oblems random manner. In addition, the software is required to carry out of modifying them all at once become immense. diagnostic checks on the hardware, provide statistical data on traffic One solution is to download new programs, routing data etc. and performance and provide call records for billing purposes. remotely via data links and to site the operations and maintenance Separate modules are provided for each of the functions in the terminals at a central location to serve a group of exchanges. Central applications software. The operating system schedules the use of the access to the databases and processors of all the exchanges permits hardware resources by these application programs, storing the status short term as well as long term changes to be made to facilities and of all registers etc. when a program is deactivated and restoring the routing. This is known as Network Management and enables plant same state when it is reactivated. This multiprogramming technique failures to be identified, located and traffic to be re-routed around enables high priority tasks (e.g. call set up) to be given precedence congestion bottlenecks. A further development of the centralised over lower priority tasks (e.g. statistics). control principle is the concept of the Intelligent Network in which Figure 31.20 shows in simplified form a typical modular break individual exchange processors interrogate a remote database for down of the software in an spc exchange. The line scan program instructions on how to process particular types of call, or route such continuously updates a tabular store of the state of each line termi- calls to a central service provider. nation (e.g. free, busy, calling etc.) and alerts the central call routing software to connection requests. The latter validates the request against a pre-determined class of service for the termination and Operational security receives called number data from the line scanner or the signalling software, depending on the type of termination. The received digits Unlike m