Subject: [Sip] Path header: Independent operation in each direction, or common o peration for both directions

From: "Drage, Keith (Keith)" <[email-masked]>
Date: Mon, 25 Feb 2002 10:43:32 -0000

I am breaking out the issues that I think need more discussion relating to
the proposed Path header. This is the first of those mails.

Currently the mechanism specified for 3GPP looks very like Record-Route and
it therefore collects the URLs of the proxies that wish to be on the path
for future transactions by use of the header within the REGISTER request,
and the response is merely a transport mechanism of the gathered information
back to the UA from the registrar.

This means that proxies so identified are intended to be in the path for
both incoming and outgoing requests, as there is no means of distinguishing
the two independently (or at least not with a single header, or separate
lists within the common header).

The mechanism proposed in Deans draft allows independent gathering of
information in each direction; a proxy that wishes to be on the path in both
incoming and outgoing directions must insert its URL in both the request and
the response. This loses the commonality of the procedures with
Record-Route.

While both mechanisms work, having discussed the requirements with a limited
set of people, we cannot think of a situation whereby a proxy would want to
be on the incoming path and not on the outgoing path, and vice-versa.
Certainly in 3GPP, the requirement needs to apply in both directions.
Therefore the real question is are we developing a solution that does more
that the requirements need, and therefore losing the commonality with
Record-Route as a result.

[While there may be advantages of code sharing with Record-Route for
implementations, I am thinking more of the advantages to understanding the
specification. People are more likely to understand and implement Path
correctly if it works the same way as something else.]

So, those who need operations independently in both directions, can you
shout up and give us some examples.

Keith

Keith Drage
Lucent Technologies
Tel: +44 1793 776249
Email: [email-masked]

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From: [email-masked]
Date: Mon, 25 Feb 2002 13:09:35 +0200

we should also discuss if the 3g requirements are at all in line with
the basic principles of the sip protocol.  in sip, register transactions
are independent of invite transactions and therefore there is no
relationship between route recording among these two.

-- juha