Subject: RE: [Sipping] draft-burger-sipping-em-rqt-00.txt

From: "Eric Burger" <[email-masked]>
Date: Fri, 2 Nov 2001 08:32:33 -0500

The problem is rather straightforward.  If you have a stateless proxy, you
need some mechanism for having the proxy-gateway signaling correct.  In a
B2BUA, things are easy: there are two call legs.  The first call leg is
between the gateway and the proxy and the second is between the proxy and
the media server.  In this scenario, the signaling between the proxy and the
media server should be a normal INVITE-200 OK protocol.  The proxy would
then be free to send a 486, or whatever is appropriate, back to the gateway.

However, a stateless proxy, by definition, will not change the messages
between the endpoints.  In this case, the media server is doing the
appropriate thing by sending the 486.

With this in mind, my comments are below.

-----Original Message From Neil Deason -----
[snip]
>
> "does not truly drive a requirement for early media between
> the proxy and the media server. There are other configurations
> that can satisfy the need for early media signaling to the
> gateway without passing early media throughout the SIP network."
>
> Whoever said there was a requirement for early media between
> the proxy and MS in the first place. The early media is required
> between the caller and answering end point. The counter example
> of 6.1.2 still needs early media signalling in the SIP network
> between the App server and the GW.

Precisely.  In this situation, the endpoint *is* the media server.  What I
wasn't clear about was that if you have a B2BUA, you *don't* need early
media everywhere.  You only need it between the B2BUA and the gateway.

How about if I clarify the last paragraph to read:

"There are other configurations that can satisfy the need for early media
signaling between the gateway and the proxy without introducing early media
signaling to the rest of the SIP network.  For example, a state-full B2BUA
can set up a normal SIP session with the media server, while sending early
media signaling to the gateway."

>
> The signalling flow of 6.1.2 also claims to have the added
> benefit of allowing outsourcing of announcement services
> but this is also possible in the 6.1.1. There is no reason
> there why the proxy and MS have to be in the same administrative
> domains. As well as not complicating possible billing the 6.1.1
> signalling retains end to end transparency by not introducing
> a B2BUA into the network.

While possible, it is not practical to outsource announcement services based
on the setup of 6.1.1.  The reason is that between network administrative
domains, the SIP messages should reflect the SIP reality.  The SIP reality
for an outsourced announcement is that the outsource network successfully
satisfies (200 OK) the request from the first network.

>
> In 6.2.2 I would have to disagree with the assertion that
> early media is not just a PSTN/SIP interworking. I find the
> example of a UA that is too dumb to play a media announcement
> but that is smart enough to be B2BUA hard to come to terms with.
> Early media is only a problem in a pure SIP environment
> if you go out of your way to make it one. There are many better
> ways of implementing a Do Not Disturb service than this.
>

I don't get your objection. Collapse the UAS and Media Server components
into a combined, very smart phone (yes Mr. Batson, I know you know they
exist :-). Can you explain how that avoids the necessity for early media?

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