TRUNK REQUIREMENTS IN ALTERNATE ROUTING NETWORKS 295 



atlministration and engineering; have been obtained with that end in 

 view. However, in alternate-routing networks the significant level of a 

 trunk group load is not that which is characteristic of its own busy hour 

 but rather that which is characteristic of the hour in which all trunk 

 •iroups in a given network are collectively carrying the greatest aggregate 

 t laffic \'olume. For each group the former level is referred to as the group 

 busy-hour (CIRH) load and th(! latter, for coiu'cnicnce, as the office busy- 

 hour (UBH) load. 



The reason for using office busy-hour loads between toll centers rather 

 than group busy-hour may be explained with reference to Fig. 8. Here 

 is a represented part of an intertoU trunk network showing 4 HU groups 

 connecting TC with four other toll offices a, b, c and d. TC homes on SC 

 and for simplicity it may be assumed that the alternate route of each 

 such group is the final group to SC. 



In the hour during which the greatest volume of traffic is leaving and 

 entering TC, i.e., the office busy-hour, the demand for trunk capacity 

 in the TC-SC group will also be greatest since by design the final group 

 to the home CSP of any TC is the route of last resort for all traffic to and 

 from the TC. Thus the group busy -hour of the TC-SC group coincides 

 with the busy-hour of TC as a whole. 



The group busy hours of the respective HU groups (TC-a, TC-b, etc.) 

 may occur outside of the office busy-hour for TC and during such hours 

 the amount of traffic offered to and hence overflowed by each of the HU 

 groups is greater on the average than that occurring in the office busy- 

 hour. But at any other hour than the office busy-hour there is less total 

 load on the network and hence there is some spare capacity in the final 

 group available for handling the group busy -hour overflow of one or more 

 of the high usage groups. By properly evaluating the average ratio be- 

 tween an}^ given toll center-toll center load in its group busy-hour and 

 its value in the office busy-hour it would be practicable to start with 

 basic data in group busy-hour terms and convert it to equivalent office 

 busy-hour levels before undertaking the procedures for separating loads 

 between direct (HU) and alternate routes. 



\/l ^ 



Fio. 8. 



