User equipment and USIM
UE consists of mobile equipment and a USIM application on a UICC. The terminal provides radio transmission, cell measurements, and protocol handling. USIM stores subscriber identity and authentication data.
Separating equipment from subscriber identity allows service transfer to a compatible terminal. The network can control subscriber permissions and IMEI-based equipment status independently.
Node B
Node B serves one or more WCDMA cells. It transmits and receives radio signals, performs channel coding, interleaving, spreading, and modulation, and reports measurements to the RNC.
- It executes fast power-control loops that require a radio-layer response.
- It combines or separates transport channels according to the RNC configuration.
- It carries user data and signaling over Iub.
Node B is not the complete cell controller. Radio bearer and UTRAN mobility decisions belong to the RNC.
RNC roles
The Radio Network Controller manages Node B resources, controls radio connections, and participates in mobility. One physical RNC can have different roles for different UEs and resources.
- CRNC owns control of a particular Node B and its resources.
- SRNC maintains a given UE connection toward the core and terminates its RRC protocol.
- DRNC supplies the SRNC with radio resources belonging to another RNS.
The SRNC and DRNC relationship supports mobility across RNC areas. Iur permits use of DRNC resources before the complete connection is relocated.
Circuit-switched domain elements
- MSC controls CS calls, mobility, and interworking with other exchanges.
- VLR holds temporary data for subscribers present in an MSC service area.
- GMSC accepts calls from other networks and determines the serving MSC.
- MGW transports media and can be controlled by an MSC server.
VLR reduces repeated access to the central subscriber database by storing the information required for current service.
Packet-domain elements
SGSN handles packet mobility, access security, and forwarding between UTRAN and the PS core. It stores device and routing-area context.
GGSN connects the UMTS core to an external packet network. It maintains PDP contexts and tunnels packets toward the SGSN serving the UE.
Subscriber and equipment databases
- HLR stores the service profile, identities, and current serving-node information.
- AuC generates material for authentication and protection-key establishment.
- EIR stores equipment-identity information and can support terminal blocking.
are generated from subscriber secret material and random input. They are not a fixed password sent to the terminal.
Element cooperation during a packet session
- UE obtains radio access through Node B and RNC.
- SGSN authenticates the subscriber using core data.
- A requested PDP context is created between SGSN and GGSN.
- GGSN binds the context to an external network and forwards packets into the tunnel.
- UE movement updates mobility state and routing in UTRAN and the core.