[OpenSIPS-Users] Need ideas to tamper with CSeq

Cindy Leung cinthia721 at gmail.com
Thu Mar 31 16:37:50 CEST 2011

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.


On Mar 31, 2011, at 5:03 AM, Anca Vamanu wrote:

> On 03/31/2011 03:21 AM, Cindy Leung wrote:
>> I know I'm doing something bad here.  However, we are having a problem with one of the SIP phones that we support.  When it sends out an INVITE and then CANCEL, the CANCEL is not being forwarded.  We are suspecting that it is caused by a wrong CSeq value.
>> INVITE #1 gets challenged.
>> INVITE #2 accepted.
>> CANCEL is sent, but CSeq is the same as the one in INVITE #1.
> It is ok (RFC compliant) for the Cseq in CANCEL to be the same as the Cseq in INVITE:
> RFC 3261 - section 9.1:
> "The Request-URI, Call-ID, To, the numeric part of CSeq, and From header
>   fields in the CANCEL request MUST be identical to those in the
>   request being cancelled, including tags. "
> Regards,
> -- 
> Anca Vamanu
> OpenSIPS Developer
>> It is less than ideal for us to contact their support and we'd like to get it fixed asap.  I've tried subst(), remove_hf and append_hf to play with CSeq with no luck.
>> Any suggestions?  Thanks!
>> Cinthi
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