Cabling Categories

The use of UTP copper wiring for multimegabit-per-second, in-building data networks was first proposed in the mid-1980s and became generally accepted after the Category 5 standards were defined in 1994. Category 5 (Cats) cables usually have four twisted pairs of 24-AWG copper wire and are terminated with eight-wire RJ45 miniature connectors. This cable delivers 100-Mbps Ethernet bitstreams up to a distance of l00m (325 ft) between the electronic equipment (e.g., a switch) and the desktop device. Typically, cabling system manufacturers will provide guarantees or "certification" of the performance of their cabling materials if the cable plant in a new installation has been designed and installed correctly.

We cannot be sure that full Cat5 performance will be delivered if the in-line components, as identified in Figure 1, between the desktop computer (or IP phone) and the server come from different cable and equipment manufacturers. For this reason cabling implementations should follow best practices for design and implementation, according to the manufacturer's specifications, and those outlined in the EIA/TIA Building Telecommunications Wiring Standards (to which the cabling performance specification must abide).


Figure 1: End-to-end components with a LAN.

Category 5 Enhanced (Cat5E) standards were defined by the telecom industry in early 2000. Cat5E performance has been so improved over the earlier standard that a string of Cat5E components will deliver guaranteed Cat5 performance, even if they come from a variety of manufacturers.

Category 6 (Cat6) cabling has been on the market, from several manufacturers, for a few years. It offers a 10 times improved performance bit rate over Cat5 (i.e., supporting 1,000 Mbps, or gigabit, Ethernet). Most applications do not justify gigabit Ethernet to the desktop, but it is used in LAN backbones and for connection to network servers. Standardization of the Cat6 specifications was due to take place by the end of 2002. Until that happens, there is some risk with using the Cat6 class of cabling and mixed-vendor implementations should certainly be avoided before there is industrywide acceptance of Cat6 standards.

Category 7 (Cat7) is a different class of cabling, because it includes a metallic mesh shield around the twisted copper pairs, underneath the outer layer of plastic insulation. Cat7 cabling was developed in Europe and is being used in several countries there, particularly in Germany, for highcapacity LAN installations.

Over the past 5 years many corporate LANs in North America have been built with Cat5E cabling, and a limited number of Cat6 infrastructures are now in place, in spite of its lack of standardization. Our experience has been that there is no more than a 10% cost differential between quotations for Cat5E and Cat6 implementations. One reason for this is that the actual cable materials make up well under one-half of the cost of a complete wiring installation.

Physical LAN costs have not changed much over the past decade, at around $200 per outlet for Cat6 (or about $180 with Cat5E), including needs analysis, system design, hardware, cable, cable-pulling, connecting, and testing, in small-to-medium installations (e.g., a school or a low-rise suburban office building). Expect cabling infrastructure costs to be above $200 per outlet in high-rise, downtown office towers, especially if installation is controlled by unionized workers.