Using data center TCP (DCTCP) in the Internet

Abstract

Data Center TCP (DCTCP) is an Explicit Congestion Notification (ECN)-based congestion control and Active Queue Management (AQM) scheme. It has provoked widespread interest because it keeps queuing delay and delay variance very low. There is no theoretical reason why Data Center TCP (DCTCP) cannot scale to the size of the Internet, resulting in greater absolute reductions in delay than achieved in data centres. However, no way has yet been found for DCTCP traffic to coexist with conventional TCP without being starved. This paper introduces a way to deploy DCTCP incrementally on the public Internet that could solve this coexistence problem. Using the widely deployed Weighted Random Early Detection (WRED) scheme, we configure a second AQM that is applied solely to ECN-capable packets. We focus solely on long-running flows, not because they are realistic, but as the critical gating test for whether starvation can occur. For the non-ECN traffic we use TCP New Reno; again not to seek realism, but to check for safety against the prevalent reference. We report the promising result that, not only does the proposed AQM always avoid starvation, but it can also achieve equal rates. We even derived how the sharing ratio between DCTCP and conventional TCP traffic depends on the various AQM parameters. The next step beyond this gating test will be to quantify the reduction in queuing delay and variance in dynamic scenarios. This will support the standardization process needed to define new ECN semantics for DCTCP deployment that the authors have started at the IETF.