Theadoption ofpacket-switched technologies in mobilecommunication systems hasenabled theprovision ofIP- basedservices tomobileusers. Yet,thesesystems, suchasthe UMTS network, arenotflexible enoughtoleavespaceforIP- oriented protocols todominate noraretheyabletomeetthe stringent QoSrequirements imposed bymultimedia services. This paperpresents aninnovative Beyond3G networkarchitecture, denoted asSIPRAN, posing anevolution tothestandard UMTS network. According totheproposed concept, theGPRS Support Nodesareintegrated intoa single entity, whiletheSession Initiation Protocol isadopted forperforming mobility andsession management; these modifications result inthesmoothevolution of theUMTS CoreNetworktowardsIP,whileaccomplishing a significant performance gain. Inordertoevaluate thetarget architecture andsubstantiate itsactual effectiveness, a series of experiments was carried out,by utilizing a fully-functional emulator.