A universal mobile telephony system (UMTS) network monitoring system for capturing intercepted UMTS data. ATM cells from a UTRAN interface may be intercepted. The UTRAN interface may be an lu interface, an lur interface, or an lub interface, which are, respectively, interfaces between a core network (CN) of the UTRAN and a radio network controller (RNC) of the UTRAN, an interface between RNCs of the UTRAN, and an interface between a Node B of the UTRAN and an RNC of the UTRAN. The ATM cells may be reassembled into UMTS packets of the UTRAN, among which user plane packets may be segregated from control plane UMTS packets based on fields and bytes of the reassembled UMTS packets. The control plane packets may be stored to a non-volatile storage medium of the network monitoring system or processed in real time and results thereof displayed graphically.