[Serusers] HELP: Why does SER not absorb this re-INVITE?

Jan Janak jan at iptel.org
Fri Mar 25 18:48:56 CET 2005 

On 20-03 08:31, Java Rockx wrote:
> Hi all.
> 
> I have a big problem and I really need some help. re-INVITE messages
> are not properly processed during __random__ call durations. Sometimes
> a call can exceed 1 hour and sometimes a call is only two minutes,
> then ser improperly processes a re-INVITE and a 408 Request Timeout is
> sent back to the Sonus GW, which then drops the call.

  It is not ser who improperly processes the re-INVITE. SER sends 100
  trying to the Sonus gateway and tries to deliver the re-INVITE to
  the grandstream phone which does not send any reply so the transaction
  times out.

  It is correct that Sonus sends a BYE after 408 becuase that is what
  re-INVITEs in this case are for -- to detect dead user agents.

  The problemy is most likely in grandstream which does not send any
  reply to the 2nd transaction in the log below. Note that that the
  messages below do not belong to the same transaction, the first INVITE
  has lower CSeq number than the second one (which times out), so there
  are two separate transactions, the first one is ok, the 2nd times out.

> Attached is a partial call log that begins with a re-INVITE.
> 
> NOTE: this is __NOT__ the first re-INVITE of this call. This call
> lasted more than 30 minutes and re-INVITEs were sent on a 2 minute
> interval.
> 
> Anyhow, the re-INVITE is processed and the SIP phone ACKed it, however
> another re-INVITE got sent from the Sonus GW which ser incorrectly
> tried to send to the SIP UA. 

  It is correct, the 2nd re-INVITE is a new transaction and thus gets
  processed exactly as the first one.

>The SIP UA correctly ignored the
> re-INVITE since it just ACKed it.

  That is incorrect, the SIP UA should not ignore it, see the cseq
  number (it differs).

> SER retransmits the re-INVITE to the SIP UA until the fr_invite timer
> expires, then it sends a 408 Request Timeout back to the Sonus GW,
> which then disconnects the call and sends ser a BYE message.
> 
> Is this a bug in the ser TM module? 

  No.

> Shouldn't ser just absorb the
> re-INVITE since it just ACKed it rather than trying to send the
> re-INVITE to the SIP UA?
> 
> The Sonus guys say that this is an error in the ser SIP stack.

  The Sonus guys always say that and mostly they are wrong. 

   Jan.

