Modern internet applications increasingly rely on multiple network paths with asymmetric characteristics, where paths exhibit significant disparities in bandwidth, latency, and reliability. This thesis investigates the optimization of Multipath QUIC performance in such heterogeneous environments through a novel dual-scheduler architecture that separates data and acknowledgment (ACK) traffic onto distinct network paths based on their performance requirements. The author designed and implemented a latency-based scheduling system that routes high-throughput data packets over highbandwidth paths while directing latency-sensitive acknowledgments through low-latency paths. The architecture was evaluated through extensive emulation-based experiments using a modified version of Cloudflare’s quiche implementation, testing various traffic patterns, congestion control algorithms (CUBIC and BBR), and network conditions. The research reveals nuanced performance characteristics that challenge conventional assumptions about multipath scheduling. In unidirectional transfers without packet loss, the vanilla multipath QUIC implementation’s simple reactive scheduler often matched or outperformed the proposed separation architecture due to its adaptive behavior. However, under more realistic and challenging conditions, specifically with packet loss on the data path and in bidirectional transfers creating true end-to-end contention, the data-ACK separation model demonstrated significant advantages, completing these contentious bidirectional transfers up to 40% faster by protecting the critical feedback loop from congestion and loss. A key technical contribution is the implementation of an adaptive ACK frequency control mechanism based on the draft Internet Engineering Task Force QUIC ACK frequency specification, which successfully reduced ACK path overhead by up to 98% while maintaining or improving transfer performance. The research also uncovered a fundamental architectural tension: the asymmetric composite round-trip time that emerges when data and ACKs traverse different paths, while correctly measuring the feedback loop delay, creates misalignment with physical path properties and network buffer provisioning. This work demonstrates that structured separation of data and control traffic in Multipath QUIC can provide substantial performance benefits under network contention, but is not universally optimal. The effectiveness of traffic separation depends critically on the specific traffic patterns, network conditions, and the ability to manage the architectural complexities introduced by asymmetric path utilization. These findings provide valuable insights for the design of next-generation multipath transport protocols in increasingly heterogeneous network environments.
Bolong Tang (Wed,) studied this question.