In the radio part of a UMTS network, the UTRAN, there are several radio interfaces called Iu interfaces. Between the Radio Network Controllers( RNC) and the radio cells there is the Iub interface and between the RNCs the Iur interface. And for femtocells, between the Home NodeB( HNB) and the Home NodeB Gateway( HNB-GW) is the Iuh interface.
The Iub interface is between the base station and the radio network controller. The signaling and the user data stream runs over both interfaces. Depending on the switching technology, a constant bit rate( CBR) data stream is used for circuit switching or a variable bit rate( VBR) data stream is used for data packet switching.
The Iuh interface, located between the Home NodeB (HNB) and the Home NodeB Gateway (HNB-GW), determines the security architecture that is instrumental in ensuring scalable communications over the Internet. In addition, the Iuh interface provides an efficient and reliable method for transporting Iu-based traffic. The voice processor present at the broadband Iu interface filters out the voice data, improves its quality and reinserts it into the ATM data stream.