> Please help. I'm really stuck with this one.
> 
> Regards,
> Paul

> U 2005/03/19 11:12:00.975247 216.229.127.60:5060 -> 10.3.0.221:5060
> INVITE sip:3212514236 at 66.90.50.230:5060;user=phone SIP/2.0.
> Via: SIP/2.0/UDP 216.229.127.60:5060;branch=z9hG4bKf7bde5e04ab-d8ee8ecc.
> Via: SIP/2.0/UDP 216.229.118.76:4060;branch=z9hG4bK023478189c606358.
> To: "Paul Hazlett" <sip:3212514236 at 216.229.127.60;user=phone>;tag=7c0456c2c49ed845.
> From: <sip:4075660914 at sip.mycompany.com;user=phone>;tag=0b845f52.
> Call-ID: fc2e388f89db4205 at 172.16.1.18.
> CSeq: 14918 INVITE.
> Max-Forwards: 69.
> Contact: sip:4075660914 at 216.229.118.76:4060.
> Record-Route: <sip:216.229.127.60:5060;lr>.
> Route: <sip:10.3.0.221:5060;ftag=7c0456c2c49ed845;lr>.
> Allow: OPTIONS, INVITE, CANCEL, ACK, BYE, PRACK, INFO.
> Accept: multipart/mixed, application/sdp, application/isup, application/dtmf, application/dtmf-relay.
> Supported: timer.
> Session-Expires: 240;refresher=uac.
> Content-Disposition: session;handling=required.
> Content-Type: application/sdp.
> Content-Length: 248.
> .
> v=0.
> o=Sonus_UAC 3174 11674 IN IP4 216.229.118.76.
> s=SIP Media Capabilities.
> c=IN IP4 216.229.118.101.
> t=0 0.
> m=audio 17812 RTP/AVP 18 101.
> a=rtpmap:18 G729/8000.
> a=fmtp:18 annexb=no.
> a=rtpmap:101 telephone-event/8000.
> a=fmtp:101 0-15.
> a=sendrecv.
> 
> #
> U 2005/03/19 11:12:00.978029 10.3.0.221:5060 -> 216.229.127.60:5060
> SIP/2.0 100 trying -- your call is important to us.
> Via: SIP/2.0/UDP 216.229.127.60:5060;branch=z9hG4bKf7bde5e04ab-d8ee8ecc.
> Via: SIP/2.0/UDP 216.229.118.76:4060;branch=z9hG4bK023478189c606358.
> To: "Paul Hazlett" <sip:3212514236 at 216.229.127.60;user=phone>;tag=7c0456c2c49ed845.
> From: <sip:4075660914 at sip.mycompany.com;user=phone>;tag=0b845f52.
> Call-ID: fc2e388f89db4205 at 172.16.1.18.
> CSeq: 14918 INVITE.
> Content-Length: 0.
> .
> 
> #
> U 2005/03/19 11:12:00.978139 10.3.0.221:5060 -> 66.90.50.230:5060
> INVITE sip:3212514236 at 66.90.50.230;user=phone SIP/2.0.
> Record-Route: <sip:10.3.0.221;ftag=0b845f52;lr>.
> Via: SIP/2.0/UDP 10.3.0.221;branch=z9hG4bK6095.c5e65715.0.
> Via: SIP/2.0/UDP 216.229.127.60:5060;branch=z9hG4bKf7bde5e04ab-d8ee8ecc.
> Via: SIP/2.0/UDP 216.229.118.76:4060;branch=z9hG4bK023478189c606358.
> To: "Paul Hazlett" <sip:3212514236 at 216.229.127.60;user=phone>;tag=7c0456c2c49ed845.
> From: <sip:4075660914 at sip.mycompany.com;user=phone>;tag=0b845f52.
> Call-ID: fc2e388f89db4205 at 172.16.1.18.
> CSeq: 14918 INVITE.
> Max-Forwards: 16.
> Contact: sip:4075660914 at 216.229.118.76:4060.
> Record-Route: <sip:216.229.127.60:5060;lr>.
> Allow: OPTIONS, INVITE, CANCEL, ACK, BYE, PRACK, INFO.
> Accept: multipart/mixed, application/sdp, application/isup, application/dtmf, application/dtmf-relay.
> Supported: timer.
> Session-Expires: 240;refresher=uac.
> Content-Disposition: session;handling=required.
> Content-Type: application/sdp.
> Content-Length: 243.
> P-hint: Loose_Route.
> P-hint: NATed re-INVITE.
> .
> v=0.
> o=Sonus_UAC 3174 11674 IN IP4 216.229.118.76.
> s=SIP Media Capabilities.
