[SIPForum-discussion] Offer-answer

[Hemant Kumar]

Hi Mrinal,

*"Once offer answer is complete Is it possible to UAS to send more 18x
responses?"*
Yes.
But the call flow that you have shown is not correct. Once UAS sends a final
response 2xx/4xx/5xx/6xx for an INVITE it can't send any further responses
for that INVITE and your flow shows 18x from UAS to UAC after 200 response.

If UAS wants to update the SDP in early dialog only(before responding with a
final resposne) it can do so by sending multiple 18x reponses with SDP
offer. So the call flow should be as below -

       UAC               UAS
        |----INVITE------>| - with Supported:100rel or Require:100rel
        |                        |
        |<----18x(o)----- | - provisional responses with Require:100rel
        |                        |
        |----PRACK(a)->| - send PRACK with answer
        |                        |
        |                        |
        |                        |
        |<----18x(o) -----| - to update the SDP
        |---PRACK(a)-->|
        |                         |
        |      200OK        |
        |<------------------|
        |                        |
        |        ACK         |
        |------------------>|


Regards,
Hemant

On Wed, Jun 29, 2011 at 11:15 AM, mrinal kuila <mrinal.80 at gmail.com> wrote:

> Hi  Forum,
>
> Coiuld you please answer my below question.
> Once offer answer is complete Is it possible to UAS to send more 18x
> responses?
>
>          UAC               UAS
>         |----INVITE------>|
>         |                 |
>          |<----18x (o)-----| - provisional responses with REQUIRE 100rel
>          |                 |
>          |-----PRACK(a)--->| - send PRACK with answer
>          |<---- 2xx--------|                 |
>           |                 |
>          |                 |
>          |<----18x --------| - >         |                 |
>         |-----PRACK------>|
>          |<----2xx---------|
>
>               200OK
>         <-----------------
>          ------------------>
>               ACK
>
>
> Regards
> Mrinal
>
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-- 
- Hemant
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