PTAS: PIFO-based Time-Aware Shaper for Massive Concurrent Flows in Time-Sensitive Networks

Time-sensitive networking (TSN) specifies a time-aware shaper (TAS) to enhance the real-time support of Ethernet for time-triggered traffic. In TAS, flow/frame isolation is necessary for obtaining a deterministic queuing order, which is the key to achieving determinism. However, this isolation is difficult to fulfill when accessing a large number of concurrent flows generated by industrial devices without TSN capabilities due to the uncontrollable sending times and a limited number of egress queues in TAS. In this paper, a novel TAS framework is designed for massive concurrent flows, named push-in-first-out (PIFO) based time-aware shaper (PTAS). Specifically, the PTAS takes advantage of a PIFO queue to buffer and sort all time-triggered frames based on expected sending time (EST), while an ephemeral memory EST allocation algorithm is proposed to obtain ESTs that can ensure a deterministic queuing order. Through frame sorting rather than conventional isolation, the PTAS efficiently provides a deterministic transmission guarantee for massive concurrent flows. Furthermore, the deterministic flow scheduling constraints for the PTAS are derived, based on which the PTAS is proven to have better schedulability than conventional TAS. In addition to simulation, the PTAS is also implemented on a TSN testbed for evaluation. Extensive experimental results demonstrate that the PTAS can reduce up to 37.0% maximum end-to-end latency, 98.8% jitter, and save 40.1% queue resources in high-concurrency scenarios while scheduling up to 15.5% more flows as compared with conventional TAS.