The Serving GPRS Support Node (SGSN) is a main component of the GPRS network, which handles all packet switched data within the network, e.g. the mobility management and authentication of the users. The SGSN performs the same functions as the MSC for voice traffic. The SGSN and the MSC are often co-located.
The SGSN is connected to the BSC. The SGSN is the service access point to the GPRS network for the mobile user. On the other side the SGSN relays the data between the SGSN and relevant GGSN (and vice versa). The SGSN handles the protocol conversion from the IP used in the backbone network to the sub-network-dependent convergence protocol (SNDCP) and logical link control (LLC) protocols used between the SGSN and the mobile users. These protocols handle compression and ciphering. The SGSN is also responsible for the authentication of GPRS mobiles. When the authentication is successful, the SGSN handles the registration of the mobile to the GPRS network and takes care of its mobility management.