Tie line problems in P.A.B.X. design

A tie line is defined as a direct connexion between two private telephone exchanges. The various types are classified as under: tie lines between two auto P.B.X's, between an auto and a manual P.B.X., with 50 ~ signalling, interconnecting a group of P.B.X's, and special tie lines. The paper describes and illustrates the arrangements of the simple tie line and its method of operation. It deals in the same manner with the different types specified above.