. The Bell System technical journal . 2 4 6 8 L=LOAD CARRIED IN ERLANGS. APOISSONP(C,L) fly >^- f I6j _, 8 10 12 14 L = LOAD CARRIED IN ERLANGS Fig. 7 —■ Comparison of trunking formulas. 434 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 I This formula provides a means for estimating the grade of servicewhich customers might he expected to receive if asked to dial their callsover moderate-delay or high-delay trunk groups. For a circuit use lengthof 150 seconds, and an average return time of 250 seconds (as on Fig. 6),both exponential, the load-versus-proportion-NC curves for 6 and IGtrunks a
. The Bell System technical journal . 2 4 6 8 L=LOAD CARRIED IN ERLANGS. APOISSONP(C,L) fly >^- f I6j _, 8 10 12 14 L = LOAD CARRIED IN ERLANGS Fig. 7 —■ Comparison of trunking formulas. 434 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 I This formula provides a means for estimating the grade of servicewhich customers might he expected to receive if asked to dial their callsover moderate-delay or high-delay trunk groups. For a circuit use lengthof 150 seconds, and an average return time of 250 seconds (as on Fig. 6),both exponential, the load-versus-proportion-NC curves for 6 and IGtrunks are given as curves (3) on Fig. 7. For example with an offered(= carried) load of a = erlangs on 6 trunks we should expect to per cent of the total attempts resulting in failure. For comparison with a fixed return time of NC-calls, the IF-formulacurves for exponential returns of 30 seconds (s = 5) and 250 seconds(s = ) averages are shown on Fig. 5. The first is far too severe anassumption for operator performance, giving NCs nearly double thoseactu
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