[SIPForum-discussion] SIP Faxing

Steve Underwood steveu at coppice.org
Mon Aug 8 16:46:53 UTC 2011

On 08/04/2011 09:40 PM, Melissa Parsons wrote:
> Hello,
> Can anyone tell me what an acceptable failure rate would be when 
> faxing over SIP? Currently we are averaging around 15%. This number is 
> high I would expect it to be somewhat higher than traditional faxing 
> but not this high.
> Thank you,
> *Melissa Parsons*|Enterprise Systems Engineer
> *MarineMax, Inc.* ( 727.531.1700 office | (727.524-3954 fax
> 18167 US Hwy. 19 N. Clearwater, Florida 33764
That's vague. Are you using A-law or u-law? Are you using G.726? Are you 
using T.38? Pretty much anything else you might use will give 0 success 
rate, so I assume its one of those. The failure rate you get will depend 
on many factors. A high packet loss rate is a disaster for FAX. High 
jitter levels for the packet delivery time can be too. T.38 
implementations are quite variable in their behaviour, and not always 
that compatible. Many quirks in the SIP signalling arrangements exist in 
various implementations, too. At the end of the day you'll get somewhere 
between 0 and 100% success, depending on all these factors. Between 
servers in large data centres, connected straight on to the internet's 
backbone you might be able to send FAXes all week without an error. In 
really bad tributaries of the internet you might get a near 100% failure 


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