[cisco-voip] T.38 Fax Issue

[Antonio Soares]

Hello group,

A few days ago, fax stopped working on one gateway. The "debug voip rtp
session nse" gives me this:

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++++++++++++++
          s=VoIP d=DSP payload 0x60 ssrc 0x509B391F sequence 0x18E timestamp
0xF8C0
  <<<Rcv> Pt:96     Evt:136     Pkt:02 80 50
          s=VoIP d=DSP payload 0x60 ssrc 0x509B391F sequence 0x18F timestamp
0xF910
  <<<Rcv> Pt:96     Evt:136     Pkt:01 40 50
          s=VoIP d=DSP payload 0x60 ssrc 0x509B391F sequence 0x190 timestamp
0xF960
  <<<Rcv> Pt:96     Evt:136     Pkt:01 40 50
          s=VoIP d=DSP payload 0x60 ssrc 0x509B391F sequence 0x191 timestamp
0xF9B0
  <<<Rcv> Pt:96     Evt:136     Pkt:01 40 50
          s=VoIP d=DSP payload 0x60 ssrc 0x509B391F sequence 0x192 timestamp
0xFA00
(...)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++++++++++++++

Most likely, the problem is on the other end, a gateway that I do not
control.

I believe for this to work I need to receive PT=100 and EVT=200:

Payload Type 100: Designates an NSE (Named Signaling Event packet). NSE
packets can signal a variety of different messages so it is helpful to know
the NSE Event ID.

Event 200: Triggered by the detection of a V.21 fax preamble when T.38 is
configured.  This message initiates the switchover of the call from voice to
T.38. This  message is sent by the terminating fax gateway to notify the
originating fax  gateway of the switch to T.38.

And I'm receiving PT=96 and EVT=136. PT=96 means " Sent by a voice gateway
to signal a switchover to Cisco fax relay". I wasn't able to find the
meaning of EVT=136.

With this information, can I assume that the problem is on the other end ?
Can I do anything on my side to force the desired PT/EVT combination ?


Thanks.

Regards,

Antonio Soares, CCIE #18473 (R&S/SP)
amsoares at netcabo.pt