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Wireshark-users: Re: [Wireshark-users] capture Q931 protocol

From: Guy Harris <guy@xxxxxxxxxxxx>
Date: Mon, 19 Jan 2009 03:50:00 -0800

On Jan 19, 2009, at 3:30 AM, Gopalakrishnan A.N wrote:

thanks for the reply, the sample data captured is attached with this mail. Its they call as G711 data.

G.711 is an audio coding standard, so if it's G.711 data, there's no Q. 931 - Q.931 is used for signaling on ISDN (and other forms of digital telephony), and G.711 is used for audio on various forms of digital telephony (as well as in, for example, .au files).

So is it Q.931 (containing signaling to set up the call) or is it G. 711 (for the audio of the call)? The text file seems to show the data as being divided into variable-length packets, which sounds more like Q.931 (possibly atop LAPD) rather than G.711 (which doesn't have any notion of packet boundaries). However, the packet data doesn't look too much like Q.931, whether atop LAPD or not.