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Fiber optics over distance

Networking expert Greg Schulz offers advice to a reader that asked about using fiber-optic cabling over long distances.

We were having a discussion the other day about using a LX GBIC to push a signal farther than the typical SX limitation of 550 m over a multimode fiber. I know we can do it, but the point I was trying to make is that the GBIC regulates whether the signal propagation is multimode (multiple paths along the fiber) or single mode (single path along the fiber) and not the actual fiber that refracts the light. The way I understand it, the multimode fiber allows the signal to reflect at the correct angle to reach the end of the tunnel. Is my assumption correct, or does the fiber actually regulate the propagation of the light?
To achieve long distances (LX) using fiber-optic technologies for Fibre Channel (FC), Ethernet, SONET/ SDH, DWDM or other networks requires several components. The components needed for long distance include a LX GBIC (aka SFP) plus single-mode (SMF) cabling. To achieve ultra-long distances, higher power LX GBICs or DWDM and possibly repeater technologies will be needed. If you have single-mode fiber, but you do not have a powerful enough LX GBIC, your distance will be limited. The fiber-optic cable is an important component, for example good quality cable fewer connections will result in less db (signal) loss or light degradation that in turn would limit your distance. The GBIC or DWDM type device is essential for generating and pushing the light wave across the fiber-optic cable. For long distances, you need the combination of SMF optic cabling and an SMF LX GBIC.

Make sure you verify what distance the LX GBIC that you plan to use is capable of supporting as the distances can vary from 10 km to 80 km. You can learn more about fiber optics over distance in chapter 5, "Fiber optic essentials," in my book "Resilient Storage Networks" (Elsevier).

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