Congestion and Pre-Congestion Notification
charter-ietf-pcn-03

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.