Core Network is devided into CS domain and PS domain. CS domain is based on original GSM network. PS domain is based on original GPRS network. CS domain is used to provide Circuit-switched service. Network mode can support TDM, ATM and IP. Physical entities include switching equipment (such as MSC/VLR, GMSCs), and inter-working equipment (IWF). PS domain is used to provide Packet-switched service. Network mode is IP. Physical entities include SGSN, GGSN, CG , BG etc.
Common Function of CS domain and PS
HLR: to realize mobile subscriber management and location information management ;
VLR: to deal with all kinds of data information of current mobile subscriber ;
AUC: to store authentication information of mobile subscriber ;
EIR: to store IMEI data of mobile subscriber;
SMS: Short Message Center.
Function entity of CS domain
MSC: to realize switching and signaling control function of circuit service.
GMSC: to realize addressing function for different network. GMSC and MSC can be integrated together or separated independently.
IWF: integrated together with MSC, to realize inter-working with PLMN and ISDN, PSTN , PDN (Mainly complete signaling transfer function), its functions can be defined based on specified services and network types.
Function entity of PS domain
SGSN: to realize packet switching function, signaling control function and route function of packet service.
GGSN: to realize inter-working with PS domain and external data network.
CG: to realize billing function of packet service.
BG: to realize inter-working of two GPRS network and guarantee the security of network.
Interface between CN and RAN/BSS
A Interface: to realize mobile station management, base station management, mobility management and call processing, etc.
Gb interface: to realize packet data transmit and mobility management.
Iu-CS interface: to realize RNS management, mobility management and call control function.
Iu-PS interface: its basic function is similar to Iu-CS interface.
CS internal interface
B interface (MSC-VLR): A private interface between VLR and MSC. It is used for the MSC to query the current location information of a Mobile Station (MS) from the Visit Location Register (VLR), or request the VLR to update the current location information of the MS or is used for the operations of supplementary services.
C interface (MSC-HLR): to get MSRN, the IN service related subscriber status and location information.
D interface (VLR-HLR): used to exchange the location information of the MS and the subscriber management information.
E interface ( between MSC): to be used for handover process between two MSCs.
F interface (MSC-EIR) : to be used for EIR to verify IMEI status information of mobile equipment.
G interface (between VLR): to exchange IMSI and authentication information when MS moves from one VLR to another VLR.
PS internal interface
Gr interface (SGSN-HLR): to exchange mobile location information and manage subscriber signed information. It is similar to C interface.
Gn, Gp interface (SGSN-GGSN): GTP is adopted, used for establish tunnel and transmit data packet between GSN equipment.
Gc interface (GGSN-HLR) : optional.
Gf interface (SGSN-EIR) .
Gi interface (GGSN – external network).
Common interfaces of CS and PS
Gs interface (MSC/VLR-SGSN): used for combined location update between MSC and SGSN) .
H interface (HLR-AUC): used for authentication and ciphering. It is a private interface.
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