TSN is a set of protocol standards to ensure the smooth transmission of deterministic information in different scenarios of standard Ethernet. The TSN protocol suite itself has high flexibility, and users can choose the corresponding protocol combination according to the specific needs of the application.
The TSN protocol suite includes four categories of sub-protocols: timing and synchronization, delay, reliability, and resource management. We use the following figure to briefly describe the role and function of each sub-protocol of TSN.
This part of time synchronization
contains only one protocol, that is, IEEE STD 802.1AS (the latest version was released in June 2020). This protocol contains two parts: timing and synchronization, which is an important mechanism for deterministic communication. It has The following features:
· It is the profile of IEEE 1588 PTP synchronization protocol, which supports different TSN devices to achieve synchronization compatibility
Provides a time reference for each node in the TSN network to participate in traffic scheduling
· This protocol adds support for fault tolerance and multiple Grand Master master clock sources, making the clock synchronization system more robust
Can seamlessly switch to the redundant clock source in the event of primary clock source failure
Delay
This section defines different shaping mechanisms to limit the delay of the data flow within a certain range, so as to meet the requirements of different low-latency scenarios. In traditional Ethernet, the communication delay of the data flow is uncertain. Due to this uncertainty, the data receiving end usually needs to preset a large buffer to buffer the output, but this will cause the data flow, such as audio and video flow, The real-time aspect is missing.
TSN must not only ensure the arrival of time-sensitive data flows, but also ensure the low-latency transmission of these data flows.
By optimizing the control of time-sensitive flows and best-effort flows, as well as the transmission process between different time-sensitive flows in the network, to ensure the transmission time requirements of data flows, the optimal control method is shaping.
802.1Qav
The original intention of this protocol is to ensure that the traditional asynchronous Ethernet data flow will not interfere with the real-time data flow transmission of AVB. Now Qav is no longer limited to the transmission of audio and video.
This protocol specifies the algorithm for ingress metering, priority regeneration, and processing time-aware queues for each type of priority (CBS, the effect is shown in the figure below).
It uses timing information generated by the IEEE 802.1AS protocol, and VLAN priority to isolate frames between controlled and uncontrolled queues, while supporting time-sensitive traffic transmission between wired or wireless LANs.
Due to the CBS mechanism defined in Qav, 802.1Qch implements only a soft real-time level mechanism, but the complexity of the network transmission path topology and various interferences will cause continuous delay increase, and the worst delay situation is related to topology, hop count, switch Buffers are correlated, and 802.1Qch (circular queue forwarding mechanism or creep shaping) is used to improve these situations.
By synchronously controlling the strategy of entering and exiting the queue, the forwarding process can be realized in one cycle, so that the time when the data flow passes through the switch is more deterministic.
The 802.1Qch protocol also defines CQF (need to be used in conjunction with the Qci protocol), where the Qci standard will filter and supervise each queue input by the Bridge node according to the arrival time, speed, and bandwidth, to protect bandwidth and increase Burst flow and error handling.
802.1Qbv
traffic scheduling is the core concept of TSN. According to the global time reference provided by the time synchronization protocol 802.1AS, scheduling tasks are created and distributed to participating network devices.
802.1Qbv defines a mechanism to control queuing traffic by controlling the switch of the gate at the exit of the TSN switch. Messages in these queues will be transmitted within a preset time window.
Usually, during these time windows, the transmission of other queues will be blocked, so as to avoid scheduled traffic being blocked by unscheduled traffic, so that the delay of data passing through the switch is deterministic.
802.1Qbu
, although Qbv's mechanism can protect critical messages from other traffic, does not necessarily achieve optimal bandwidth usage and minimum communication delay. If these factors are very important for the data to be transmitted, the frame preemption mechanism defined by 802.1Qbu + 802.3br can be used to guarantee.
The 802.1Qbu protocol defines a mechanism that interrupts the transmission of standard Ethernet frames and jumbo frames, allowing high-priority frames to pass through first, and can resume the transmission of previously interrupted frames.
As shown below, the purpose is achieved by reducing the size of the protection area set for the interference frame and reasonably slicing the interference frame.
The shaping algorithms designed in 802.1Qcr Qch and Qbv are mainly used for ultra-low-latency data, which are highly dependent on network time synchronization and enhanced packet transmission in mandatory cycles, but the bandwidth utilization is not high, so there are Qcr (also called ATS) is used for asynchronous stream scheduling.
Through this shaping method, the bridge and the terminal node do not need time synchronization, and the application of mixed periodic and aperiodic data stream transmission can be more efficiently utilized in bandwidth.
Reliability
Applications that require high real-time data transmission not only need to ensure the timeliness of data transmission, but also need a highly reliable data transmission mechanism to deal with various problems caused by Bridge node failure, line disconnection and external attacks to ensure functionality Security and cybersecurity.
In order to reduce the impact on the network due to link and node failure, 802.1CB
improves reliability by setting redundant messages and setting redundant links in the network for parallel transmission.
The 802.1Qca Path Control and Reservation standard defines how such paths are set up, and then redundancy management mechanisms combine these redundant messages to generate a single flow of information from sender to receiver.
802.1Qci
802.1Qci isolates faults to specific areas in the network to prevent network faults or malicious attacks from interfering with the network. It works on the ingress of the switch, policing the input of each flow with various constraints to prevent the outbound queue from being flooded with illegal frames.
Resource Management
In a TSN network, each real-time application has specific network performance requirements.
A feature of enabling a TSN network is the process of configuring and managing available network resources, which allows a series of TSN sub-protocols to be configured in the same network to rationally allocate resources on network paths to ensure that they can be used as expected normal operation.
802.1Qat
Stream Reservation Protocol (SRP). It specifies admission control based on the resource requirements of the flow and the available network resources, reserves resources and notifies all network nodes from the data source sender to the data receiver, ensuring that the specified flow has sufficient network on the entire transmission path Resources are available.
802.1Qcc
This protocol is an enhancement of the stream reservation protocol (802.1Qat), including support for more streams, configurable stream reservation classes and streams, better stream feature identification, support for high-level streams, and deterministic streams Reservation convergence and User Network Interface (UNI) for routing and reservations.
802.1Qcc supports offline or online configuration of TSN network scheduling.
802.1Qcp
YANG data model. It defines an information model and a YANG data model based on the Unified Modeling Language (UML), which allows configuration and status reporting of Bridge nodes.
It also defines the relationship between the information and data models, other management functions specified in the protocol, and the models of IEEE Std 802.1AX and IEEE Std 802.1X.