This paper presents methods and tools for the optimal dimensioning of Differentiated Services Networks and, in particular, for the Expedited Forwarding Class of Service. The proposed method minimises the bandwidth reservation of a traffic aggregate to provide a given maximum delay. The paper also introduces several methods to generate multimedia traffic aggregation using real video traces. The method is evaluated in several scenarios using these traffic traces. The results of these simulations allow us to discover the relationship between a required delay and the necessary bandwidth reservation (or the achievable utilisation limit). An interesting conclusion of these scenarios is that, following several recommendations, the link utilisation can reach values of around 80% or higher. The advantages of using short-term provisioning versus long-term provisioning are also studied.