Hello, cseq is per UA, each side has its own independent value that it (usually) increments when sending a new request within dialog to the other party.
Cheers, Daniel On 12.05.26 13:23, Benoit Panizzon via sr-users wrote: > Hi Gang > > I am aware, this is a generic SIP question, not strictly related to > Kamailio. But we are experiencing a strange issue with a 3CX PBX (and > we use Kamailio as VSP) > > Yes, I have read: > https://datatracker.ietf.org/doc/html/rfc3261#section-8.1.1.5 > https://datatracker.ietf.org/doc/html/rfc3261#section-12.2.1.1 > > But I still have a question: Are cseq number independent for each side, > or has the B side to increment the last cseq seen from the A side on a > new request? > > Is this a VALID example? > > Initial Invite A=>B > > A=>B INVITE: cseq 5 INVITE > A<=B 100 Trying: cseq 5 INVITE > A<=B 180 Ringing: cseq 5 INVITE > A<=B 200 OK: cseq 5 INVITE > - trancation ended > A<=B Re-INVITE: cseq 1 > A=>B 200 OK: cseq 1 > - transaction ended > A=>B BYE: cseq 6 BYE > A<=B 200 OK: cseq 6 BYE > - transaction ended > > Here A started with cseq 5 and increased to cseq 6 for the next > transaction. > B started with cseq 1 which is lower than what A started with. > > So both side use a different starting point, and each side increments > their cseq by one independently of what the other side told. > > Or is this not allowed and B should have sent the Re-Invite with cseq 2? > > > What about this example (which is the one we see failing) with nested > transactions? > > A=>B INVITE: cseq 1 INVITE > A<=B 100 Trying: cseq 1 INVITE > A<=B 180 Ringing: cseq 1 INVITE > A<=B UPDATE: cseq 1 UPDATE > A=>B 500 Server Error: cseq 1 UPDATE > > Looking at logs on PBX A seems to indicate it detected a problem with > the sequence number in the UPDATE message. > > So what is the linkely cause? > * Two concurrent transactions with same sequence number from different > sides not allowed by some RFC (if so, which one?) > * Each side has to take care to start every new transaction with a > higher sequence number as the other side? > * PBX buggy? > > Mit freundlichen Grüssen > > -Benoît Panizzon- > -- > I m p r o W a r e A G - Leiter Commerce Kunden > ______________________________________________________ > > Zurlindenstrasse 29 Tel +41 61 826 93 00 > CH-4133 Pratteln Fax +41 61 826 93 01 > Schweiz Web http://www.imp.ch > ______________________________________________________ > __________________________________________________________ > Kamailio - Users Mailing List - Non Commercial Discussions -- > [email protected] > To unsubscribe send an email to [email protected] > Important: keep the mailing list in the recipients, do not reply only to the > sender! -- Daniel-Constantin Mierla (@ asipto.com) twitter.com/miconda -- linkedin.com/in/miconda Kamailio Consultancy, Training and Development Services -- asipto.com Kamailio World Conference, May 7-8, 2026 - Berlin, Germany -- kamailioworld.com
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