862 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 



signals must be in a form suitable for propogation over the medium 

 which carries them. 



4. It must exercise control over the amount of amplification of voice 

 currents introduced at the switching point so that a proper grade of trans- 

 mission will be furnished. 



All of these functions are performed by toll crossbar systems already 

 in service. The features that distinguish the new system are those pe- 

 culiarly characteristic of CSP operation. 



CSP Functions 



The following features which will be built into the equipment at Con- 

 trol Switching Points are commonly referred to as CSP features: 



1. Storing and sending forward digits as needed. 



2. Automatic alternate routing. 



3. Code conversion. 



4. Six-digit translation. 



The first of these features is basically essential for implementation of 

 the plan. The second produces faster service and important economies 

 in outside plant. It also provides protection against complete interrup- 

 tion of service in case of failure of all circuits on particular routes. This 

 aspect of the feature is so important that automatic alternate routing 

 may also be considered essential. The other two features are provided 

 for reasons of economy, and produce economies of such magnitude that 

 they are very much worth while. 



1. Storing and Sending Forward Digits as Needed 



The necessity of providing this feature in CSP switching systems 

 arises from the nature of the numbering and switching plans. The num- 

 bering plan is constructed with the objective of using a minimum 

 number of digits to give each telephone user in the country a distinctive 

 number. 



Numbers delivered to the CSP equipment are in the form ABX- 

 XXXX if the called place is in the same numbering area as the CSP. 

 AB represents the first two letters of any office name and X represents 

 any numeral. If the called place is in another numbering area this set of 

 digits will be preceded by XOX or XIX. XOX or XIX is the area code, 

 ABX the local office code, and these are the digits used for routing 

 purposes. Regardless of the number of switches required to complete the 

 call, these two sets of code digits are all that will be supplied. They are 

 universal codes in that they identify specific destinations - any place 



