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For no apparent reason my Snom phone ends the current call after about 15 minutes!
To Understand the issue let's take a look at the following SIP communication between Snom Phone and PBX:
Sent to Udp:217.x.xx.xx:5060 from Udp:192.168.2.124:50422 at Jan 30 12:57:23.743 (1419 bytes): INVITE sip:7890@testpbx.de;user=phone SIP/2.0 From: "Test" <sip:123456@testpbx.de>;tag=dzadbqiwhi To: <sip:7890@testpbx.de;user=phone> Call-ID: 313538303338353434303531333530-mxeagr7ulapk CSeq: 2 INVITE User-Agent: snomD765/10.1.49.11 Contact: <sip:123456@192.168.2.124:50422>;reg-id=1 X-Serialnumber: 000413xxxxxx Supported: timer, 100rel, replaces, from-change Accept: application/sdp Session-Expires: 3600 Min-SE: 90 ------------------------ Received from Udp:217.x.xx.xx:5060 on Udp:192.168.2.124:50422 at Jan 30 12:57:28.017 (1339 bytes): SIP/2.0 200 OK Via: SIP/2.0/UDP 192.168.2.124:50422;received=84.141.56.123;rport=50422;branch=z9hG4bK-qa5k4ddrhvok To: <sip:7890@testpbx.de;user=phone>;tag=h7g4Esbg_p65542t1580385444m252622c553395349s1_688083261-1877431650 From: "Test" <sip:123456@testpbx.de>;tag=dzadbqiwhi Call-ID: 313538303338353434303531333530-mxeagr7ulapk CSeq: 2 INVITE Contact: <sip:partner@217.x.xx.xx;transport=udp> Session-Expires: 1800;refresher=uas Supported: timer
In this case it is very important what is negotiated between the Snom phone and the other party (PBX server).
What does the RFC say: The refresher has to send an update after the half of the time. In our case it is exactly 15 minutes.
Here you can see the BYE being sent by the phone after 15 minutes and 13 seconds:
Sent to Udp:217.x.xx.xx:5060 from Udp:192.168.2.124:50422 at Jan 30 13:12:41.714 (699 bytes): BYE sip:partner@217.x.xx.xx;transport=udp SIP/2.0 From: "Test" <sip:123456@testpbx.de>;tag=dzadbqiwhi To: <sip:7890@testpbx.de;user=phone>;tag=h7g4Esbg_p65542t1580385444m252622c553395349s1_688083261-1877431650 Call-ID: 313538303338353434303531333530-mxeagr7ulapk CSeq: 4 BYE User-Agent: snomD765/10.1.49.11 Contact: <sip:123456@192.168.2.124:50422>;reg-id=1 Content-Length: 0
In the SIP Trace we also see that right after the Snom phone sends the BYE, the PBX sends an update for the session, but this comes late(13:12:43.583).
Received from Udp:217.x.xx.xx:5060 on Udp:192.168.2.124:50422 at Jan 30 13:12:43.583 (716 bytes): UPDATE sip:123456@192.168.2.124:50422 SIP/2.0 To: "Test" <sip:123456@testpbx.de>;tag=dzadbqiwhi From: <sip:7890@testpbx.de;user=phone>;tag=h7g4Esbg_p65542t1580385444m252622c553395349s1_688083261-1877431650 Call-ID: 313538303338353434303531333530-mxeagr7ulapk CSeq: 3 UPDATE Contact: <sip:partner@217.x.xx.xx;transport=udp> Min-Se: 900 Session-Expires: 1800;refresher=uac Supported: timer Content-Length: 0
Conclusion:
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