THE OCCURRENCE AND EFFECT OF LOCKOUT 



261 



indicated on the figure with appropriate subscripts and the two direc- 

 tions of transmission are differentiated by the primed and unprimed 

 notation. The suppression points are indicated by arrows which repre- 

 sent an opening of the transmission path when the relays, or other sup- 



fw+T'+Te=T 



w — 



— E 



Tyv+r + Te^T 



Fig. 1 — Schematic of generalized four-wire circuit equipped with two 

 echo suppressors. 



pression devices are operated. The suppressing relays are specified 

 by a notation which refers either to the particular relay or to its hang- 

 over, or releasing time. According to the definition given above a 

 lockout exists during the time that both the relays he and hj are 

 operated.* 



With the exception of the beginning and end of the conversation the 

 occurrence of lockout can be described in terms of the resumption and 

 response times following a pause by one talker, and the constants of 

 the circuit. Referring to Fig. 1, and considering the sequence of events 

 following a pause by E, we shall see that two types of lockout can occur. 



The first type, which is the one usually met in practice, can occur 

 when he < hw -\- r, and hw releases after he. A response by W and a 

 resumption by E are necessary to produce a lockout. It will persist as 

 long as both E and PF continue to talk and for an additional time equal 

 to the delay from the end of the circuit to the first relay to release after 

 a pause by one talker, plus the hangover time of that relay. A lockout 

 of this type may be termed a lasting lockout. 



The second type can occur when hu, -\- t < he, and //„ releases before 

 he. It is possible for a response by W to arrive at hw and operate A,„' 

 before he has released thus causing a lockout wihch will be terminated 

 when he releases. A lockout of this type, which may be termed a 

 releasing lockout, can occur without a resumption by E, or if £'s 

 resumption reaches h/ after he releases. If a releasing lockout has oc- 



* Also, according to the definition, when both the relays hw and he' are operated, 

 a condition of no practical importance. 



