PACE: Redundancy Engineering in RLNC for Low-Latency Communication

Random linear network coding (RLNC) is attractive for data transfer as well as data storage and retrieval in complex and unreliable settings. The existing systematic RLNC approach first sends all source symbols in a generation without encoding followed by the coded redundant packets at the tail of the generation. This systematic tail RLNC achieves low delay when packet drops are rare; however, recovery of any dropped source symbol requires to wait for the coded packets at the end of the generation. We propose and evaluate a novel PACE RLNC approach that paces the transmissions of coded redundant packets throughout the generation of source symbols. The paced coded packets enable the recovery of dropped source symbols without waiting for the tail end of the generation. More specifically, we propose PACE-Uniform, which uniformly intersperses individual coded packets throughout the generation, and PACE-Burst, which intersperses bursts of code packets. Our extensive simulation evaluations indicate that PACE-Uniform significantly reduces the mean source symbol delay compared to tail RLNC, while achieving nearly the same loss probability. We also demonstrate that PACE-Burst generalizes the concept of pacing the redundant packet transmissions and can be flexibly tuned between PACE-Uniform and the conventional tail RLNC by controlling the number of coded packets in a burst.