# Development of Traffic Scheduling Based on TSN in Smart Substation Devices
## 1 Introduction  
The development of computer and network technology has promoted the development and application of smart technology. The communication architecture of a substation automation system has also evolved gradually with the development of computer technology and network communication technology [1; 2]. At the beginning of the 21 st century, the IEC 61850 communication protocol was applied to smart substation automation systems, and the \"three-layer and two-network\" object-oriented communication model, which contains complex IT/OT data traffic, was used for the digitalization, intelligence and communication standardization of substations [3; 4]. Traditional Ethernet transmits data in a \"best-effort\" way, which can only reduce the end-to-end delay jitter by tens of milliseconds, and it is difficult to meet the communication service requirements of low latency, low jitter, and high reliability in smart substations [5; 6]. Therefore, there is an urgent need to establish a new generation of networks that can provide \"on-time and accurate\" quality of service for data transmission [7; 8]. Currently, the domestic and international technical solutions that can provide deterministic transmission mainly include Flexible Ethernet (FlexE), Time-Sensitive Networking (TSN), Deterministic Networking (DetNet) [9], Deterministic IP (DIP) technology, Deterministic WiFi (DetWiFi) [10; 11], and 5G Deterministic Networking (5 GDN) [12], etc. Among them, FlexE inserts an intermediate layer, FlexE Shim, between the physical layer and the link layer to decouple the service rate and the physical channel rate, providing a more flexible bandwidth granularity than traditional Ethernet and supporting the evolution ofhigh-speed large-port 400 GE, 1 TE, etc. However, it is a little worse in terms of deterministic latency guarantee, and substations have not yet reached the bandwidth demands of 400 GE and 1 TE. However, in a smart substation environment, network requirements are more about ensuring the reliability and timeliness of critical control information (such as protection information) than simply bandwidth expansion. In addition, the deployment of FlexE may affect the interoperability of existing devices because not all devices can support the FlexE standard. DetNet and DIP both provide three-layer deterministic network transmission, and deterministic WiFi and 5 GDN both focus on wireless transmission, which is difficult to deploy in substation automation systems that currently transmit data traffic through cables. The deterministic low-latency, low-jitter transmission capability that TSN provides to Layer 2 (the link layer) is the basis for the deterministic network technologies described above. TSN can better address Layer 2 network deterministic guarantees than traditional Ethernet. It achieves transmission without congestion and packet loss through a set of protocol standards, provides low latency and jitter with upper bound guarantees, and provides deterministic transmission guarantees for latency-sensitive traffic. To achieve deterministic transmission in Layer 2 networks, TSN can achieve sub-microsecond time synchronization by IEEE 802.1 AS and the newer revision IEEE 802.1 AS-REV, and it can achieve priority scheduling of time-sensitive traffic by using traffic-shaping mechanisms such as IEEE 802.1 Qav (Credit-based Shaper, CBS), IEEE 802.1 Qbv (Time-aware Shaper, TAS), 802.1 Qch (Cyclic Queuing and Forwarding, CQF), IEEE 802.1 Qbu (Frame Preemption), and IEEE 802.1 Qcr (Asynchronous Traffic Shaping, ATS). In addition, IEEE 802.1 Qcc provides a centralized set of tools for globally managing and controlling the network, which can perform resource reservation, scheduling, and other configurations via remote management protocols (such as NETCONF or RESTCONF), enabling quality of service guarantees for time-sensitive data streams.