Subject: Re: [Sip] Local vs Remote ringback on 180

From: "Alexeitsev, D" <[email-masked]>
Date: Thu, 4 Jul 2002 14:17:55 +0200

Hello Bert, Christer

Thank you for the clarifications

Some comments inline

Again, AFAIK a UAS can send media to the UAC after receiving the UAC's
SDP.  No response is required to be sent back to the UAC.  Sending a
response with SDP is the "polite" thing to do IMHO as it's an explicit
indication that the UAS will send media (and allows RTP/RTCP to "work").

[DA] That was my understanding as well. I think, that in some scenarios, it is better to wait for the answer before playback for the prevention of receiving media from hosts that are not invited to the session. Even by the cost of user convenience.

My read indicates answers MUST be in a reliable response, which is only
200 in bis-09.  This is stated pretty clearly IMHO.  I'm not sure what a
"early media session" is but if you want to complete the offer-answer
exchange prior to sending/receiving a 200 OK, then there's the 100-rel
extension (as I'm sure you're aware :).

[DA] Is the use of the TCP/SCTP is good enough to say that e2e provisional responses with answer are reliable?

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From: "Bert Culpepper" <[email-masked]>
Date: Thu, 4 Jul 2002 10:42:57 -0400

Hi,

comments below...

Alexeitsev, D wrote:
> [DA] That was my understanding as well. I think, that in some
> scenarios, it is better to wait for the answer before
> playback for the prevention of receiving media from hosts
> that are not invited to the session. Even by the cost of user
> convenience.

Yes, this has been discussed before :)  I think this can be handled for
Christer's scenario if the B2BUA completes the initial INVITE
transaction and uses reINVITE instead of UPDATE to provide the service.
Again, the B2BUA will have to manage the caller's user experience in
this case.

> [DA] Is the use of the TCP/SCTP is good enough to say that
> e2e provisional responses with answer are reliable?

I don't think so for "reliable provisional responses".  Retransmissions
are not needed when using TCP but a PRACK from the UAC is still needed
for "reliable provisional responses".

Regards,
Bert