HORIZONTAL CABLING (CABLING SUBSYSTEM 1)

Horizontal cabling includes horizontal cable, telecommunications outlet/connectors in the work area (WA), mechanical terminations and patch cords or jumpers located in a telecommunications room (TR) or telecommunications enclosure (TE) and may incorporate multi-user telecommunications outlet assemblies (MUTOAs) and consolidation points (CPs). The pathways and spaces to support horizontal cabling shall be designed and installed in accordance with the requirements of TIA-569-B.

Some networks or services require applications-specific electrical components (such as impedance matching devices). These application-specific electrical components shall not be installed as part of the horizontal cabling. When needed, such electrical components shall be placed external to the telecommunications outlet/connector. Keeping application-specific components external to the telecommunications outlet/connector will facilitate the use of the horizontal cabling for varying network and service requirements. 

A minimum of two permanent links shall be provided for each work area. The cabling should beplanned to accommodate future equipment needs, diverse user applications, ongoing maintenance, relocation and service changes. Indeed, horizontal cabling is often less accessible than backbone cabling and adding or changing horizontal cabling may cause disruption to occupants and their work once the building walls and ceilings are closed after the initial installation. The time, effort, and skills required for these subsequent changes are significant and make the choice and design layout of the horizontal cabling very important to the building occupants and to the maintenance of the telecommunications infrastructure. Therefore, it is incumbent on the designer to accommodate user needs and to reduce or eliminate the probability of requiring changes to the horizontal cabling as user requirements evolve.

Each 4-pair cable at the equipment outlet shall be terminated in an eight-position modular jack. The telecommunications outlet/connector for 100-ohm balanced twisted-pair cable shall meet the requirements of ANSI/TIA/EIA-568-B.2.

Optical fibers at the equipment outlet shall be terminated to a duplex optical fiber outlet/connector meeting the requirements of ANSI/TIA-568-C.3

Using a Single Horizontal Cable Run for Two 10Base-T Connections

Let's face it, you will sometimes fail to run enough cable to a certain room. You will need an extra workstation in an area, and you won't have enough connections. Knowing that you have a perfectly good four-pair UTP cable in the wall, and that only two of those pairs are in use, makes your mood even worse. Modular Y-adapters can come to your rescue.

Several companies make Y-adapters that function as splitters. They take the four pairs of wire that are wired to the jack and split them off into two separate connections. The Siemon Company makes a variety of modular Y-adapters (see Figure 1) for splitting 10Base-T, Token Ring, and voice applications. This splitter will split the four-pair cable so that it will support two separate applications, provided that each application requires only two of the pairs. You must specify the type of splitter you need (voice, 10Base-T, Token Ring, etc.). Don't forget, for each horizontal cable run you will be splitting, you will need two of these adapters: one for the patch-panel side and one for the wall plate.

Figure 1: A modular Y-adapter for splitting a single four-pair cable into a cable that will support two separate applications

Warning

Many cabling professionals are reluctant to use Y-adapters because the high-speed applications such as 10Base-T Ethernet and Token Ring may interfere with one another if they are operating inside the same sheath. Certainly you should not use Y-adapters for applications such as 100Base-TX. Furthermore, Y-adapters eliminate any chance of migrating to a faster LAN system that may utilize all four pairs.

Horizontal and Backbone Cables

The terms horizontal cable and backbone (sometimes called vertical or riser) cable have nothing to do with the cable's physical orientation toward the horizon. Horizontal cables run between a cross-connect panel in a telecommunications room and a telecommunications outlet located near the work area. Backbone cables run between telecommunications rooms, and enclosures, and the main cross-connect point of a building (usually located in the equipment room). Figure 1 illustrates the typical components found in a structured cabling environment, including the horizontal cable, backbone cable, telecommunication outlets, and patch cords.

 

Figure 1: Typical components found in a structured cabling system

Horizontal Cables

Horizontal runs are most often implemented with 100 ohm, four-pair, unshielded twisted-pair (UTP), solid-conductor copper cables, as specified in the ANSI/TIA-568-C.2 standard for commercial buildings. The standard also provides for horizontal cabling to be implemented using 62.5/125 micron or 50/125 micron multimode optical fiber. Optical fiber is typically used when electromagnetic interference (EMI) or radio-frequency interference (RFI) is a problem and when security is critical. Coaxial cable is not a recognized horizontal cable type for voice or data installations.

Backbone Cables

Backbone cables can be implemented using 100 ohm UTP, ScTP or STP; 62.5/125 micron or 50/125 micron multimode optical fiber; or 8.3/125 micron single-mode optical cable. Neither 150 ohm STP nor coaxial cable is allowed. Optical fiber is the preferred cabling medium because of distance limitations associated with copper wiring (90 meters is the maximum distance). Optical fiber cable can transmit over distances up to 40,000 meters depending on f