The No. 2 Electronic Switching System has been planned with dependability, maintainability, and operational ease representing a major portion of the total system design concept. The major characteristics that jail under these headings are redundancy, trouble detection, trouble recovery, diagnosis, repair, man‐machine inter j ace, data protection, and operational and administrative procedures for growth and change. All these factors play a large role in both the hardware and software portions of the system design. This article reviews the highlights in each of these areas and describes how they interact in the overall system across both the control complex and peripheral system areas.

Operator services position system (OSPS) architecture builds on the 5ESS® switch Integrated Services Digital Network (ISDN) base to provide modern, flexible operator services. This article details some major operator system innovations provided by the OSPS system architecture.

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Abssirucsi-Range extension allows the No. 2 electronic switching system (No. 2 ESS) to serve subscriber loops out to 2500 SZ as part of the Bell System's unigauge plan. Rangeextender circuits provide both audio and dc gain for loops greater than 1300 SZ. These circuits have been designed specifically to be low cost, as small as possible, and to use minimum power. Network concentration allows 70 percent fewer range extenders to be provided than customer Lines served. All trunk, service, and test circuits that had to be modified to work range extended are provided on a standard basis in every No. 2 ESS office. This means that range extension can be provided in a No. 2 ESS office at very low cost; essentially the cost of the rangeextender circuits.

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