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Time-sensitive networking

The meaning of «time-sensitive networking»

Time-Sensitive Networking (TSN) is a set of standards under development by the Time-Sensitive Networking task group of the IEEE 802.1 working group.[1] The TSN task group was formed in November 2012 by renaming the existing Audio Video Bridging Task Group[2] and continuing its work. The name changed as a result of the extension of the working area of the standardization group. The standards define mechanisms for the time-sensitive transmission of data over deterministic Ethernet networks.

The majority of projects define extensions to the IEEE 802.1Q – Bridges and Bridged Networks, which describes Virtual LANs and network switches.[3] These extensions in particular address the transmission of very low transmission latency and high availability. Applications include converged networks with real-time Audio/Video Streaming and real-time control streams which are used in automotive or industrial control facilities.

Standard IT network equipment has no concept of “time” and cannot provide synchronization and precision timing. Delivering data reliably is more important than delivering within a specific time, so there are no constraints on delay or synchronization precision. Even if the average hop delay is very low, individual delays can be unacceptably high. Network congestion is handled by throttling and retransmitting dropped packets at the transport layer, but there are no means to prevent congestion at the link layer. Data can be lost when the buffers are too small or the bandwidth is insufficient, but excessive buffering adds to the delay, which is unacceptable when low deterministic delays are required.

The different AVB/TSN standards documents specified by IEEE 802.1 can be grouped into three basic key component categories that are required for a complete real-time communication solution based on switched Ethernet networks with deterministic quality of service (QoS) for point-to-point connections. Each and every standard specification can be used on its own and is mostly self-sufficient. However, only when used together in a concerted way, TSN as a communication system can achieve its full potential. The three basic components are:

Applications which need a deterministic network that behaves in a predictable fashion include audio and video, initially defined in Audio Video Bridging (AVB); control networks that accept inputs from sensors, perform control loop processing, and initiate actions; safety-critical networks that implement packet and link redundancy; and mixed media networks that handle data with varying levels of timing sensitivity and priority, such as vehicle networks that support climate control, infotainment, body electronics, and driver assistance. The IEEE AVB/TSN suite serves as the foundation for deterministic networking to satisfy the common requirements of these applications.

AVB/TSN can handle rate-constrained traffic, where each stream has a bandwidth limit defined by minimum inter-frame intervals and maximal frame size, and time-trigger traffic with an exact accurate time to be sent. Low-priority traffic is passed on best-effort base, with no timing and delivery guarantees.

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