With the continuous development of industrial intelligence, the industrial Internet has become the key comprehensive information infrastructure for the development of industrial intelligence. As the infrastructure for the development of the industrial Internet, the basic network will require stronger interconnection, high-quality transmission and intelligent operation and maintenance capabilities in the future. , Under the general trend of IT and OT integration of intelligent manufacturing and industrial Internet, a unified network technology solution is required to open up the underlying basic network. TSN network end-to-end extremely low latency and reliable data transmission have become the foundation for industrial scenarios. The best choice for networking.

TSN Time Sensitive Networking

The TSN network is a time-sensitive network. It is usually called a time-sensitive network or a time-sensitive network in Chinese. TSN is a two-layer technology. The IEEE 802.1Q standard operates at OSI layer 2. TSN is an Ethernet standard, not an IP protocol standard. The forwarding decisions made by the TSN bridge are based on the content of the Ethernet header, not the IP address. The payload of the Ethernet frame can be anything, not limited to the IP protocol. It is actually a set of "sub-standards" based on the framework of IEEE 802.1 to meet special needs. Rather than saying that TSN is a new technology, it is an improvement to the existing network technology Ethernet. On this basis, key technologies such as clock synchronization, traffic scheduling, and network configuration are added to provide transmission services with low latency, low latency jitter, and low packet loss rate for time-sensitive data.

Key Features of TSN Time Sensitive Networks

time synchronization

Traffic scheduling of TSN is based on time slots, so clock synchronization is the basis of TSN. TSN uses a precise time protocol to ensure that the clocks of all network devices are consistent, and do not need to be synchronized with the natural clock. IEEE 802.1AS-2011 specifies the clock synchronization mechanism of the entire TSN network, and proposes a general precision time protocol (gPTP). gPTP is an extension based on the precision time protocol (PTP) of IEEE 1588-2008, and the two work in the same mode.

Global time synchronization is the basis of most TSN standards and is used to ensure the correct matching of the transmission time slots of data frames in various devices to meet the end-to-end deterministic delay and queue-free transmission requirements of the communication flow. TSN uses IEEE 802.1AS to transmit synchronization messages between various time-aware systems. It improves the synchronization protocol of Ethernet, increases the synchronization of distributed networks, and adopts bidirectional information channels to improve the accuracy of transmission signals.

flow control

The flow control process of TSN mainly includes flow classification, flow shaping, flow scheduling and flow preemption.

The main function of traffic classification is to determine the corresponding traffic type and priority information by identifying the attribute information or statistical information of the flow, and the evaluation index is mainly the classification accuracy.

The main function of flow shaping is to limit the maximum rate of sending and receiving flows and buffer the flows exceeding this rate, and then control the flow to be sent at a more even rate to achieve the purpose of stably transmitting burst traffic.

The main function of flow scheduling is to schedule the queued and shaped flows to the output port through certain rules (scheduling algorithms or mechanisms) to determine the corresponding forwarding order of flows in the switch, so as to ensure the QoS requirements of various flows during transmission and ensure that the flows are transmitted within a certain period of time. Reduce network congestion to a certain extent.

Flow preemption changes the scheduling order of low-priority flows and ensures timely forwarding of high-priority flows. It is a special form of flow scheduling and one of the key technologies of TSN. The main function of stream preemption is to avoid stream priority inversion by interrupting the transmission of low-priority frames through inter-frame slicing, so as to ensure the real-time performance of high-priority frames or ultra-low latency performance requirements.

Network Configuration

For time-sensitive network applications, TSN needs to configure the sender, receiver, and switches in the network to provide services such as reserved bandwidth for time-sensitive data. The configuration models of time-sensitive networks defined in IEEE 802.1Qcc are divided into three types: fully centralized configuration model, hybrid configuration model and fully distributed configuration model.

Centralized user configuration (CUC), responsible for the configuration of the sender and receiver; Centralized network configuration (CNC), responsible for the configuration of the TSN switch, the fully centralized model supports the centralized user configuration (CUC) entity to discover terminal and user requirements, and configure TSN features in the terminal.

Figure 1. Fully centralized model

The hybrid configuration model uses a centralized network configuration controller (CNC, Centralized Network Configuration controller) and a distributed user configuration controller (CUC, Centralized User Configuration controller). In a centralized network/distributed model, configuration information is directed to or from a centralized network configuration (CNC) entity.

Figure 2. Hybrid configuration model

The fully distributed configuration model uses a distributed network configuration controller (CNC, Centralized Network Configuration controller) and a distributed user configuration controller (CUC, Centralized User Configuration controller). In this mode, the terminal of the user flow communicates user requirements directly through the TSN user/network protocol. The network is configured in a fully distributed fashion, with no centralized network configuration entity.

Figure 3. Fully distributed model

Example of TSN Time Sensitive Network Application Scenario

Industrial Internet

With the continuous development of the Industrial Internet, the rapid upgrading of industrial applications towards digitization, networking and intelligence is constantly being promoted. It is necessary not only to ensure the exchange of information, but also to ensure the data security between production equipment. IT (information technology), OT ( The three-body integration of operational technology) and CT (communication technology) has become the general trend of the development of the industrial Internet, and finally industrial interconnection will be realized. Only on such an underlying basic network can a new generation of factory-level, workshop-level and field-level be better supported. Applied industrial applications.

TSN technical standards are mainly used in related protocols in the industrial field, including IEEE 802.1AS clock synchronization, IEEE 802.1Qbv time-aware scheduler, IEEE 802.1Qcc network management and configuration, IEEE 802.1CB high reliability, IEEE 802.1Qci stream-by-stream filtering and management, etc. .

Autopilot

With the rise of autonomous driving and the Internet of Vehicles, the large amount of data interaction of in-vehicle devices, the complexity and high cost of traditional in-vehicle network technologies and other issues have put forward strict requirements on the transmission bandwidth, interoperability and cost of in-vehicle networks.

At present, the in-vehicle network still has multiple buses that coexist independently. Auxiliary media signals and control signals represented by audio and video are still transmitted separately on different buses, and cannot be uniformly transmitted on the same link. The reason for this is because there is a major technical difficulty here. TSN technology can improve the best-effort forwarding characteristics of traditional Ethernet, and provide different degrees of end-to-end bounded delay according to different priorities of data streams. Guaranteed and smaller jitter, etc., can provide high-bandwidth, high-reliability, low-latency, and time-synchronized audio/video streaming services in Layer 2 networks. These features can meet the development needs of in-vehicle networks and thus meet the application of in-vehicle Ethernet. Require.