Congestion Exposure

Document Charter Congestion Exposure WG (conex)
Title Congestion Exposure
Last updated 2010-06-03
State Approved
WG State Concluded
IESG Responsible AD Martin Stiemerling
Charter Edit AD (None)
Send notices to (None)


The purpose of the CONEX working group is to develop a mechanism
  by which senders inform the network about the congestion encountered
  by previous packets on the same flow. Today, the network may signal
  congestion by ECN markings or by dropping packets, and the receiver
  passes this information back to the sender in transport-layer
  acknowledgements. The mechanism to be developed by the CONEX WG
  will enable the sender to also relay the congestion information
  back into the network in-band at the IP layer, such that the total
  level of congestion is visible to all IP devices along the path,
  from where it could, for example, be provided as input to traffic
  The primary goal of the CONEX WG is to develop experimental
  specifications to achieve the above in IPv6 networks. The WG will
  also develop an abstract, higher-level description of the congestion
  exposure mechanism.
  Primary work items are:
  * An Informational document containing an abstract description of
  the congestion exposure mechanism that is independent of specific
  transport protocols and congestion information encoding techniques
  needed for different IP protocol versions.
  * An Experimental specification of an IPv6 packet structure that
  encapsulates CONEX information, defining a packet format and an
  * An Experimental specification of a modification to TCP, for the
  timely transport of congestion information from the destination to
  the sender.
  It is believed that the CONEX mechanism will be useful as a generative
  technology that can be applied as a key element of congestion
  management solutions in a wide variety of use cases. However, the
  CONEX WG will initially focus on one use case, where the end hosts
  and the network that contains the destination end host are CONEX-enabled
  but other networks need not be. CONEX information can assist the
  network operator's traffic management and, for example, incentivize
  LEDBAT-like applications. Congestion-based billing is not within the
  scope of the WG.
  Experiments on use cases are encouraged and the WG will solicit
  feedback from such deployments. The WG may decide to document the
  experience from such use cases in Informational documents, covering:
  * Assumptions made
  * Deployment considerations
  * Advice on how to use the CONEX mechanism as an element of a
  congestion management solution
  * Security threats and advice on mitigation approaches (detailed
  specifications of threat mitigation techniques are out of scope)
  * Descriptions of results from experiments with the use case
  The CONEX WG is only chartered to work on a congestion exposure mechanism
  for IPv6 networks. When the output of the WG has seen adoption and
  has proven to be useful, the WG may propose to the IESG that it
  should be rechartered to extend this effort. The first result of
  the WG is the usage scenarios document. Other documents will not
  be considered for publication before this first document has seen
  IETF consensus (but may be worked on in the WG).