It was also proposed, at one stage, to support packet radio services in the US D-AMPS TDMA system, however, in practice, all of these networks have been converted to GSM so this option has become irrelevant.
It maintains routing necessary to tunnel the protocol data units (PDUs) to the SGSN that services a particular mobile station (MS).
For this purpose, the GGSN stores the current SGSN address of the user and his or her profile in its location register.
The GGSN is responsible for IP address assignment and is the default router for the connected user equipment (UE).
Other functions include subscriber screening, IP pool management and address mapping, QoS and PDP context enforcement.
[3] A SGSN is responsible for the delivery of data packets from and to the mobile stations within its geographical service area.
The location register of the SGSN stores location information (e.g., current cell, current VLR) and user profiles (e.g., IMSI, address(es) used in the packet data network) of all GPRS users registered with it.
This process (called APN resolution) finally gives the IP address of the GGSN which should serve the access point.
The packet data protocol (PDP; e.g., IP, X.25, FrameRelay) context is a data structure present on both the serving GPRS support node (SGSN) and the gateway GPRS support node (GGSN) which contains the subscriber's session information when the subscriber has an active session.