Coexistence of delay-based TCP congestion control: Challenges and opportunities

With the emergence of delay-sensitive applications like cloud gaming, remote driving, and virtual/augmented reality (VR/AR), there has been renewed research interest in the development of low latency congestion control protocols. However, these efforts have been impeded by the difficulty associated with designing an end-to-end protocol that reacts to delay signals, but that also shares a link effectively (i.e., without causing harm to other flows and without being starved by other flows). This is a critical requirement for use in the public internet. To help protocol designers, we summarize the literature on coexistence of delay-based congestion controls. We implement a selection of the coexistence techniques described in the literature, and evaluate them in a set of controlled experiments designed to showcase the benefits and limitations of each approach. Through our experimental analysis, we highlight coexistence-related pitfalls of delay as a congestion signal. We hope that this work will help inform the design of new low latency congestion control protocols or improvements to existing protocols.