What are SGSN and GGSN in the GPRS architecture, and what roles do they play?

SGSN (Serving GPRS Support Node) handles routing and mobility for data sessions within the network; GGSN (Gateway GPRS Support Node) connects the GPRS network to external data networks like the internet.

SGSN — Serving GPRS Support Node:

• Connected to the BSC via the Gb interface
• Handles routing of data packets to/from the mobile device
• Manages mobility — tracks which cell the device is in
• Handles session management — establishes and maintains data sessions
• Analogous to the MSC but for packet data

GGSN — Gateway GPRS Support Node:

• The gateway to external networks (internet, corporate networks)
• Assigns IP addresses to mobile devices
• Routes packets between the GPRS backbone and external networks
• Analogous to the GMSC but for packet data

Architecture comparison:

Voice: MS → BTS → BSC → MSC → GMSC → PSTN
Data:  MS → BTS → BSC → SGSN → GGSN → Internet

Tip: Think of it as two parallel highways sharing the same on-ramp (BTS/BSC). Voice traffic goes left to the MSC, data traffic goes right to the SGSN. Both share the same radio resources but diverge at the BSC level.

Go deeper:

• GPRS network architecture — SGSN & GGSN (Electronics Notes) — how the packet core overlays GSM: the SGSN's mobility/session role and the GGSN as the gateway to external IP networks.