Time Sensitive Networking (TSN) refers to a set of new and evolving IEEE 802.1 Standards designed to enable deterministic real-time communication over Ethernet. It is designed to co-exist with the best-effort communication that Ethernet currently provides. TSN was originally aimed to address the challenges with real-time audio and video communication over Ethernet, but now has application across multiple verticals; e.g., IEC/IEEE 60802 TSN Industrial Automation profile that aims to apply this technology for industrial automation applications deployed over Ethernet. TSN enhancements primarily focuses on time synchronization of all nodes involved in the packet flow, minimizing latency of packets as they traverse through the nodes, ensuring reliability so that the packets reach their destination on time, and providing a way to manage the resources to be deployed at each node for a particular application or traffic pattern. These enhancements are primarily done at the Layer 2 (Data Link Layer) of the network nodes.
- IEEE 802.1AS Standard defines the timing and time-synchronization methods required for TSN. It uses a profile of the IEEE 1588 Precision Time Protocol (PTP) over Ethernet. By using the specified method, we can ensure that all the nodes involved in the packet flow are time-synchronized to a global time.
- IEEE 802.1Qbv Standard describes the use of multiple queues at the egress port and a schedule that dictates which queue will be opened for transmission. Higher priority can be given to schedule queues having critical traffic, while ensuring that non-critical traffic also gets serviced simultaneously. Such scheduling based transmission ensures that latency can be predicted and managed efficiently. This also known as Time-Aware traffic Shaper (TAS) in TSN.
- IEEE 802.1Qbu Standard introduces the concept of frame preemption, wherein a low priority packet transmission can be interrupted mid-way to transmit a high priority packet and then resume transmitting the low priority packet. This ensures that low priority packet transmission is not blocked in anticipation of critical high priority packets.
- IEEE 802.1CB Standard specifies ways to handle single-point failures by using redundancy and/or to guarantee latency. It is compatible with the other redundancy protocols such as the HSR and PRP.
Enhancing an Ethernet node to support TSN will require refactoring of the existing Layer 2 (Data Link Layer) implementation. Note that Layer 2 implementation can be either purely software, a mix of software and hardware (e.g., Texas Instruments Industrial Communication Sub-system [ICSS]), or a specialized hardware (e.g. FPGA) implementation. We have advanced level expertise on Layer 2 Ethernet implementation for 10/100/1000 Mbps line rates. We have worked on multiple projects enhancing such implementations on the Texas Instruments Sitara devices in conjunction with their ICSS (e.g., 5-port switch, HSR, PRP, RSTP, etc.). The ARM core either runs the Linux or RTOS OS with device drivers along with custom firmware running on the ICSS PRU, together optimized to support the TSN features.These enhancements may include modifying the queue architecture, enhancing the time-synchronization implementations, enhancing the frame-preemption for custom support for express traffic, or custom enhancements required to support specific end-user applications. Supporting TSN enhancements on Linux is still evolving and new frameworks are being defined. We have also worked extensively on integrating XDP stack with custom driver and firmware modifications to support TSN on TI Linux SDK for Sitara devices.