The TIA-568-C Commercial Building Telecommunications Wiring Standard describes a generic cabling system that can support many types of LANs, as well as many other telecommunications applications.
TIA-568 Cabling Options
The TIA-568-C cabling system actually includes four types of cable options:
- unshielded twisted-pair (UTP).
- shielded twisted-pair (STP).
- multimode 50/125 and 62.5/125 optical fiber.
- single-mode fiber (50-ohm coax is grandfathered for existing installations only).
TIA-568 Component Categories
TIA-568-C cabling combines the low cost of modular wiring connections and twisted-pair cable with a system of performance classifications and installation procedures. The use of modular connectors and twisted-pair wire for LANs was made popular by the availability of inexpensive, existing components that were originally intended for telephone system use. Unfortunately, users soon learned that the cable needed to have specific characteristics, such as minimum twists per foot, to work properly. The cable needed to meet certain performance levels that varied with the application. A cable vendor’s rating system, supplemented by Underwriters Laboratories testing, eventually was incorporated into the TIA-568 cabling system. The rating system divides wire and components into numbered categories that are associated with increasing levels of performance needed for LAN operation.
Seven numbered categories of TIA-568-C cabling are now specified, as shown in below Table , although low-performance Categories 1 and 2 are specifically excluded from consideration in the standard. Two of the remaining categories, Category 3 and Category 4, are officially dropped for new installations, although both may continue to be used for the appropriate purposes in existing locations. Category 3 can support 10 and 16 MHz networks, such as traditional Ethernet and Token-Ring, and rarely-seen Category 4 supports up to 20 MHz.
Category 5 has been dropped for new installations, and replaced by Category 5e, which is now the “entry level” for UTP cabling. Category 5e supports 100 MHz (100 to 1000 Mbps) networks, as well as the lower speeds.
Cabling devices are often rated by the industry both in bandwidth (in MHz or GHz) and in throughput or data rate (in Mbps or Gbps). Regardless of which number you see, the bandwidth of a component is the limiting parameter. This is because data encoding techniques often obscure the actual cable signaling-rate, which is bandwidth limited. For example, the older 10 and 16 Mbps Ethernet and Token-Ring networks require matching cable bandwidths of 10 and 16 MHz because their signaling structure actually operates at those bandwidths. But 100 Mbps network techniques can range from 15 MHz (per pair) to 33 MHz because of encoding of the data. If a certain multi-pair encoding is used for 100 Mbps Ethernet (100BaseT4), it can actually run on older Category 3 cable, which is rated to 16 MHz.
TIA-568 Connector Standards
Standard 8-pin (RJ-45 style) modular connectors are used for the TIA-568-C (nontraditional connectors are added for Category 7 support, as will be covered later). Four-pair, 24 AWG, UTP provides the station cable. All eight wires are connected to the jack. A system of optional punchdown termination blocks and patch panels completes the connection system. Wiring connection is straight through, which means simply that Pin 1 at one end of a cable will correspond to pin 1 at the other end. This is true whether we are talking about a user cord, a patch cord, or the in-wall station cable. This is a departure from normal 6-wire telephone cords, which reverse the connections from end to end.
The TIA-568-C system allows two different color-coded wiring patterns for the specified 8-pin modular connectors. below Figure shows the two patterns, called T568A and T568B (not to be confused with the “A” or “B” revisions of the original standard). The two wiring patterns are electrically equivalent, but the positions of Pair 2 and Pair 3 are reversed.
Practically, this means that the color-to-pin correspondence varies between the two wiring standards, and it makes little difference which you use, as long as both ends of the cable are pinned the same. In other words, if you use the T568A pattern at the workstation outlet (called the telecommunications outlet in the standard), you must also use a matching T568A patch panel or fan-out cable in the telecommunications room. Pairs 2 and 3 just happen to be the two pairs used by 10/100BaseT Ethernet, so ignoring this wiring convention will cause the connection to fail. Token-Ring and 4-wire communications circuits, including T1, will also have a failure.Many prewired components are not marked as to wiring pattern, particularly nonrated octopus fan-out cables, so be aware of what you install.