. The Bell System technical journal . ntinue with a more specific example, let us consider a telephoneconnection consisting of two four-wire circuits each equipped with anecho suppressor in the center of the circuit as show^n in Fig. 10. In thenotation of Fig. 10 the relay hangovers are each equal to r + the constants of integration are a = , b = + r. c = -f 3t. Since the two circuits are assumed equal, only lasting lockouts aretheoretically possible and the curves of Fig. 8 may then be used todetermine p in terms of r as defined by equation (7), which in turn maybe u
. The Bell System technical journal . ntinue with a more specific example, let us consider a telephoneconnection consisting of two four-wire circuits each equipped with anecho suppressor in the center of the circuit as show^n in Fig. 10. In thenotation of Fig. 10 the relay hangovers are each equal to r + the constants of integration are a = , b = + r. c = -f 3t. Since the two circuits are assumed equal, only lasting lockouts aretheoretically possible and the curves of Fig. 8 may then be used todetermine p in terms of r as defined by equation (7), which in turn maybe used to determine the expected number of lockouts from equation(3). The mean duration of lockout is obtained by inserting the value 276 BELL SYSTEM TECHNICAL JOURNAL of the relay hangover in equation (5) giving D = + r. The product of D with the expected number of lockouts per hundredseconds is then equal to the per cent of time locked out, which is shownin Pig. 10 as a function of r. By using the relation shown in Fig. 3 a. 0 T IN SECONDS Fig. 10—Calculated per cent of time locked out, and repetition rate for the indicated circuit conditions. second scale is shown in Fig. 10 to give the relation between the repeti-tion rate and the delay between the suppressors. This curve showsthat the repetition rate increases with the delay between the suppres-sors, at a gradually increasing rate up to a delay of about seconds,beyond which the impairment increases linearly with the delay. Summary It has been shown that two types of lockout, lasting and releasinglockouts, may occur in telephone connections involving two echo sup-pressors, and the manner of their occurrence has been discussed. The results of an experimental investigation show that the occur-rence of lockouts causes an increase in repetition rate, which is ap-proximately proportional to the per cent of time locked out. There has been presented a theoretical met
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