Getting channel ‘SIP/’ refused to negotiate T.38

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Asterisk Users 4 Comments


I recently configured T.38 on Asterisk 10.4.2. When I send the fax to
Asterisk, it gives the errors as listed below;

WARNING[25986]: app_fax.c:442 transmit_audio: channel
‘SIP/’ refused to negotiate T.38
WARNING[25986]: app_fax.c:174 span_message: WARNING T.30 ECM carrier not

As in sip.conf the configuration is listed below;

t38pt_udptl = yes,fec,maxdatagram=400
faxdetect = t38

And the rest are the standard configuration.

Please advise to resolve this issue.

4 thoughts on - Getting channel ‘SIP/’ refused to negotiate T.38

  • Here is my setup;

    Fax machine -> PSTN -> Cisco Voice GW -> IP cloud -> Asterisk. As on Cisco
    Voice GW, T.38 fax already configured on SIP protocol.

  • Apparently your configuration of the ‘Cisco Voice GW’ was not
    successful, as it refused to accept a re-INVITE from Asterisk that
    wanted to switch the SIP channel to T.38 mode.

  • The configuration I did in Cisco Voice GW is listed below;

    dial-peer voice 2852 voip
    description Incoming Fax Calls to Asterisk
    destination-pattern 329..
    session protocol sipv2
    session target ipv4:
    codec g711ulaw
    fax protocol t38 ls-redundancy 0 hs-redundancy 0 fallback none

    Please advise to overcome this warning.