Code Switching

in telegraphy, the automatic transmission of telegrams via specific routes according to a coded address in the heading of the telegram.

Code switching is used in systems incorporating automatic retransmission by means of a reperforator, in which each automated telegraph center or station within the code-switching network is assigned a six-digit code-routing index. The first three digits denote the number assigned to the last automated telegraph center through which the telegram must pass. The last three digits (the local index) denote the number assigned to a city branch office or to a district communications center where the recipient of the telegram resides. The index is marked on the telegram when the sender hands it to the cashier at the communications office. The telegram is then transmitted to a reperforator at the code switching center and enters the transmitter of an automatic device as a punched tape. This device decodes the routing index, thus finding the ultimate destination point of the telegram, and transmits it to that point. If the numeral assigned to a city branch office or to a district communications center where the recipient resides is not marked on the telegram, the telegraph operator at the last code-switching station reads the address of the recipient from the tape and then transmits the telegram to the required city branch office or district communications center, using an automatic sender and a regional key switchboard.