Subject: [Sipping] comments on connection reuse requirements

From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 15 Apr 2003 00:24:48 -0400

Much of the discussion so far on connection reuse has been on the 
mechanism. However, if we wish to make progress on this (and we do), we 
need to separate the mechanism from the requirements, and make sure we 
are happy with the requirements. So, a few comments:

> 2.  A connection sharing mechanism SHOULD allow SIP entities to reuse
>        existing connections with closely coupled nodes which act as a
>        single SIP entity (for example a cluster of nodes acting as a
>        proxy server).

this requirement is hard to understand, and its actually the driving 
force behind the current design decision. I think what you are really 
trying to say is:

A connection sharing mechanism SHOULD ensure that a UA can maintain 
multiple connections, each one to a server in a cluster, so that if an 
element in the cluster fails, the UA can still receive requests from a 
connection to a different server in the cluster.

There is also this unwritten requirement:

The mechanism must be backwards compatible, so that if a peer doesn't 
support it, the result is that two connections will be opened, as per 
the current specification.

The current mechanism, however, doesn't let a UA know if the next hop 
supports the alias mechanism or not. I suggest this requirement:

There must be a way for a client to determine if the server supported 
the extension.

This is easily done the same way rport works. The alias is "filled in" 
by the server when the resposne is forwarded. If the client sees it 
filled in, it knows the extension was supported. Here, the value filled 
in is irrelevant; just a flag to indicate it was supported.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Scientist                             Parsippany, NJ 07054-2711
dynamicsoft
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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