Database Systems: A Real-Time Database Management System for No. 5 ESS

The Bell System's newest addition to its family of electronic switching systems is the No. 5 ESS (Electronic Switching System).1 It represents a departure from past local switching systems and it presented a unique opportunity to apply the principles of database management to a distributed switching network characterized by severe real-time constraints and stringent reliability requirements. The No. 5 ESS provides a software-controlled switching capability for local telephone offices. The system consists of a central processor and a series of microprocessor-controlled modules that interface with the switching periphery. It is programmed in the programming language "C." The database is based on the relational data model and distributed across each processor in the network. All accesses to data, both local and remote, are controlled by the Data Base Manager (DBM). The modular hardware and software design allows offices to be economically grown. In addition, the introduction of a processorindependent language along with the distributed nature of the system will help ensure that the No. 5 ESS will keep pace with today's rapid 2423