Telecommunications Cabling Systems

The typical telecommunications-cabling infrastructure in a building is illustrated in the drawing below "Typical Telecom Cabling System". The cabling system is installed in the Telecommunications Spaces and Pathways.

Typical Telecom Cabling System

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Text Description of Cabling System is available on a separate page.

Horizontal cabling consists of two (or more) cables (typically one for voice and one for data) that are run to each work area from a telecommunications room (TR) located on the same floor as the work area. This is called "star wiring" with the TR being analogous to the centre of the star and each work area being analogous to the points of the star. Each cable is terminated on a jack at the work area and on a cross-connection field in the TR. A number of spare horizontal cables are typically installed to facilitate changes. Horizontal pathways usually transport the horizontal cabling to the vicinity of the work areas. Note that a single blue line is used to represent all wiring to a work area (i.e. at least two 4-pair cables) and a single blue box is used to represent all jacks (at least 2) installed in the work area. For clarity, horizontal cabling is shown on only one floor, although it would be installed on all floors.

Various types of cabling may be used for horizontal and backbone cabling. Standards limit the length of horizontal cabling to 90 metres. By far the most common horizontal cabling is 4-pair unshielded-twisted pair (UTP) cable. It is used for both voice and data applications. The capacity or bandwidth of 4-pair UTP is indicated by its category with a higher number indicating a greater capacity. Current standards recognize enhanced Category 5 (Category 5e), Category 6 or augmented Category 6 (Category 6a) UTP cables for horizontal cabling.

The only other type of recognized horizontal cable is multi-mode optical fiber. There are various types of optical fiber, as indicated by two numbers representing the diameter of the fiber core and the diameter of the cladding surrounding the core respectively. In the past, the most common fiber was 62.5/125 micron. However, its capacity is more limited than laser-optimized 50/125 micron fiber, which is preferred for new installations.

Backbone cables connect each TR to the main cross-connect located in the Equipment Room. Backbone pathways transport the backbone cabling. A "star" topology is also used for backbone cabling with the main cross-connect in the Equipment Room being the center of the star and the cross-connect is each TR being its points. The backbone cabling extends from the main cross-connect located in the Equipment Room to the points of demarcation with the facilities of various telecommunications common carriers serving the building that are typically located in the Entrance Room / Common Equipment Room.

Backbone cabling usually consists of large Category 3 multi-pair UTP for traditional voice (telephone) service and optical fiber for data. For the backbone, single-mode fiber is recognized in addition to the multi-mode fiber that is also recognized for horizontal cabling. If the backbone cabling does not exceed a length of 90 metres, 4-pair UTP (Category 5e, 6 or 6a) may also be used for data.

Coaxial cable may be used in both the horizontal and backbone cabling for special purposes, such as CATV.