ntinued) Traffic capacity table (continued from previous page) Number of 1 lost call in Number of 1 lost call in trunks trunks 50 (0.02) 100 (0.10) 50 (0.02) 100 (0.10) (0.005) E (0.001) E, (0.005) E (0.001) E connection contains n links with GOS given by B1, n' the overall loss is then mainly determined by the links which are busiest overall loss probability is given by Equation 29.3. at the time considered. It has been noted that large groups of trunks are more efficient (29.3) than small groups, since each trunk can have a higher occupancy for a given grade of service. In the example shown in Figure 29.15, trunks in a group of five each carry less than 0.2E of traffic, whereas those in a group of 40 each carry over 0.6E with the same grade of Thus, if the losses are small (which they should be) then B is given service. The price paid for the greater efficiency of a large group of approximately by Equation 29.4. trunks is greater susceptibility to overload. For the same example, Figure 29.16 shows that an increase in traffic of 10% increases the (29.4) loss probability for a group of 5 trunks by 45%, but for a group of Grades of service are specified for the busy-hour traffic. Thus, if 100 trunks it increases by 550%. the busy hours of the links are non-coincident, the loss probabilities For this reason, it is common practice to specify two grades of of some links may be very low when those of others are high. The service: one for the specified traffic and a higher value for a given References 29/19 If automatic alternative routing is used, the traffic which over- flows from a high usage route to the tandem route consists only of the peaks of the traffic which is offered to the high-usage route. At times when the number of calls is less than the number of trunks on the high-usage route, the overflow traffic is zero. Consequently, the overflow traffic is non-poissonian; it is 'peaky'. Equation 29.1 and traffic tables based on it should not be applied. It is necessary to take into account the variance of the traf