We evaluate an expectation model for the dimensioning
problem in optical networks. The expectation model
predicts the average number of hops, the spare capacity and the
number of ports analytically, without requiring knowledge of the
network topology. We apply the model to a set of realistic network
topologies and the analytical approximations are compared with
the results obtained using a commercial numerical dimensioning
tool, the OPNET WDM Guru. We discuss the agreement between
the analytical approximations and the numerical results.