The core network of UMTS is called the Core Network (CN).

The Radio Network Controller (RNC) is responsible for managing radio resources in UMTS.

The interface between the RNC and the NodeB is called the Iub interface.

The Serving GPRS Support Node (SGSN) is responsible for connecting the user to the core network.

The interface between the SGSN and the GGSN is called the S5 interface.

The Gateway GPRS Support Node (GGSN) is responsible for providing IP connectivity to the user.

The Radio Resource Control (RRC) protocol is used for signaling between the UE and the NodeB.

The RNC is responsible for managing mobility in UMTS.

The GPRS Tunneling Protocol (GTP) is used for signaling between the RNC and the SGSN.

The Home Location Register (HLR) is responsible for providing authentication and authorization services in UMTS.

The Mobile Application Part (MAP) protocol is used for signaling between the HLR and the SGSN.

The Visitor Location Register (VLR) is responsible for providing location information in UMTS.

The Service Location Register (SLR) protocol is used for signaling between the VLR and the SGSN.

The Policy and Charging Rules Function (PCRF) is responsible for providing charging and billing services in UMTS.

The Gx protocol is used for signaling between the PCRF and the SGSN.