The Post Office and automatic telephones

Abstract

(1) Introductory.–The paper attempts to describe points of general interest rather than detail. Absence of automatic aids to manipulation in early telephone switchboards; increasing introduction of such aids as manual systems developed; early automatic systems; the fundamental “Strowger” step-by-step system, and power-driven systems.(2) Post Office experience and practice.—Systems already in use; results obtained; methods of comparing costs; advantageous field of manual and automatic systems.(3) The semi-automatic system.—Claims and objections.(4) Layout of telephone areas.—Economic studies; differences between manual and automatic layout of exchange positions and external lines; subscribers' lines, junction plant, sites and buildings; synthesis of costs.(5) Internal plant and wiring.—Calculation and layout of exchanges; traffic data; grades of service; availability of switches; grading of switching outlets in accordance with theory of probabilities; “artificial traffic,” “trunk-hunting” facilities and methods of increasing them.(6) Services reserved for manual operating.—Trunk calls, extra-fee calls, coin-box and call-office traffic; automatic dialling to and from distant exchanges.(7) The problem of very large areas.—Transition difficulties of schemes involving a rigid plan of subscribers' numbers.(8) The “panel” system of the American Bell Companies.—Solution of numbering-scheme difficulties by exchange-code translation; brief description of “panel” system.(9) The choice of a system for London.—Strong attraction of the “panel” system; ultimate adoption of the Automatic Electric Co.'s “director” system; anticipated development in London; agreements for supply of apparatus; standardization of Post Office “step-by-step” automatic system.(10) The “director system.”—General description of the system; methods of translation; intercommunication between manual and automatic exchanges during transition period; “key sender” and “call indicator” equipment; the London “ mechanical tandem” exchange; various classes of service provided; tone signals; alarms and guarding devices; private branch exchange lines.(11) The subscriber's automatic telephone set.—Standardization of signalling impulses and calling dials; circuit arrangements to avoid high-voltage surges, tinkling of bells, and impulse clicks in receiver.(12) Tariffs for automatic systems.—“Message rate” versus “flat rate” “time and distance” tariff.(13) Progress of automatic exchange construction.— New exchanges required in London and the provinces; training of staff; output capacity of factories.