The parts of the GPRS system that carry out the switch of packet data are called the Serving GPRS Support Node (SGSN) and the Gateway GPRS Node (GGSN). The SGSN provides a packet routing to and from the geographical SGSN service area. The GGSN makes up the interface towards the external IP packet networks, the SGSN.GGSN is physically separated from the circuit-switched part of the GSM system. The other parts of the GPRS architecture utilize the current GSM network elements.
Figure 20 GPRS Logical Architecture
(Adapted from ETIS 1998 EN 301 344)