Desktop Encyclopedia of Telecommunications, Second Edition
Explanations, not just definitions.
TABLE OF CONTENTS Desktop Encyclopedia of Telecommunications, Second Edition
K: Key Telephone Systems Kiosks
Key Telephone Systems
Traditionally, key telephone systems functioned like Private Branch Exchanges (PBXs), but offered only a subset of the available features. Being more economical than PBXs, small and mid-size businesses found them very appealing, especially for the key system s configuration flexibility, which allowed multiple lines to be terminated at each telephone. Within certain limits, each line can be answered from any multi-line telephone in the system by pressing the appropriate line key.
Since the introduction of the first key telephone system by Bell Telephone in 1938, key systems have evolved from cumbersome units with toggle switches to the sophisticated, electronic systems of today. Key systems have advanced to the point where they can be incrementally equipped with a wealth of call processing and system management features, rivaling those of higher-cost PBXs.
Evolution of Key Systems
The first standard key systems were electromechanical devices (designated 1A key telephones) that used adjunct key units and toggle switches for line control. These 1A systems had clearly defined system components and wiring schemes, and offered an attractive alternative to prior, custom-built telephone systems that lacked standardization.
In 1953, Bell replaced its 1A systems with 1A1 systems that packaged line control equipment into the telephone set. Line status indicators on the 1A1 telephones lit steadily to show a line in use, and flashed to indicate held calls. Current key system standards evolved from early 1A and 1A1 system designs.
In 1963, further technological improvements led to the introduction of 1A2 systems, which used plug-in...
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