PBX Cabling Guidelines

Telephony wiring dates back 125 years ago, to the days when Alexander Graham Bell was tinkering with the first telephone. Telephones traditionally have used loop current for voice communications and signaling transmission. For many years single-pair (two-wire) cabling had supported telephones working behind a PBX system, but system equipment innovations, beginning with the introduction of digital switching and stored program call control, forced changes in the cabling infrastructure during the late 1970s. The first generation of proprietary PBX telephones, first electronic and then digital, required multiple wiring pairs to support the more advanced features and functions available with the new technology. At the same time, the early data LANs required a wiring infrastructure of their own, based on coaxial cable. As customer premises voice networks and data networks evolved in the mid-1980s, issues such as a common infrastructure and increasing transmission bandwidth requirements needed to be addressed. The existing telephony wiring system, fine for voice but inadequate for data, needed a major overhaul.

In 1985, two standards committees began working on specifications for a generic telecommunications cabling system to support a mix of communications media (voice, data, video) in a multivendor environment. The TIA and the Electronic Industries Association (EIA) formed a joint committee known as the EIA/TIA 41.8 Committee. After 6 years of work, the TIA/EIA 568 standard was issued. TIA/EIA 568 is more formally known as the Commercial Building Cabling Standard and outlines specifications for a generic telecommunications cabling system. The American National Standards Institute (ANSI) also adapted this standard, so it is sometimes referred to as ANSI/TIA/EIA 568.

There is a corresponding series of specifications known as ANSI/TIA/EIA 569: Commercial Building Standard for Telecommunications Pathways and Spaces. The purpose of ANSI/TIA/EIA 569 is to standardize design and construction practices within and between buildings that support telecommunications equipment and transmission media. The standards are outlined for rooms or areas and pathways into and through areas where telecommunications media and equipment are installed. To simplify the implementation and administration of the cabling infrastructure, another series of specifications were developed, ANSI/TIA/EIA 606: The Administration Standard for the Telecommunications Infrastructure of Commercial Building.

In addition to the standards specified by the ANSI/TIA/EIA recommendations, the International Standards Organization (ISO) defined a generic cabling system recommendation known as ISO/IEC IS 11801. The ISO standard is intended for global usage and is broader in scope than the ANS/TIA/EIA standards for the North American market. The European version of ANSI/TIA/EIA standard is EN 50173 and is more similar to 568 than to the ISO standard.