DualQ Coupled AQMs for Low Latency, Low Loss and Scalable Throughput (L4S)

Document Type Expired Internet-Draft (tsvwg WG)
Last updated 2019-05-08 (latest revision 2018-11-04)
Replaces draft-briscoe-tsvwg-aqm-dualq-coupled
Stream IETF
Intended RFC status (None)
Expired & archived
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Stream WG state WG Document (wg milestone: Jun 2019 - Submit "DualQ Couple... )
Document shepherd Wesley Eddy
IESG IESG state Expired
Consensus Boilerplate Unknown
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Send notices to Wesley Eddy <wes@mti-systems.com>

This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


The Low Latency Low Loss Scalable Throughput (L4S) architecture allows data flows over the public Internet to predictably achieve ultra-low queuing latency, generally zero congestion loss and scaling of per-flow throughput without the problems of traditional TCP. To achieve this, L4S data flows use a 'scalable' congestion control similar to Data Centre TCP (DCTCP) and a form of Explicit Congestion Notification (ECN) with modified behaviour. However, until now, scalable congestion controls did not co-exist with existing TCP Reno/ Cubic traffic---scalable controls are so aggressive that 'Classic' TCP algorithms drive themselves to starvation. Therefore, until now, L4S controls could only be deployed where a clean-slate environment could be arranged, such as in private data centres (hence the name DCTCP). This specification defines `DualQ Coupled Active Queue Management (AQM)', which enables these scalable congestion controls to safely co-exist with Classic Internet traffic. The Coupled AQM ensures that a flow runs at about the same rate whether it uses DCTCP or TCP Reno/Cubic. It achieves this indirectly, without having to inspect transport layer flow identifiers, When tested in a residential broadband setting, DCTCP also achieves sub-millisecond average queuing delay and zero congestion loss under a wide range of mixes of DCTCP and `Classic' broadband Internet traffic, without compromising the performance of the Classic traffic. The solution also reduces network complexity and eliminates network configuration.


Koen Schepper (koen.de_schepper@nokia.com)
Bob Briscoe (ietf@bobbriscoe.net)
Olga Bondarenko (olgabnd@gmail.com)
Ing Tsang (ing-jyh.tsang@nokia.com)

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)