UTRAN

UTRAN, or Universal Terrestrial Radio Access Network, is the radio access network component of the UMTS mobile telecommunications standard. It provides the wireless connection between user equipment (UE) and the core network, and is responsible for managing radio resources, mobility signaling, and session control within the UMTS system. UTRAN uses the W-CDMA air interface and supports the transport of both circuit-switched and packet-switched traffic.

The UTRAN architecture is composed of two main elements: the Radio Network Controller (RNC) and the Node B. The RNC handles radio resource management, admission control, mobility management, and control plane signaling, coordinating multiple Node Bs and performing functions such as handovers and power control. Node B functions as the radio base station that communicates directly with the UE and implements the physical and lower-layer protocols of the air interface under the RNC’s supervision. The RNC and Node B are connected by the Iub interface, while the RNC may interconnect with other RNCs via the Iur interface for inter-RNC handovers and mobility management.

UTRAN interfaces with the core network through the Iu reference interface, which is subdivided into Iu-CS (circuit-switched) and Iu-PS (packet-switched) to support traditional voice services and data services, respectively. The RNC coordinates with the Core Network to route user data and signaling, enabling services such as voice calls, messaging, and data sessions.

In the evolution of mobile networks, UTRAN is the predecessor to E-UTRAN, the radio access network used in LTE. UTRAN supports UMTS and High-Speed Packet Access enhancements, while E-UTRAN provides higher data rates and lower latency characteristic of LTE.