Capturing local VoIP data stream / Capture a TCP trace

Have you been asked to send us a capture or a call trace?

On occasion, we may ask you for more information to find where an issue may be coming from.
In that case, we will usually ask for a trace or capture of the phone call data stream at your location.

A good tutorial on how to do that is provided by the software manufacturer that also has the software solution you would probably want to use for that.
So please see:
https://wiki.wireshark.org/VoIP_calls

Another good and slightly more extensive explanation of the capture process itself can be found here:
https://www.linuxjournal.com/article/9398

The short and sweet explanation on how to use Wireshark

To troubleshoot or analyze a particular problem, it is often handy to take a closer look at the actual SIP traffic being sent between your devices and our servers.

For example:

  • You can check whether SIP traffic is arriving at the server, and thus verify that traffic is not blocked by a firewall on the client or by a firewall sitting in between the server and the VOIP provider
  • You can check the exact format of INVITES and other SIP messages sent by your VOIP provider or VOIP gateway
  • You can view registrations made by phones

To create a SIP capture:

  1. Download and install a Network Capture tool.
    In this example, we use the free Wireshark tool, which can be downloaded from www.wireshark.org
  2. Activate the interfaces from the menu.
    Go to the menu option Capture > Interface
  3. Now select the network interface on which the traffic is being sent and received (be sure to select the correct one) and click on the start button.
    Traffic will now be captured.
  4. Make a call or reproduce the particular action that you wish to analyze (for example registration with Voyced, or an outbound call via the Voyced servers)
  5. You will see the SIP traffic appear in the main window.
    When done, you can stop the capture and then save the capture from the file menu for future analysis.

To create an UNFILTERED Wireshark Capture:

When saving the capture, make sure that in the "Packet Range" section, at the bottom of the "Save" dialog box, you select the options labelled "Captured" and "All Packets".
That way, the Support team can also check if any other traffic is interfering with your main SIP traffic, or if, for example, a port, codec, DNS or HTTP request failed for some reason.

  • capture, trace, error, troubleshooting, wireshark, pcap
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