With the push towards HTTP/3, most modern browsers have started supporting it. HTTP/3 uses QUIC, which runs on top of UDP. However, a few Internet middle-boxes tend to block or rate-limit UDP traffic; therefore, the browsers ensure compatibility by enabling connection racing via simultaneously initiating a TCP connection with the QUIC one. Each time the QUIC protocol suffers, connection racing is activated, and whichever protocol wins the race is further used for the application. In this paper, we study how browsers implement this connection racing mechanism and analyze its impact on applications that require a long-lived Internet connection, such as video streaming. We perform a large-scale measurement study across different browsers (Chrome/Chromium and Firefox), which helps to analyze why and how the repeated connection racing between protocols affects adaptive streaming QoE over 6013 YouTube sessions covering 5474 hours of streaming. Interestingly, we observe that YouTube QoE over an HTTP/3 supported browser suffers many times, and repeated connection racing is one of the major reasons that hinder the performance. We modified the Chromium browser source code to disable the connection racing altogether and observed that it improves the QoE for YouTube streaming over this modified browser. We then design and implement a solution that dynamically decides when to enable connection racing. We observe that it improves the QoE compared to the original browser. The analysis presented in this paper highlights the requirement of revisiting how browsers handle and switch between protocols through connection racing to ensure compatibility with middleboxes.

HTTP/3 is a new application layer protocol supported by most browsers. It uses QUIC as an underlying transport protocol. QUIC provides multiple benefits, like faster connection establishment, reduced latency, and improved connection migration. Hence, most popular browsers like Chrome/Chromium, Microsoft Edge, Apple Safari, and Mozilla Firefox have started supporting it. In this paper, we present an HTTP/3-supported browser dataset collection tool named H3B. It collects the application and network-level logs during YouTube streaming. We consider YouTube, as it the most popular video streaming application supporting QUIC. Using this tool, we collected a dataset of over 5936 YouTube sessions covering 5464 hours of streaming over 5 different geographical locations and 5 different bandwidth patterns. We believe our tool and as well as the dataset could be used in multiple applications such as a better configuration of application/transport protocols based on the network conditions, intelligent integration of network and application, predicting YouTube's QoE etc. We analyze the dataset and observe that during an HTTP/3 streaming not all requests are served by HTTP/3. Instead whenever the network condition is not favorable the browser chooses to fallback, and the application requests are transmitted using HTTP/2 over the old-standing transport protocol TCP. We observe that such switching of protocols impacts the performance of video streaming applications.