> c=IN IP4 10.3.0.221.
> t=0 0.
> m=audio 35366 RTP/AVP 18 101.
> a=rtpmap:18 G729/8000.
> a=fmtp:18 annexb=no.
> a=rtpmap:101 telephone-event/8000.
> a=fmtp:101 0-15.
> a=sendrecv.
> 
> #
> U 2005/03/19 11:12:01.191163 66.90.50.230:5060 -> 10.3.0.221:5060
> SIP/2.0 200 OK.
> Via: SIP/2.0/UDP 10.3.0.221;branch=z9hG4bK6095.c5e65715.0.
> Via: SIP/2.0/UDP 216.229.127.60:5060;branch=z9hG4bKf7bde5e04ab-d8ee8ecc.
> Via: SIP/2.0/UDP 216.229.118.76:4060;branch=z9hG4bK023478189c606358.
> Record-Route: <sip:10.3.0.221;ftag=0b845f52;lr>.
> Record-Route: <sip:216.229.127.60:5060;lr>.
> From: <sip:4075660914 at sip.mycompany.com;user=phone>;tag=0b845f52.
> To: "Paul Hazlett" <sip:3212514236 at 216.229.127.60;user=phone>;tag=7c0456c2c49ed845.
> Call-ID: fc2e388f89db4205 at 172.16.1.18.
> CSeq: 14918 INVITE.
> User-Agent: Grandstream BT100 1.0.5.22.
> Contact: <sip:3212514236 at 172.16.1.18;user=phone>.
> Allow: INVITE,ACK,CANCEL,BYE,NOTIFY,REFER,OPTIONS,INFO,SUBSCRIBE.
> Content-Type: application/sdp.
> Supported: replaces.
> Content-Length: 217.
> .
> v=0.
> o=3212514236 8000 8020 IN IP4 172.16.1.18.
> s=SIP Call.
> c=IN IP4 172.16.1.18.
> t=0 0.
> m=audio 5004 RTP/AVP 18 101.
> a=sendrecv.
> a=rtpmap:18 G729/8000.
> a=ptime:20.
> a=rtpmap:101 telephone-event/8000.
> a=fmtp:101 0-11.
> 
> #
> U 2005/03/19 11:12:01.193221 10.3.0.221:5060 -> 216.229.127.60:5060
> SIP/2.0 200 OK.
> Via: SIP/2.0/UDP 216.229.127.60:5060;branch=z9hG4bKf7bde5e04ab-d8ee8ecc.
> Via: SIP/2.0/UDP 216.229.118.76:4060;branch=z9hG4bK023478189c606358.
> Record-Route: <sip:10.3.0.221;ftag=0b845f52;lr>.
> Record-Route: <sip:216.229.127.60:5060;lr>.
> From: <sip:4075660914 at sip.mycompany.com;user=phone>;tag=0b845f52.
> To: "Paul Hazlett" <sip:3212514236 at 216.229.127.60;user=phone>;tag=7c0456c2c49ed845.
> Call-ID: fc2e388f89db4205 at 172.16.1.18.
> CSeq: 14918 INVITE.
> User-Agent: Grandstream BT100 1.0.5.22.
> Contact: <sip:3212514236 at 66.90.50.230:5060;user=phone>.
> Allow: INVITE,ACK,CANCEL,BYE,NOTIFY,REFER,OPTIONS,INFO,SUBSCRIBE.
> Content-Type: application/sdp.
> Supported: replaces.
> Content-Length: 217.
> P-hint: NATed Reply.
> .
> v=0.
> o=3212514236 8000 8020 IN IP4 172.16.1.18.
> s=SIP Call.
> c=IN IP4 10.3.0.221.
> t=0 0.
> m=audio 35366 RTP/AVP 18 101.
> a=sendrecv.
> a=rtpmap:18 G729/8000.
> a=ptime:20.
> a=rtpmap:101 telephone-event/8000.
> a=fmtp:101 0-11.
> 
> #
> U 2005/03/19 11:12:01.271300 216.229.127.60:5060 -> 10.3.0.221:5060
> ACK sip:3212514236 at 66.90.50.230:5060;user=phone SIP/2.0.
> Via: SIP/2.0/UDP 216.229.127.60:5060;branch=z9hG4bK023478189c606358.
> Via: SIP/2.0/UDP 216.229.118.76:4060;branch=z9hG4bK023478189c606358.
> To: "Paul Hazlett" <sip:3212514236 at 216.229.127.60;user=phone>;tag=7c0456c2c49ed845.
> From: <sip:4075660914 at sip.mycompany.com;user=phone>;tag=0b845f52.
> Call-ID: fc2e388f89db4205 at 172.16.1.18.
> CSeq: 14918 ACK.
> Max-Forwards: 69.
> Record-Route: <sip:216.229.127.60:5060;lr>.
> Route: <sip:10.3.0.221:5060;ftag=7c0456c2c49ed845;lr>.
> Content-Length: 0.
> .
> 
> #
> U 2005/03/19 11:12:01.271682 10.3.0.221:5060 -> 66.90.50.230:5060
