Reliability and maintenance of telecommunications equipment is evolving and continues to evolve. Improved hardware, development of software engineering principles, and better understanding of procedures have reduced system downtime. This is reflected in more stringent downtime specifications in the telecommunications industry. The makeup of failures leading to downtime has also changed. Advances in digital equipment have dramatically reduced hardware problems. Although software has also improved, more is demanded of it, and it has not improved at the same rate as hardware. Procedural techniques have also improved-better user interfaces, and improvements in process have led to fewer failures. However, maintenance personnel maintain more equipment than before, and in consequence, procedural failure rates have not improved as fast as those for hardware. Software and procedural problems-not hardware-are now the dominant reasons for outages. Not only do they cause most outages, but the public perceives these outages to be worse. Yet the current in-service auditing of telecommunications equipment may still be based on a paradigm of preventing outages caused by relatively unreliable hardware. Auditing-the inspection and testing of communications equipment-is performed on a regular basis. The purpose of auditing telecommunications switching equipment is to improve system reliability. For duplex equipment (equipment consisting of two identical units, one of which takes over if the other breaks down) auditing takes place on both the active and inactive units. If problems are found, repairs can be made before service is impacted. Despite this clear benefit, audits also incur costs. Auditing invokes software which itself has a failure rate. Audit testing can lead to two types of incorrect conclusion, both of which can lead to unnecessary repairs, or to a dangerous misperception that the equipment is working properly. The first type of incorrect conclusion is a false positive-the audit shows there is a problem
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