NADA: A Unified Congestion Control Scheme for Low-Latency Interactive Video

Low-latency, interactive media applications (e.g., video conferencing) present a unique set of challenges for congestion control. Unlike TCP, the transport mechanism for interactive media needs to adapt fast to abrupt changes in available bandwidth, accommodate sluggish responses and output rate fluctuations of a live video encoder, and avoid high queuing delay over the network. An ideal scheme should also make effective use of all types of congestion signals from the network, including packet losses, queuing delay, and explicit congestion notification (ECN) markings. This paper presents a unified approach for congestion control of interactive video: network-assisted dynamic adaptation (NADA). In NADA, the sender regulates its sending rate based on a composite congestion signal calculated and reported by the receiver, which combines both implicit (e.g., loss and delay) and explicit (e.g., ECN marking) congestion indications from the network. Via a consistent set of sender adaptation rules, the scheme can reap the full benefits of proactive, explicit congestion notifications supported by advanced queue management schemes. It remains equally responsive in the absence of such notifications. Extensive simulation studies show that NADA interact well with a wide variety of queue management schemes: conventional drop-tail, random early detection (RED), recently proposed CoDel (controlled delay) and PIE (Proportional Integral controller Enhanced), as well as a token-bucket-based random marking scheme based on Pre-Congestion Notification (PCN). Furthermore, NADA reacts fast to changes over the network, allows for weighted bandwidth sharing among multiple competing video streams, and sustains a substantial share of bottleneck bandwidth when coexisting with TCP.