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The SGSN is a Core Network switching node within the GPRS network whose primary function is to support the mobile. These functions can be split into four distinct areas:
§ MM (Mobility Management) - When a GPRS mobile attaches to the PS (Packet Switched) domain of the Core Network, the SGSN generates MM information based on the mobile’s current location.
§ SM (Session Management) - Prior to data being routed across the GPRS network with the appropriate QoS (Quality of Service), the mobile must have activated a PDP Context. The SGSN establishes the context within the network based on variables supplied within a PDP Context activation message.
§ Interaction with the GSM Part - The creation of both MM and SM contexts for a subscriber is dependent upon interaction with the HLR (Home Location Register) and AuC (Authentication Centre). Information relating to the users subscription and level of security are contained within these databases. The SGSN may also interface with MSC (Mobile Switching Centre) if CS (Circuit Switched) paging is supported via the GPRS domain.
§ Billing - The SGSN billing function is responsible for monitoring the flow of user data across the GPRS network. CDR (Call Detail Record) are generated at the SGSN before being transferred to the CGF (Charging Gateway Function).
