) 6 Dimensioning for Single ATM-Based lub The delay factor fR quantifies the increase of the average transfer time or the reduction of the effective throughput of individual flows as a result of link congestion. It is a quantitative measure of how link congestion affects the transaction times, taking into account the economy of scale effect. It is noted that fR is always larger than 1. From the average transfer time given in equation (6.18), the consequent application throughput (2 = =x/E{T(x)}) can be derived: (6.21) the special case of R=1(i.e. M/G/1-PS), " dy=C.(1-p). Figure 6.18 shows the delay factor fR and normalized throughput a function of the offered load (or link utilization) p with different R values. It can be seen that for R>1 with small P the delay factor fR is close to 1, and thus the normalized throughput is close to 1/R. This means that all connections receive an average rate, which is almost equal to their peak rate rpeak As the load increases (higher utilization), the delay factor fR increases dramatically, and the throughput drops accordingly. Moreover, from the graphs it can be observed that the delay factor reflects the economy of scale characteristics. Links with larger capacities (i.e. higher R) can be higher utilized than smaller ones (i.e. lower R) while still achieving the same delay factor. Furthermore, the sensitivity of the delay factor regarding traffic variation increases more drastically for smaller link capacities (i.e. lower R) when the utilization approaches 1. Therefore, one has to be careful when dimensioning links with lower capacities. In addition, as M/G/R-PS model is insensitive to the service time distribution, the results derived from M/G/R-PS model, i.e. the average sojourn time by equation (6.18) and average throughput by equation (6.21) are independent of object size distributions. load (utilization) load (utilization) Figure 6.18: Delay factor and normalized throughput vs. load - M/G/R-PS Model 6.3 Dimensioning for Elastic Traffic 6.3.6 Extended M/G/R-PS Model The b