Re: [Ieprep] proposed charter 5 priority levels

John Rosenberg <> Wed, 27 September 2006 00:11 UTC

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Date: Tue, 26 Sep 2006 19:10:49 -0500
From: John Rosenberg <>
Subject: Re: [Ieprep] proposed charter 5 priority levels
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At 05:52 PM 9/26/2006, wrote:

 >Date: Tue, 26 Sep 2006 12:56:15 -0400
 >From: Curtis Villamizar <>

 >In message 
 >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
 >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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