[BUG] B2BUA Module: rseq need to be handled independently per leg or toTag passed along.

[hb9eue]

Hi

I'm not sure if this is a bug or rather a feature request. But I consider this a bug as it probably breaks a situation which I think is not that uncommon.

opensips 3.4.6 in use als B2BUA in this call scenario

Issue short description:

When forking a call on the B leg, different endpoints send provisional messages each with a unique To-Tag and if reliable transport is requested, with most probably an identical rseq number.

The current implementation of the B2BUA Module on opensips does generate a to tag on the A leg an uses that same to-tag for all provisional messages received with different to-tags from the B side. The rseq header of provisional messages routed to the A side is copied from the B side.

This causes the 'different' provisional messages on the A side to be misidentify as re-transmits because of non RFC compliant same rseq number.

Example:

A => Commercial SBC => OpenSIPS => Kamailio Registrar => CPE B (ringing timeout)
                                                          |->  CFW => CPE C

OpenSIPS is use to perform topology hiding and also solves situations where a 2nd leg needs a unique CallID. Kamailio implements call forwarding delayed aka no-answer functionality to Customer B.

INVITE from A to B

• OpenSIPS generates a new CallID on the B Side.
• CPE B replies with 180 RINGING, no SDP! => ToTag: I-Am-B and rseq 1
• 180 RINGING, with is passed along OpenSips with Generates a new ToTag: I-Am-OpenSIPS and passes along rseq 1
• Commercial SBC sends PRACK.
• OpenSIPS answers 200 OK to PRACK.
• A receives this 180 RINGING message.
• CPE B does not answer within timeout, kamailio triggers CFW
• INVITE from A is sent to C
• CPE C replies with 180 RINGING, WITH SDP! => ToTag: I-Am-C and rseq 1
• 180 RINGING + SDP is passed to OpenSips which routes this to leg A with ToTag: I-Am-OpenSIPS and passes along rseq 1
• Commercial SBC drops this 180 RINGING + SDP as it has identical ToTag and rseq as the previous one.
• CPE C connects: 200 OK to INVITE, no SDP (it was already sent via reliable provisional message).
• OpenSIPS and Commercial SBC route that message to A
• A has never received the 180 RINGING + SDP and is unable to establish an RTP connection.

From my point of view, there would be two options to remedy that situation:

I think the more sensible one, would be to make the B2BUA Module of Kamailio to keep track of and increment the rseq counter on leg A and B individually and not just copy the rseq counter from leg B to A.

Alternatively it might also be an option to make OpenSIPS just pass the ToTag unaltered which would definitely prevent our commercial SBC from dropping the provisional message.

What are the opinions of to that issue? Did I maybe misconfigure something or miss how this can already be solved?

-Benoit-

[github-actions[bot]]

Any updates here? No progress has been made in the last 15 days, marking as stale. Will close this issue if no further updates are made in the next 30 days.

[github-actions[bot]]

Marking as closed due to lack of progress for more than 30 days. If this issue is still relevant, please re-open it with additional details.