Automatic telephony; a comprehensive treatise on automatic and semi-automatic systems (1921)
Smith, Arthur Bessey, b. 1875, Campbell, Wilson Lee · New York : McGraw-Hill · leaf 164
l-S … Separate Levels and Trunks \ -^-for Ultimate Use Fig. 142.—Trunking, inter-office, two levels combined for initial service. Combination use of trunks is sometimes practised if traffic for specialservice (information, complaint, etc.) is light, and call numbers beginningwith l are used for that…
Telephone
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