Testing recently conducted in Anixter's Levels Lab suggests that some 62.5/125-micron multimode fiber has the capability to handle Gigabit Ethernet traffic over distances far greater than the minimums put forth by the Institute of Electrical and Electronics Engineers (IEEE), the body that developed the Gigabit Ethernet standard. The tests exclusively examined Corning Cable Systems cable, which includes optical fiber manufactured by Corning. Several different brands of Corning's 50-micron and 62.5-micron fibers were included in the test; each of those fibers was engineered with Gigabit Ethernet transmission in mind.
"Our preliminary results showed that 50-micron and 62.5-micron fiber from Corning Cable Systems are both capable of handling Gigabit Ethernet traffic error-free over much longer distances than the minimum distance that the standards require," says Pete Lockhart, Anixter's vice president of technology. He added that the study was intended "to address the perception that multimode fiber might not be adequate for transporting data over long lengths on Gigabit Ethernet links."
Not created equal
In a white paper that details the test procedures and test results, Anixter notes that millions of feet of 62.5/125-micron multimode fiber have been installed over the past decade. "While the installed base of 62.5-micron multimode might be a concern for Gigabit Ethernet over very long lengths, it remains viable over short lengths," the paper says. "Short lengths of less than 300 meters are typical. Three hundred meters would accommodate the backbone riser for an 82-story building."
Yet this testing, the first fiber-optic cabling testing done in Anixter's Levels Lab, indicates that some 62.5-micron fiber can support Gigabit Ethernet over 1,100 meters-more than three times the standard- specified minimum. Additionally, both Anixter and Corning Cable Systems made note of a test setup that included a 62.5-micron InfiniCor I-300 fiber-optic cable fitted with 12 MT-RJ connectors. Both companies emphasized the fact that the link, with 12 connection points, supported Gigabit Ethernet to 450 meters.
"With 12 MT-RJ connector pairs, 62.5-micron multimode fiber could, ostensibly, provide the background riser in a building taller than the Petronas Towers in Malaysia-the world's tallest," says Anixter's Lockhart.
That 12-connection link may raise questions for some, particularly because the IEEE has a rather tight 3.5-decibel attenuation limit for short-wavelength Gigabit Ethernet transmission over multimode links. When asked if 12 connection points would introduce more attenuation than a multimode link could handle, Corning's private networks marketing manager Bob Pollock said the IEEE's model is "extremely conservative," and noted that some systems can actually handle significantly more loss than what is in the model. "We didn't run into any performance issues until we got to 7 to 8 dB of attenuation," Pollock noted.
50- and 62.5-micron
Overall, 50-micron fiber-optic cable performed better than 62.5-micron fiber-optic cable. But the results of this testing suggest that 50-micron fiber is not an absolute necessity for gigabit-capable infrastructures; 62.5-micron fiber is very much a viable option. Anixter stresses that point in its white paper. "The higher-grade 62.5/125-micron multimode can support Gigabit Ethernet signals without error for distance 150 to 200% of the expectation, even with a large number of mated connections along the fiber length," the paper says. "Laser-optimized 62.5/125-micron enhanced multimode can support Gigabit Ethernet signals without error for distances over a kilometer."
Furthermore, the paper says, installing 50-micron fiber in a backbone that already includes 62.5-micron fiber may produce difficulty if the user employs legacy light-emitting-diode transmitters. "This is because of the difference in core diameter and core acceptance angle, or numerical aperture," the paper says. Plus, "the man-hours and expense involved in converting the entire fiber portion from 62.5- to 50-micron, including splices, connectors, and patch panels, would be extraordinary."
With this information in mind, the message to many network managers appears to be upbeat: you can continue to use 62.5-micron fiber for Gigabit Ethernet transmission. Provided, of course, it is the right 62.5-micron fiber.
The 62.5-micron fibers under test in Anixter's lab were Corning's InfiniCor I-300 and CL-1000. The I-300 fiber, with five MT-RJ Unicam connections, carried Gigabit Ethernet traffic to 550 meters with no errors. As noted earlier, the same fiber with 12 MT-RJ connections carried gigabit-speed traffic to 450 meters with no errors. The 62.5-micron CL-1000 fiber, with eight MT-RJ Unicam connections, carried gigabit-speed traffic to 1,100 meters without errors.
Corning's InfiniCor I-600 50-micron fiber, with five MT-RJ connections, carried the traffic to 1,750 meters without errors; with 13 MT-RJ connections, it carried the traffic to 1,400 meters error-free. And Corning's High Band I-600 50-micron fiber with two SC connections carried gigabit-speed traffic to 2,000 meters without errors.
Corning's InfiniCor I-300, CL-1000, and I-600 fibers were engineered and manufactured specifically to accommodate gigabit-speed transmission. Neither the test-result announcement nor Anixter's white paper mentions performance figures for any previous-generation multimode fiber.
Anixter's white paper can be accessed through the company's Web site, www.anixter.com.
-Patrick McLaughlin