 technique known as 'packet switching'. In packet switching information is broken into blocks of data known as packets, which are then sent to an intended receiver independent of each other. Each packet is designed to be self-contained and may travel a different route to reach its destination. The receiver puts the packets back together and retrieves the transmitted information. Packet-switched data communication applies equally to analogue, such as music, as well as digital, such as an email, information. In data communications, information is generated by or through a machine which sends it to another machine. As a result, it is characterised by well-defined protocols which indicate the beginning and end of calls, ensure errors are detected and dealt with, maintain a correct order of information transfer and SO on. Photograph by Dan Anderson, Imagining the Internet Center, School of Communications, Elon University, Elon, North Carolina, USA. Copyright Elon University. CC 3Y-ND. Broadband Telecommunications Technologies and Management Data communications can therefore be defined as systems and protocols which facilitate transmission of mainly discrete but also analogue source information from one point to another. In effect data communications is the superset of digital communications, in that digital communications applies to an analogue information source, whereas data communica- tions applies to all information transfer regardless of the source. Data communications can also generally apply to mostly delay insensitive information transfer. For example, in contrast to telephony which must be carried out in real-time, transfer of emails for example can tolerate some delay. This facilitates transmission over links of diverse speeds and diverse routes: part of a message may be carried on a satellite link and another part on a submarine cable. One part of a message may be received later and another part earlier. A receiver's capability to re-order received data and re-construct the transmitted information in the co