[OpenSIPS-Users] Need ideas to tamper with CSeq

Daniel Goepp dan at goepp.net
Thu Mar 31 18:55:53 CEST 2011

I don't mean to step on Cinthia's toe here, but I would like to add a little
to her comments / questions in response some follow ups here.  The problem
being presented has been acknowledged as a "bad" device, in violation of the
RFC.  And although it's not popular to work around issues, sometimes it is
necessary, and one of the great things about OpenSIPS is how flexible and
powerful it is.  The only problem here is the CANCEL, all other signaling
including the BYE appear to work fine with this phone.  Calls complete and
end just fine in all other cases.  I agree that perhaps a proxy shouldn't
have to do this, it is not an absolute in the real world that it would never
have to.  So this comes back to the initial question, and regardless of best
practice, is there a way when OpenSIPS receives a CANCEL to "help" it by
incrementing it's CSeq for it?



On Thu, Mar 31, 2011 at 7:48 AM, Ovidiu Sas <osas at voipembedded.com> wrote:

> On Thu, Mar 31, 2011 at 10:37 AM, Cindy Leung <cinthia721 at gmail.com>
> wrote:
> > I guess I wasn't being clear enough in the call flow.  I assume the CSeq
> in the CANCEL has to be the same as the second INVITE.
> >
> > 1. Phone sends out INVITE #1, OpenSIPS responds with 401, Phone ACK'd.  I
> believe the transaction is over at this point.
> > 2. Phone sends out INVITE #2 with auth, OpenSIPS accepts the INVITE and
> send back 180.  Phone now sends out a CANCEL, but the CSeq is not the same
> as INVITE #2.
> >
> > As far as I can tell, everything else (ruri, call-id...) is the same
> except for CSeq.
> Exactly!  You broke the CSeq between caller and callee.  A proxy
> should never do that!
> Even if you fix somehow your CANCEL issue, calls will never complete.
> The 200ok will have a different CSeq then the initial INVITE (for the
> caller) and it will be discarded (by the caller).
> Also, BYE will not work.
> You have bigger issues here then just a CANCEL.
> Regards,
> Ovidiu Sas
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