[Freeswitch-users] T.38 via UPDATE request

[Peter P GMX]

Hello,

we have the following problem.
2 Fax machines are communicating via Freeswitch. One is externally
attached via a Telco who is able to handle T.38. The other one is
attached locally.

When 2 Fax machines start syncing each other, the Telco sends a SIP
UPDATE message with T.38 SDP, as it detects fax during the fax negociations.
Freeswitch answers with an SIP OK message back to the telco, and I can
see the T.38 SDP on the debug console of freeswitch.
Then nothing happens any more until one of fax machines detects timeout.

We have set proxy-media to true. However is was done during call setup
when both machines communicated with G711 SDP.
The UPDATE message was commited by FS to the telco, but was not sent to
the other fax, so I think in this case Freeswitch is supposed to
transcode between T.38 and G711 which it cannot do, as we know.

How can I overcome this scenario? Is this a defect, should freeswitch
send the UPDATE message to the other fax?  Or is there a workaround?

Best regards
Peter

Here's the UPDATE message:
UPDATE sip:mod_sofia at 82.115.xx.xxx:5080 SIP/2.0.
Call-ID: 5283fe4e-334f-122d-d1b9-001517956764.
Contact: <sip:212.91.xxx.xxx:5060>.
Content-Type: application/sdp.
CSeq: 16340063 UPDATE.
From: <sip:06912345678 at sip.telco.de>;tag=00-08135-017e041a-4d21f6037.
Max-Forwards: 31.
Route: <sip:82.115.96.165;lr;ftag=pH663F4S02erm>.
To: "030987654321" <sip:030987654321 at 82.115.xx.xxx>;tag=pH663F4S02erm.
User-Agent: Cirpack/v4.41e (gw_sip).
Via: SIP/2.0/UDP 212.91.xxx.xxx:5060;branch=z9hG4bK-178C-1923B31.
Content-Length: 300.
.
v=0.
o=cp10 125551618103 125551618105 IN IP4 212.91.xxx.xx.
s=SIP Call.
c=IN IP4 212.91.xxx.xx.
t=0 0.
m=image 6860 udptl t38.
a=sendrecv.
a=T38FaxVersion:0.
a=T38MaxBitRate:9600.
a=T38FaxRateManagement:transferredTCF.
a=T38FaxMaxBuffer:1000.
a=T38FaxMaxDatagram:200.
a=T38FaxUdpEC:t38UDPRedundancy.