			      ?, ?);
	var charstring sip_expect_str := log2str(exp_req);

	[] SIP.receive(exp_req) -> value g_rx_sip_req {
		var template (value) PDU_SIP_Response tx_resp;
		var Via via;
		var template (omit) charstring tx_sdp;
		var boolean peer_support_precondition := match(g_rx_sip_req.msgHeader.supported.optionsTags,
							       superset("100rel", "precondition"));

		/* Obtain params: */
		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);
		f_ims_validate_invite_P_Preferred_Service(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,
						log2str(g_name & ": Missing '100rel,precondition' in INVITE Supported header: ",
						g_rx_sip_req.msgHeader.supported));
		}

		/* Tx 100 Tyring */
		tx_resp := ts_SIP_Response_Trying(g_pars.subscr.cp.sip_call_id,
						   g_pars.subscr.cp.from_addr,
						   g_pars.subscr.cp.to_addr,
						   via,
						   g_pars.subscr.cp.sip_seq_nr,
						   "INVITE",
						   allow := omit,
						   server := g_pars.server_name,
						   userAgent := omit);
		SIP.send(tx_resp);

		if (g_pars.subscr.cp.mo.tx_coord_cmd_invite_trying) {
			/* Signal used to inform that Dedicated bearer can be established: */
			COORD.send(IMS_COORD_CMD_CALL_TRYING);
		}

		/* Use precondition ? */
		if (g_pars.subscr.cp.require_precondition_ext or
		    (g_pars.subscr.cp.support_precondition_ext and peer_support_precondition)) {
			var template (present) SDP_attribute_list preconds;
			/* Validate SDP in INVITE contains the preconditions:
			 * a=curr:qos local none
			 * a=curr:qos remote none
			 * a=des:qos mandatory local sendrecv
			 * a=des:qos optional remote sendrecv
			 */
			preconds := superset(
				tr_SDP_curr(c_SDP_PRECON_STATUS_TYPE_local,  c_SDP_PRECON_DIR_TAG_none),
				tr_SDP_curr(c_SDP_PRECON_STATUS_TYPE_remote, c_SDP_PRECON_DIR_TAG_none),
				tr_SDP_des(c_SDP_PRECON_STRENGTH_TAG_mandatory, c_SDP_PRECON_STATUS_TYPE_local, c_SDP_PRECON_DIR_TAG_sendrecv),
				tr_SDP_des(c_SDP_PRECON_STRENGTH_TAG_optional,  c_SDP_PRECON_STATUS_TYPE_remote, c_SDP_PRECON_DIR_TAG_sendrecv));
			if (not ispresent(g_pars.subscr.cp.peer_sdp.attributes) or
			    not match(g_pars.subscr.cp.peer_sdp.attributes, preconds)) {
				Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
							log2str(g_name & ": Unexpected precondition attrs in INVITE : ",
								g_pars.subscr.cp.peer_sdp.attributes));
			}

			/* Tx 183 Session Progress */
			tx_sdp := f_gen_sdp(IMS_GEN_SDP_MT_Session_Progress);
			tx_resp := ts_SIP_Response_SessionProgress(g_pars.subscr.cp.sip_call_id,
							g_pars.subscr.cp.from_addr,
							g_pars.subscr.cp.to_addr,
							via,
							g_pars.subscr.cp.sip_seq_nr,
							rseq := ts_RSeq(1),
							body := tx_sdp);
			SIP.send(tx_resp);

			/* Rx PRACK */
			exp_req := tr_SIP_PRACK(f_tr_SipUrl_opt_defport(ts_SipUrl_from_Addr_Union(g_pars.subscr.cp.called.addr)),
					g_pars.subscr.cp.sip_call_id,
					g_pars.subscr.cp.from_addr,
					g_pars.subscr.cp.to_addr,
					f_tr_Via_response(via),
					g_pars.subscr.cp.sip_seq_nr + 1,
					rack := tr_RAck(1, g_pars.subscr.cp.sip_seq_nr, "INVITE"),
					body := omit);
			as_SIP_expect_req(exp_req);

			/* Tx 200 OK (PRACK) */
			tx_resp := ts_SIP_Response(g_pars.subscr.cp.sip_call_id,
						g_pars.subscr.cp.from_addr,
						g_pars.subscr.cp.to_addr,
						"PRACK", 200,
						g_pars.subscr.cp.sip_seq_nr,
						"OK",
						via,
						body := omit);
			SIP.send(tx_resp);

			/* Rx UPDATE */
			exp_req := tr_SIP_UPDATE(f_tr_SipUrl_opt_defport(ts_SipUrl_from_Addr_Union(g_pars.subscr.cp.called.addr)),
					g_pars.subscr.cp.sip_call_id,
					g_pars.subscr.cp.from_addr,
					g_pars.subscr.cp.to_addr,
					f_tr_Via_response(via),
					g_pars.subscr.cp.sip_seq_nr + 1,
					require := tr_Require(superset("precondition")),
					body := ?);
			as_SIP_expect_req(exp_req);

