Broadband ISDN ( B ‐ ISDN ) and the Asynchronous Transfer Mode (ATM)
Roger L. Freeman · 2002
Abstract B‐ISDN is modestly defined as a service or a system requiring transmission channels capable of supporting (transmission) rates greater than the primary rate (i.e., >1.544 or 2.048 Mbps) (CCITT Rec. I.121 ). ATM and B‐ISDN are designed to work together. ATM provides the underlying digital format; B‐ISDN supplies the necessary transmission facility. The asynchronous transfer mode (ATM) is a compromise digital format with the design objective of transporting and routing voice, data, and image media. ATM standards have been and are being developed by three agencies: ANSI, ITU‐T, and the ATM Forum. Conventional ISDN is now commonly called narrow‐band ISDN to distinguish it from B‐ISDN. Their basic objectives are similar: the capability of transporting and switching a wide range of media. The approach to reach the objectives is quite different. There is also a notable similarity in the reference circuit model of each. Whereas in ISDN network elements such as NT1, NT2, TE, and TA appear; in B‐ISDN they are denominated B‐NT1, B‐NT2, B‐TE, and B‐TA. Signaling is handled differently in each technique. One will note many operational similarities between ATM with frame relay and SMDS. Narrowband ISDN was designed around the copper pair. In B‐ISDN, fiber‐optic transmission is the medium of choice. We hasten to add that there is no reason why copper pairs cannot be used to transport B‐ISDN signals at the lower data rates. This holds equally for various forms of radio transmission so long as the bandwidth (Hz), with the implied impairments such as group delay, can support the digital transmission rate.