Nedo Celandroni°, Franco Davoli, Erina Ferro°, Alberto Gotta °ISTI-CNR, Area della Ricerca del C.N.R., Via Moruzzi 1, I-56124 Pisa, Italy [email protected], [email protected] *Italian National Consortium for Telecommunications (CNIT) University of Genoa Research Unit, Via Opera Pia 13, 16145 Genova, Italy National Laboratory for Multimedia Communications, Via Diocleziano 328, Na...