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SIP register timeout

asked 2019-11-23 13:28:13 +0000

sugar76 gravatar image

updated 2019-11-26 14:41:04 +0000

Hi all,

I have a fax server running on a Windows Server 2019 machine. The fax server communicates via VoIP and registers itself on a PBX in the local network.

Problem: the fax server sends regularly SIP REGISTER requests to the PBX which results in a time out.

I recorded a trace from the fax server ( and the PBX (

An example:

  • in a REGISTER request is sent (packet no. 310)
  • in I am not able to find the correspondig request. It seems that it didn't even reach it's destination.

Am I missing something? Can you witness my observation?

EDIT There is a successful registration in the fax server trace at 13:46:45 (Packat no. 88). The next registration at 13:47:40 fails as the PBX sends a tcp ack but no SIP response code.

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answered 2019-11-23 19:54:13 +0000

Jaap gravatar image

Looking at the fax server capture the initial SIP registrations (for ext #34 and #35) work as normal.The PBX capture seems to have been started after these successful SIP registrations. This makes it difficult to figure out what's going on. The subsequent SIP requests for options seem to choke the SIP server, which doesn't respond. There are also TLS connections being made, is the SIP registration made there as well?

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The TLS connections don't come from the fax server. On the trace, packet no. 34 is a ping reply so I am not sure what you mean by initial SIP registrations (for ext #34 and #35). The SIP Options maybe interesting as in the configuration of the fax server sending of SIP Options is disabled. I will check that.

sugar76 gravatar imagesugar76 ( 2019-11-24 18:03:08 +0000 )edit

Maybe my first comment was a bit unclear, sorry for that :-) I see a successful registration at 13:46:45 (Packet no. 88-101). You see this on the PBX side at almost the same time. But the next registration at 13:47:40 fails (starting at Packet no 250). The PBX answers with a tcp ack, but sends no sip response with a status code ... Is my observation correct?

sugar76 gravatar imagesugar76 ( 2019-11-26 14:38:36 +0000 )edit

Your capture file at the PBX side (trace- has the following properties:

First packet: 2019-11-23 13:47:01
Last packet: 2019-11-23 13:48:13
Elapsed: 00:01:12

Therefore does not show the SIP registration.

Jaap gravatar imageJaap ( 2019-11-26 17:30:54 +0000 )edit

You are completely right, the capture on the PBX side is incomplete. My fault. I will wait until the problem rises again and then do a complete capture.

sugar76 gravatar imagesugar76 ( 2019-11-27 08:04:50 +0000 )edit

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Asked: 2019-11-23 13:28:13 +0000

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Last updated: Nov 26 '19