Subject: [Sip] Question about resource management

From: [email-masked]
Date: Fri, 2 May 2003 14:34:57 +0100

Dear all,

I have a question regarding resource management and in particular related to
at which point in the session establishment may resource reservation be
initiated. I would appreciate any comments on this.

I have noticed that the examples given in RFC 3312 seem to indicate that
resource reservation may be initiated as soon as an answer has been sent (by
the answerer) or received (by the offerer). At some point the RFC says:

"If the resource reservation mechanism used requires participation of
   both user agents, the answerer SHOULD start resource reservation
   after having sent the answer and the offerer SHOULD start resource
   reservation as soon as the answer is received.  If participation of
   the peer user agent is not needed (e.g., segmented status type), the
   offerer MAY start resource reservation before sending the offer and
   the answerer MAY start it before sending the answer."

My question is: if the answer (lets assume that it is carried in a 183
response) is carrying a list of codecs taken from the initial offer (my
understanding is that this is possible under the answer/offer model),
shouldn't both user agents wait for the updated (final) answer to be sent
and received (in the PRACK or the 200 OK to the PRACK) before initiating
resource reservation? 

Following on that, I have also noticed that 3GPP call flows as specified in
TS 24.228 show resource reservation happening after the 200 OK for the PRACK
is sent and received. Couldn't the reservation start just after the PRACK
message (carrying the final answer) is sent/received?

So, when can we assume that resource reservation can start? Can we assume
that it can start as soon as a final offer is sent/received?

Thank you very much in advance.
Regards
Maria 

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From: [email-masked]
Date: Fri, 2 May 2003 18:33:11 +0300

Hi Maria, 

a quick clarification for the 3GPP call flows:
according to the very latest changes to the last version of the call flows document (3GPP TS 24.228 5.4.0): 
- the offerer can start the resource reservation procedure right after receiving the answer in 183, if the answer is satisfactory, i.e. it contains single codecs per media flows. In case there is a need to include a second offer in PRACK in order to reduce to the "single codec per media" case, the resource reservation can be started right after sending the PRACK.
- the answerer can start the resource reservation procedure right after having sent the answer in 183, if the answer contains single codec per media flows. In case the first answer has multiple codecs per media, the answerer should wait with resource reservation until generating the second answer.

Regards,
Krisztian

> -----Original Message-----
> From: ext [email-masked] [mailto:[email-masked]]
> Sent: Friday, May 02, 2003 4:35 PM
> To: [email-masked]
> Subject: [Sip] Question about resource management
> 
> 
> Dear all,
>

---

From: [email-masked]
Date: Fri, 2 May 2003 16:45:31 +0100

Krisztian, thanks a lot for your answer.

I have a further question on this same subject though:
- Could the updated offer in the PRACK contain more than one codec again?
And, if the answer in the 200 OK (PRACK) still contains a list of codecs,
when will resource reservation happend then?

Is any of the user agents (offerer or answerer) obliged to reduce the list
to a single codec at some point in the offer/answer model? 

Thank you very much
Regards
Maria

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: 02 May 2003 16:33
To: Cuevas,MA,Maria,XGH4 R; [email-masked]
Subject: RE: [Sip] Question about resource management

Hi Maria, 

a quick clarification for the 3GPP call flows:
according to the very latest changes to the last version of the call flows
document (3GPP TS 24.228 5.4.0): 
- the offerer can start the resource reservation procedure right after
receiving the answer in 183, if the answer is satisfactory, i.e. it contains
single codecs per media flows. In case there is a need to include a second
offer in PRACK in order to reduce to the "single codec per media" case, the
resource reservation can be started right after sending the PRACK.
- the answerer can start the resource reservation procedure right after
having sent the answer in 183, if the answer contains single codec per media
flows. In case the first answer has multiple codecs per media, the answerer
should wait with resource reservation until generating the second answer.

Regards,
Krisztian