TCP at 100 Gbit/s – Tuning, Limitations, Congestion Control

Link capacities increase at an enormous pace, with 100 Gbit/s becoming standard in data centers, campus networks, and the Internet. These ever increasing data rates are challenging since end-system performance (esp. CPU performance) cannot keep up with the growth rates.Still, the TCP protocol and today's hardware are capable of transferring 100 Gbit/s with a single sender/receiver pair. However, extensive tuning is necessary down to manual interrupt configuration and corresponding CPU core pinning for the applications. A major issue is packet loss within the receiving end-system that cannot be prevented by TCP's flow control. This, in turn, affects TCP's default congestion control that interprets the losses as congestion signal. In this paper we show how to tune end-systems that are driven at their performance limits, what data rates are feasible, where the limitations are, and discuss the impact on and by TCP's congestion control.