> ACK sip:3212514236 at 66.90.50.230:5060;user=phone SIP/2.0.
> Record-Route: <sip:10.3.0.221;ftag=0b845f52;lr>.
> Via: SIP/2.0/UDP 10.3.0.221;branch=0.
> Via: SIP/2.0/UDP 216.229.127.60:5060;branch=z9hG4bK023478189c606358.
> Via: SIP/2.0/UDP 216.229.118.76:4060;branch=z9hG4bK023478189c606358.
> To: "Paul Hazlett" <sip:3212514236 at 216.229.127.60;user=phone>;tag=7c0456c2c49ed845.
> From: <sip:4075660914 at sip.mycompany.com;user=phone>;tag=0b845f52.
> Call-ID: fc2e388f89db4205 at 172.16.1.18.
> CSeq: 14918 ACK.
> Max-Forwards: 16.
> Record-Route: <sip:216.229.127.60:5060;lr>.
> Content-Length: 0.
> P-hint: Loose_Route.
> .
> 
> ########################################################################################################
> U 2005/03/19 11:14:01.299130 216.229.127.60:5060 -> 10.3.0.221:5060
> INVITE sip:3212514236 at 66.90.50.230:5060;user=phone SIP/2.0.
> Via: SIP/2.0/UDP 216.229.127.60:5060;branch=z9hG4bK948d9f13945-93eca6cd.
> Via: SIP/2.0/UDP 216.229.118.76:4060;branch=z9hG4bK023564be9c606358.
> To: "Paul Hazlett" <sip:3212514236 at 216.229.127.60;user=phone>;tag=7c0456c2c49ed845.
> From: <sip:4075660914 at sip.mycompany.com;user=phone>;tag=0b845f52.
> Call-ID: fc2e388f89db4205 at 172.16.1.18.
> CSeq: 14919 INVITE.
> Max-Forwards: 69.
> Contact: sip:4075660914 at 216.229.118.76:4060.
> Record-Route: <sip:216.229.127.60:5060;lr>.
> Route: <sip:10.3.0.221:5060;ftag=7c0456c2c49ed845;lr>.
> Allow: OPTIONS, INVITE, CANCEL, ACK, BYE, PRACK, INFO.
> Accept: multipart/mixed, application/sdp, application/isup, application/dtmf, application/dtmf-relay.
> Supported: timer.
> Session-Expires: 240;refresher=uac.
> Content-Disposition: session;handling=required.
> Content-Type: application/sdp.
> Content-Length: 248.
> .
> v=0.
> o=Sonus_UAC 3174 11674 IN IP4 216.229.118.76.
> s=SIP Media Capabilities.
> c=IN IP4 216.229.118.101.
> t=0 0.
> m=audio 17812 RTP/AVP 18 101.
> a=rtpmap:18 G729/8000.
> a=fmtp:18 annexb=no.
> a=rtpmap:101 telephone-event/8000.
> a=fmtp:101 0-15.
> a=sendrecv.
> 
> #
> U 2005/03/19 11:14:01.301186 10.3.0.221:5060 -> 216.229.127.60:5060
> SIP/2.0 100 trying -- your call is important to us.
> Via: SIP/2.0/UDP 216.229.127.60:5060;branch=z9hG4bK948d9f13945-93eca6cd.
> Via: SIP/2.0/UDP 216.229.118.76:4060;branch=z9hG4bK023564be9c606358.
> To: "Paul Hazlett" <sip:3212514236 at 216.229.127.60;user=phone>;tag=7c0456c2c49ed845.
> From: <sip:4075660914 at sip.mycompany.com;user=phone>;tag=0b845f52.
> Call-ID: fc2e388f89db4205 at 172.16.1.18.
> CSeq: 14919 INVITE.
> Content-Length: 0.
> .
> 
> #
> U 2005/03/19 11:14:01.301327 10.3.0.221:5060 -> 66.90.50.230:5060
> INVITE sip:3212514236 at 66.90.50.230;user=phone SIP/2.0.
> Record-Route: <sip:10.3.0.221;ftag=0b845f52;lr>.
> Via: SIP/2.0/UDP 10.3.0.221;branch=z9hG4bK5095.9db7d786.0.
> Via: SIP/2.0/UDP 216.229.127.60:5060;branch=z9hG4bK948d9f13945-93eca6cd.
> Via: SIP/2.0/UDP 216.229.118.76:4060;branch=z9hG4bK023564be9c606358.
> To: "Paul Hazlett" <sip:3212514236 at 216.229.127.60;user=phone>;tag=7c0456c2c49ed845.
