asterisk users - Sep 2005 - SIP Gateway wants T38, Asterisk rejects but media path not established.

Disclaimer: Yes, I know faxing over G711 is unreliable. :-)

We're running Asterisk 1.0.9 which talks to a Audiocodes SIP Gateway. 
We're
running Sipura SPA-2002's as ATA's and faxing within our own voice
network is
working.  If we try and fax out to the world however, we're running into a
problem.

When the call connects and the modem tones begin to negotiate, our SIP/PSTN
Gateways's SIP server determines it's a fax call and sends an INVITE to
our
Asterisk box asking us to negotiate T38.  To this, Asterisk replies with a
488: Not acceptable here message.  There is no SDP payload in this 488
message.  The SIP/PSTN gateway sends an ACK to this.

At this point, nothing happens.  Eventually Asterisk gets bored and sends a
BYE to the SIP/PSTN gateway and the call ends.

Our SIP/PSTN gateway provider seems to think that Asterisk should initiate a
renegotiation to G711 when it sends the 488 message rejecting T38.

Is this how it should work?  I've asked them to look into disabling T38
support for us completely, but it seems like Asterisk and the SIP/PSTN gateway
should be able to negotiate G711, I just don't know what the proper sequence
of events should be.

Any ideas?

Ray

Ray Van Dolson wrote:
> Our SIP/PSTN gateway provider seems to think that Asterisk should initiate
a
> renegotiation to G711 when it sends the 488 message rejecting T38.
This is not correct. The 488 response 'cancels' the INVITE, so no codec 
change was ever actually involved. The gateway should continue sending 
G711 since the other device (Asterisk) did not accept the change.