[OT] Possible causes of Q.850 cause=127?

Asterisk Asterisk Support
1

Hello,

I’ve got a case on an Asterisk 20.10 instance. My setup is
PSTN <—SIP —> Asterisk <— SIP— > Bicom PBX <— SIP—> SIP phone (hard or soft)

  • some calls from the PSTN, to a specific destination are randomly cut at the very start (out of 3 consecutive attempts: 1 success, 2 failures)
  • looking at signalling, I see that Asterisk:
    • gets an INVITE from ITSP (which Asterisk propagates downstream)
    • propagates to ITSP a 200 OK
    • ITSP replies with ACK

During failures, just after sending an ACK, ITSP sends a BYE message with Reason “Q.850; cause=127”.

From experience, what are the most common causes for such Reason “Q.850; cause=127” given this issue has only been reported for a specific number ?

Best regards

2

The normal reason for a BYE immediately after ACK is that the codecs in the 200 OK were unacceptable. That might also extend to an unacceptable encryption offer. There is no way for 200 OK to be rejected, so the call has to be accepted and immediately closed.

127 is defined as “Internetworking Unspecified”, so it is a catch all, but might well cover that case.

With normal, early offer, SDP, the 200 OK should really be compatible with hte initial offer, but some systems (e.g. some Cisco ones) use late offer SDP, and the SDP on the 200 OK is the initial offer, so can’t take account of the initiator’s requirements.

3

@david551
Thank you very much for replying.

Your reply helped to dig deeper in codec negociation and find a work around.

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