Simulation-Based Analysis of Eligibility Time Assignment Behavior and Delay Performance

IEEE 802.1Qcr standard was presented for Asynchronous Traffic Shaping (ATS) by the Time Sensitive Networking (TSN) task group. The eligibility time assignment (ETA) defined in ATS is one of implementations of urgency-based flow scheduling mechanism comparing with another implementation called Token Bucket Emulation (TBE). The ETA mechanism calculates and assigns an eligibility time value to each frame. It could be shown by simulation-based analysis that the ETA has some features better than TBE in the first-in-first-out (FIFO) order preserving and per-hop delay statistic. To be specific, the ETA is able to keep the FIFO order of frames either by using a single queue or by using multi-queues while the TBE can only keep FIFO order by using a single queue; and the mean squared error of the per-hop delay under the ETA shaping is smaller than the one under the TBE shaping, in the meaning that the ETA leads to a smaller delay jitter. In addition, simulation results show that for a flow with the same TSN configuration, the maximum per-hop delays using either the ETA or the TBE are approximately equal.