In order to transmit audio and video streams with higher bandwidth and meet the requirements of low delay and high reliability transmission in automobiles, the IEEE 802. 1 Audio and Video Bridging (AVB) working group has defined a set of implementation methods based on communication protocols independent of TCP/IP protocol family. The protocols involved are generally as follows: IEEE802. 1Qat, stream reservation protocol (SRP).
Criteria for reserving bandwidth for specific data streams; IEEE802. 1Qav, forwarding and queuing of time-sensitive flows (FQTSS), the standard of traffic shaping, can guarantee the delay parameters of bandwidth and QoS. And other upper communication schemes: IEEE 1722, Audio/Video Bridging Transmission Protocol (AVBTP).
IEEE 1733, Real-time Transport Protocol (RTP); Universal Precise Time Protocol (gPTP)IEEE 802. 1AS is a standard to ensure strict time synchronization between sending and receiving terminals. The purpose of gPTP is to synchronize the clocks of each node in the vehicle network.
Because the clocks of each node run independently of each other, some applications need to be executed synchronously by each node. For example, the task of playing audio and video may be implemented on different nodes, so the two devices must have the same clock reference, otherwise the picture and sound may not be aligned. In essence, clock synchronization means that all parties have to set their watches.
GPTP is based on the master-slave relationship, that is, all nodes in the local network synchronize their local clocks with those of the master node. The following is a simple schematic diagram. It should be noted that clock synchronization is gradual, and the slave can also be the master of the next network.