Risks of Exceeding the Max Length of Fiber Optic MXI Cables

Updated May 21, 2018

Reported In

Hardware

  • PXIe-8375
  • PCIe-8375

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

NI sells a Fiber Optic cable that is 300m long, its part number is 783329-300. You can connect PXIe chassis together that are further apart than 300m by creating a repeater using a chassis and a NI PXIe-8375 module. The module contains an uplink terminal and a downlink terminal for daisy chaining.

How Does Extending the Cable Affect the Performance?

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

Additional Information

The NI PXIe-8375 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.

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