Re: [Ieprep] proposed charter 5 priority levels

John Rosenberg <jrrosenberg@lucent.com> Wed, 27 September 2006 00:11 UTC

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Date: Tue, 26 Sep 2006 19:10:49 -0500
To: ieprep@ietf.org, ieprep@ietf.org
From: John Rosenberg <jrrosenberg@lucent.com>
Subject: Re: [Ieprep] proposed charter 5 priority levels
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At 05:52 PM 9/26/2006, ieprep-request@ietf.org wrote:

 >Date: Tue, 26 Sep 2006 12:56:15 -0400
 >From: Curtis Villamizar <curtis@occnc.com>

 >In message 
<OFBAA95066.05652C8C-ON852571F5.004A9C8A-852571F5.004B6690@csc.com>
 >Janet P Gunn writes:
 >>
 >>
 >> As RFC 4412 makes perfectly clear, the RPH serves a dual role of signalling
 >> priority across an IP network (e.g. from an originating circuit switched
 >> access network to a terminating circuit switched access network) as well as
 >> signalling  priority within the IP network.
 >>
 >> For each of the namespaces described in RFC 4412, the number of priority
 >> values (5 in most cases, 6 in one) is driven by the former role, based on
 >> the number of priority values in use, or being considered, in the access
 >> network priority scheme.
 >>
 >> The issue of how many priority levels to differentiate WITHIN the IP
 >> network is an issue currently being addressed by vendors and providers.
 >>
 >> Janet
 >
 >
 >Janet,
 >
 >You are right, but you may be just focusing on SIP which is one peice
 >of the puzzle.
 >
 >RFC 4412 does not make it perfectly clear whether we need 1 DSCP code
 >point, EF, or 5 DSCP code points (IP Prec 0-4?)  or 15 DSCP code
 >points (the 4 AF classes plus one more AF class.  Or is it some
 >multiple of 6?  This RFC doesn't even mention DSCP.
 >

Let me add my voice and suggest that we're really in need of some mechanism 
that allows the application (e.g. MLPP, ETS, whatever) to determine a 
"priority level" for a session and indicate to the endpoint that it's 
serving what DSCP value that the endpoint should use for its bearer packets.

It could be a header or parameter in some subset of SIP messages, it could 
be an attribute in SDP, it could be something else entirely. I think the 
whole question of how many and which DSCP values should be used for some 
arbitrary application is a little premature if we don't have a way for the 
application to get that value used.

John Rosenberg


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