This paper describes specialized techniques to extract parametric models for long interconnects, modeled as transmission lines. An important step in the modeling is the extraction of the per unit length parameters. The novelty of the study is the parameterization with respect both to the geometric parameters and the frequency. The parameterization with respect to the geometry is based on the computation of first order sensitivities from electromagnetic field models, whereas the influence of the frequency is approximated by rational polynomials obtained by fitting. The approach proposed is validated by experiments.