No. 5 ESS Maintenance Software

No. 5 ESS is a stored program controlled digital switching system using distributed processing to provide smooth growth across the entire central office line range. The No. 5 ESS maintenance hardware and software is designed to meet all Bell System reliability and maintenance requirements. New approaches for maintenance software design have been required to accomplish this in a distributed processing environment. The responsibility for carrying out maintenance functions is distributed so that major functional units are almost totally responsible for their own maintenance. This allows system evolution to take place with minimum impact on the overall software structure and also allows loose coupling of system elements. Loose coupling means that relatively slow control channels can be used for intrasystem communication. All of these features facilitate the remoting of major functional units away from No. 5 ESS. Switch maintenance, terminal maintenance, system integrity, and human-machine interface software are present in each of No. 5 ESS´s distributed processors. Software in these processors is decomposed into small, easily understood components with well-defined interfaces. Operating systems are used to switch messages between software processes and to provide common services for the maintenance subsystems. Most of the software is written in the C high-level language. This simplifies software development by allowing the same coding language to be used for all system processors and provides future code portability when new generations of processors are introduced into the system. The No. 5 ESS maintenance software architecture and design approach helps ensure a high-quality end product. It should also minimize future effort needed to introduce new hardware, services, and features into the system.