r sound, text and image, usually on network, so they can get on with managing their core business. the same computer workstation (Francik et al., 1991; Weber, 1992). 6. There is greater reliability compared to a private circuit, since The components within a multimedia system are: the network; still the PSTN can provide diversity of traffic routing, which is only image; video telecommunications; audio; motion video; graphics. possible in large private networks. Television or a computer may be used as the delivery vehicle. Small organisations, with few small remote sites, cannot justify having their own private network but can more readily justify the use of a virtual private network. Large organisations may wish to use private circuits, but would still use virtual private networks in order to: Multi Increase network resilience by providing a secondary routing media Image for the main traffic, as illustrated in Figure 11.11. 2. Access the smaller locations of the company which are not linked by a private line, as also illustrated in Figure 11.11. Voice Figure 11.10 Simplified illustration of multimedia services Television may have an optical disk associated with it for accessing games, training courses, etc. Multimedia will play an increasing roll in telecommuting (Payne, 1991). It allows remote users to participate fully in joint work, including database access. However the bandwidth needed can be very high, requiring broadband to the home. This would arise, for example, if five users were conferencing and each had a workstation with sound and five images, along with the document being re- viewed. ISDN is key to the growth of multimedia applications, especially Main routes VPN routes for the home market. Applications include videophony, videocon- ferencing, desktop conferencing, where files can be shared between participants and changed in real time, etc. Figure 11.11 A hybrid network of private and public (VPN) links 11.5.2.5 Private and virtual private circuits 3. To extend the private network to other business