UTRAN

UTRAN (short for "Universal Terrestrial Radio Access Network") is a collective term for the Node B's and Radio Network Controllers (RNCs) which make up the UMTS radio access network. This communications network, commonly referred to as 3G (for 3rd Generation Wireless Mobile Communication Technology), can carry many traffic types from real-time Circuit Switched to IP based Packet Switched. The UTRAN allows connectivity between the UE (user equipment) and the core network.
The UTRAN contains the base stations, which are called Node Bs, and Radio Network Controllers (RNC). The RNC provides control functionalities for one or more Node Bs.

There are four interfaces connecting the UTRAN internally or externally to other functional entities: Iu, Uu, Iub and Iur.

Ø  The Iu interface is an external interface that connects the RNC to the Core Network (CN).

Ø  The Uu is also external, connecting the Node B with the User Equipment (UE).

Ø  The Iub is an internal interface connecting the RNC with the Node B.

Ø  And at last there is the Iur interface which is an internal interface most of the time, but can, exceptionally be an external interface too for some network architectures. The Iur connects two RNCs with each other.