Optical fiber in the data center: new structured wiring solutions provide for future growth and support rapid changes

Communications News, Feb, 2004 by David C. Hall

Over the past several years, enterprise data centers have been installed using a wide variety of methods for connecting the contained electronics. To eliminate the potential clutter while providing a robust, scalable data center cabling infrastructure, structured wiring solutions are available that provide for future growth and support rapid changes.

Data center design should follow industry standards for best practices. Industry guidance is on the way in the form of an emerging industry standard for data centers. This document, to be published as Telecommunications Industry Association ANSI/TIA/EIA-942, Telecommunications Infrastructure Standard for Delta Centers, lists requirements and provides recommendations for data center design and construction. TIA-942 helps consultants and end-users design an infrastructure that will last years without forklift renovations. The standard also gives information on cooling, power, room sizing and other information useful in data center design.

The entrance room should provide the interconnection point between the data center and the outside network. Service-provider connections enter the data center through this room. In many data center designs, this area is located directly inside the computer room, which houses the bulk of the data center space. This space also includes the zone distribution area (ZDA), where pre-wiring allows simple moves, adds and changes without disrupting the general computer room. Cabling changes, therefore, impact only the small area served by the zone.

Optical-fiber cable is often the media of choice for a number of reasons: it provides the greatest bandwidth of all media types; it is immune to EMI and RFI; it does not require grounding; it is less expensive than copper cabling for the available bandwidth; and optical fiber can scale from 10 Mbps to 10,000 Mbps.

With multimode fibers at 50-[micro]m core size, 10-Gbps traffic can go 300 meters. Many data centers are running 1-Gigabit Ethernet (GigE) links, and some are installing 10-GbE aggregating links.

ASSESS THE COMPONENTS

Begin an assessment by examining the components that make up the cabling infrastructure in the computer room. The main areas are the main distribution area (MDA), the equipment distribution area (EDA) and the ZDA. The MDA contains core routers and switches (located near the MDA to minimize cable lengths) and the fiber distribution frame (FDF), a line of equipment cabinets or racks containing optical fiber patch panels. The FDF serves as the central administration point for all functional areas in the data center.

M1 the optical cabling in the computer room feeds back into this area. In the MDA, freestanding equipment cabinets are common for holding the rack-mounted, cross-connect parch panels or electronics.

Advantages of equipment cabinets are security (front and rear doors are lockable) and aesthetics. Advantages for using equipment racks are accessibility and cooling, since there are no obstructions to air flow. Cooling is not an issue for FDFs, since they do not contain heat-generating electronics.

Whether a rack or cabinet is used, the most common height of each is seven feet. Taller cabinets and racks are available, but a ladder is needed to access the top components. This is often a safety hazard and creates additional obstacles to easy data center management. The patch panels used in the FDF for cross-connect patching are typically 4-rack units (4U) tall, since that height is the most common used by manufacturers.

Using patch panels that are 4U tall allows for vertical orientation (the preferred orientation by end-users) of the modular connector panels, also known as strips, plates or six-packs. The connector panels let end-users add capacity as needed in affordable increments, and the connector type can be changed by simply removing the panel and snapping in a new one, eliminating the need to remove the patch panel housing.

Connector panels have 1- or 2-fiber connector ports on the face of the panel. The panels come in 6-, 8-, 12-, 16- and 24-fiber increments, and are fast to bring online since the installer simply snaps them into an unused spot in the housing and plugs the pre-terminated cables into the back of the panel. Cross-connect or equipment patch cords are then added to the front, as needed. Connector panels are available in the standard data center connectors--ST compatible, SC duplex, MT-RJ and LC duplex.

Patch panel housings used in the FDF contain provisions for attaching the cables entering the rear of the housing. The cable-attachment device must be strong enough to withstand accidental pulling and twisting of the cable outside of the housing. The patch panel will also have patch cord management rings that maintain fiber minimum bend radii and facilitate orderly arrangement of the patch cords as they exit the housing.

The next element of the data center is the ZDA. This area provides the interconnect point between the FDF and the EDA. The ZDA may be an equipment cabinet or lack, or it could be a smaller housing mounted on the building column, in the ceiling or under die access flooring. This area does not contain electronics.