Subject: [Sip] Comments on draft-willis-sip-path-04

From: "Finnie, Donald" <[email-masked]>
Date: Wed, 1 May 2002 17:25:56 +0100

Section 2. "Applicability Statement" seems to have some ambiguous wording in
my opinion.  

2.2 says "One or more of the intermediate proxies MUST be visited by
messages between REGISTRAR and UA."

The use of the words "between" and "messages" seem ambiguous.  I assume this
refers only to dialog-initiating messages sent *from* REGISTRAR *to* UA?  If
my understanding of the Path mechanism is correct, it does not effect INVITE
messages, for example, sent from UA to some target via REGISTRAR/home
service proxy.  Nor does it imply Record-Routing at intermediate proxies so
they will only remain in the signalling path if they choose to Record-Route.

2.2 says "The same set of proxies must be visited by messages between a home
service proxy and UA.  That is,  the proxy route between  the UA and its
home service proxy is identical to the proxy route between the UA and its
registrar."

The Path mechanism only forces this situation for incoming messages arriving
at the registrar/home service proxy destined to the UA. Correct?

Regards

Donald Finnie

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From: Dean Willis <[email-masked]>
Date: Sun, 5 May 2002 15:21:57 -0500

> they will only remain in the signalling path if they choose to

The applicability statement says messages because it means" all messages, not 
just dialog-inititaing messages and replies". SIP gives us mechanisms (Via 
and Record-Route) to force replies subsequent messages in a dialog to 
traverse the route of the original message.  We also have a mechanism (the 
preloaded Route)  which allows us to force an out-of-dialog request to visit 
certain nodes. What we don't have is a way to tell the UA what Route to 
pre-load (P-Service-Route) or a way to tell a retargeting proxy what Route to 
add in order to reach a Contact that once must reach through a specific route.

Specifically, Path is applied to any SIP request (not just a dialog 
initiating message) originating at or traversing the retargetting proxy 
associated with the registrar.

I'll see if I can clarify this slightly in the next revision.

> at the registrar/home service proxy destined to the UA. Correct?

Yes. Other techniques meet other requirements in the applicability statement.

--
Dean