Development of integrated digital telecommunication network

Ultimately the cost of providing a telephony service using digital techniques will be considerably lower than that incurred with the present techniques. However, a carefully planned sequence of introduction is necessary to avoid high costs during the period when analogue and digital techniques coexist. A proposal for expanding the present digital provision using an overlay network technique, which permits some commonality for the telephony and data services, is outlined. Some design problems relating to traffic concentration and digital switching are discussed, and a plan is developed that should ensure that the security of the network and the service to the subscriber are adequate.