ISDN user-network interface layer 3 specification for basic call control (Q.931)


XXX - add a brief description of Q.931 history

Protocol dependencies

Q.931 was originally used as the call control protocol for ISDN. It is also used for VoIP; when used for VoIP, it's usually transported atop TPKT atop TCP.

Example traffic

XXX - Add example traffic here (as plain text or Wireshark screenshot).


The Q.931 dissector is fully functional.

Preference Settings

  • Make sure that preferences in TCP and TPKT are set to allow reassembly of packets.

  • Whether to reassemble Q.931 messages spanning multiple TCP segments or not. (Default: yes)

  • Reassemble segmented Q.931 messages or not. (Default: yes)

Example capture file

XXX - Add a simple example capture file to the SampleCaptures page and link from here. Keep it short, it's also a good idea to gzip it to make it even smaller, as Wireshark can open gzipped files automatically.

Display Filter

A complete list of Q.931 display filter fields can be found in the display filter reference

Show only the Q.931 based traffic:


Capture Filter

You cannot directly filter Q.931 protocols while capturing. However, if you know the TCP port used (see above), you can filter on that one.

External links

  • Q.931 is specified by ITU in Q.931.


Imported from on 2020-08-11 23:23:44 UTC