Low-Latency, Line-Rate Variable-Length Field Parsing for 100+ Gb/s Ethernet

Field-programmable gate arrays (FPGAs) are widely employed in network-interface cards across applications including cloud services, machine learning, and high-frequency trading. These applications often share a common optimization goal: minimizing latency while meeting throughput constraints. In addition, these applications ideally aim to achieve "line-rate" operation, where the FPGA operates at full bandwidth without using back-pressure to stall incoming data. However, these goals are often conflicting. For example, to minimize latency, application protocols must effectively utilize network bandwidth by encoding variable-length data in variable-length fields. However, variable-length fields often have prohibitively complex processing requirements that prevent line-rate throughput or have excessive latency. In this paper, we present a novel variable-length field parser capable of scaling to accommodate the bus widths and clock frequencies necessary for 100+ Gb/s Ethernet, while still achieving low latency. Our experiments demonstrate parsing variable-length fields at line rate for anticipated bus widths and throughputs, achieving ultra-low latencies under 2 ns for some use cases. To the best of our knowledge, this latency surpasses existing work, including fixed-length field parsing.