Structured Cabling System Design Considerations

The Six Subsystems of a Structured Cabling System

Diagram: The six subsystems of a structured cabling system.

1. Building Entrance

Building entrance facilities provide the point at which outside cabling interfaces with the intrabuilding backbone cabling. The physical requirements of the network interface are defined in the EIA/TIA-569 Standard.

2. Equipment Room

The design aspects of the equipment room are specified in the EIA/TIA 569 Standard. Equipment rooms usually house equipment of higher complexity than telecommunication closets. Any or all of the functions of a telecommunications closet may be provided by an equipment room.

3. Backbone Cabling

The backbone cabling provides interconnection between telecommunication closets, equipment rooms and entrance facilities. It consists of the backbone cables, intermediate and main cross-connects, mechanical terminations and patch cords or jumpers used for backbone-to-backbone cross-connection. This includes:

  • Vertical connection between floors (risers)
  • Cables between an equipment room and building cable entrance facilities
  • Cables between buildings (interbuilding)

Cabling Types Recognized and Maximum Backbone Distances

100 ohm UTP  (24 or 22 AWG)               800 meters (2625 ft) Voice*
150 ohm STP                               90 meters (295 ft) Data*
Multimode 62.5/125 m optical fiber       2,000 meters (6560 ft)
Single-mode 8.3/125 m optical fiber      3,000 meters (9840 ft)

*Note: Backbone distances are application dependent. The maximum distances specified above are based on voice transmission for UTP and data transmission for STP and fiber. The 90 meter distance for STP applies to applications with a spectral bandwidth of 20 MHz to 300 MHz. A 90 meter distance also applies to UTP at spectral bandwidths of 5 MHz - 16 MHz for CAT 3, 10 MHz20 MHz for CAT 4 and 20 MHz100 MHz for CAT 5.

Lower speed data systems such as IBM 3270, IBM System 36, 38, AS 400 and asynchronous (RS232, 422, 423, etc.) can operate over UTP (or STP) for considerably longer distances‹typically from several hundred feet to over 1,000 feet. The actual distances depend on the type of system, data speed and the manufacturer's specifications for the system electronics and the associated components used (i.e., baluns, adapters, line drivers, etc.). Current state-of-the-art distribution facilities usually include a combination of both copper and fiber optic cables in the backbone.

Other Design Requirements

  • Star topology
  • No more than two hierarchical levels of cross-connects
  • Bridge taps are not allowed
  • Main and intermediate cross-connect jumper or patch cord lengths should not exceed 20 meters (66 feet)
  • Avoid installing in areas where sources of high levels of EMI/RFI may exist
  • Grounding should meet the requirements as defined in EIA/TIA 607

Note: It is recommended that the user consult with equipment manufacturers, application standards and system providers for additional information when planning shared sheath applications on UTP backbone cables.

Specified Backbone Cabling Topology: Star
Diagram: Backbone cabling in star topology

4. Telecommunications Closet

A telecommunications closet is the area within a building that houses the telecommunications cabling system equipment. This includes the mechanical terminations and/or cross-connect for the horizontal and backbone cabling system. Please refer to EIA/TIA-569 for the design specifications of the telecommunications closet.

5. Horizontal Cabling

(Specified Horizontal Cabling Topology: Star)

The horizontal cabling system extends from the work area telecommunications (information) outlet to the telecommunications closet and consists of the following:

  • Horizontal Cabling
  • Telecommunications Outlet
  • Cable Terminations
  • Cross-connections

Three media types* are recognized as options for horizontal cabling, each extending a maximum distance of 90 meters:

  1. 4-pair 100 ohm UTP cable (24 AWG solid conductors)
  2. 2-pair 150 ohm STP cables
  3. 2 fiber 62.5/125 m optical fiber cable

*At this time, 50 ohm coaxial cable is a recognized media type. It is not, however, recommended for new cabling installations and is expected to be removed from the next revision of this standard.

Maximum Distances for Horizontal Cabling Diagram: Maximum distances for horizontal cabling

In addition to the 90 meters of horizontal cable, a total of 10 meters is allowed for work area and telecommunications closet patch and jumper cables.

Telecommunications Outlet

Diagram: Information outlet voice and data wiring

Each work area shall have a minimum of TWO information outlet ports, one for voice and one for data. The cabling choices are indicated in the diagram above.

8-Position Modular Jack Pair Assignments for UTP Diagram: Eight-position modular jack pair assignments for UTP

6. Work Area

The work area components extend from the telecommunications (information) outlet to the station equipment. Work area wiring is designed to be relatively simple to interconnect so that moves, adds and changes are easily managed.

Work Area Components

  • Station Equipment computers, data terminals, telephones, etc.
  • Patch Cables modular cords, PC adapter cables, fiber jumpers, etc.
  • Adapters baluns, etc. must be external to telecommunications outlet

Return to Structured Cabling Standards Guides

TIA source materials for this document are reproduced under written permission from the Telecommunications Industry Association. Complete TIA documents are available through Global Engineering Documents at 1-800-854-7179 or 303-792-2181.

All contents 1997 Anixter Inc.