Information Highways are widely considered as the next generation of high speed communication systems. These highways will be based on emerging Broadband Integrated Services Digital Networks (B-ISDN), which - at least in principle - are envisioned to support not only all the kinds of networking applications known today but also future applications which are not as yet understood fully or even anticipated. Thus, B-ISDNs release networking processes from the limitations which the communications medium has imposed historically. The operational generality stems from the versatility of Asynchronous Transfer Mode (ATM) which is the transfer mode adopted by ITU-T for broadband public ISDN as well as wide area private ISDN. A transfer mode which provides the transmission, multiplexing and switching core that lies at the foundations of a communication network. ATM is designed to integrate existing and future voice, audio, image and data services. Moreover, ATM aims to minimise the complexity of switching and buffer management, to optimise intermediate node processing and buffering and to bound transmission delays. These design objectives are met at high transmission speeds by keeping the basic unit of ATM transmission - the ATM cell - short and of fixed length.