Figure 1 shows the standard GPRS reference model in a
GSM network context [3]. In this model, in addition to the
network components defined in a voice-based GSM network,
such as Home Location Register (HLR), Mobile Switching
Center (MSC), and Base Station Subsystem (BSS), two new
core network functions are required to support GPRS: the
Serving GPRS Support Node (SGSN) and the Gateway GPRS
Support Node (GGSN).
The SGSN monitors the state of the mobile stations and
track their movements within a given geographical area. It is
also responsible for establishing and managing data
connections between mobile users and the destination
network.