design has accommodated the needs of a specific system or systems. With technology changing regularly, the cabling systems being installed now must be much more flexible and universal, capable The Telecom Handbook * 261 CABLE of supporting all of the communications of a building including voice, data, images and video. The cabling being installed now will be expected to last at least ten to fifteen years if not more, yet the technology of the equipment using the cable often has a life cycle that is much shorter. Transmission speeds are continually increasing. This points to the importance of installing what is sometimes called a structured wiring system. Not all building owners are interested in installing a structured wiring system for the entire building due to the expense (unless the building is occupied and owned by a single tenant). In multi-tenant buildings, different companies have different ideas about what their cabling system should look like. Strictly speaking, the structured wiring system addresses the needs for connectivity from the entrance to the build- ing through the workstation/desktop. The riser cable system, also called the backbone, extends vertically from the main distribution frame for the entire build- ing (often located in the basement). It provides service to the telephone closet on each floor of the building. The riser cable may be copper or fiber or a combination of the two. In a large spread out building such as a factory, the equivalent of a riser cable may be placed horizontally. A predetermined number of cable pairs are terminated on each floor. These will be used to bring telephone service from the out- side world into the space of the company occupying that floor. The copper riser cable typically uses 24 gauge cable formed into binder groups of 25 pairs each. The groups are identified by dis- tinctively colored binders and are assembled to form a single compact core covered by a protective sheath. The gauge of the cable relates to the transmission properties and the diameter. The