General Packet Radio Service

Description

General Packet Radio Service (GPRS) is a packet-oriented mobile data standard that overlays the circuit-switched GSM network. It introduced a new packet-switched core network architecture alongside the existing circuit-switched core. The key components are the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN). The SGSN manages the mobility and session for mobile devices within its service area, handling functions like attachment, authentication, and routing data packets to/from the correct Base Station System (BSS). The GGSN acts as the gateway between the GPRS network and external Packet Data Networks (PDNs), like the internet or a corporate intranet. It assigns IP addresses to mobile devices and routes IP packets.

On the radio access side, GPRS uses the same TDMA frames and frequencies as GSM but allocates time slots dynamically for data traffic. Multiple users share the same time slots through statistical multiplexing, a significant efficiency improvement over dedicated circuit-switched channels. GPRS introduced new channel types (PDCHs) and coding schemes to adapt to varying radio conditions. A mobile device establishes a Packet Data Protocol (PDP) context, which is a logical association between the mobile, SGSN, and GGSN defining the session parameters, including the requested QoS profile and the assigned IP address.

Data is transported using GPRS Tunneling Protocol (GTP) over IP-based interfaces (Gn between SGSN/GGSN, Gb between BSS and SGSN). This tunneling encapsulates user data and signaling, enabling mobility across SGSNs without disrupting the IP session. GPRS laid the groundwork for later 3G/4G/5G packet cores, establishing concepts like always-on connectivity, QoS classes, and volume-based charging. It supported data rates from 9.6 kbps up to theoretically 171.2 kbps (using all 8 time slots), marking the beginning of mobile internet access.

Purpose & Motivation

GPRS was developed to address the severe limitations of circuit-switched data services in GSM (like CSD and HSCSD), which were inefficient, slow, and expensive for bursty, interactive data applications. Circuit-switched connections reserved a dedicated channel for the entire session, leading to poor resource utilization and billing based on connection time, which was unsuitable for web browsing or email.

GPRS was created to bring true packet-switching to mobile networks, inspired by the success of the internet. Its purpose was to enable efficient, 'always-on' data services, allowing multiple applications to share the radio resources dynamically. This solved the problem of resource inefficiency and enabled new usage models like mobile email and web access. It also introduced a billing model based on the volume of data transmitted, which was more aligned with internet service paradigms. GPRS was the critical evolutionary step that transformed GSM from a voice-centric network into a platform for mobile data, paving the way for EDGE, UMTS, and ultimately LTE and 5G.