Theory and Practice of RRC State Transitions in UMTS Networks

3GPP has been enhancing UMTS networks by issuing new standard releases recurrently. However, the RRC state transition model has remained rather unchanged through several releases, namely, Rel. 99, Rel. 05 and Rel. 06. We review RRC state transitions and study them in practice using our novel 3G Transition Triggering Tool (3G3T), focusing on the network configuration parameters that prompt these transitions. We employ 3G3T in a landmark measurement study involving four UMTS networks in three countries and validate our findings using a state-of-the art proprietary measurement tool. Our results show that 3G3T is able to discover RRC configuration parameters without operator involvement or cooperation. We observe significant differences in UMTS network configurations, which directly impact end-user data service performance. We find that, in practice, the behavior of public UMTS networks cannot be solely described based on the theoretical constructs found in the literature, and that tools such as 3G3T are necessary in order to obtain a complete picture. The results presented in this paper aim to assist simulationists in developing better models for UMTS networks. Moreover, we expect that operators can use 3G3T to configure their networks more efficiently. Finally, our methods and algorithms should be of great interest to application developers for mobile broadband networks based on 3GPP standards.