Size-based queuing: an approach to improve bandwidth utilization in TSN networks

Ethernet has become one of the most researched network technologies for modern, safety-critical, distributed systems due to its maturity and low cost. Standard Ethernet, however, is unsuitable for safety-critical applications due to its lack of delivery guarantees and lack of delay bounds. The Time-Sensitive Networking (TSN) task group proposes several extensions to Standard Ethernet to address these shortcomings. One of the proposed extensions is the Time-Aware Shaper (TAS, IEEE 802.1Qbv-2015) which introduces a gate mechanism that enables scheduled transmissions and minimal jitter for high-priority messages. In order to achieve low jitter for these messages, guard bands are inserted into the schedule of the other traffic classes to ensure that the outgoing link is idle when the transmission of the high-priority message is scheduled to occur. This can result in wasted bandwidth. In this work, we propose Size-Based Queuing (SBQ) - an approach to improve bandwidth utilization in TSN networks that utilize TAS and guard bands. After a detailed description of SBQ, we provide a method to schedule an SBQ-enabled TSN network and conduct a qualitative analysis of the impact of SBQ on the transmission time of messages and the improvements on bandwidth utilization. We show that SBQ can reduce the amount of wasted bandwidth in a network, without impacting the transmission of high-priority messages or requiring extensive changes of the TSN network.