2.8.8 Congestion and Pre-Congestion Notification (pcn)

NOTE: This charter is a snapshot of the 72nd IETF Meeting in Dublin, Ireland. It may now be out-of-date.

Last Modified: 2008-01-25


Scott Bradner <sob@harvard.edu>
Steven Blake <steven.blake@ericsson.com>

Transport Area Director(s):

Magnus Westerlund <magnus.westerlund@ericsson.com>
Lars Eggert <lars.eggert@nokia.com>

Transport Area Advisor:

Lars Eggert <lars.eggert@nokia.com>

Mailing Lists:

General Discussion: pcn@ietf.org
To Subscribe: pcn-request@ietf.org
In Body: (un)subscribe
Archive: http://www.ietf.org/mail-archive/web/pcn/index.html

Description of Working Group:

The Congestion and Pre-Congestion Notification (PCN) working group
develops mechanisms to protect the quality-of-service of established
inelastic flows within a DiffServ domain when congestion is imminent
or existing. These mechanisms operate at the domain boundary, based
on aggregated congestion and pre-congestion information from within
the domain. The focus of the WG is on developing standards for the
marking behavior of the interior nodes and the encoding and transport
of the congestion information. To allow for future extensions to the
mechanisms and their application to new deployment scenarios, they
are logically separated into several components, namely, encoding and
transport along forward path from marker to egress, metering of
congestion information at the egress, and transport of congestion
information back to the controlling ingress. Reaction mechanisms at
the boundary consist of flow admission and flow termination. Although
designed to work together, flow admission and flow termination are
independent mechanisms, and the use of one does not require or
prevent the use of the other. The WG may produce a small number of
informational documents that describe how specific quality-of-service
policies for a domain can be implemented using these two mechanisms.

The PCN WG will specify the following components to protect the
quality-of-service of flows within a DiffServ domain:

(1) a general architecture for flow admission and termination
based on aggregated (pre-)congestion information

(2) a specification of conditions under which interior nodes
generate (pre-)congestion information

(3) encoding and transport of (pre-)congestion information
between the interior and domain egress

(4) metering of (pre-)congestion information at the domain egress

(5) encoding and transport of (pre-)congestion information
between the egress and the controlling domain ingress

(6) ingress node control mechanisms for flow admission or
termination, based on aggregated (pre-)congestion information

The WG focuses on the marking behavior and encoding and transport
mechanisms needed to realize the overall PCN architecture. Standards-
track protocols and mechanisms are only developed where necessary for
interoperability. For other components of the architecture, the WG
may document examples or provide recommended solutions in
informational documents. The architecture document will be
comprehensive, and include security, manageability and operational
considerations. All PCN mechanisms, including transport and encoding
of (pre-congestion) information, are required to cleanly integrate
with existing architectures and protocols such as DiffServ and ECN.
If the PCN WG requires extensions or modifications to protocols that
are products of other WGs, it may motivate their need and describe
requirements in informational documents; design of such extensions
and modifications will take place in the appropriate WGs.

The initial scope of the PCN WG is restricted by the following

(A) these components are deployed in a single DiffServ domain,
where all boundary and interior nodes are PCN-enabled
and trust each other for correct PCN marking, encoding,
transport and aggregation

(B) all flows handled by these mechanisms are inelastic and
constrained to a known maximum rate through policing or shaping

(C) the number of flows across any potential aggregation bottleneck
is sufficiently large for stateless, statistical mechanisms
to be effective

(D) flows may have different precedence, but the applicability
of the PCN mechanisms for emergency use (911, GETS, WPS,
MLPP, etc.) is out of scope

After completion of the initial phase, the PCN WG may re-charter to
develop solutions for scenarios where some of these restrictions are
not in place. It may also re-charter to consider applying the PCN
mechanisms to additional deployment scenarios (operation over
concatenated DiffServ domains, PCN-aware application mechanisms,
etc.). The WG may also consider to investigate additional response
mechanisms that act on (pre-)congestion information. One example
could be flow-rate adaptation (rather than flow admission/
termination) during times of congestion. The details of these work
items are outside the scope of the initial phase; but the WG may
consider their requirements to design components that are
sufficiently general to support such extensions in the future.

Goals and Milestones:

Nov 2007  Submit 'Survey of Encoding and Transport Choices of (Pre-)Congestion Information within a DiffServ Domain' to the IESG for consideration as an Informational RFC
Nov 2007  Submit 'Flow Admission and Termination Architecture within a Diffserv Domain' to the IESG for consideration as an Informational RFC
Mar 2008  Submit '(Pre-)Congestion Detection within a DiffServ Domain' to the IESG for consideration as a Proposed Standard RFC
Mar 2008  Submit 'Requirements for Signaling of (Pre-)Congestion Information from Egress to Ingress in a DiffServ Domain' to the IESG for consideration as a Informational RFC
Jul 2008  Submit 'Suggested Flow Admission and Termination Boundary Mechanisms' to the IESG for consideration as an Informational RFC
Jul 2008  Submit 'Encoding and Transport of (Pre-)Congestion Information from within a DiffServ Domain to the Egress' to the IESG for consideration as a Proposed Standard RFC
Nov 2008  Submit 'Encoding and Transport of (Pre-)Congestion Information from the Domain Egress to the Ingress' to the IESG for consideration as a Proposed Standard RFC


  • draft-ietf-pcn-architecture-03.txt

    No Request For Comments

    Meeting Minutes


    Agenda, Milestones, and ITU-T Liaison Discussion
    ITU-T Liaison to PCN Summary with Context
    PCN Architecture and Marking Behavior
    Baseline Encoding for PCN
    3 State Encoding for PCN
    Multiple PCN Experiments
    PCN Encoding for Packet-Specific Dual Marking (PSDM)
    End-to-end Extension for PCN Encoding
    PCN baseline encoding experiment supporting admission control and termination
    Layered Encapsulation of Congestion Notification
    LC-PCN The Load Control PCN solution