			/* Validate SDP in UPDATE contains the preconditions:
			 * a=curr:qos local sendrecv
			 * a=curr:qos remote none
			 * a=des:qos mandatory local sendrecv
			 * a=des:qos mandatory remote sendrecv
			 */
			preconds := superset(
				tr_SDP_curr(c_SDP_PRECON_STATUS_TYPE_local,  c_SDP_PRECON_DIR_TAG_sendrecv),
				tr_SDP_curr(c_SDP_PRECON_STATUS_TYPE_remote, c_SDP_PRECON_DIR_TAG_none),
				tr_SDP_des(c_SDP_PRECON_STRENGTH_TAG_mandatory, c_SDP_PRECON_STATUS_TYPE_local, c_SDP_PRECON_DIR_TAG_sendrecv),
				tr_SDP_des(c_SDP_PRECON_STRENGTH_TAG_mandatory,  c_SDP_PRECON_STATUS_TYPE_remote, c_SDP_PRECON_DIR_TAG_sendrecv));
			if (not ispresent(g_pars.subscr.cp.peer_sdp.attributes) or
			    not match(g_pars.subscr.cp.peer_sdp.attributes, preconds)) {
				Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
							log2str(g_name & ": Unexpected precondition attrs in UPDATE: ",
								g_pars.subscr.cp.peer_sdp.attributes));
			}

			/* Tx 200 OK (UPDATE) */
			tx_sdp := f_gen_sdp(IMS_GEN_SDP_MT_UPDATE_200OK);
			tx_resp := ts_SIP_Response(g_pars.subscr.cp.sip_call_id,
						g_pars.subscr.cp.from_addr,
						g_pars.subscr.cp.to_addr,
						"UPDATE", 200,
						g_pars.subscr.cp.sip_seq_nr,
						"OK",
						via,
						body := tx_sdp);
			SIP.send(tx_resp);

			g_pars.subscr.cp.sip_seq_nr := g_pars.subscr.cp.sip_seq_nr + 1;
			/* 200 OK (INVITE) has no SDP if we use precondition: */
			tx_sdp := omit;
		} else {
			/* Check no precondition is sent in SDP */
			if (ispresent(g_pars.subscr.cp.peer_sdp.attributes) and
			    match (g_pars.subscr.cp.peer_sdp.attributes, superset(tr_SDP_curr_present,
										  tr_SDP_des_present,
										  tr_SDP_conf_present))) {
				Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
							log2str(g_name & ": Unexpected precondition attrs in INVITE: ",
								g_pars.subscr.cp.peer_sdp.attributes));
			}
			/* 200 OK (INVITE) has SDP if no precondition is used: */
			tx_sdp := f_gen_sdp();
		}

		/* Tx 180 Ringing */
		tx_resp := ts_SIP_Response_Ringing(g_pars.subscr.cp.sip_call_id,
						g_pars.subscr.cp.from_addr,
						g_pars.subscr.cp.to_addr,
						via,
						g_pars.subscr.cp.sip_seq_nr);
		SIP.send(tx_resp);


		/* Tx 200 OK */
		tx_sdp := f_gen_sdp();
		tx_resp := ts_SIP_Response(g_pars.subscr.cp.sip_call_id,
					   g_pars.subscr.cp.from_addr,
					   g_pars.subscr.cp.to_addr,
					   "INVITE", 200,
					   g_pars.subscr.cp.sip_seq_nr,
					   "OK",
					   via,
					   body := tx_sdp);
		SIP.send(tx_resp);

		/* Wait for ACK */
		exp_req := tr_SIP_ACK(f_tr_SipUrl_opt_defport(ts_SipUrl_from_Addr_Union(g_pars.subscr.cp.called.addr)),
				      g_pars.subscr.cp.sip_call_id,
				      g_pars.subscr.cp.from_addr,
				      g_pars.subscr.cp.to_addr,
				      f_tr_Via_response(via),
				      g_pars.subscr.cp.sip_seq_nr, *);
		as_SIP_expect_req(exp_req);
	}
	[fail_others] as_SIP_fail_resp(sip_expect_str);
	[fail_others] as_SIP_fail_req(sip_expect_str);

}

/* Call is terminated by peer: */
altstep as_IMS_exp_call_hangup(template (present) integer exp_seq_nr := ?, boolean fail_others := true) runs on IMS_ConnHdlr
{
	var template (present) PDU_SIP_Request exp_req :=
		tr_SIP_BYE(f_tr_SipUrl_opt_defport(ts_SipUrl_from_Addr_Union(g_pars.subscr.cp.called.addr)),
			   g_pars.subscr.cp.sip_call_id,
			   g_pars.subscr.cp.from_addr,
			   g_pars.subscr.cp.to_addr,
			   tr_Via_from(f_tr_HostPort(g_pars.subscr.remote_sip_host, g_pars.subscr.ipsec_remote_port_s)),
			   exp_seq_nr);
	var charstring sip_expect_str := log2str(exp_req);

	[] SIP.receive(exp_req) -> value g_rx_sip_req {
		var template (value) PDU_SIP_Response tx_resp;
		var charstring tx_sdp;
		var Via via;

		/* Update parameters: */
		g_pars.subscr.cp.sip_seq_nr := g_rx_sip_req.msgHeader.cSeq.seqNumber;
		/* "branch" has changed: */
		via := g_rx_sip_req.msgHeader.via;

		/* Tx 200 OK */
		tx_sdp := f_gen_sdp();
		tx_resp := ts_SIP_Response(g_pars.subscr.cp.sip_call_id,
					g_pars.subscr.cp.from_addr,
					g_pars.subscr.cp.to_addr,
					"BYE", 200,
					g_pars.subscr.cp.sip_seq_nr,
					"OK",
					via,
					body := tx_sdp);
		SIP.send(tx_resp);
	}
	[fail_others] as_SIP_fail_resp(sip_expect_str);
	[fail_others] as_SIP_fail_req(sip_expect_str);
}

}