Smart dimensioning of IP network links

Link dimensioning is generally considered as an effective and (operationally) simple mechanism to meet (given) performance requirements. In practice, the required link capacity C is often estimated by rules of thumb, such as C=dM, where M is the (envisaged) average traffic rate, and d some (empirically determined) constant larger than 1. This paper studies the viability of this class of `simplistic' dimensioning rules. Throughout, the performance criterion imposed is that the fraction of intervals of length T in which the input exceeds the available output capacity (i.e., CT) should not exceed epsilon, for given T and epsilon. We first present a dimensioning formula that expresses the required link capacity as a function of M and a variance term V(T), which captures the burstiness on timescale T. We explain how M and V(T) can be estimated with low measurement effort. The dimensioning formula is then used to validate dimensioning rules of the type C=dM. Our main findings are: (i) the factor d is strongly affected by the nature of the traffic, the level of aggregation, and the network infrastructure; if these conditions are more or less constant, one could empirically determine d; (ii)we can explicitly characterize how d is affected by the "performance parameters", i.e., T and epsilon.