Storage Basics - Fibre Channel Cables and Connectors, Part 2 Page 3


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Inside the Core

The inside core of the fiber optic cable varies in size. The size of the core determines the type of optical cable — either single-mode or multimode cable. These modes describe the way in which light travels within the cable. Light signals can propagate through the core of the optical fiber on a single path (single-mode fiber) or on many paths (multimode fiber).

Of the two, multimode fiber optic cable has a larger core that allows for multiple streams of light signal to pass through simultaneously. These numerous light rays within the cable bounce around inside the core as they travel toward their destination. When light beams reflect off the sides of the core, they slow down and suffer from a reduction in strength.

There are two different types of multimode fiber cables, 50/125 micron and 62.5/125 micron. The 50 and 62.5-micron measurements identify the core's diameter, and the 125 micron size refers to the cladding diameter. The maximum transfer distance for 50/125 micron fiber is 500 meters, while the maximum transfer distance of 62.5/125 micron fiber is about 250 meters.

Both types of multimode fiber types offer data transfer rates of 133 Mbps. The smaller the diameter of the core, the farther a signal is propagated, as it uses a more focused path for the light rays to follow.

Single-mode fiber cables use a very small, focused core through which light can travel. This smaller core allows light to pass directly through the cable without bouncing off the walls. Single-mode cable has a center core of 9 microns and a cladding diameter of 125 microns. This smaller core provides for a maximum distance of 10 kilometers and a data transfer rate exceeding the Gigabit barrier.

Making the Connection

When it comes time to connect fiber-optic cable to the network, there are two types of fiber connectors used most often — 568SC connectors and optical GBICs. 568SC connectors are a color-coded duplex connector (beige for multimode and blue for single-mode). 568SC connectors are keyed to prevent incorrectly connecting the connectors. SC connectors use a push-pull design to mate and unmate a connection.

The other common connector type is the optical GBIC connector. Optical GBICs are used to convert optical signals to electrical signals and vise versa. There are two distinct types of optical GBICs available, shortwave and longwave. Shortwave optical GBICs are used with multimode fiber-optic cable, while longwave GBICs are used with single-mode fiber.

At the end of the day, there is little doubt that fiber optics has become the industry standard for terrestrial transmission of telecommunication information. The bandwidth needs of today's organizations simply require a medium that can deliver large amounts of information at fast speeds. While fiber solutions may be more costly and difficult to implement, it seems unlikely that copper cable will provide for future bandwidth needs.

» See All Articles by Columnist Mike Harwood

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