. Automatic telephony; a comprehensive treatise on automatic and semi-automatic systems . o. 3, whileoffice No. 5 represents the conditions in any of the other offices in thispart. The center for the same service for the lower part is office No. 2,and office No. 7 represents the rest of the offices in that part. 148 AUTOMATIC TELEPHONY Special second and third selectors are installed in each office andreached from the first level of first selectors. Toll is called by 100. This gives a direct trunk from any officeto the toll recording operator. Information is called by 1202. The special second
. Automatic telephony; a comprehensive treatise on automatic and semi-automatic systems . o. 3, whileoffice No. 5 represents the conditions in any of the other offices in thispart. The center for the same service for the lower part is office No. 2,and office No. 7 represents the rest of the offices in that part. 148 AUTOMATIC TELEPHONY Special second and third selectors are installed in each office andreached from the first level of first selectors. Toll is called by 100. This gives a direct trunk from any officeto the toll recording operator. Information is called by 1202. The special second selectors havetheir second levels multipled onto the regular trunks leading to thecentral office. In the upper part, if any office (No. 5) calls 12, thecall goes to an incoming second selector in office No. 3. Calling Olifts the incoming second selector to the tenth level, leading to specialthird selectors, on whose banks are the information trunks, level 2. Office 5 -Local Switched. Office ,. ~ ~~1 [local ^==r [Switches — — Complaint i^^^ J In formation. l^ \sMs =^frnplaJc 1 rzr~—In formati T ■ Fig. 143.—Trunking, recording toll and miscellaneous service. Calling the same number from any office (No. 7) in the lower partroutes the call over a regular trunk to office No. 2, where similar condi-tions prevail. Complaint is called by 1303. Levels 2 and 3 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 upo
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttelephone, bookyear19
