Subject: Mobile Computing

Difficulty: Medium

Marks: 4 Marks

Serving GPRS Support Node: (SGSN):

• A seving GPRS support node (SGSN) is at the same hierarchical level as the MSC. Whatever MSC does for voice, SGSN does the same functions for packet data. SGSN‘s tasks include packet switching, routing and transfer, mobility management (attach/detach and location management), logical link management, and authentication and charging functions.
• SGSN processes registration of new mobile subscribers and keeps a record of their location inside a given service area. The location register of the SGSN stores location information (e.g., current cell, current VLR) and user profiles of all GPRS users registered with this SGSN.
• SGSN sends queries to Home Location Register (HLR) to obtain profile data of GPRS subscribes.The SGSN is connected to the base station system with Frame Relay.

Gateway GPRS Support Node (GGSN):

• A gateway GPRS support node (GGSN) acts as an interface between the GPRS backbone network and the external packet data networks. GGSN‘s function is similar to that of a router in a LAN.
• GGSN maintains routing information that is necessary to tunnel the Protocol Data Units (PDUs) to the SGSNs that service particular mobile stations. It converts the GPRS packets coming from the SGSN into the appropriate packet data protocol (PDP) format for the data networks like Internet or X.25.
• PDP sends these packets out on the corresponding packet data network. In the other direction, PDP receives incoming data packets from data networks and converts them 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 also performs authentication and charging functions related to data transfers.