Serial 1: Automotive Ethernet time-sensitive network application scenarios and implementation difficulties
Development trends of automotive Ethernet, types and current status of commonly used TSN protocols
With the rapid development of electrification, intelligence, and connectivity of automobiles, the scale and complexity of in-vehicle electronic systems are increasing day by day, and intelligent systems such as lane departure warning and active collision avoidance are becoming more and more common. The application of these systems puts forward higher requirements for the real-time performance, bandwidth and reliability of the vehicle network. At the same time, for the electronic and electrical architecture of future smart cars, the in-vehicle network also needs new communication technology support.
Compared with traditional in-vehicle networks, in-vehicle Ethernet can reach transmission speeds of 100 Mbit/s or better, and can support high data bandwidth and high communication rates. It is very suitable for ADAS, in-vehicle entertainment and other systems in automobiles, and has gradually become the backbone of automobiles. network. With the development of Ethernet communication protocols, it can overcome the shortcomings of transmission uncertainty while retaining the advantages of traditional Ethernet, and its point-to-point working mode makes network planning more flexible and can satisfy various subnets through different topologies. Real-time, redundancy and cost requirements.
In order to provide synchronized and low-latency real-time streaming media services on Ethernet, the IEEE 802.3 working group established the AVB working group in November 2005 and formulated a series of audio and video transmission technology protocols, making real-time audio and video transmission technology based on Ethernet be able to go to the market. The Ethernet Audio/Video Bridging (hereinafter referred to as AVB) developed by the AVB group is a new IEEE 802 standard. Based on traditional Ethernet, it guarantees bandwidth, limits delay and precise clock synchronization. Provide perfect service quality for the network to support various network multimedia applications based on audio and video. AVB focuses on enhancing the real-time audio and video performance of traditional Ethernet, while maintaining 100% backward compatibility with traditional Ethernet. It is a next-generation network audio and video real-time transmission technology with great development potential.
In order to more accurately reflect the continued development of AVB, the name of the IEEE AVB Task Group was officially changed to "Time Sensitive Network (TSN) Group" in November 2012. The TSN task group is based on the original AVB standard architecture and is committed to developing stronger functions to achieve ultra-low latency control networks. Although the terms AVB and TSN are often used interchangeably, many new concepts and functions are proposed in the TSN protocol suite to support more application areas. Time Sensitive Networking (TSN) is not a single standard, but consists of a series of standards.
The following table is a series of TSN protocol standards. However, not all protocols are suitable for vehicle scenarios. Among them, IEEE 802.1 AS, IEEE 802.1 Qbv, IEEE 802.1 CB, IEEE 802.1 Qci, IEEE 802.1 Qbu, IEEE 802.1 Qch, IEEE 802.1 Qcc and IEEE 802.1 Qcr are considered suitable for vehicle scenarios. The first four standards are the most commonly used among them and are most likely to become the first batch of TSN protocols applied in vehicles. These protocols can guarantee time synchronization, deterministic transmission and reliability of in-vehicle networks. However, in automobiles, a typical physical information system, many factors such as the complexity of the system communication network, startup time requirements, functional safety, and information security force these standard protocols and their parameter designs to be further studied and optimized.
Application scenarios of commonly used TSN protocols
In the automotive field, TSN can be applied to the following scenarios:
Vehicle infotainment system: TSN can be used to transmit audio, video and other multimedia data in the vehicle entertainment system to ensure real-time transmission and synchronization of data and provide a better entertainment experience in the car. The specific scene is shown in the figure. The high-definition map and positioning information are transmitted to the vehicle HUT and instruments through the T-BOX through the central gateway; the multimedia video stream on the HUT vehicle is transmitted to the entertainment screens of the two back seats through the gateway, which requires two The same video content is played simultaneously on the screen. Since data requires large bandwidth, fast redundancy switching and precise clock synchronization, protocols such as 802.1AS-Rev, 802.1CB, 802.1Qci, and 802.1Qbv need to be used.
Advanced driver assistance system (ADAS): TSN can be used to realize real-time data exchange between different modules in the ADAS system, such as the transmission of sensor data, decision-making, and the transmission of control commands. Ensure time synchronization and deterministic transmission of these data to ensure that sensor fusion or decision planning algorithms work properly. Data fusion of environmental sensing sensors such as radar, lidar, ultrasonic, and camera requires large data transmission bandwidth. Sensor data fusion, especially solutions that use back-end data fusion, requires that data from different sensors can be synchronously transmitted to central computing in real time. platform. For security-related multimedia data streams; the transmission cycle is less than 10ms; the transmission delay is less than 1ms; no data loss is allowed. Therefore, 802.1AS-Rev, 802.1Qbv, and 802.1Qbu will be used.
