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Interfaces in the GPRS network
Ga The interface serves the CDRs (accounting records) which are written in the GSN and sent to the charging gateway (CG). This interface uses a GTP-based protocol, with modifications that supports CDRs (Called GTP’ and GTP prime).
Gb Interface between the base station subsystem and the SGSN the transmission protocol could be Frame Relay or IP.
Iu Interface between the Radio Network Controller and the SGSN. The interface exchanges signaling and payload.
Gc Interface between the GGSN and HLR so that the GGSN can get the location details of a mobile station. To avoid implementing MAP/SS7 in the GGSN, this interface is optional. When not present, the GGSN routes inquires to the HLR via an SGSN.
Gd Interface between the SGSN and the SMS Gateway. Can use MAP1, MAP2 or MAP3.
Ge The interface between the SGSN and the service control point (SCP); uses the CAP protocol.
Gf The interface between the SGSN and the Equipment Identity Register (EIR), used for checking the mobile’s equipment identity number (IMEI) against a list of reported stolen mobile phones.
Gi IP based interface between the GGSN and a public data network (PDN) either directly to the Internet or through a WAP gateway.
Gmb The interface between the GGSN and the Broadcast-Multicast Service Center (BM-SC), used for controlling MBMS bearers.
Gn IP Based interface between SGSN and other SGSNs and (internal) GGSNs. DNS also shares this interface. Uses the GTP Protocol.
Gp IP based interface between internal SGSN and external GGSNs. Between the SGSN and the external GGSN, there is the border gateway (which is essentially a firewall). Also uses the GTP Protocol.
Gr Interface between the SGSN and the HLR. Messages going through this interface uses the MAP3 protocol.
Gs Interface between the SGSN and the MSC (VLR). Uses the BSSAP+ protocol. This interface allows paging and station availability when it performs data transfer. When the station is attached to the GPRS network, the SGSN keeps track of which routing area (RA) the station is attached to. An RA is a part of a larger location area (LA). When a station is paged this information is used to conserve network resources. When the station performs a PDP context, the SGSN has the exact BTS the station is using.
Gx The on-line policy interface between the GGSN and the charging rules function (CRF). It is used for provisioning service data flow based on charging rules. Uses the diameter protocol.
GyThe on-line charging interface between the GGSN and the online charging system (OCS). Uses the diameter protocol (DCCA application).
Gz The off-line (CDR-based) charging interface between the GSN and the CG. Uses GTP’.
Lg The interface between the SGSN and the Gateway Mobile Location Center (GMLC), used for location based services.
S6d The interface between SGSN and Home Subscriber Server (HSS).It is a diameter based interface which is used for transferring subscription and authentication data of the user to HSS for authenticating and authorizing user access.
S6a Authentication, more in TS 29.272
Gy Prepaid charging, more in TS 23.203, TS 32.299;