Reducing First-Frame Delay of Live Streaming by Simultaneously Initializing Window and Rate

The first-frame delay is an essential indicator for evaluating the performance of cloud CDN vendors and affects the client-side QoE of live streaming. Instead of the traditional way of tuning the initial congestion window (cwnd) for all connections to a fixed value based on expert experience, this paper explores the using of transport signals unique to each connection (e.g., application-layer framing, historical QoS metrics) to initialize the sending parameters for each connection. Thus we propose Wira, a first-frame optimization mechanism that adjusts both initial cwnd and initial rate, which are two key parameters for decreasing the first-frame completion time (FFCT). Particularly, Wira provides cross-layer Frame Perception that parses frames and adapts the initial cwnd to the first-frame size. Meanwhile, Wira introduces the Transport Cookie to enable cloud-client collaborations, in which the historical QoS metrics from the clients can be reported and reused by rate initialization in the stateless cloud. This assures the initial rate matches the actual network conditions while avoiding non-trivial storage overhead in the cloud. We implement Wira upon QUIC and evaluate it via real-world deployments of commercial services. Results demonstrate the profitability of Wira, in which the average and 90th-percentile FFCT are reduced by 10.6% and 16.7%, respectively.