[tsvwg] Delay vs. Loss draft: Terminology
"Black, David" <david.black@emc.com> Wed, 17 July 2013 21:37 UTC
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From: "Black, David" <david.black@emc.com>
To: tsvwg WG <tsvwg@ietf.org>
Date: Wed, 17 Jul 2013 17:37:21 -0400
Thread-Topic: Delay vs. Loss draft: Terminology
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Subject: [tsvwg] Delay vs. Loss draft: Terminology
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<WG chair hat off> This note concerns draft-polk-tsvwg-delay-vs-loss-ds-service-classes I believe I see some sloppy use of terminology in this draft and the related discussion. CS4 was originally defined as a DSCP value in RFC 2474 (Diffserv field in IP headers) and is used only as a DSCP value in RFC 4594 (Diffserv Service classes). That said, RFC 2474 can be read to allow use of CS4 as a PHB name - it's effectively shorthand for "the PHB assigned to the CS4 DSCP - as is done in draft-polk-tsvwg-rfc4594-update does. While that may not be the best usage, I think it's ok. OTOH, draft-polk-tsvwg-delay-vs-loss-ds-service-classes appears to be using strings such as "CS4", "CS4-Discardable" and "CS4+" as service class names (see Sections 5 and 6). That inclusion of the DSCP name in the service class name is (IMHO), a stunningly bad idea that is going to lead to confusion, and moreover is at odds with one of the basic principles of the Diffserv architecture, namely separation of traffic behavior (PHB and subsequently, service class) from the DSCP used in the IP header to request suitable treatment in a particular network. As an author of both RFC 2474 and 2475, I really would like to see draft-polk-tsvwg-delay-vs-loss-ds-service-classes revised to be clear on DSCP vs. PHB vs. service class and in particular to cease and desist from using CS4 (or any other DSCP name) as the name or part of the name of a service class - that will inevitably lead to the bad and wrong assumption that such a service class can only ever be deployed with the CS4 DSCP - while that sort of relationship is RECOMMENDED by RFC 4594, it is not REQUIRED (where "RECOMMENNDED" and "REQUIRED" have their RFC 2119 meanings). An example of the possible confusion that is that there will be networks in which the CS4 DSCP will be deployed with only one of the service classes currently called "CS4" and "CS4-Discardable" in draft-polk-tsvwg-delay-vs-loss-ds-service-classes. Is anyone prepared to try to explain with a straight face why the "CS4" service class isn't using the "CS4" DSCP? Thanks, --David ---------------------------------------------------- David L. Black, Distinguished Engineer EMC Corporation, 176 South St., Hopkinton, MA 01748 +1 (508) 293-7953 FAX: +1 (508) 293-7786 david.black@emc.com Mobile: +1 (978) 394-7754 ----------------------------------------------------
- [tsvwg] Delay vs. Loss draft: Terminology Black, David
- Re: [tsvwg] Delay vs. Loss draft: Terminology Brian E Carpenter