50 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 



2. Three Second Rule for the Bridging of Calls 



Referring to Fig. 8, again, at h a request for service is originated on 

 trip circuit 5 and at h this request is withdrawn. At tw apparently a 

 new request for service is initiated which is then withdrawn at ^n. From 

 manual service observations it is found that subscribers often flash when 

 dial tone is slow. A few pens were used to observe individual subscribers, 

 and Fig. 9 shows a case where a subscriber made several flashes when 

 his tone was slow. When a subscriber flashes it appears as though he 



20 



19 



18 



Q. 17 



OtE 14- 



muj 13 



^Z 10 



3z 9 



CTuj 8 

 OQ- 7 



- I 



H 4 



3 



2 

 1 



10 

 tr 9 

 UJ 8 

 "" 7 



Z2 



to 



1)12^3 t4 



ts te ty tg tg 

 15 SECONDS 



t,2 



Fig. 8 — Section of a hypothetical tape showing activities on trip circuit sub- 

 groups and on line finders. 



were making several bids for service. Actually he is making only one 

 real bid. On the trip circuit sub-group pens it was generally impossible 

 to distinguish between flashes and requests for service by two or more 

 subscribers. To resolve this problem many observations of subscriber 

 lines recorded on the tapes were examined from which it was concluded 

 that no great error would result if a break in the demand for service 

 on a trip circuit sub-group of less than three seconds were considered 

 as a flash and was to be bridged, and a break greater than three seconds 

 was to be considered as the termination of one call attempt and the 

 start of another 



