[asterisk-bugs] [JIRA] (ASTERISK-27913) Fax reception fails when remote end rejects UDPTL stream in SDP with port 0 (no G711 fallback?)

[George Diamantopoulos (JIRA)]

George Diamantopoulos created ASTERISK-27913:
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             Summary: Fax reception fails when remote end rejects UDPTL stream in SDP with port 0 (no G711 fallback?)
                 Key: ASTERISK-27913
                 URL: https://issues.asterisk.org/jira/browse/ASTERISK-27913
             Project: Asterisk
          Issue Type: Bug
      Security Level: None
          Components: Channels/chan_pjsip, Channels/chan_sip/T.38, Resources/res_pjsip_sdp_rtp, Resources/res_pjsip_t38
    Affects Versions: 13.21.0, 11.25.3
         Environment: For Asterisk 13:
  Debian Stretch
  Asterisk built from source: 13.21.0

For Asterisk 11:
  Debian Jessie
  Asterisk built from source: 11.25.3
            Reporter: George Diamantopoulos


I have come across the following issue with what I believe to be Cisco SIP Endpoints initiating a fax call to an Asterisk running the ReceiveFax application in the dialplan or acting as a T.38 gateway for another endpoint.

The issue manifests as follows:
# Incoming INVITE from remote (Cisco) endpoint
# Asterisk answers with 200 OK
# Asterisk sends re-INVITE with a single offer for UDPTL in SDP
# Cisco endpoint replies with 200 OK, and the has the following contents:
{noformat}
    v=0
    o=- 29768103 29768104 IN IP4 0.0.0.0
    s=SBC call
    c=IN IP4 0.0.0.0
    t=0 0
    m=image 0 udptl t38
    a=sendrecv
{noformat}
# Fax transmission fails, instead of Asterisk issuing a re-INVITE with an audio offer in either alaw or ulaw



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