[asterisk-users] Unable to get Fax t38 working with IrisTel trunk

[Karim Mardhani]

Hi everyone,
I have been trying to get T.38 Faxing to work with Iristel sip trunks for
last few days but havn't been sccussful.  I am using Asterisk 1.6.2.8 and
SpanDSP 0.6.  Here is what I see in the tcpdump capture:
1.  Call come in from the trunk as regular voice call with g.711 codec
2.  Asterisk answers the call and recognizes the CNG and sends the call to
fax extension
3.  Eventually Receive fax is called with a file name
4.  Asterisk sends update message to remote gateway with T38 codec
information
5. Remote server doesn't respond.  Asterisk resends update messages multiple
times.
6. Eventually remote gateway sends the invite with T38 codecs listed in the
SDP
7. Asterisk Responds back with 488 "Not acceptable here"
8. Another invite is send from the remote gateway with T38 codecs in the SDP
9. Asterisk sends OK but g.711 codecs listed in SDP.
10. remote gateway sends the BYE message and call is completed.

The questions I have are:
Why Asterisk sends update message in step 4 above instead of send an invite?
Why Asterisk responds back with 488 in step 7 above?
Why asterisk sends g.711 codecs in step 9 above?

Thanks

Karim
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