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What's the Difference Between TSN (802.1AS) and IEEE-1588?

Updated Sep 12, 2018

Reported In

Hardware

  • cRIO-9035
  • cRIO-9039
  • cRIO-9040
  • cRIO-9041
  • cRIO-9042
  • cRIO-9043
  • cRIO-9045
  • cRIO-9046
  • cRIO-9047
  • cRIO-9048
  • cRIO-9049
  • cDAQ-9189
  • cDAQ-9185
  • IC-3173
  • IC-3172
  • IC-3171

Driver

  • NI-TimeSync

Issue Details

I have 802.1AS-enabled controllers but I do not have a TSN compliant switch. Can I still use Time Sensitive Networks to sync my devices? What are my other Ethernet-based synchronization options and what are the differences between them?

Solution

There are three types of Ethernet-based network synchronization supported by National Instruments products: IEEE-1588 software timed synchronization, IEEE-1588 hardware timed synchronization, and 802.1AS, as part of the TSN ethernet standard. All NI controllers will support 1588 software timed synchronization, however not all will support 1588 hardware timed synchronization or TSN. A controller able to use TSN can also utilize 1588 hardware synchronization. You can utilize these synchronization methods using the NI-TimeSync driver. See below for more information on each type of sync.

1588 Software Timed Synchronization
IEEE 1588-2008, also known as IEEE 1588v2 is a synchronization method made for cabled networks by allowing clock sharing between devices. A grandmaster device is automatically selected from available devices and distributes timing packets to nodes on the network in order to sync their system clocks to that of the grandmaster. Synchronization with 1588 software time sync is guaranteed to 1ms or less, which is less tight than hardware timed synchronization due to the latency induced between sending the timing packet, receiving the timing packet, and processing the data in the packet itself to set the system clock. IEEE-1588 is relatively robust in that if a grandmaster is removed from the network, an election process will occur to select another grandmaster so that operation can continue.

While any industrial switch will allow 1588 software timed synchronization, a switch that is 1588 compliant may show tighter synchronization between devices.

1588 Hardware Timed Synchronization
1588 hardware timed synchronization is similar to software based synchronization in that it selects a grandmaster among the available devices and distributes timing packets. 1588 hardware timed sync, however, timestamps each timing packet to allow nodes to sync their clocks to a greater accuracy of 1µs or less. This is accomplished through a direct connection from the NIC to the timing source. In the case of cRIO controllers, this allows synchronization of the system clock, the FPGA clock, and DSA modules. Because of the hardware connection, only certain NI controllers (TSN enabled) are able to support 1588 hardware timed synchronization

Much like the 1588 software profile, 1588 hardware timed synchronization does not require a 1588 compliant switch, but tighter synchronization may be seen with hardware that explicitly supports it. 1588 hardware timed synchronization is compatible with 1588 software timed synchronization but not with 802.1AS, meaning that you would need to bridge 1588 and 802.1AS networks with compatible hardware.

Time Sensitive Networks (TSN)
TSN is a timing and synchronization standard built on the Ethernet standard that uses a profile of IEEE-1588 hardware synchronization. TSN requires the same hardware consideration for controllers as 1588 hardware timed sync in that it needs a direct connection from the NIC to the timing source. TSN differs from 1588 hardware in that TSN networks will generate an error if synchronization falls out of expected bounds, unlike 1588 hardware sync, and that TSN timing packets have priority scheduling. Having priority means that TSN timing packets will be sent out from the grandmaster and from TSN enabled switching devices without latency as they will not have to wait for other packets in the buffer to be sent. This guarantees tight synchronization regardless of the amount of network traffic. TSN and 1588 networks are not compatible and would need to be bridged with compliant hardware.

TSN requires switches that are 802.1AS compliant to allow for priority packet scheduling. You can read more about TSN on NI's TSN Forum.

Additional Information

This KnowledgeBase article describes just a few methods of synchronization for NI controllers. Other synchronization methods are available for cDAQ controller systems and cRIO controller systems.

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