[1] Ericsson Telecom AB, Inovat Dev, KA EP LU RR, S-37123 Karlskrona, Sweden
[2] Accenture, Amsterdam, Netherlands
[3] Univ Groningen, Dept Math & Comp Sci, NL-9700 AB Groningen, Netherlands
[4] Vrije Univ Amsterdam, Fac Sci, Div Math & Comp Sci, Amsterdam, Netherlands