Subject: RE: [Sipping] BCP for Offer/Answer Use - PLEASE COMMENT

From: "Christer Holmberg (JO/LMF)" <[email-masked]>
Date: Wed, 2 Nov 2005 10:42:33 +0100

Hi,

>>CHH: Technically, and it has been brought up on the implementor's list

>>every now and then, I guess it's possible to send reliable provisional

>>responses and PRACKs, containing offer/answers, also for re-INVITE 
>>requests.
>> 
>[TS] Yes, it is possible for re-INVITE without an SDP.
>And it is not allowed to send NEW offer in a reliable 
>provisional response once offer/answer exchange is completed 
>in the dialog.

[CHH] Technically you can also send a re-INVITE WITH an SDP offer, and
receive an answer in a 18x response.

>>In table 2, I don't like the way offers in PRACKs are rejected. It's a

>>very "heavy" procedure, and it would require support of UPDATE 
>>(re-INVITE cannot be used at this point). I would propose that the 
>>PRACK 200 OK is sent without SDP, and that means that the offer is
rejected.
>>No, it's not the cleanest solution in the world, but that is the 
>>problem with PRACK.
>[TS] This is the reason to include the following sentense in 2.2;
> 
>"UA can send a PRACK request with a new offer when acknowledging the
>reliable response. Compared to UPDATE method, using PRACK can save
>messages to be exchanged between the UAs. However, as a PRACK request
>should not be rejected, UA is recommended to send a PRACK 
>request only when it is sure that the peer accepts a new offer in a 
>PRACK request."

[CHH] I don't like that text, because the sender can't "be sure" whether
the receiver will accept an offer or not.

However, I would support saying something like "the sender should only
use PRACK to send offers when it has strong reasons to assume the
receiver will accept". I.e. using PRACK to propose the adding of new
streams etc should be avoided.

>At a first glance, I feel a little bit strange the solution 
>you proposes, 200 OK without SDP to reject an offer and 
>accept an acknowledgement.

[CHH] You are going to send a 200 OK to the PRACK anyway...

>But I admit that the solution of accepting an offer in PRACK 
>and then sending new offer with UPDATE will cause several problems.
>I really want to put stress on "Offer should not be sent with 
>PRACK request unless it is sure to be accepted."
>I even want to restrict the PRACK offer usage to the case 
>described in RFC 3312 and recommend to support UPDATE.

[CHH] No matter how much you put stress on it, you still need to
describe how an offer in PRACK is rejected. We can't assume offers in
PRACKs will always be accepted.

Regards,

Christer

_______________________________________________
Sipping mailing list  https://www1.ietf.org/mailman/listinfo/sipping
This list is for NEW development of the application of SIP
Use [email-masked] for questions on current sip
Use [email-masked] for new developments of core SIP

---

From: Gonzalo Camarillo <[email-masked]>
Date: Wed, 02 Nov 2005 12:16:56 +0200

Hi,

> PRACKs will always be accepted.

As Takuya has pointed out in the draft, it is the same thing as with 
offers in 200 OK for an INVITE or a re-INVITE. You return an acceptable 
answer, and then, do whatever you feel it is appropriate (e.g., send a 
new offer or terminate the session)

Cheers,

Gonzalo