Efficient Robust Schedules (ERS) for Time-Aware Shaping in Time-Sensitive Networking

Abstract

Time-Sensitive Networking (TSN) extends Ethernet bridging with features for deterministic transmission. Periodic streams may be scheduled such that their frames hardly interfere in bridges. Additionally, the Time-Aware Shaper (TAS) can keep egress ports free from other traffic when scheduled traffic arrives. TAS scheduling determines transmission starts of scheduled streams at end stations and configures the TAS in bridges. Most TAS scheduling algorithms disregard jitter and synchronization errors at end stations and bridges, race conditions from simultaneously arriving frames with same egress ports, and hardware-based configuration limits of the TAS. We call the resulting schedules tight schedules (TS). However, all these challenges apply to real hardware bridges. Therefore, we present an algorithm using event times with uncertainty to compute efficient robust schedules (ERS) that respect these constraints. We also propose a repair for existing scheduling approaches and call their output naïve robust schedules (NRS). We evaluate and compare their bandwidth usage and stream admission with those of TS. ERS are more efficient than NRS, and the performance gap between ERS and TS quantifies the price for robust schedules. Moreover, the presented algorithm for ERS computes significantly faster than four well-known methods for TS, and it can solve larger problem instances.