Abstract

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.

Authors

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.)