What is TSN?

By Comcores

TSN, or Time-Sensitive Networking, is a technology based on the IEEE 802.1Q standard. It has evolved from the Ethernet technology currently used to carry all types of traffic, for which ethernet was not originally intended, such as multiple data flows with different timing requirements, commonly found in Audio Video Bridging (AVB), automotive and industrial automation applications. TSN sits in Layer 2 of the OSI Model (figure 1).

Figure 1: Illustration of the OSI model, with description of what occurs in each layer.

TSN is designed to provide deterministic guarantees on Quality of Service (QoS) metrics and reliability in a switched Ethernet network. This means it guarantees deliveries and minimizes jitter for real-time applications that require determinism, unlike Ethernet which is not a deterministic system, due to packet buffering, various queuing delays and lack of priority in data flows.

Some of the main characteristics of TSN include time synchronization of the network, resource management in the network and the coexistence of multiple flows with best-effort services.

Time synchronization refers to the nodes or bridges in a network being synchronized to a grand master clock's time. Resulting in several benefits such as allowing data to become available at a specific time for specific tasks, enabling bounded latency, and allowing for distributed measurements and control.

In a network there are devices called “talkers” and “listeners”. The talker sends out a data stream, while the listener is the destination of that data stream. The talkers and listeners can communicate in various ways in the network, and the network also needs to be capable of managing those resources.

The coexistence of multiple flows with best-effort services refers to the priority of data packets and how this flow can be set up to interrupt non-time-critical data packets in favor of time-critical packets.

Origin of TSN

TSN is not a single standard, but a toolset consisting of many standards that are published as amendments to the IEEE 802.1Q standard and are developed by the IEEE 802.1 TSN Task Group. The task group focuses on extending existing IEEE 802.1Q standards to accommodate the needs of time-sensitive networking.

TSN is a broad concept with use cases in numerous industries. Different features of TSN are critical based on the needs of that industry. This has led to the creation of TSN Profiles, which provide their own configuration and how to apply TSN to the requirement. Some examples of TSN profiles include mobile fronthaul, aerospace, industrial automation and in-vehicle communications.

Overall, there are four main components of TSN; Time Synchronization, Latency, Resource Management and Reliability (figure 2).

Figure 2: Illustration of the 4 components of TSN and the TSN profiles, which will be our focus of discussion

The IEEE 802.1 TSN working group has published some TSN profiles (AVB and TSN for Fronthaul), while still developing the remaining four profiles (as seen in Figure 2). The know profiles are:

• IEEE Std 802.1BA for Audio-Video Bridging (AVB) networks
• IEEE Std 802.1CM TSN for Fronthaul
• IEC/IEEE 60802 TSN Profile for Industrial Automation
• P802.1DF TSN Profile for Service Provider Networks
• P802.1DG TSN Profile for Automotive In-Vehicle
• P802.1DP TSN Profile for Aerospace onboard Ethernet

Benefits of TSN and industries where it’s applicable

There are many benefits of TSN as it overcomes limitations of conventional Ethernet. The majority of limitations in conventional Ethernet fall into categories like lack of real-time communication and QoS. As mentioned earlier, there are many different use cases and numerous industries. Below is a list of the benefits that TSN provides.

• Time synchronization within a network
• TSN brings efficiency, easier management and cost-effectiveness to the world of automation
• TSN reduces latency and improves reliability
• Converged Network: TSN ensures vital process data is handled in a reliable and deterministic manner, while providing the essential mechanisms for all sorts of network traffic to coexist on the same network
• Scalability, as TSN is not defined for a specific transmission rate

Stay tuned for our two follow up articles. The first is to understand the 4 components of TSN and the second takes a deeper dive into the TNS profiles that can be seen in Figure 2.

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