time-sensitive networking (802.1) (TSN)
Time-Sensitive Networking (TSN) is an Ethernet-based technology that evolved from AudioVideoBridging( AVB) and is characterized by very low latency and high availability. The 802.1working group, which deals with time-sensitive networking, has developed several protocols for real-time transmission over Ethernet around the TSN standards, such as the Stream Reservation Protocol( SRP) or the Forwarding and Queuing for Time-Sensitive Streams. Ethernet is essentially about additions for deterministic transmission characteristics.
If we look at Audio Video Bridging (AVB) and Time-Sensitive Networking (TSN), we can see that the AVB protocol is used for real-time communication, while Time-Sensitive Networking is used for difficult real-time communication with high availability, reliability and precise timing. It is designed for multiple traffic types. The TSN standard provides the perfect feature set for synchronous control of devices in production. TSN technology reduces the worst case for delay times to less than 4 µs per hop at data rates of 1 Gbps. As a central principle, TSN networking uses Time Aware Shaper( TAS), a queuing method with priority control.
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One of the essential functions of TSN networks is time synchronization of all devices that communicate in real time. They receive a uniform time measure, usually via IEEE 1588 time synchronization, which distributes the reference time throughout the network. Furthermore, there is a function for scheduling and traffic shaping. This function ensures that all devices operate according to the same rules and that data packets are forwarded according to uniform rules. Another function is the reservation of bandwidth and time slots by the connected devices. This allows several connections to be assigned to one device at the same time.
The functions covered are ensured by various standards. For example, improved clock synchronization is specified in the 802.1AS standard. The time-triggered communication for Ethernet by means of Time Aware Shaper (TAS), specified in 802.1Qbv, the establishment of redundant communication paths (802.1Qca) and the improvements in the reservation of resources according to 802.1Qcc. The 802.1Qbu specifications ensure the prioritization ofmessages. According to this, messages can be interrupted during transmission in order to let more important messages pass preferentially, without large delays. And with 802.1CB, data packets can be duplicated and later reassembled at a defined point in the network, thus ensuring redundancy. In this process, one data packet is forwarded. The other redundant data packets are recognized by the sequence number and discarded.
In addition, TSN technology allows alternative paths with direct switching and ensures seamless redundancy with multiple data streams transmitted simultaneously. This is why TSN technology is used in automotive applications, where it meets a wide range of requirements. For example, it can bridge distances of 30 m with 5 hops and communicate with over a hundred electronic control units(ECUs), sensors and actuators. In the work cell, where the robots are networked together, the networking can have 5 hops; in terms of the factory, it can be 64. As Indusrie 4.0 and the Internet of Things( IoT) are increasingly about wireless radio communication, the AVnu Alliance has authoritative institution for TSN networks developed specifications for a wireless TSN.