NATIOXW IDK AITOMATIC SWircillNci 827 



NATIONWIDE XU.MBKHING I'LAX 



In the previous use of automatic switchiiif!; by loll operators, the 

 operators wei'c furnished with codes by means of which could be selected 

 the various circuits necessary to reac^h the destination. These codes Avere 

 dialed, followed by the local number of the called party. With this sys- 

 tem, toll operators calling a given telephone from diffei'ent remote cities 

 would, in general, use different codes coi-respoiiding to the different 

 circuit groups which the}' must select. 



For nationwide toll dialing even by operators this system would luivc 

 impossible complications, and for nationwide customer dialing it is clear 

 that the code to be dialed must uniquely represent the office which 

 serves the called telephone and that office only and not be dependent 

 upon the route to be followed to reach it. In other words, it in\{)l\es the 

 development of what is called a destination type code. Anothtn- descrip- 

 tion of this code plan is to say that for toll dialing purposes each tele- 

 phone in the country (and Canada) must have a distinctive telephone 

 number different from that of every other telephone. 



It is also clear that as a practical matter this number should be based 

 upon the local telephone number of the customer prefixed b}- a minimum 

 number of digits, following easily understood rules. 



To bring this about has involved a very high order of planning. Such 

 a plan has been perfected and forms currently the basis for the deter- 

 mination of the coding of all new telephone offices and for changes in 

 office codes when these are necessary. The development of this is the 

 subject of Mr. Nunn's paper. 



CUSTOMER TOLL DL\L1NG 



When the customer is to dial long distance calls directly without as- 

 sistance from any operator, two additional requirements are imposed 

 beyond those necessary for nationwide operator dialing. 



1. The customer normally is connected to a local central office but 

 for the purpose of nationwide toll dialing he must be connected to the 

 nationwide toll network. At present he does this by dialing a code such 

 as '211" which comiects him with the long distance operator. This pro- 

 cedure could be continued. However, since the customer must in any 

 event dial 10 digits for the longest hauls to designate the called telephone, 

 it is desirable if possible to cut out this preliminary step. That would 

 mean modifying the local central office equipment so that it would 

 receive the 10 digit numbers and transmit them on to the toll equipment. 

 This is a simple undertaking for local central offices using the latest 



