Video-on-demand (VoD) is one of the core CDN services, yet current VoD services commonly face video stuttering and long first-frame latency due to poor transmission path conditions. Existing solutions using Multi-path QUIC (MPQUIC) to address these issues cannot activate cellular paths on demand, causing massive traffic waste; additionally, some solutions depend on dedicated clients for application-layer information, precluding large-scale deployment. To address these limitations, we propose EMVOD, an elastic multi-path QUIC scheme deployed only on CDN edge nodes. It parses client-requested videos, dynamically activates cellular networks on demand, and prioritizes smooth video playback with minimal cellular traffic, while significantly reducing stuttering duration and first-frame latency.

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.

With the rapid advances in high-speed mobile networks such as 5G, Wi-Fi 6, and the upcoming 6G and Wi-Fi 7, streaming live video has become ubiquitous for mobile users. However, live video is susceptible to short-term network condition fluctuations which could lead to video stalls. Our investigations revealed that a substantial portion of such fluctuations were in fact caused by RTT spikes that were not congestion-related. These often confuse the transport protocol into dropping the transmission rate significantly, resulting in video stalls. This motivated us to develop a novel scheme called CWnd-loan to reduce the sender's CWnd-limited idle time during RTT spikes. We applied CWnd-loan to the QUIC protocol with BBR/CUBIC congestion control and strategically deployed it in a tier-1 live video service. The results show that CWnd-loan can effectively reduce sender CWnd-limited idle time by up to 18%, consequently reducing the duration and number of live video stalls by as much as 8.9% and 10.6%. Furthermore, CWnd-loan can also reduce the first-frame time and the playback failure rate by up to 3.2% and 2.7%, respectively. CWnd-loan is designed to complement existing congestion control algorithms and thus could potentially be applied to current as well as future TCP/QUIC designs to tackle RTT spikes commonly found across mobile and wireless networks.