Interface used in telecom network

Reference points and interfaces:

Within the GPRS core network standards there are a number of interfaces and reference points (logical points of connection which probably share a common physical connection with other reference points).

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' or GTP prime).

-Gb

Interface between the base station subsystem and the SGSN the transmission protocol could be Frame Relay or IP.

-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 use 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.

-Gy

The 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.

Interfaces in the GRAN:

Um:       The air interface between the mobile equipment and the BTS.

Abis:      Interface between BTS and BSC.

A:            Interface between GRAN and circuit switched part of core network (CN).

Location area:

LA is the area in which the network searches for a registered mobile (not currently active) – for circuit switched services

Routing area:

RA similarly for packet switched service