Quantifying the Impact of Frame Preemption on Combined TSN Shapers

TL;DR

This paper evaluates how integrating Frame Preemption with existing TSN shapers affects QoS, showing significant delay reductions and stable jitter, with practical configuration insights for complex network architectures.

Contribution

It introduces and quantifies the integration of Frame Preemption with CBS and GCL in TSN, providing experimental analysis and practical configuration recommendations.

Findings

Up to 40% reduction in AVB flow delay with preemptable class.

Jitter of TT traffic remains unaffected in 'with Hold/Release' mode.

Guardband reduces jitter in 'without Hold/Release' mode.

Abstract

Different scheduling mechanisms in Time Sensitive Networking (TSN) can be integrated together to design and support complex architectures with enhanced capabilities for mixed critical networks. Integrating Frame Preemption (FP) with Credit-Based Shaper (CBS) and Gate Control List (GCL) opens up different modes and configuration choices resulting in a complex evaluation of several possibilities and their impact on the Quality of Service (QoS). In this paper, we implement and quantify the integration of preemptive CBS with GCL by incorporating FP into the architecture. Our experiments show that the end-to-end delay of Audio Video Bridging (AVB) flows shaped by CBS reduces significantly (up to 40\%) when AVB flows are set to preemptable class. We further show that the jitter of Time Triggered (TT) traffic remains unaffected in "with Hold/Release" mode. Furthermore, we propose to introduce Guardband (GB) in the "without Hold/Release" to reduce the jitter of the TT flow. We compare all the different integration modes, starting with CBS with GCL, extending it further to FP. We evaluate all feasible combinations in both synthetic and realistic scenarios and offer recommendations for practical configuration methods.