[SIPForum-techwg] Question of SIP dialog match

[Robert Sparks]

If you are a 3261 device, you will match responses to requests using  
the branch parameter
in the topmost via, not the (call-id,from-tag,to-tag,cseq,via)  
combination from 2543.

Then, and only in the case of 200OKs to INVITEs, you'll use the to- 
tag to tell whether
you have responses from multiple legs or if you're just seeing  
retransmissions of the
response from one endpoint.

If you were to travel back in time several years and had to implement  
at 2543 device,
you would do what you are trying to ask about, and you would notice  
that your request
had a null to tag, so you would ignore the to tag in the comparison  
to match this transaction.
(but your code must not do this anymore - use the branch parameter as  
above instead).

RjS

On Jul 11, 2007, at 9:27 PM, mike xu wrote:

> Hi Robert,
>
> Thank you for your reply.
> After I got the far side response (200 OK) with to-tag added, how
> could I confirm that this response is for my INVITE? Call-ID and
> from-tag is equal, but the to-tag is not equal since the INVITE
> request has no to-tag.
> Do you know that how to deal with this case? Update far side
> response's to-tag into local before dialog match? Or just skip to-tag
> match (only match from-tag and Call-ID) if the response is for the
> INVITE without to-tag?
>
> Best regards,
> Mike
>
> On 7/11/07, Robert Sparks <rjsparks at nostrum.com> wrote:
>> Mike -
>>
>> The far side must add a to-tag to the responses it sends to your  
>> INVITE.
>> This is how you tell responses from different legs of a forked
>> request apart.
>>
>> RjS
>>
>> On Jul 10, 2007, at 9:39 PM, mike xu wrote:
>>
>> > Hi,
>> >
>> > In RFC3261 section 12 Dialogs, it said "A dialog is identified  
>> at each
>> > UA with a dialog ID, which consists of a Call-ID value, a local tag
>> > and a remote tag".
>> > And as you know that the first INVITE request has no to-tag, in  
>> order
>> > to match the 200 OK response for the INVITE, could I update the  
>> to-tag
>> > in 200 OK response into my local INVITE's to header? If I it was
>> > updated then the dialog could be matched without any problem,
>> > otherwise the dialog couldn't be matched since the first INVITE's
>> > to-tag is NULL. Does this operation comply with RFC3261?
>> > Would you like to give me any suggestions on such dialog match
>> > problem?
>> >
>> > Thanks in advance,
>> > Mike
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