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.

2) If not, should I be looking elsewhere in SER/Asterisk to solve this problem?

regards,

SCM