You can get answers to a lot of your questions in
http://www.ietf.org/internet-drafts/draft-ietf-sipping-sip-offeranswer-03.txt
More inline.
Paul
Vikram Chhibber wrote:
> I have further queries on re-INVITE without SDP,
> If this is a query mechanism where the UAS returns the session
> parameters of existing dialog in 200 OK,
It isn't exactly a "query mechanism". While the UAS MAY return the
parameters of the existing session, it need not. While there are some
constraints on what it may offer (e.g. it must have at least as many
m-lines as the previous offer had) it MAY change many things.
Likely things that it might do are to offer codecs and media streams
that are not currently in use, but which it is willing and able to use.
It is legal for it to change the directionality - e.g. offer a=inactive
even though the current stream is active - though that seems an
illogical thing to do.
> what should go in the ACK
> sent for this 200 OK?
The above reference will help. It must return a valid answer to the
offer, the same as if it had received an a reINVITE with an offer.
> Is empty ACK valid here or or the UAC MUST return its session
> parameters in the request?
It must.
> Again, if this is a query mechanism, can I assume the "o" line does
> not change in the SDP of 200 OK or do I need to be prepared for
> re-negotiation?
You must be prepared.
> In my opinion, re-negotiation does not makes sense here as the UAC
> sends the offer and does not instructs UAS to initiate offer-answer.
Sorry. Thats not the way it is.
Thanks,
Paul
> Thanks in advance,
> ~Vikram
>
> On 9/12/07, Vikram Chhibber <[EMAIL PROTECTED]> wrote:
>> Thanks everyone. I missed out section "8 Modifying the Session" of RFC 3264
>>
>> On 9/12/07, Retesh <[EMAIL PROTECTED]> wrote:
>>> Comments inline
>>>
>>> On 9/12/07, Vikram Chhibber <[EMAIL PROTECTED]> wrote:
>>>> Hi,
>>>>
>>>> i have few queries on SIP offer/answer for which I couldn't find a
>>>> straightforward answers:
>>>>
>>>> 1. We all are aware that we should be prepared to receive initial
>>>> INVITE with no offer. In this case, the UAS is supposed to send its
>>>> offer in the 200 Ok response.
>>>> Is sending re-INVITE with no SDP valid case? I know sending UPDATE
>>>> with no SDP is valid.
>>>>
>>> Yes, it is a valid case.
>>>
>>>> 2. Once a unicast session is established, can any of the party send a
>>>> new offer with entirely new "o" line?. The motivation for asking this
>>>> question is that suppose I have a B2BUA who doesn't do much on SDP
>>>> part and simply copies SDP from incoming messages to the outgoing
>>>> messages. Now if this B2BUA wants to send re-INVITE (for hold or
>>>> inactive media) to either party, does it needs to remember previous
>>>> SDP negiotiation and modifies that SDP to send re-INVITE or can it
>>>> create a SDP without considering anything form previous offer/answer.
>>> The session id in the o line cannot be changed within a session.
>>>
>>>> Thanks,
>>>> ~Vikram
>>>> _______________________________________________
>>>> Sip-implementors mailing list
>>>> [email protected]
>>>> https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
>>>>
>>>
>>> --
>>> With Regards
>>> Retesh Chadha
>>>
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