Dimensioning bandwidth for elastic traffic in high-speed data networks

Simple and robust engineering rules for dimensioning bandwidth for elastic data traffic are derived for a single bottleneck link via normal approximat ions for a closed-queueing network (CQN) model in heavy traffic, Elastic da ta applications adapt to available bandwidth via a feedback control such as the transmission control protocol (TCP) or the available bit rate transfer capability in asynchronous transfer mode, The dimensioning rules satisfy a performance objective based on the mean or tail probability of the per-flo w bandwidth. For the mean objective, we obtain a simple expression for the effective bandwidth of an elastic source. We provide a new derivation of th e normal approximation in CQNs using more accurate asymptotic expansions an d give an explicit estimate of the error in the normal approximation. A CQN model was chosen to obtain the desirable property that the results depend on the distribution of the file sizes only via the mean, and not the heavy- tail characteristics. Ne view the exogenous "load" in terms of the file siz es and consider the resulting flow of packets as dependent on the presence of other flows and the closed-loop controls. We compare the model with simu lations, examine the accuracy of the asymptotic approximations, quantify th e increase in bandwidth needed to satisfy the tail-probability performance objective as compared with the mean objective, and show regimes where stati stical gain can and cannot be realized.