870 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 



A new 2600-cycle system to be used only on the broader band circuits 

 has since been developed. It is simpler and more economical than the 

 1600-cycle system. The older carrier systems, having been designed when 

 practically all toll operation was by the ringdown method, made no 

 provision for signaling since that was all done by short applications of 

 the 1000 cycles when there was no speech on the line. Some of the new 

 carrier systems for short haul applications are designed to provide their 

 own signaling channel for each voice channel. 



PRINCIPAL ELEMENTS OF THE CSP SYSTEM 



1. Crossbar Switch Frames 



Crossbar switches are used for incoming and outgoing link frames 

 on which the trunks (both toll lines and trunks to and from local offices 

 and switchboards) are terminated, and for sender link frames used ^o 

 give trunks access to senders. These frames are similar to those in the 

 toll crossbar systems now in service. Since they have been described in 

 a previous paper they will be passed over with only a mention of their 

 capacity. 



Each incoming or outgoing link frame normally has terminals for 300 

 trunks. As many frames are provided as required for the size of the office. 

 In the smaller offices one train of switches with complete interconnection 

 of incoming and outgoing frames is pro\nded. In the larger offices two 

 trains each with its own set of markers are provided. When this is done 

 the incoming trunks are multipled to both trains and an extra build out 

 bay is provided on the incoming frame to provide 400 terminals per 

 frame. Since each train has a theoretical limit of 40 incoming and 40 

 outgoing frames the maximum size of an office is theoretically 80 of each. 

 Practical considerations, however, such as the number of markers that 

 can be efficiently operated in a group and the maximum size office it is 

 feasible to operate as a single administrative unit will limit an installa- 

 tion to about 60 incoming and 60 outgoing frames. 



The sender link frame gives 100 trunks access to 40 senders. 



2. Senders 



Two separate groups of incoming senders are provided, one to receive 

 DP and the other MF pulsing. Whether the system is installed in a 

 step-by-step or a panel-crossbar area both groups of senders will always 

 be needed. MF will be received from senders in other CSP's and from 

 switchboard positions. DP will be received from switchl>oard positions 



