[Freeswitch-users] fax, debuggin

Steve Underwood steveu at coppice.org
Tue Sep 9 06:50:51 MSD 2014

On 09/09/2014 06:17 AM, Robert Stevens wrote:
> Check out this doc from Audio Codes: https://copy.com/aiF9RZpbLZre, specifically ‘Table 1: Fax Relay Versus PCM Transfer’.  Its full of data about faxing in general.  g.711 faxes are extremely susceptible to jitter.  Theres not much you can do unless you use T.38 which can have a lot of redundancy built in.  I guess if you were a savant you could listen to the g.711 rtp stream from the spa but most of us can’t do this.. ;)
FAXes are susceptible to poorly designed jitter buffers. They are also 
susceptible to jitter buffers which try to be too clever, and end up 
very voice specific (e.g. the ones which do continuously variable time 
scaling). The more practical jitter buffers switch from dynamic 
buffering to fixed buffering when they detect that FAX is present. Even 
if the jitter is small, those poorly thought out dynamic jitter buffers 
will break things.


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