[Asterisk-Users] Problems with fax failing when bridged across TDM400Pvers E

[Lee Howard]

Andrew Kohlsmith wrote:

>Faxes are designed to work around the noise and other signal problems inherent 
>in analog telephony.  VOIP introduces an entirely different set of noise 
>factors that fax machines are frankly ill-equipped to deal with.  Jitter and 
>dropped packets are the biggest of these issues.
>

Jitter and dropped packets usually translate into either periods of 
silence (and I believe that this is more common) or periods of 
synthesized audio.  The latter will mean in corrupted data and the 
former will often result in a premature carrier drop detection.

If a receiver prematurely detects a carrier drop in Phase C fax image 
data then it *must* wait around up to perhaps 60 seconds for the sender 
signals to return.  Many fax machines (and more particularly fax 
programs) are not this tolerant.

Lee.