Rethinking End-to-End Congestion Control in Software-Defined Networks

Monia Ghobadi, Soheil Hassas Yeganeh and Yashar Ganjali

The central suggestion is that centrally controlled SDN networks are in a position to choose which version of TCP will work best. OpenTCP tunes TCP for traffic and network conditions. Different TCP flavours perform better at different times or in different conditions e.g. datacentre TCP (DCTCP).

Congestion Update Epistles sent to end hosts summarising network conditions. Congestion Control Agent at each end host is kernel module which selects appropriate TCP version and parameters. Congestion control policies allow network operator to specify conditions for various tuning TCP to network. Time step T slower than RTT needed for updates to policy. Stability conditions based on previous work given. Work is Pang et al.

Open TCP implemented on half hosts in a 4,000 host data centre (SciNet). 59% reduction in flow completion times simply by adapting init_cwnd and RTO. Network characterised by link utilisation < 50% around 80% of time (claimed typical for data centre) and high utilisation and packet loss the rest of the time. Overheads are measured and found to be low in terms of both CPU and network utilisation.

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