The UMTS interfaces can be categorised as follows:

1. Uu :

• This is the interface between the user equipment and the network. That is, it is the UMTS air interface.
• The equivalent interface in GSM/GPRS networks is the um interface.

2. Luis:

• The Iuis split functionally into two logical interfaces, Iups connecting the packet switched domain to the access network and the Iucs connecting the circuit switched domain to the access network.
• The standards do not dictate that these are physically separate, but the user plane for each is different and the control plane may be different.

3. Iu –CS :

• This is the circuit-switched connection for carrying (typically) voice traffic and signalling between the UTRAN and the core voice network.
• The main signalling protocol used is Radio Access Network Application Part (RANAP).
• The equivalent interface in GSM/GPRS networks is the A-interface.

4. Iub :

• This is the interface used by an RNC to control multiple Node Bs.
• The main signalling protocol used is Node B Application Part (NBAP).
• The equivalent interface in GSM/GPRS networks is the A-bis interface.
• The Iubi interface is the main standardised and open, unlike the A-bis interface.

5. Iu –PS :

• This is the packet-switched connection for carrying (typically) data traffic and signalling between the UTRAN and the core data GPRS network.
• The main signalling protocol used is RANAP.
• The equivalent interface in GSM/GPRS networks is the Gb-interface.

6. Iur :

• The primary purpose of the Iur interface is to support inter-MSC mobility. When a mobile subscriber moves between areas served by different RNCs, the mobile subscriber’s data is now transferred to the new RNC via Iur.
• The original RNC is known as the serving RNC and the new RNC is known as the drift RNC.
• The main signalling protocol used is Radio Network Subsystem Application Part (RNSAP).
• There is no equivalent interface in GSM/GPRS networks.