Data Communications Networking Devices - 4th Ed.pdf

3.2 TECHNOLOGICAL CHARACTERISTICS ___________________________________________ 281Cabling standards: generalThere are two general types of cabling standards by which many types of twistedpairwiring can be categorizedÐde facto and de jure from the Latin phrases defacto and dejure).De facto standards represent a commonly used set of cabling rules and requirementswhich were developed by one or more vendors and do not carry the backing ofa standards-making organization. Examples of defacto cabling `standards' includethe original Ethernet cabling, which speci®ed the type of coaxial cable to be usedin developing a LAN, and IBM's cabling system. The latter speci®es a variety oftwisted-pair and optical cables for use with the development of Token-Ringnetworks.A de jure standard represents a standard developed by a standards-makingorganization. In the area of twisted-pair cabling the Electronics IndustryAssociation and the Telecommunications Industry Association EIA/TIA) workingtogether developed several standards which have also been adopted by the AmericanNational Standards Institute ANSI). Probably the most important standard isEIA/TIA-568, Commercial Building Telecommunications Wiring Standard. Thisstandard contains detailed speci®cations on the electrical and physical characteristicsof twisted-pair coaxial and optical ®ber cable as well as guidelines concerning thecabling of new and existing buildings. In discussion cabling standards I will reviewthe characteristics of IBM's cabling system and the TIA/EIA-568 standard,focusing my discussion towards the twisted-pair cabling used by each standard.IBM cabling systemThe IBM cabling system was introduced in 1984 as a mechanism to support thenetworking requirements of of®ce environments. By de®ning standards for cables,connectors, faceplates, distribution panels, and other facilities IBM's cabling systemwas designed to support the interconnection of personal computers, conventionalterminals, mainframe computers, and of®ce systems. In addition, this systempermits devices to be moved from one location to another or added to a networkthrough a simple connection to the cabling system's wall plates or surface mounts.The IBM cabling system speci®es seven different cabling categories. Dependingupon the type of cable selected you can install the selected wiring indoors, outdoors,under a carpet, or in ducts and other air spaces.The IBM cabling system uses wire which conforms to the American WireGauge or AWG. As previously discussed, as the wire diameter gets larger theAWG number decreases, in effect resulting in an inverse relationship between wirediameter and AWG. The IBM cabling system uses wire between 22 AWG 0.644mm) and 26 AWG 0.405 mm). Since a larger diameter wire has less resistance tocurrent ¯ow than a smaller diameter wire, a smaller AWG permits cablingdistances to be extended in comparison to a higher AWG cable.Type 1The IBM cabling system Type 1 cable contains two twisted-pairs of 22 AWGconductors. Each pair is shielded with a foil wrapping and both pairs are