. Automatic telephony; a comprehensive treatise on automatic and semi-automatic systems . of the specialsecond selectors are tied together, so that the result is the same as if12 had been called. This choice of numbers is made to render iteasier for the public to remember them. The separation occurs on thebanks of the special third selectors, because the complaint trunks are onthe third level. Mixed System.—The use of the terms thousand-line exchangeten thousand-line exchange etc., seems to indicate definite, fixedlimits to the growth of a central office equipment. This is not true. TRUNKING,
. Automatic telephony; a comprehensive treatise on automatic and semi-automatic systems . of the specialsecond selectors are tied together, so that the result is the same as if12 had been called. This choice of numbers is made to render iteasier for the public to remember them. The separation occurs on thebanks of the special third selectors, because the complaint trunks are onthe third level. Mixed System.—The use of the terms thousand-line exchangeten thousand-line exchange etc., seems to indicate definite, fixedlimits to the growth of a central office equipment. This is not true. TRUNKING, ITS PHYSICAL ARRANGEMENTS AND VARIATIONS 149 The expansion of a system does not depend upon its original design, andit may grow as rapidly or as gradually as may be desired. A thousand-line exchange (Fig. 144) has originally not over ten groupsof 100 lines each. To expand it beyond 1000 lines, insert second selectorsbetween the first selectors and the connectors of one of the lower hundreds(second hundred, for example). Attach the connectors to the same level 900 Connectors 800 700. Fig. 144.—Thousand lines being expanded. on the second selectors that they formerly occupied on the first new numbers for these subscribers will be the old numbers with thefirst digit doubled. Thus, 245 will become 2245, etc. The remaininglevels of the newly installed second selectors are now available for open-ing new hundreds, so that the capacity is now 1900 lines instead of 1000lines. Connectors l& ?nd SelS. 1 1 CD
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttelephone, bookyear19
