No. 1 ESS Call Store - A 0.2-Megabit Ferrite Sheet Memory

l.i System Requirements As the name of the call store implies, its prime function is to provide the read-write or erasable storage for all the call-related temporary information processed by the No. 1 electronic switching system (ESS). Aside from the conventional call processing functions, 1 other common system functions involving administration, maintenance, AM A and T T Y buffering and network simplification (by map and queue techniques) are also assigned to the call store. This concentration of system functions has imposed rather large capacity requirements on the store. Of course the total number of bits required is a function of both the number of lines in the office and the number of calls per busy hour. A range of 100,000 to 4,000,000 bits is required to cover the gamut of office sizes and calling rates envisioned for No. 1 ESS. To achieve a compatible solution, a specific store size is required to provide a modular building block with few stores in small offices and many in large offices. Maintainability and dependability considerations imposed rather extensive requirements 2 on the call store. A duplication scheme to permit 2147