Congestion and Pre-Congestion Notification (pcn)
------------------------------------------------

 Charter
 Last Modified: 2008-01-25

 Current Status: Active Working Group

 Chair(s):
     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 

assumptions:



(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 


 Internet-Drafts:

Posted Revised         I-D Title   <Filename>
------ ------- --------------------------------------------
Aug 2007 Feb 2008   <draft-ietf-pcn-architecture-03.txt>
                Pre-Congestion Notification Architecture 

 Request For Comments:

  None to date.