Theory and Practice of RRC State Transitions in UMTS Networks

GPP has been enhancing UMTS networks by issu- ing new standard releases recurrently. However, the RRC state transition model has remained rather unchanged through sev- eral releases, namely, Rel. 99, Rel. 05 and Rel. 06. We review RRC state transitions and study them in practice using our nov- el 3G Transition Triggering Tool (3G3T), focusing on the net- work configuration parameters that prompt these transitions. We employ 3G3T in a landmark measurement study involving four UMTS networks in three countries and validate our find- ings 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 configura- tions, which directly impact end-user data service performance. We find that, in practice, the behavior of public UMTS net- works cannot be solely described based on the theoretical con- structs found in the literature, and that tools such as 3G3T are necessary in order to obtain a complete picture. The results pre- sented 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 effi- ciently. Finally, our methods and algorithms should be of great interest to application developers for mobile broadband net- works based on 3GPP standards.