IX-BAXD SIXGLE-FREQUENCY SIGNALING 



1311 



Table I — Calling to Called Direction 



Trunk Condition 



Idle (disconnect) 



Connect 



Dial pulsing* 



Ring forward 

 Disconnect (idle) 



Signaling Frequency 



On 

 Off 

 On, then off, on ])ulses corresponding with dial break 



intervals 

 On, then off, one pulse 

 On 



* Multifrequency pulsing,^ a separate a-c signaling sj'stem, is a faster means 

 of transmitting number information often used instead of dial pulsing. Its use 

 eliminates only the dial pulsing signals. 



* Stop- and start-pulsing control signals are required only in connection with 

 common control switching equipment. 



t Flashing supervision signals are required only for operators; the on intervals 

 light cord circuit lamps to inform operators of the status of calls independently 

 of the position of cord circuit talking keys. 



the signaling interpretation. The latter is conveniently identified by 

 different names for the trunk signals in the two directions. Only two 

 signal conditions, that is, tone on or tone off, in each direction are re- 

 quired for all dial trunk signals. Continuous dependence upon these two 

 conditions assures a high degree of reliability because of signal redun- 

 dancy. Tables I and II show the required dial intertoll trunk signals, 

 together with the action taken in regard to the signaling frequency. 



The signaling system must be able to handle minimum and maximum 

 length signals. The minimum times occur in dial-pulsing where the 

 shortest signal element may be as low as 30 milliseconds. All other types 

 of signals have longer durations. 



The maximum peiTnissible transmission time for signals between trunk 

 terminals is determined by the allowable imguarded intervals on two- 

 way trunks, during which double connections may occur, and also by 

 the stop-pulsing signal recognition interval. This time is limited to 

 about 175 milliseconds. 



The distortion permitted in the transmission of signals is proportional 



