Structured Cabling System Design Considerations
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
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 µm optical fiber 2,000 meters (6560 ft)
Single-mode 8.3/125 µm 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
distancestypically 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
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
Three media types* are recognized as options for horizontal cabling, each extending a
maximum distance of 90 meters:
- 4-pair 100 ohm UTP cable (24 AWG solid conductors)
- 2-pair 150 ohm STP cables
- 2 fiber 62.5/125 µm 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
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.
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
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
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