Congestion Exposure (conex)

Last modified: 2016-01-21


Transport Area Director:

Mailing Lists:

General Discussion:
To Subscribe:

Description of 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 management.

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 interpretation.
  • 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).

Goals and Milestones

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


Request for Comments

Internet SocietyAMSHome - Tools Team - Datatracker - IASA - IAB - RFC Editor - IANA - IRTF - IETF Trust - ISOC - IETF Journal - Store - Contact Us
Secretariat services provided by Association Management Solutions, LLC (AMS).
Please send problem reports to: