The author highlights various concepts related to software patching in the stored program control (SPC) environment. He introduces the concept of software maintenance and studies the effect of the software patching process on switching system reliability. The importance of managing the software change process, including patch testing and patch tracking, is discussed. The types of patches that are typically applied in the SPC switching environment are described. It is pointed out that the prime objective of real-time software suppliers, especially those supporting SPC switching systems, should be to minimize online patching. It is concluded that proper design specification of SPC switching functions and patches, coupled with exhaustive testing of software/hardware interfaces, could help reduce the number of patches in the field.>

The recent trend toward distributed processing in stored-program-controlled (SPC) switching systems has resulted in increased use of firmware. The impact of firmware on SPC switching system reliability and maintainability, after sale of the product to user companies, can be substantial. The author examines both life cycle practices for firmware and the impact of firmware on switching systems, and he suggests means to lessen this impact. He examines present firmware technologies, which indicate a trend toward electrically erasable/programmable firmware devices; shows the importance of parallel development methodologies for firmware and software; shows the advantages of loose coupling between firmware and software; shows a relationship between the quality of firmware product and the quality of service a telephone company provides; and suggest a classification of firmware devices.>