Radio Network Controller - Interfaces

Interfaces

The logical connections between the network elements are known as interfaces. The interface between the RNC and the Circuit Switched Core Network (CS-CN) is called Iu-CS and between the RNC and the Packet Switched Core Network is called Iu-PS. Other interfaces include Iub (between the RNC and the Node B) and Iur (between RNCs in the same network). Iu interfaces carry user traffic (such as voice or data) as well as control information (see Protocols), and Iur interface is mainly needed for soft handovers involving 2 RNCs though not required as the absence of Iur will cause these handovers to become hard handovers.

Until 3gpp R4, all the interfaces in the UTRAN are implemented using ATM only, except the Uu interface which uses WCDMA technology. Starting R5, IP bearers can be used over Ethernet instead. Physically, these interfaces can be carried over SDH over optical fiber, E1 (sometimes referred to as PDH) - over a copper wire or microwave radio. Several E1s can be bundled to form an IMA Group. Since the interfaces are logical, many interfaces can be multiplexed onto the same transmission line. The actual implementation depends on the network topology; examples are chain, distant star,mesh and loop configurations.