[Serusers] Fax problem with SER/Asterisk

[Klaus Darilion]

scm-j at nuntius.com wrote:

> I am facing some problems with sending fax calls. I am using G.711 
> codec. However, my service provider (Level-3) does not support T.38 fax 
> relay.
> 
>  
> 
> According to Level-3 they “think” the problem lies in the “Media 
> Description” field of the SDP message I am sending them. The problem is 
> related to the “Media Format”  sub-field (value 101) that I am sending, 
> which according to them should be removed.
> 
>  
> 
> The SDP “Media Description” field I am sending, looks as follows:
> 
>  
> 
> “m=audio 20744 RTP/AVP 0 101”
> 
>  
> 
> which is decoded by Ethereal as follows:
> 
>  
> 
> Media Type: audio
> 
> Media Port: 20744
> 
> Media Proto: RTP/AVP
> 
> Media Format: ITU-T G.711 PCMU
> 
> Media Format: 101
> 
>  
> 
> My call is initiated by Asterisk which is sent to Level-3 via SER
> 
>  
> 
> Asterisk -à SER -à Level-3
> 
>  
> 
> The SIP call flow looks fine for the call. The sending fax sends the 
> page and then gives an error. The receiving side gives me an error and 
> prints a blank page.
> 
>  
> 
> My questions are as follows:
> 
>  
> 
> 1)       Could the “Media Format” 101 be the problem? If so, how do I 
> remove the 101? This change is probably in Asterisk, as it initiates the 
> call, and not SER, or probably both.

I don't think that this will cause problem. If this is really the 
problem, than the L3 gateway su$%s.
> 
> 2)       If not, should I be looking elsewhere in SER/Asterisk to solve 
> this problem?
How is the fax generated? A PSTN fax machine connected to asterisk? 
span_dsp?

regards,
klaus