Max Length of Fiber Optic MXI Cables and Risks of Exceeding It

Updated Jul 11, 2019

Reported In

Hardware

  • PXIe-8375
  • PCIe-8375
  • PCIe-8381
  • PXIe-8381
  • PXIe-8384

Issue Details

I have a system that involves two PXIe chassis that I want to connect via MXI. They are 500 meters apart. The specification for the Fiber Optic MXI Devices notes that max length is 100m. How do I connect these PXIe chassis together. How is bandwidth and reliability effected when when we exceed that length?

Solution

Setting Up a Long Distance System

The maximum Fiber Optic cable length NI sells depends on the MXI interface that you are using. The part numbers are below.
  • PCIe-PXIe-8381 / PXIe-8384: PN 783329-300 - 300 m, Gen 2 X8, Fiber Optic Cable (Gen 2 x4 speed)
  • PCIe-PXIe-8375: PN 781042-100 - 100 m, Gen 1 x4, Fiber Optic Cable

If you need to connect PXIe chassis that are further apart, you can create a repeater by using a chassis and the corresponding MXI interface. Refer to Additional Information for further details.
 

How Does Extending the Cable Affect the Performance?

After 300 m there is a long enough delay time that has the potential to time out the modules flow control. When a time out of this fashion occurs, the module may think it's a bit error, indicating a hardware failure and potentially causing a BSoD.

Even at 300 m, there may be bandwidth problems. If your application is pushing the bandwidth limit, then extending the length to 300 m may cause problems.

Additional Information

The NI PXIe-8375 Gen 1 interface has two Fiber-Optic ports on its front panel: an upstream port (for connecting towards the host) and a downstream port (which allows for daisy chaining). In the daisy-chain configuration, only a single PCI Express x4 slot is required in the host, but the data throughput might be lower, especially for devices further down the chain. Figure 1-2 also shows an example of a daisy chain configuration.

If you are a Gen 2 connection, you will need a PXIe-8381 MXI interface and a PXIe-8384 bus extension card in the repeater.
 

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