Select the right hardware: a good interconnection strategy takes time and study

Communications News, March, 1990 by Paul D. Hawkins

SELECT THE RIGHT HARDWARE

Integrating fiber optics into the latest system designs is becoming popular for premises communications wiring. In addition to basic point-to-point links, fiber is being incorporated into backbone wiring applications such as:

* channel extensions and PBX nodal links;

* data and voice multiplexing such as 3270, T1, and RS-232;

* and local-area networks (LANs) such as Token Ring, Ethernet, and emerging Fiber Distributed Data Interface (FDDI) standards.

The cabling plant is an important element of the premises communications, system. It serves as the transmission highway for the system electronics.

The cabling plant includes fiber-optic cable, cable assemblies, connectors, splices, interconnection hardware, and testing instruments.

In order to specify fiber-optic hardware, you must first determine cable fiber count and routing design. Required at all splice points and cable termination points, this hardware includes splice closures, trays, organizers, cabinets, patch panels, and wall outlets. A flexible interconnection system using the proper hardware allows for future growth and easy reconfigurations.

Interconnection hardware should accept different types of cables and splices, and be compatible with all types of OEM computer systems.

All types of commonly used fiber-optic connectors should fit in the hardware--including the ST-compatible, Biconic, FC, D4, and SMA. Though the ST-compatible connector is emerging as the de facto standard in the premises industry, other connector types are required with some equipment.

The hardware construction should also be considered, as the unit's main function is to store and protect splices and terminations. The minimum bend radius of fiber-optic cables must be maintained, and adequate cable strain relief points are needed. Labels on the hardware serve as system records, so that interconnection documentation can be completed right on the units.

Ungradeability is a must. With advancements in premises communications systems, hardware is required to take a system all the way to the desk-top--from the highest-fiber-count patch panels to information outlets at the workstation.

Outside Plant Hardware

Outside plant products should be capable of withstanding environmental conditions. Hardware may become damp, wet, or directly exposed to weather conditions while still protecting splices and connectors.

The most commonly used outdoor hardware is the splice closure, used to protect fiber-optic splices. The splices are generally considered permanent connections that are rarely, if ever, remade. Closures are designed for use in buried, underground, or aerial environments. When assembled, the closure is completely sealed from moisture by use of sealing tape, cords, and paste.

The consideration of fiber count and the use of multi- or single-mode fiber are the major determining factors in closure selection. Closures are available in a wide range of sizes, from low to high fiber counts, to accommodate different requirements.

In many instances, closures require specially designed tools such as drills, tensioning tools, and closure measuring tapes. Siecor has modified the standard closure to allow installation using only standard tools. This simplifies the procedure and shortens installation time.

Outside plant products are also needed in areas where moisture may be a factor, such as in parking garages or basements. A wall-mountable product, such as Siecor's Outside Building Entrance Terminal, is needed to house splices or to house connectors.

For areas that may flood, splice closures are required. Generally these will be used for splice points but can accommodate terminations as well.

The building entrance terminal is best suited for wall mounting where limited environmental protection is needed.

These housings should store either splices or connectors.

Both indoor and outdoor hardware sometimes require splice trays at points where splices are stored.

Fiber-optic splice trays used to organize and protect splices are designed to ensure the minimum fiber bend radius is maintained.

They should be able to store various splicing methods, including both mechanical and fusion splicing.

Intrabuilding Hardware

For indoor hardware, first identify the termination method to be used. Options include pigtail splicing, preconnectorization, factory connectorization, field connectorization, and direct selicing. The selection of the best, most cost-effective method for your system should be carefully considred. Siecor supports all these methods, identifying advantages and tradeoffs for each.

Secondly, determine the mounting location of your hardware. Products are designed for rack mounting, wall mounting, and workstation applications. The rack-mounted hardware generally is installed in a standard 19-or 23-inch equipment rack or cabinet. Rack space normally is available in locations where communications equipment is installed--equipment rooms and computer rooms, for example. Wall-mounted hardware is installed where rack space is not available, and space is at a premium. Such locations include wiring closets and satellite closets. The workstation products allow fiber-optic outlets to be installed directly at the desk. This permits jumpers to adapt to workstation equipment.