G interface (GPRS)
The GPRS network architecture has specified several reference points as G interfaces. The various G interfaces are used for communication among the different GPRS components and to other mobile networks. There are diverse G interfaces, which are labeled Gb, Gc, Gd, Gf, Gi, Gn, Gp, Gr, and Gs. In addition, there are also the G interfaces Ga, Gx and Gy in the telecommunications control network.
The Gb interface is the interface between the Base Station Subsystem( BSS) and the Serving GPRS Support Node( SGSN). It is used to exchange signalling information and subscriber data. The Gb interface supports multiplexing of multiple subscribers over the same physical medium.
The Gc interface is used to exchange data between the gateway GPRS Support Node( GGSN) and the site directory( HLR). The Gd interface forms the connection between the Serving GPRS Support Node (SGSN) with the Gateway Switching Center (GSMC) and with the Internetworking Mobile Switching Center (IWMSC).
The Gi interface is an internetworking interface in GPRS networks. The Gi reference point is located between the Gateway GPRS Support Node (GGSN) and an external IP network. The GGSN acts as a router from the point of view of the IP network.
The Gn interface is an interface between Serving GPRS Support Nodes (SGSN) and between Gateway GPRS Support Nodes (GGSN). The GPRS Tunnneling Protocol( GTP) is defined as the transport protocol.
The Gp interface is an interface for a virtual connection of different mobile networks via the Border Gateway in the Gateway GPRS Support Node (GGSN). The nodes are interconnected using the GPRS Tunneling Protocol (GTP).
In GPRS networks, the location directory (HLR) contains the GPRS subscriber data and routing information. This directory is accessible by the Serving GPRS Support Node (SGSN) through the Gr interface, which connects the SGSN to the Home Subscriber Server( HSS). Information about the location of the mobile is transmitted via the Gr interface. This data is signaling data about the radio cell and the GPRS services that the mobile station supports and that are enabled for it. The signaling protocol used on the Gr interface is Mobile Application Part( MAP).
The Gs interface is a GPRS interface located between the Serving GPRS Support Node (SGSN) and the Mobile Switching Center( MSC). The Gs interface is used for signaling between the aforementioned GPRS components.
Another interface of the telecommunication control network is the Gx interface, which is located between the Policing and Charging Enforcement Function( PCEF) and the Policing and Charging Rules Function( PCRF).
The Gy interface is an interface of the Policy Control and Charging( PCC) functional unit of LTE networks, namely between the Traffic Detection Function ( TDF) and the Online Charging System( OCS) or the Policing and Charging Enforcement Function (PCEF) functional module.
In addition to the online interface, there is another for offline charging for the Offline Charging System( OFCS), the Gz interface. It is located between the Offline Charging System (OFCS) and the Policing and Charging Enforcement Function (PCEF) function module and supports the offline billing of services.