A Lower-Effort Per-Hop Behavior (LE PHB) for Differentiated Services

Approval announcement
Draft of message to be sent after approval:

From: The IESG <iesg-secretary@ietf.org>
To: IETF-Announce <ietf-announce@ietf.org>
Cc: The IESG <iesg@ietf.org>, tsvwg@ietf.org, draft-ietf-tsvwg-le-phb@ietf.org, david.black@dell.com, tsvwg-chairs@ietf.org, rfc-editor@rfc-editor.org, David Black <david.black@dell.com>, spencerdawkins.ietf@gmail.com
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 K├╝hlewind and Spencer Dawkins.

A URL of this Internet Draft is:

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

   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.


   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 

   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).