> From: <sip:4075660914 at sip.mycompany.com;user=phone>;tag=0b845f52.
> Call-ID: fc2e388f89db4205 at 172.16.1.18.
> CSeq: 14919 INVITE.
> Max-Forwards: 16.
> Contact: sip:4075660914 at 216.229.118.76:4060.
> Record-Route: <sip:216.229.127.60:5060;lr>.
> Allow: OPTIONS, INVITE, CANCEL, ACK, BYE, PRACK, INFO.
> Accept: multipart/mixed, application/sdp, application/isup, application/dtmf, application/dtmf-relay.
> Supported: timer.
> Session-Expires: 240;refresher=uac.
> Content-Disposition: session;handling=required.
> Content-Type: application/sdp.
> Content-Length: 243.
> P-hint: Loose_Route.
> P-hint: NATed re-INVITE.
> .
> v=0.
> o=Sonus_UAC 3174 11674 IN IP4 216.229.118.76.
> s=SIP Media Capabilities.
> c=IN IP4 10.3.0.221.
> t=0 0.
> m=audio 35366 RTP/AVP 18 101.
> a=rtpmap:18 G729/8000.
> a=fmtp:18 annexb=no.
> a=rtpmap:101 telephone-event/8000.
> a=fmtp:101 0-15.
> a=sendrecv.
> 
> #
> U 2005/03/19 11:14:01.416042 10.3.0.221:5060 -> 66.90.50.230:5060
> INVITE sip:3212514236 at 66.90.50.230;user=phone SIP/2.0.
> Record-Route: <sip:10.3.0.221;ftag=0b845f52;lr>.
> Via: SIP/2.0/UDP 10.3.0.221;branch=z9hG4bK5095.9db7d786.0.
> Via: SIP/2.0/UDP 216.229.127.60:5060;branch=z9hG4bK948d9f13945-93eca6cd.
> Via: SIP/2.0/UDP 216.229.118.76:4060;branch=z9hG4bK023564be9c606358.
> To: "Paul Hazlett" <sip:3212514236 at 216.229.127.60;user=phone>;tag=7c0456c2c49ed845.
> From: <sip:4075660914 at sip.mycompany.com;user=phone>;tag=0b845f52.
> Call-ID: fc2e388f89db4205 at 172.16.1.18.
> CSeq: 14919 INVITE.
> Max-Forwards: 16.
> Contact: sip:4075660914 at 216.229.118.76:4060.
> Record-Route: <sip:216.229.127.60:5060;lr>.
> Allow: OPTIONS, INVITE, CANCEL, ACK, BYE, PRACK, INFO.
> Accept: multipart/mixed, application/sdp, application/isup, application/dtmf, application/dtmf-relay.
> Supported: timer.
> Session-Expires: 240;refresher=uac.
> Content-Disposition: session;handling=required.
> Content-Type: application/sdp.
> Content-Length: 243.
> P-hint: Loose_Route.
> P-hint: NATed re-INVITE.
> .
> v=0.
> o=Sonus_UAC 3174 11674 IN IP4 216.229.118.76.
> s=SIP Media Capabilities.
> c=IN IP4 10.3.0.221.
> t=0 0.
> m=audio 35366 RTP/AVP 18 101.
> a=rtpmap:18 G729/8000.
> a=fmtp:18 annexb=no.
> a=rtpmap:101 telephone-event/8000.
> a=fmtp:101 0-15.
> a=sendrecv.
> 
> #
> U 2005/03/19 11:14:03.436047 10.3.0.221:5060 -> 66.90.50.230:5060
> INVITE sip:3212514236 at 66.90.50.230;user=phone SIP/2.0.
> Record-Route: <sip:10.3.0.221;ftag=0b845f52;lr>.
> Via: SIP/2.0/UDP 10.3.0.221;branch=z9hG4bK5095.9db7d786.0.
> Via: SIP/2.0/UDP 216.229.127.60:5060;branch=z9hG4bK948d9f13945-93eca6cd.
> Via: SIP/2.0/UDP 216.229.118.76:4060;branch=z9hG4bK023564be9c606358.
> To: "Paul Hazlett" <sip:3212514236 at 216.229.127.60;user=phone>;tag=7c0456c2c49ed845.
> From: <sip:4075660914 at sip.mycompany.com;user=phone>;tag=0b845f52.
> Call-ID: fc2e388f89db4205 at 172.16.1.18.
> CSeq: 14919 INVITE.
> Max-Forwards: 16.
> Contact: sip:4075660914 at 216.229.118.76:4060.
> Record-Route: <sip:216.229.127.60:5060;lr>.
> Allow: OPTIONS, INVITE, CANCEL, ACK, BYE, PRACK, INFO.
