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Concluded WG Congestion Exposure (conex)

Note: The data for concluded WGs is occasionally incorrect.

WG Name Congestion Exposure
Acronym conex
Area Transport Area (tsv)
State Concluded
Charter charter-ietf-conex-01 Approved
Document dependencies
Additional resources Issue tracker, Wiki
Personnel Chairs Marcelo Bagnulo, Nandita Dukkipati
Area Director Martin Stiemerling
Mailing list Address
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Final Charter for Working Group

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).


Date Milestone Associated documents
Nov 2011 Submit specification for modification to TCP to IESG as Experimental
Nov 2011 Submit specification of IPv6 packet structure to IESG as Experimental
Jul 2011 Submit abstract specification for the congestion exposure mechanism to IESG as Informational
Mar 2011 Submit use case description to IESG as Informational