The B2BUA has the burden of making things right here, and as shown it
did not. It should only be adding the Supported:100rel if it has a
workable strategy for generating PRACKs, because it is the element
responsible for doing so.
Its true that the offer in the 18x then requires an answer in the PRACK,
so the B2BUA will need to make that up. In general there is no way it
can do that in a way that is guaranteed to be consistent with the answer
that UA1 will eventually provide. So the B2BUA will need some strategy
to reconcile the different answers. The only way to do that for certain
is if the B2BUA is terminating the media as well. In that case it can in
principle transcode between the two.
If its not prepared to do all that, then it ought not add the
Supported:100rel to the INVITE.
Paul
M. Ranganathan wrote:
> On Fri, Dec 12, 2008 at 10:24 PM, kaiduan xie <[email protected]> wrote:
>> But how B2BUA generates SDP answer to be carried in PRACK?
>>
>
> Can replay the previously played SDP
>
>
>>
>> ----- Original Message ----
>> From: Neelakantan Balasubramanian <[email protected]>
>> To: kaiduan xie <[email protected]>;
>> "[email protected]"
>> <[email protected]>
>> Sent: Friday, December 12, 2008 8:18:46 PM
>> Subject: RE: [Sip-implementors] PRAC/B2BUA
>>
>> See below.
>>
>>> -----Original Message-----
>>> From: [email protected] [mailto:sip-
>>> [email protected]] On Behalf Of kaiduan xie
>>> Sent: Friday, December 12, 2008 6:28 PM
>>> To: [email protected]
>>> Subject: [Sip-implementors] PRAC/B2BUA
>>>
>>> Hi, all,
>>>
>>> An inter-operation problem is encountered, the scenario is,
>>>
>>> UA 1 B2BUA GW
>>> | INVITE-1 | |
>>> |-------------------->| INVITE-2 |
>>> | |----------------------->|
>>> | | 183-3 |
>>> | |<----------------------|
>>> | 183-4 | |
>>> |<--------------------| 183-5 |
>>> | |<----------------------|
>>>
>>> INVITE-1 does not have SDP, and no Supported header.
>>> INVITE-2 does not have SDP, but INVITE-2 has Supported header with
>>> 100rel.
>>> 183-3 has SDP, and Required header with 100rel. 183-3 is re-
>>> transmitted in 183-5. I omits further retransmission.
>>> 183-4 has SDP, but no Required header.
>>>
>>> The call fails.
>>>
>>> My question is: is legal for B2BUA to put Supported header with 100rel
>>> if UA1 indicates that it does not support 100rel? I think B2BUA is
>>> wrong in this case.
>> [Neelakantan Balasubramanian]
>> B2BUA can provide different behavior on two legs of the call. There is no
>> requirement on what B2BUA should do, as for UA1, the B2BUA is the UAS.
>> There is no 100rel supported on this leg of the call. For GW, the B2BUA is
>> the UAC. In this leg 100rel is supported.
>>
>> So, the B2BUA should handle retransmits of 183, send the PRACK for each
>> provisional responses.
>> [Neelakantan Balasubramanian]
>>
>>> In the above picture, B2BUA is from a very big company :)
>> [Neelakantan Balasubramanian]
>> You should talk with the vendor.
>>
>>> What is your point?
>>>
>>> Thanks
>>>
>>> kaiduan
>>>
>>
>>
>> __________________________________________________________________
>> Looking for the perfect gift? Give the gift of Flickr!
>>
>> http://www.flickr.com/gift/
>> _______________________________________________
>> Sip-implementors mailing list
>> [email protected]
>> https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
>>
>
>
>
_______________________________________________
Sip-implementors mailing list
[email protected]
https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
