A Lower-Effort Per-Hop Behavior (LE PHB) for Differentiated Services
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From: The IESG <email@example.com> To: IETF-Announce <firstname.lastname@example.org> Cc: The IESG <email@example.com>, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, David Black <email@example.com>, firstname.lastname@example.org Subject: Protocol Action: 'A Lower Effort Per-Hop Behavior (LE PHB) for Differentiated Services' to Proposed Standard (draft-ietf-tsvwg-le-phb-10.txt) The IESG has approved the following document: - 'A Lower Effort Per-Hop Behavior (LE PHB) for Differentiated Services' (draft-ietf-tsvwg-le-phb-10.txt) as Proposed Standard This document is the product of the Transport Area Working Group. The IESG contact persons are Mirja Kühlewind and Spencer Dawkins. A URL of this Internet Draft is: https://datatracker.ietf.org/doc/draft-ietf-tsvwg-le-phb/
Technical Summary This document specifies properties and characteristics of a Lower Effort (LE) per-hop behavior (PHB). The primary objective of this LE PHB is to protect best-effort (BE) traffic (packets forwarded with the default PHB) from LE traffic in congestion situations, i.e., when resources become scarce, best-effort traffic has precedence over LE traffic and may preempt it. Alternatively, packets forwarded by the LE PHB can be associated with a scavenger service class, i.e., they scavenge otherwise unused resources only. There are numerous uses for this PHB, e.g., for background traffic of low precedence, such as bulk data transfers with low priority in time, non time-critical backups, larger software updates, web search engines while gathering information from web servers and so on. This document recommends a standard DSCP value for the LE PHB. This specification obsoletes RFC 3662 and updates the DSCP recommended in RFC 4594 and RFC 8325 to use the DSCP assigned in this specification. When Diffserv was originally designed, interest in less-than-best effort (aka scavenger) forwarding behavior eventually resulted in publication of RFC 3662 which specified the Diffserv Lower Effort (LE) PHB/PDB. In 20/20 hindsight, RFC 3662 had a number of drawbacks, as it was not a full PHB specification and in particular did not recommend a default DSCP (Diffserv Codepoint) for Lower Effort traffic. The default DSCP recommendation eventually occurred in practice as a side effect of publishing RFC 4594 on Diffserv Service Classes. The recommended DSCP, CS1, has turned out to be problematic in practice - e.g., see the discussion of CS1 in RFC 7657 on Diffserv interaction with real time communication. This draft cleans up the LE PHB situation by providing a full PHB specification of the Lower Effort PHB that obsoletes RFC 3662 and recommends a newly chosen default DSCP, 000001, which is expected to avoid the problems encountered with CS1 and provide a solid Diffserv specification for lower effort/less-than-best-effort/scavenger traffic. Proposed Standard is appropriate for this document in support of consistent deployment of the updated LE PHB as part of Diffserv. Working Group Summary The Transport Area WG (tsvwg) is a collection of people with varied interests that don't individually justify their own working groups. Specifying the Lower Effort PHB was relatively straightforward in the WG. In contrast, determining which DSCP to recommend as the default for that PHB was not. The underlying problem is that a non-negligible amount of deployed Internet equipment "bleaches" the three most significant bits of the DSCP field in IP headers to zero, even though that violates Diffserv requirements. This made it problematic to use the initially suggested 000010 value, as that value can and does result from this three-bit bleaching of DSCP values for higher priority traffic that should not be forwarded as lower effort (LE) traffic. After much discussion and evaluation of measurement results on Internet traffic in both TSVWG and MAPRG, the TSVWG working group chose 000001 value as the recommended default DSCP. This decision necessitated publication of RFC 8436 to change the IANA procedures for managing the DSCP registry so that this DSCP value 000001 could be assigned as the default DSCP for the LE PHB in this document. Document Quality This draft is supported by the portion of the tsvwg working group that is familiar with and interested in Diffserv. The draft has received significant review and critique from a number of Diffserv experts, including the draft shepherd, David Black, and Brian Carpenter, one of the original chairs of the Diffserv WG. There is clear consensus in the TSVWG WG on the need to update the LE PHB specification to replace and obsolete RFC 3662. Personnel Document Shepherd: David Black Responsible AD: Spencer Dawkins
RFC Editor Note Because this draft formally updates draft-ietf-tsvwg-rtcweb-qos, which is approved but waiting in the MISSREF state, we ask the RFC Editor to take the following actions: Please make the changes described in Section 12 of this draft to draft-ietf-tsvwg-rtcweb-qos. Please replace [RFCXXXX] in the updated text with the RFC number assigned to this draft. Please add [RFCXXXX] (with the RFC number assigned to this draft) as a normative reference in draft-ietf-tsvwg-rtcweb-qos. Please remove Section 12 from this draft (because all those changes have already been applied).