Bounded Latency with Bridge-Local Stream Reservation and Strict Priority Queuing

Abstract

Bridge-local latency computation is often regarded with caution, while new shaping mechanisms and timed gates are developed to achieve deterministic guarantees. However, these new concepts require additional hardware support in the forwarding devices, and many of them are based on assumptions of central control and network-wide information being available. This document presents a per-hop latency bound for individual streams in a class-based network that applies the IEEE 802.1Q strict priority transmission selection algorithm. It does not rely on shaping or timed gates and uses the accumulated latency fields during the reservation process to provide upper bounds with bridge-local information. The presented delay bound is proven formally and then evaluated with respect to its accuracy. It shows that deterministic latency with priority queuing is indeed feasible, and it indicates the required information that must be provided during resource reservation, e.g., to protocols developed in IEEE 802.1Qdd. This document presents a per-hop latency bound for individual streams in a class-based network that applies the IEEE 802.1Q strict priority transmission selection algorithm. It does not rely on shaping or timed gates and uses the accumulated latency fields during the reservation process to provide upper bounds with bridge-local information. The presented delay bound is proven formally and then evaluated with respect to its accuracy. It shows that deterministic latency with priority queuing is indeed feasible, and it indicates the required information that must be provided during resource reservation, e.g., to protocols developed in IEEE 802.1Qdd.