> Accept: multipart/mixed, application/sdp, application/isup, application/dtmf, application/dtmf-relay.
> Supported: timer.
> Session-Expires: 240;refresher=uac.
> Content-Disposition: session;handling=required.
> Content-Type: application/sdp.
> Content-Length: 243.
> P-hint: Loose_Route.
> P-hint: NATed re-INVITE.
> .
> v=0.
> o=Sonus_UAC 3174 11674 IN IP4 216.229.118.76.
> s=SIP Media Capabilities.
> c=IN IP4 10.3.0.221.
> t=0 0.
> m=audio 35366 RTP/AVP 18 101.
> a=rtpmap:18 G729/8000.
> a=fmtp:18 annexb=no.
> a=rtpmap:101 telephone-event/8000.
> a=fmtp:101 0-15.
> a=sendrecv.
> 
> ##
> U 2005/03/19 11:14:07.476044 10.3.0.221:5060 -> 66.90.50.230:5060
> INVITE sip:3212514236 at 66.90.50.230;user=phone SIP/2.0.
> Record-Route: <sip:10.3.0.221;ftag=0b845f52;lr>.
> Via: SIP/2.0/UDP 10.3.0.221;branch=z9hG4bK5095.9db7d786.0.
> Via: SIP/2.0/UDP 216.229.127.60:5060;branch=z9hG4bK948d9f13945-93eca6cd.
> Via: SIP/2.0/UDP 216.229.118.76:4060;branch=z9hG4bK023564be9c606358.
> To: "Paul Hazlett" <sip:3212514236 at 216.229.127.60;user=phone>;tag=7c0456c2c49ed845.
> From: <sip:4075660914 at sip.mycompany.com;user=phone>;tag=0b845f52.
> Call-ID: fc2e388f89db4205 at 172.16.1.18.
> CSeq: 14919 INVITE.
> Max-Forwards: 16.
> Contact: sip:4075660914 at 216.229.118.76:4060.
> Record-Route: <sip:216.229.127.60:5060;lr>.
> Allow: OPTIONS, INVITE, CANCEL, ACK, BYE, PRACK, INFO.
> Accept: multipart/mixed, application/sdp, application/isup, application/dtmf, application/dtmf-relay.
> Supported: timer.
> Session-Expires: 240;refresher=uac.
> Content-Disposition: session;handling=required.
> Content-Type: application/sdp.
> Content-Length: 243.
> P-hint: Loose_Route.
> P-hint: NATed re-INVITE.
> .
> v=0.
> o=Sonus_UAC 3174 11674 IN IP4 216.229.118.76.
> s=SIP Media Capabilities.
> c=IN IP4 10.3.0.221.
> t=0 0.
> m=audio 35366 RTP/AVP 18 101.
> a=rtpmap:18 G729/8000.
> a=fmtp:18 annexb=no.
> a=rtpmap:101 telephone-event/8000.
> a=fmtp:101 0-15.
> a=sendrecv.
> 
> #
> U 2005/03/19 11:14:11.516074 10.3.0.221:5060 -> 66.90.50.230:5060
> INVITE sip:3212514236 at 66.90.50.230;user=phone SIP/2.0.
> Record-Route: <sip:10.3.0.221;ftag=0b845f52;lr>.
> Via: SIP/2.0/UDP 10.3.0.221;branch=z9hG4bK5095.9db7d786.0.
> Via: SIP/2.0/UDP 216.229.127.60:5060;branch=z9hG4bK948d9f13945-93eca6cd.
> Via: SIP/2.0/UDP 216.229.118.76:4060;branch=z9hG4bK023564be9c606358.
> To: "Paul Hazlett" <sip:3212514236 at 216.229.127.60;user=phone>;tag=7c0456c2c49ed845.
> From: <sip:4075660914 at sip.mycompany.com;user=phone>;tag=0b845f52.
> Call-ID: fc2e388f89db4205 at 172.16.1.18.
> CSeq: 14919 INVITE.
> Max-Forwards: 16.
> Contact: sip:4075660914 at 216.229.118.76:4060.
> Record-Route: <sip:216.229.127.60:5060;lr>.
> Allow: OPTIONS, INVITE, CANCEL, ACK, BYE, PRACK, INFO.
> Accept: multipart/mixed, application/sdp, application/isup, application/dtmf, application/dtmf-relay.
> Supported: timer.
> Session-Expires: 240;refresher=uac.
> Content-Disposition: session;handling=required.
> Content-Type: application/sdp.
> Content-Length: 243.
> P-hint: Loose_Route.

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