Saulle Mattei
I know, that UMTS backbone is based on SDH or DWDM backbone, because in the 3gpp release '99 all is ATM based, so propably all will be ATM over SDH. Infact between Node B and RNC there are AAL2 and AAL 5 interfaces so it will be ATM.
Instead in the 3gpp release '00 (or R4 and R5) all will be over IP.
Regards.
Saulle Mattei