Editing Explicit Congestion Notification (section)

==Effects on performance==
Since ECN is only effective in combination with an [[Active Queue Management]] (AQM) policy, the benefits of ECN depend on the precise AQM being used.  A few observations, however, appear to hold across different AQMs.

As expected, ECN reduces the number of packets dropped by a TCP connection, which, by avoiding a retransmission, reduces latency and especially jitter.  This effect is most drastic when the TCP connection has a single outstanding segment,{{Ref RFC|2884}} when it is able to avoid an [[Transmission Control Protocol#Congestion control|RTO]] timeout; this is often the case for interactive connections, such as remote logins, and transactional protocols, such as HTTP requests, the conversational phase of SMTP, or SQL requests.

Effects of ECN on bulk throughput are less clear<ref>Marek Małowidzki, Simulation-based Study of ECN Performance in RED Networks, In ''Proc. SPECTS'03''. 2003.</ref> because modern TCP implementations are fairly good at resending dropped segments in a timely manner when the sender's [[Transmission Control Protocol#Flow control|window]] is large.

Use of ECN has been found to be detrimental to performance on highly congested networks when using AQM algorithms that never drop packets.<ref name="kuzmanovic" />  Modern AQM implementations avoid this pitfall by dropping rather than marking packets at very high load.