100 BELL SYSTEM TECHNICAL JOURNAL 



the sender link frame. There are ten sender Hnks serving the selected 

 district junctor. These ten sender links and the ten sender groups to 

 which they have access on the secondary switches are then tested 

 simultaneously to find an idle sender link with access to a group of 

 senders in which there are one or more idle senders. When this 

 choice has been made an idle sender in the group is then selected. 



4. The two control circuits in cooperation with each other first oper- 

 ate the selecting magnets and then the holding magnets associated 

 with the paths selected on the switches of both the line link and sender 

 link frames, and thereby establish the connection from the calling 

 subscriber to an idle subscriber sender. 



This connection may be traced by referring to Fig. 11, from the 

 calling line on the vertical unit on a primary switch of the line link 

 frame, through a line link and a secondary switch, through a district 

 junctor circuit, to a vertical unit on a primary switch of the sender 

 link frame, through a sender link and a secondary switch to a subscriber 

 sender which is connected to a horizontal circuit path on the secondary 

 switch. 



5. The two control circuits are then released and made available 

 for use on other calls. The connections through the switches to the 

 sender are held established by means of the holding magnets which 

 are held operated over a signal control lead, called the "sleeve" lead, 

 under control of the relays in the sender, which in turn are under 

 control of the subscriber telephone. 



Upon completion of these operations which take but a fraction of a 

 second the subscriber sender transmits the dial tone to the calling 

 subscriber as an indication to dial the number. When the subscriber 

 dials, electrical impulses are transmitted to the sender, which receives 

 and registers them. When the sender has registered the office code, 

 which in New York City for example is contained in the first three 

 digits dialed, the sender will connect itself to an idle originating marker 

 by means of multi-contact relays of a marker connector circuit. 



Before proceeding further it is desirable to mention several other 

 functions of the two common control circuits used for setting up this 

 part of the connection. 



1. The control circuits signal to the sender the class of the calling 

 line, that is, for example, whether the line is a coin line or a non- 

 coin line. 



2. The sender link control circuit signals to the sender the number 

 of the district link switch frame on which the selected district junctor 

 appears, since this identification will be used later in the establishment 

 of the connection. 



