Presto: A Match-Action TCP Stack for the Terabit Era

We present Presto, the first TCP stack that delivers ASIC-class performance and energy efficiency on programmable Reconfigurable Match-Action Table (RMT) pipelines, providing flexibility while retaining standard TCP semantics and POSIX socket compatibility. The key challenge in designing Presto is reconciling TCP's complex, dependent state updates with RMT's unidirectional, lock-step execution model. To overcome this challenge, Presto introduces three novel techniques: optimistic concurrency (speculative updates validated downstream), pseudo-segment injection (circular dependency resolution without stalls), and bump-in-the-wire processing (singlepass segment handling). Together, these enable TCP retransmission, reassembly, flow, and congestion control, as a pipeline of simple match-action operations.