864 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 



late both the area and office codes. If all points in the called area are 

 reached by the same route out of the particular CSP concerned the area 

 code will suffice for selection of the route. If some points are reached by 

 one route and others by one or more different routes the office code must 

 also be translated to determine which route should be selected. 



BASIC ARRANGEMENT 



In the CSP switching equipment talking connections are established 

 through crossbar switches.'' Incoming and outgoing toll lines and toll 

 connecting trunks are terminated on crossbar switch frames with linkage 

 between them to provide full access. The switches are controlled by 

 equipment common to the office, each item of which is held only long 

 enough to perform its task in setting up the connection. 



The major items of common control equipment are senders, markers, 

 decoders and translators. The basic functions of the senders are the 

 same as in other common control systems, i.e., registering incoming 

 digits and sending them out as directed. A departure from prior practice 

 is made in the design of the marker. In other crossbar systems the marker 

 is the principal seat of the mechanical brains. It not only controls the 

 actual establishment of the connection but also does the translating to 

 determine what connection should be established and what information 

 should be passed to the sender for further disposition of the call. In this 

 system the marker still controls the actual setting up of the connection, 

 but it acts on instructions received from the decoder where the major 

 portion of built-in intelligence resides. 



The decoder accepts code digits from the sender, translates them, 

 makes selection of alternate routes and gives instructions to markers and 

 senders to enable them to carry out their assignments. To do the trans- 

 lating job the decoder has one, and in some cases two translators perma- 

 nently associated with it and in addition has access to a common group 

 of translators called foreign area translators which can be used by all 

 decoders as required. 



The relationship of the principal elements of the system to each other 

 is depicted in the schematic diagram, Fig. 1. 



METHODS OF OPERATION 



The manner in which the various elements of the CSP sj^stem and the 

 CSP systems at various locations cooperate to implement the nationwide 

 switching plan may best be understood by following the progress of a 

 call which demands the exercise of the characteristic CSP functions. 



