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  • Why does my Snom phone always end the current call after a certain time

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Problem

For no apparent reason my Snom phone ends the current call after about 15 minutes!

Solution

To Understand the issue let's take a look at the following SIP communication between Snom Phone and PBX:

  • The Snom Phone with number 123456 sends an Invite to 7890;
  • The call comes in and is established between 123456 and 7890, so far so good.

Info
Note: For better overview I we have removed some SIP headers from the communication and highlighted the most important ones in this error analysis.


Code Block
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).

  • Let us concentrate on the parameters that are important for the duration of the session ( call ).
  • The Snom phone suggests a session duration of 3600 seconds; see: Session Expires: 3600
  • In the 200 OK the PBX changes this value to Session Expires: 1800 (=30 minutes).
  • Additionally it defines who renews the session: refresher=uas. This means that the (uas: user agent server) takes over the session refresh. In this case the PBX.

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.

  • If the client (in this case the Snom phone) does not receive any message from the server after half the time to keep the session running, the client terminates the session.
  • What the Snom phone also does with the sending of the BYE.
  • This procedure is described here: https://tools.ietf.org/html/rfc4028


Here you can see the BYE being sent by the phone after 15 minutes and 13 seconds:

Code Block
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).

Code Block
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:

  • This proves that the problem is on the server side, because it does not update the session in time.

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Note: For better overview I have removed some SIP headers from the communication and highlighted the most important ones in this error analysis

Ohne ersichtlichen Grund beendet mein Snom-Telefon das laufende Gespräch nach etwa 15 Minuten!

Lösung

Um das Problem zu verstehen, schauen wir uns die folgende SIP-Kommunikation zwischen Snom Telefon und PBX an:

  • Das Snom Telefon mit der Nummer 123456 sendet einen Invite an die 7890.
  • Der Anruf kommt an und wird zwischen 123456 und 7890 aufgebaut, so weit so gut.

German

Pagetitle
Warum beendet mein Snom-Telefon das aktuelle Gespräch immer nach einer bestimmten Zeit?
Warum beendet mein Snom-Telefon das aktuelle Gespräch immer nach einer bestimmten Zeit?

Problem

For no apparent reason my Snom phone ends the current call after about 15 minutes!

Solution

  • To Understand the issue let's take a look at the following SIP communication between Snom Phone and PBX:
  • The Snom Phone with number 123456 sends an Invite to 7890;
  • The call comes in and is established between 123456 and 7890, so far so good.
    Info
    Info
    Hinweis: Zur besseren Übersicht haben wir einige SIP-Header aus der Kommunikation entfernt und die wichtigsten in dieser Fehleranalyse hervorgehoben.


    Code Block
    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
    


    Snom suggests a session duration of 3600 seconds; see

    In this case it is very important what is negotiated between the Snom phone and the other party (PBX server).

  • Let us concentrate on the parameters that are important for the duration of the session ( call ).
  • diesem Fall ist es sehr wichtig, was zwischen dem Snom-Telefon und der anderen Partei (PBX-Server) ausgehandelt wird.

    • Konzentrieren wir uns auf die Parameter, die für die Dauer der Sitzung ( Anruf ) wichtig sind.
    • Das Snom-Telefon schlägt eine Sitzungsdauer von 3600 Sekunden vor; siehe: Session Expires: 3600
    • In the Im 200 OK the PBX changes this value to ändert die PBX diesen Wert auf Session Expires: 1800 (=30 minutesMinuten).
    • Additionally it defines who renews the session

      Zusätzlich definiert sie, wer die Sitzung erneuert: refresher=uas.

      This means that the

      Das bedeutet, dass der (uas: user agent server)

      takes over the session refresh. In this case the

      die Sitzungserneuerung übernimmt. In diesem Fall die PBX.

    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.

  • If the client (in this case the Snom phone) does not receive any message from the server after half the time to keep the session running, the client terminates the session.
  • What the Snom phone also does with the sending of the BYE.

    This procedure is described here

    Was besagt der RFC: Der Refresher muss nach der Hälfte der Zeit ein Update senden. In unserem Fall sind das genau 15 Minuten.

    • Wenn der Client (in diesem Fall das Snom-Telefon) nach der Hälfte der Zeit keine Nachricht vom Server erhält, um die Sitzung aufrecht zu erhalten, beendet der Client die Sitzung.
    • Was das Snom-Telefon auch mit dem Senden des BYEs macht.
    •  Dieser Vorgang ist hier beschrieben: https://tools.ietf.org/html/rfc4028


    Here you can see the BYE being sent by the phone after 15 minutes and 13 secondsHier sehen Sie, wie das BYE vom Telefon nach 15 Minuten und 13 Sekunden gesendet wird:

    Code Block
    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 Im SIP Trace we also see that right after Snom sends the BYE, the PBX sends an update for the session, but this comes late-Trace sehen wir auch, dass direkt nachdem das Snom-Telefon das BYE sendet, die Telefonanlage ein Update für die Sitzung sendet, aber das kommt zu spät(13:12:43.583).

    Code Block
    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: This proves that the problem is on the server side, because it does not update the session in time


    Schlussfolgerung:

    • Dies beweist, dass das Problem auf der Serverseite liegt, da er die Sitzung nicht rechtzeitig aktualisiert.


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