Research : Explicit Congestion Notification for RTP

Explicit Congestion Notification (ECN) is getting attention as a method to minimise the impact of congestion on real-time multimedia traffic. When ECN is used, the network can signal to applications that congestion is occurring, whether that congestion is due to queuing at a congested link, limited resources and coverage on a radio link, or other reasons. This congestion signal allows applications to reduce their transmission rate in a controlled manner, rather than responding to uncontrolled packet loss, and so improves the user experience while benefiting the network.

The introduction of ECN into the Internet requires changes to both the network and transport layers. At the network layer, IP forwarding has to be updated to allow routers to mark packets, rather than discarding them in times of congestion. Transport protocols also need to be modified to inform that sender that ECN marked packets are being received, so it can respond to the congestion. TCP, SCTP, and DCCP have long been updated to support ECN. This project developed a standard specification for use of ECN with RTP running over UDP/IP transport, and is working to measure the usability of ECN with UDP in the public Internet.

Thanks to Ericsson Research for funding the IETF standards activities in this project.