288 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 



ministrative functions could be economically performed when concen- 

 trators become common telephone plant facilities. The more important 

 of these miscellaneous features are discussed under the following head- 

 ings : 



a. Traffic Recording 



J 

 To measure the amount and characteristics of the traffic handled by 



the concentrator a magnetic tape recorder, Fig. 31, was provided for 



each trial. The number of the lines and trunks in use each 15 seconds 



during programmed periods of each day were recorded in coded form 



with polarized pulses on the 3-track magnetic tape moving at a speed of 



1}/2" per second. Combinations of these pulses designate trunks busy on 



intra-concentrator connections and reverting calls. 



The line busy indications were derived directly from the line busy 

 information received during regular scanning at the concentrator. Dur- 

 ing one cycle in each 15 seconds new service requests were delayed to 

 insure that a complete scan cycle would be recorded. Terminating calls 

 were not delayed since marker holding time is involved. Trunk condi- 

 tions are derived for a trunk scanner provided in the recorder. 



In addition to recording the line and trunk usage, recordings were 

 made on the tape for each service request detected during a programmed 

 period to measure the speed with which each call received dial tone 

 and the manner in which the call was served. In this type of operation 

 the length of the recording for each request made at a tape speed of 

 only \i!' per second is a measure of service delay time. 



As may be observed from Fig. 31 the traffic recorder equipment was 

 built with vacuum tubes and hence required a rather large power supply. 

 It is expected that a transistorized version of this traffic recorder serv- 

 ing all concentrators in a central office will be included in the standard 

 model of the line concentrator equipment. With this equipment, traffic 

 engineers will know more precisely the degree to which each concentra-- 

 tor may be loaded and hence insure maximum utilization of the concen- 

 trator equipment. 



b. Line Condition Tester 



It has been a practice in more modern central office equipment to 

 include automatic line testing equipment.^^ An attempt has been made 

 to include similar features with the concentrator trial equipment. The 

 line condition tester (see Fig. 30) provides a means for automatically 

 connecting a test circuit to each line in turn once a test cycle has been 



I 



