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 = d·M, 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 vailable output capacity (i.e., CT) should not exceed $\varepsilon$, for given T and $\varepsilon$. 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 = d·M. 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 $\varepsilon$.