GGSN - Gateway GPRS Support Node

A gateway GPRS support node (GGSN) acts as an interface between the GPRS backbone network and the external packet data networks (radio network and the IP network). It converts the GPRS packets coming from the SGSN into the appropriate packet data protocol (PDP) format (e.g. IP or X.25) and sends them out on the corresponding packet data network. In the other direction, PDP addresses of incoming data packets are converted to the GSM address of the destination user. The readdressed packets are sent to the responsible SGSN. 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 UE (User Equipment).The GGSN also performs authentication and charging functions

SGSN - Serving GPRS Support Node

A Serving GPRS Support Node (SGSN) is responsible for the delivery of data packets from and to the mobile stations within its geographical service area. Its tasks include packet routing and transfer, mobility management (attach/detach and location management), logical link management, and authentication and charging functions. 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 this SGSN.

Common SGSN Functions

• Detunnel GTP packets from the GGSN (downlink)
• Tunnel IP packets toward the GGSN (uplink)
• Carry out mobility management as Standby mode mobile moves from Routing Area to Routing Area.
• Billing user data