. The Bell System technical journal . TANEOUS CALLS Fig. 34 — Distribution of calls from crossbar tandem trunks; negative binomialtheory versus throwdown observations. ! THEORIES FOR TOLL TRAFFIC ENGINEERING IN THE U. S. A. 479 of siniiiltaneoiis calls. The agreement again is reasonably good, in spiteof the considerable disparity in variances. The overflow from XBT and the load which by-passed it, as well assome other miscellaneous parcels of traffic, were now combined for finaloffer to the Suburban Tandem group of 17 trunks. The comparison ofparameters here is again available in Table XI. On
. The Bell System technical journal . TANEOUS CALLS Fig. 34 — Distribution of calls from crossbar tandem trunks; negative binomialtheory versus throwdown observations. ! THEORIES FOR TOLL TRAFFIC ENGINEERING IN THE U. S. A. 479 of siniiiltaneoiis calls. The agreement again is reasonably good, in spiteof the considerable disparity in variances. The overflow from XBT and the load which by-passed it, as well assome other miscellaneous parcels of traffic, were now combined for finaloffer to the Suburban Tandem group of 17 trunks. The comparison ofparameters here is again available in Table XI. On Fig. 35 are shownthe observed and calculated distributions of simultaneous calls for theload offered to the ST trunks. The agreement is once again seen to bevery satisfactory. We now estimate the loss from the ST trunks for comparison with theactual proportion of calls which failed to find an idle path, and finally Table XI — Load Offered to Suburban Tandem Theory Observed THEORY OBSD f(n). P^n 10 20 30 40 n = NUMBER OF SIMULTANEOUS CALLS ^ ^ \ ^ ,--NEGATIVE BINOMIAL V ^-THROWDOWN \ \ x^^^ 0 1 -r-^ 10 20 30 40 n^NUMBER OF SIMULTANEOUS CALLS 50 Fig. 35 — Distribution of load offered to suburban tandem trunks; negativelinomial theory versus throwdown observations. 480 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 Table XII - — Grade of Service on ST Group Theory Obser-vation Observation Load submitted (erlangs) Load overflowing (er-langs) Proportion load over-flowing Number of calls sub-mitted 1057 Number of calls over-flowing 200 Proportion of calls over-flowing Table XIII — Grade of Service on the System Total load submitted Total load overflowing Proportion of load not served Theory Observed 475 34,001 calls200 compare the proportions of all traffic offered the system which failed tofind a trunk immediately. See Tables XII and XIII
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