GSM was designed primarily for voice (circuit-switched). Data was an afterthought, limited to 9.6 kbps. As the internet grew, there was massive demand for wireless packet data (email, web browsing, WAP). GPRS added packet-switched data service to GSM without replacing the voice infrastructure — “2.5G.”
GPRS (General Packet Radio Service) adds packet-switching capability to the existing GSM circuit-switched voice network. It creates a parallel packet network (using the same air interface and base stations) optimized for bursty data traffic instead of continuous voice.
- Architecture Addition: Two new network elements are added to GSM:
- SGSN (Serving GPRS Support Node): Handles packet routing, mobility, and authentication for data
- GGSN (Gateway GPRS Support Node): Interfaces GPRS to the internet (IP networks)
- Channel Allocation: Data uses physical channels differently than voice:
- Up to 8 timeslots can be combined for a single user
- Channels are dynamically allocated only when data traffic exists
- No dedicated circuit — shared, packet-based
- New Air Interface:
- Uses the same TDMA/FDMA frame structure but with new channel coding schemes (CS-1 to CS-4, up to 21.4 kbps per timeslot)
- Theoretical maximum: 171.2 kbps (8 timeslots × 21.4 kbps)
- Practical: 40–50 kbps typical, up to 115 kbps in best conditions
- Data Packets: All data is in IP packets, routed through the GPRS backbone
- Always-On: No dial-up — IP address is assigned and connection is always available
- Packet-switched: bandwidth used only when transmitting data, not continuously
- Dynamic allocation: 1–8 timeslots per user based on traffic
- Theoretical max: 171.2 kbps; typical 40–50 kbps
- Always-on IP connection; no circuit establishment delay
- Works simultaneously with voice (uses different channel set from voice)
- First deployed in 2000; enabled first mobile internet era
- Built from: GSM Architecture — GPRS builds on existing GSM infrastructure
- Built into: GSM — GPRS is an integral part of GSM Phase 2+ specifications
- Builds into: EDGE — EDGE (3G) builds on GPRS infrastructure
- Related: WCDMA — the competing 3G technology
- Related: SMS — SMS was separate from GPRS; both now use the GPRS backbone
- GPRS was never intended for streaming video or high-speed data — too slow
- First-gen GPRS was often sold as “wireless internet” with poor throughput
- Billing: early GPRS was charged per packet (kilobyte), causing bill shocks
- Handover between voice and data: GSM handles voice first; data gets preempted