A path with pitfalls

By Stan Schatt, ITworld.com |  Networking

Back when 3Com was still in the enterprise networking business, it began a campaign to upgrade customers from FDDI backbones to Fast Ethernet or Gigabit Ethernet. It was a prescient move, because many network managers with FDDI backbones are now planning migration strategies.

There's no question FDDI is dying. The number of vendors making FDDI equipment keeps dropping, while the price difference between FDDI ($750 per port) and Fast Ethernet ($150 per port) keeps widening. While some companies are converting to ATM, Fast Ethernet and Gigabit Ethernet appear to be the major beneficiaries of the migration.

There is a nagging problem, though, for companies planning a move to Gigabit Ethernet. Many companies have installed multimode fiber, preferring it to single-mode fiber because it is much cheaper. Unfortunately, some cabling vendors believe about 40 percent of that multimode fiber exceeds the 550-meter maximum distance specified by the IEEE Gigabit Ethernet standard.

Single-mode fiber can handle greater distances than multimode fiber because
single-mode cabling has a very small core and utilizes a laser to generate the light signal. This keeps light dispersion to a minimum. Multimode cabling often uses a
light-emitting diode to generate the light signal, and the cabling has a relatively large core that results in much higher dispersion levels.

Switching to single-mode fiber for its ability to transmit data at Gigabit Ethernet speed over greater distances would be expensive, especially since much of the fiber is buried.

A possible solution is emerging from a California-based startup. Blaze Network Products has developed transceivers that can be swapped for existing multimode transceivers and can transport data at Gigabit-Ethernet speed for up to two kilometers. Its target market is Gigabit Ethernet switch vendors such as Cisco, Nortel Networks, Foundry, Extreme, Lucent, and Alcatel. The company is now shipping product to several of those manufacturers. Blaze Network Products has patents pending on its technology and expects its transceivers will cost switch manufacturers only slightly more than existing transceivers. The cost will be minimal to end-users.

If you're planning to migrate from FDDI to Gigabit Ethernet, keep this new technology in mind. It might preclude a very expensive cabling upgrade.

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