Time-Sensitive Networking: An Introduction

Ethernet is cheap and ubiquitous. As such, people want to use it to carry all sorts of traffic for which it was not originally intended. A popular current application area is the transport of multiple flows of data, each having different timing requirements. Such applications exist in professional audio, industrial and automotive networks, among others. This article briefly traces the history of the features of IEEE 802 Bridging intended to address those needs, and then describes recent advances in time-sensitive networking in more detail. As well as completed standards, some current projects are described. Areas for future standardization are identified. Encoding the priority of packets in the header allows high-priority packets to be scheduled for transmission ahead of lower-priority packets, providing a better quality of service for urgent traffic. Time-sensitive flows have varying requirements for maximum latency and latency variation. Audio-video bridging provides guaranteed quality of service in terms of those parameters, for booked traffic in a bridged network comprising only compliant bridges. Some types of flow (particularly in industrial networks) are very sensitive to packet loss. Time-sensitive networking can provide bounded latency and zero packet loss due to congestion. The most stringent guarantees and most efficient use of network resources is provided by cyclic queuing and forwarding, which combines time synchronization, transmission scheduling and per-stream filtering and policing to provide just-in-time delivery of time-sensitive streams. This requires careful planning and centralized control. Less stringent use cases allow use of distributed control techniques.