Tech Talk: Cable Evolution

Which fiber is right for you?

Recently a school district said it wanted to replace its existing 62.5 multimode backbone fiber with 50 micron laser-optimized fiber. This change was going to cost in the neighborhood of a half-million dollars. Why make this change?

Over the past 25 years, Ethernet standards have evolved from 10 Mbps and 100 Mbps to 1 Gigabit and now 10 Gigabit. The rapid growth of Internet use and bandwidth-intensive applications combined with routine transmission of large files is driving the need for 10 Gigabit Ethernet in many network backbones, especially on college campuses.

Older optical-fiber systems used in premises applications operate at relatively slow speeds, in the range of 4 to 155 Mbps. These systems use light-emitting diodes (LEDs), which were adequate for slower speeds. As the demand for bandwidth and higher throughput increased, especially on college and university backbones, LEDs could not keep pace. In response, the industry developed a high-speed laser light source called a vertical cavity surface-emitting laser (VCSEL). This technology is inexpensive and well-suited for lower-cost, 850-nm multimode transmission systems, allowing for data rates of 1 and 10 Gbits per second in the enterprise. With the emergence of VCSELs, however, multimode fiber had to be “optimized” for operation with lasers.

At this point, conventional 62.5 multimode fiber optic cable is capable of handling only 1Gb/s with laser-optimized electronics. Laser-optimized electronics over 62.5/125 fibers are limited to about 35 meters at 10 Gb per second, and laser-optimized 50/125 fibers to about 90 meters. To the high-end user, it has become apparent that 62.5/125 multimode fiber would not be capable of meeting the high-performance demand of 10 Gb per second capability.

However, before pulling out all your existing 62.5 multimode fiber, keep in mind that a 1Gb/s speed backbone still is light speed of the 100 Mbps that has been in use for years. With virtual servers entering the marketplace, the need for a robust backbone is increasing rapidly. Higher-education research facilities may see the need to go to a 10 GB/s backbone sooner than K-12 institutions because of the need for increased bandwidth. But a 1GB/s backbone is adequate in 90 percent of existing data applications. This advancement in fiber-optic cable should be used in new construction and should be specified from now on in fiber building infrastructure cabling specifications.

Today, 62.5 fiber is still used in 1GB/s backbones (1000SX), but according to fiber manufacturers, the new laser technology will require higher reflection properties than 50 Micron and single-mode fiber possesses. It looks like it is near the end of life for 62.5 multimode fiber. And what a life it was — nearly 40 years in production and still able to pass gigabit speeds.

C. William Day is senior analyst at KBD Planning Group, Young Harris, Ga., a firm specialized in education facilities and technology planning. He can be reached at [email protected].

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