n investigating it for the last The rationales in Europe and the USA in pressing for these decade in various forms. It can be thought of as a technique that is standards has been fundamentally different. In the USA pressure has between the pure circuit switching technique used for the B channel arisen for B-ISDN standards because of the perceived need for high of N-ISDN (which can be called a Synchronous Transfer Mode speed local area network (LAN) interconnect to form wide area (STM)) and the packet switching technique of a datagram packet networks (WANs). As a consequence contributions to these stand- network (conforming to X.25 Datagram Protocols). ards are heavily influenced by LAN and WAN procedures. In In circuit switching a connection is established for the duration of Europe on the other hand, B-ISDN is seen as an integrated network the call between the two end users, usually providing a transparent capable of supporting all services from a few bit/s up to the band- path between the two, the connection being established by means of widths required for high definition TV. signalling messages at the start of the call. This is called a connec- tion oriented service. Although information may not be sent all the time the connection is held and the user is paying for it until the connection is cleared (unless a leased line is being used). This 44.8.1 Services happens in narrowband ISDN and the exact structure of the infor- mation carried over the connection is of little interest to the carrier. The main need for a broadband network capability comes from two In the X.25 datagram protocol, information to be carried to the main areas, those services requiring high quality video and those remote user is assembled into packets of varying length and the requiring the exchange of large amounts of data such as certain routeing information for each packet is contained within it. A computer automated design applications and the interconnection of connection is therefore not established, making it a connectionless high-sp