[Serusers] Fax problem with SER/Asterisk

[scm-j at nuntius.com]

> How is the fax generated? A PSTN fax machine connected to asterisk? 
> span_dsp?

A PSTN fax machine comes in to the Asterisk (via SIP or IAX. tested both
ways but neither works), where the caller gets authenticated (via ANI or
DTMF) and the destination leg of the call is originated by Asterisk to
Level-3 via SER...



-----Original Message-----
From: Klaus Darilion [mailto:klaus.mailinglists at pernau.at] 
Sent: Thursday, February 17, 2005 9:46 AM
To: scm-j at nuntius.com
Cc: serusers at lists.iptel.org
Subject: Re: [Serusers] Fax problem with SER/Asterisk

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