SGSN

SGSN stands for Serving GPRS Support Node. It is a core network element used in GSM and its GPRS extension to provide packet data services. The SGSN is responsible for delivering data packets to and from mobile stations within its service area, handling user mobility, session management, authentication, charging, and quality of service.

Key functions include mobility management, such as attach/detach procedures and location updates, and session management through PDP context activation and deactivation. When a data session is established, the SGSN allocates an IP address to the mobile device and maintains the routing information and QoS parameters for the session. It then tunnels user data to the gateway GPRS support node (GGSN) over the GPRS Tunneling Protocol (GTP), enabling access to external networks. The SGSN also manages security functions, authenticating subscribers with data from the home subscriber data repository (via the HLR and authentication center) and enforcing policy and charging rules.

In operation, the SGSN communicates with other network elements through various signaling interfaces. It exchanges subscriber data and authentication information with the Home Location Register and the authentication center, and coordinates with the GGSN to establish and maintain GTP tunnels for user plane traffic. It supports roaming and handovers by coordinating with appropriate mobile network elements.

Deployment and evolution: In traditional GSM/GPRS networks, multiple SGSN nodes serve different routing areas and can interwork with multiple GGSNs. With the advent of 3G and later LTE, the core network architecture has evolved, reducing the central role of SGSN in favor of newer nodes such as the S-GW and PGW in the evolved packet core, though the term and concept remain relevant in legacy GPRS deployments.