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thanks. -----Original Message-----
We are hoping to organize a BOF on PCN (pre-congestion notification) at the next IETF. Some of us have now put together a first draft of a Charter - below. We’d very much appreciate your comments and suggestions – for instance: is the scope right? Is the range of deployment models ok? Is it a reasonable set of milestones and are the timescales ok?
We’re now working on a Problem Statement draft.
Thanks.
PCN Draft Charter (Pre-Congestion Notification)
The PCN BOF (WG) will tackle the problem of how to provide scalable, resilient admission control and strong QoS assurance while using packet marking techniques. Current attempts to deliver QoS using only packet marking (e.g. DiffServ) are limited in the level of QoS assurance that can be provided without substantial over-provisioning. To improve the QoS assurance, PCN will add flow admission control and flow pre-emption. In normal circumstances admission control should protect the QoS of previously admitted flows. In times of heavy congestion (for example caused by route changes due to link or router failure) pre-emption of some flows should preserve the QoS of remaining flows.
The initial scope of the BOF (WG) is the use of PCN within a single DiffServ region. The overall approach will be based on a separation of functionality between the interior routers and edge nodes of the DiffServ region. Interior routers mark packet headers when their traffic is above a certain level, as an early warning of incipient congestion (“pre-congestion”); this builds on concepts from RFC 3168 "The Addition of Explicit Congestion Notification to IP". Edge nodes of the DiffServ Region monitor the markings and that information is used to make flow admission control and pre-emption decisions. The decisions could be made by the edge nodes or by a centralised system (which is informed of the edge nodes’ measurements).
The WG will address the following specific problems and develop standards track solutions to them: · When should an interior router mark a packet (i.e. at what traffic level) in order to give early warning of its own congestion? · How should such a mark be encoded in a packet (in the ECN and/or DSCP fields)? · How should these markings (at packet granularity) be converted into admission control and flow pre-emption decisions (at flow granularity)?
To support this, the WG will work on the following Informational documents: · a Problem Statement, to describe the problems the group is tackling and the assumptions made · at least two deployment models, initially to help focus the problem statement and later to check that the solutions being developed satisfy the deployment scenario. Possible deployment models may be: o IntServ over DiffServ (RFC2998): the DiffServ region is PCN-enabled and its edge nodes decide about admission and flow pre-emption o SIP-controlled PCN: routers within the DiffServ region are PCN-capable and trusted SIP endpoints (gateway or host) perform admission and flow pre-emption o Pseudowire: PCN may be used as a congestion avoidance mechanism for end-user deployed pseudowires (collaborate with the PWE3 WG) · a generic analysis of the signalling extensions required to support PCN. Note that extensions/enhancements to specific signalling protocols (e.g. RSVP, NSIS, SIP) will not be done in the PCN WG. · at least one example solution implementing the framework and its performance evaluation (e.g. simulation results), to provide evidence of the viability of the proposed standard in the proposed deployment models · an analysis of the tradeoffs of different encoding possibilities (e.g. ECN and DCSP marking)
The initial scope of the WG will restrict the problem space in the following ways: · By assuming the PCN-enabled Internet Region is a controlled environment, i.e. all the interior routers and edge nodes of the region run PCN and trust each other · By assuming there are many flows on any bottleneck link in the PCN-enabled region · By focusing on the QoS assurance required by real time applications generating inelastic traffic like voice and video requiring low delay, jitter and packet loss, i.e. as defined by the Controlled Load Service [RFC2211].
Subsequent re-chartering may investigate solutions for when some of these restrictions are not in place.
Topics out of scope for the WG include a general investigation of admission control mechanisms.
The WG will draw on the substantial prior academic and IETF work on measurement-based admission control.
Milestones Nov 2006 initial Problem statement Nov 2006 initial deployment models March 2007 initial router marking behaviour (including encoding) March 2007 initial flow admission control and pre-emption mechanism (including edge node measurements) March/July 2007 submit Problem statement March/July 2007 submit deployment models Nov 2007 submit router marking behaviour Nov 2007/Mar 2008 submit flow admission control and pre-emption mechanism Nov 2007 initial signalling analysis Mar 2008 re-charter or close
Philip Eardley Networks Researcher BT Group
Phone: +44 (0)1473 645938 Fax : +44 (0)1473 640929 Email: [EMAIL PROTECTED] BT MeetMe: +44 (0)870 241 2994 Passcode: 16851189#
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