TCP Alternative Backoff with ECN (ABE): RFC 8511

Naeem Khademi, Michael Welzl, Grenville Armitage, Godred Fairhurst

Research output: Contribution to conferenceOtherpeer-review


Active Queue Management (AQM) mechanisms allow for burst tolerance
while enforcing short queues to minimise the time that packets spend
enqueued at a bottleneck. This can cause noticeable performance
degradation for TCP connections traversing such a bottleneck,
especially if there are only a few flows or their bandwidth-delay
product (BDP) is large. The reception of a Congestion Experienced
(CE) Explicit Congestion Notification (ECN) mark indicates that an
AQM mechanism is used at the bottleneck, and the bottleneck network
queue is therefore likely to be short. Feedback of this signal
allows the TCP sender-side ECN reaction in congestion avoidance to
reduce the Congestion Window (cwnd) by a smaller amount than the
congestion control algorithm’s reaction to inferred packet loss.
Therefore, this specification defines an experimental change to the
TCP reaction specified in RFC 3168, as permitted by RFC 8311.
Original languageEnglish
Number of pages12
Publication statusPublished - 19 Dec 2018

Bibliographical note



  • RFC 8511
  • ABE
  • ECN


Dive into the research topics of 'TCP Alternative Backoff with ECN (ABE): RFC 8511'. Together they form a unique fingerprint.

Cite this