Fibre distance limitations

Unanswered Question
May 5th, 2004

What is the distance limitation on a 6500 switch fibre module using multimode fibre not singlemode?

I have this problem too.
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konigl Thu, 05/06/2004 - 14:20

As others have said previously, it depends on the quality of the fiber and the wavelength of the transmission optics.

Gigabit Ethernet over multimode: Cisco's Gigabit fiber interfaces run in full-duplex mode only.

If you follow the standards, maximum distance is 220m to 275m using SX GBICs (850nm wavelength) and up to 550m using LX/LH GBICs (1300nm) and mode conditioning patch cables.

Mode conditioning patch cables are not the same as regular patch cables. They have a combination of single mode fiber and multimode fiber fusion-spliced together to specific tolerances on the transmit strand of the patch cable, and multimode fiber only on the receive strand. This helps launch the LX signal at an offset from the center of the multimode fiber strand to avoid imperfections in the fiber. (SX optics don't have this problem.)

LX optics and mode conditioning patch cables have been tested and will work out to 700m over the worst-grade multimode fiber. It is up to you if you want to exceed the standard distance, though.

Fast Ethernet over multimode: the standard calls for half-duplex transmission out to 412m, and full-duplex out to 2km. Fast Ethernet over multimode fiber transmits at the 1300nm wavelength.

If this is existing multimode fiber, use these numbers as your guide. On the other hand, if it is new construction, check into what kind of multimode fiber it is. Some of the newer multimode is optimized by the manufacturer to carry certain wavelengths much farther than the standards.

Hope this helps.

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Posted May 5, 2004 at 2:52 AM
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