Asterisk 1.6.2 How To Debug T.38 Udptl Problems

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Hi all

I know, a fairly old asterisk installation.

Is there any way to debug T.38 handshaking issues?

We have a C3 Voice Switch with link to the Asterisk server.

I see this Dialogue:

C3 => Asterisk
=> Invite g711
<= 200OK C3 detects Fax and send re-invite => Invite T.38

So, this is only a very basic invite.

The Asterisk picks that up and replies with details:

<= 200 OK + SDP T.38 Version:0 BaxBitRate:14400 RateManagement:transferredTCF MAxDatagramm:1400 UdpEC:t38UDPFEC The C3 Switch then compares this whith it's capabilities and answers with one more re-invite: => Invite + SDP T.38


Well so the C3 just tells the asterisk, that it only support 512 byte datagramm, but everything else is the same.

The Asterisk replies to this invite with:

488 Not acceptable here.

Now I would like to find out what is not acceptable for the asterisk.

core set verbose 99 and debug 99 does not show any futher information. udptl set debug on neither.

Any other way to debug the T.38 handshake?

Or does anyone have an idea over what the asterisk is stumbling?

-BenoƮt Panizzon-

I m p r o W a r e A G – Leiter Commerce Kunden

One thought on - Asterisk 1.6.2 How To Debug T.38 Udptl Problems

  • What if you set the maxdata in asterisk to a value lower than the other side? e.g. sip.conf:
    t38pt_udptl = yes,fec,maxdatagram@0