Intelligent networked vehicle cross-domain communication: In the context of new automotive electronic and electrical architecture, vehicle Ethernet serves as the backbone network to connect various regional controllers as shown in the figure. Computing power sharing is a typical scenario. For example, a regional controller uses the computing power of a central computing platform to implement vehicle control calculations. This scenario involves traffic transmission with different bandwidths and different real-time requirements. TSN can meet the communication needs of different types of traffic. In order to achieve optimal allocation of communication capabilities in the backbone network and achieve low-latency, highly reliable and deterministic transmission, the TSN protocols that may be used include 802.1AS-Rev, 802.1CB, 802.1Qci, 802.1Qbv, 802.1Qbu, etc.
With the development of autonomous driving and intelligent transportation technology, the application of TSN in the automotive field will continue to expand.
Difficulties in implementing common TSN protocols
The difficulties in implementing TSN protocol vehicle applications are as follows:
1. There is a lack of mature protocol function performance simulation platform. Existing ones such as OMNet++, RTaW and TSN System have limitations in functions and vehicle scenario adaptation, and cannot truly simulate vehicle scenarios for simulation.
2. In-vehicle Ethernet switches and end node chips have limited support and openness to the protocol.
3. There is a lack of test standards related to the TSN protocol for vehicles, and the industry does not have a system-level TSN network test solution.
4. The TSN protocol is highly complex. It is difficult to design parameters in complex network scenarios, and the configuration methods of different switches are different. Automated design and configuration methods are needed to reduce the difficulty and cost of technical implementation.
The implementation difficulties at the protocol level are as follows:
1. Time window design and alignment for IEEE 802.1Qbv: A comprehensive design needs to take into account the priority, bandwidth requirements, timing requirements, link transmission delay and other factors of each traffic flow.
2. For IEEE 802.1CB redundant path selection and redundant frame processing: The copying of messages will occupy the bandwidth resources of multiple paths, and a trade-off between reliability and bandwidth utilization is required. When designing redundant paths, you need to consider that the hop count difference between redundant paths cannot be too large, otherwise it may cause a network failure or a packet burst or disorder when a link is broken.
3. Regarding the IEEE 802.1AS synchronization start time and redundant synchronization scheme: the time from startup to synchronization completion and how to switch to the backup clock or backup redundant link as quickly as possible after synchronization failure while ensuring the stability of synchronization accuracy is Difficulties in vehicle applications.
4. Configuration of monitoring and filtering parameters for IEEE 802.1Qci: In complex vehicular networks, it is difficult to correctly design monitoring and filtering parameters to make the communication network sufficiently resilient to foreseeable and unforeseen anomalies.
Solutions based on Infineon AURIX™
In response to the above implementation difficulties, Tongji University developed a time-sensitive network demonstration system based on Infineon AURIX™ TC3xx.
The overall structure of the system is shown in the figure, which consists of a main control node N1, two video forwarding nodes N2 and N3, an audio node N4 and two Raspberry Pi nodes with cameras. The N2 node is also the control node of the car model. Each node N1-N4 contains an Ethernet switch and main control MCU TC3x7. The backbone network composed of four nodes is connected through 1000BASE-T1 to form a ring network.
The video stream is generated by two Raspberry Pi nodes and transmitted to N2 and N3, and finally reaches the PC according to the designed path and is displayed on the host computer. The audio files are stored in the host computer and sent to the N4 audio node by the host computer for playback through the audio module and speakers. The control message is sent from the host computer in Ethernet format. After reaching the N2 node, it is converted into a CAN message and sent to the car model node to realize the control of the car doors and lights.
IEEE 802.1AS is the basis of the network and is used for time synchronization of all nodes. Among them, TC377 of N2 is the global master clock node, and other node switches and controllers use this node time as a reference for time synchronization. At the same time, the host computer can dynamically configure the TSN protocol for the above-mentioned established audio and video traffic and control traffic, such as IEEE 802.1Qbv, IEEE 802.1CB, IEEE 802.1Qci and the end node time-sharing scheduling mechanism based on the TC3 series. In addition, the host computer can also control the generation of interfering traffic in the network. Through the intuitive feeling of video lagging and the real-time end-to-end delay scatter plot of the video stream, the actual effect and performance of applying the TSN protocol in the end and bridge can be Received clear and intuitive responses.
The whole system is shown in the figure:
In the next article, we will combine the IEEE 802.1AS, IEEE 802.1Qbv, and IEEE 802.1CB protocol standards to deeply analyze how the time-sensitive network demonstration system based on Infineon AURIX™ TC3xx solves the above difficulties.
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