Description
3GPP Release 1999, often abbreviated as R99 or Rel-99, is the initial set of specifications that defined the Universal Mobile Telecommunications System (UMTS), the third-generation (3G) mobile network technology. It was a monumental release that introduced a completely new radio access network, the UMTS Terrestrial Radio Access Network (UTRAN), based on Wideband Code Division Multiple Access (WCDMA) technology. Simultaneously, it evolved the existing 2G GSM core network by introducing a packet-switched domain alongside the circuit-switched domain, creating a split architecture that would define mobile networks for decades.
The architecture of R99 is characterized by two main domains. The UTRAN consists of Node Bs (base stations) and Radio Network Controllers (RNCs). The WCDMA air interface uses 5 MHz carriers and employs CDMA spreading codes to separate users, supporting variable data rates up to 384 kbps for early high-speed data services. The core network is divided into the Circuit-Switched (CS) domain, built upon the GSM Mobile Switching Centre (MSC), and the Packet-Switched (PS) domain, which introduced new nodes: the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN). The SGSN manages mobility and session management for packet data users, while the GGSN acts as the gateway to external packet data networks like the internet. A critical interface, the Iu, connects the UTRAN to both the CS and PS core domains, separating transport from control through the use of ATM (Asynchronous Transfer Mode) as the primary transport technology.
How the system works involves distinct procedures for voice and data. For a voice call, signalling establishes a dedicated circuit through the UTRAN and CS core. For packet data, a Packet Data Protocol (PDP) context is activated between the UE and the GGSN, creating a virtual tunnel for IP traffic. The RNC performs key radio resource management functions like handover, power control, and congestion control. R99's role was to provide a clear evolutionary path from GSM/GPRS networks, allowing operators to overlay a new radio network while reusing and upgrading their core assets. Its specifications, particularly the 21-series (requirements) and 25-series (radio aspects), laid down principles for quality of service (QoS) classes, security mechanisms (based on but enhanced from GSM), and service architecture that influenced all later releases.
Purpose & Motivation
Release 1999 was created to fulfill the International Telecommunication Union's (ITU) vision for International Mobile Telecommunications-2000 (IMT-2000)—a global standard for 3G providing significantly higher data rates, support for multimedia services, and improved spectral efficiency compared to 2G. The primary problem it solved was the limited data capability of GSM and GPRS, which were insufficient for emerging internet applications. It also aimed to create a single, global standard to replace the fragmented 2G landscape, although multiple radio interfaces (UTRA FDD & TDD) were ultimately defined.
The historical context is crucial. In the late 1990s, the internet was booming, and mobile operators needed a technology to offer 'mobile broadband.' The European-led 3GPP consortium was formed to develop a 3G standard based on the evolved GSM core network. R99's purpose was to make a decisive technological leap while ensuring backward compatibility and a smooth migration path. It addressed the limitations of previous approaches by introducing a wideband air interface (WCDMA) for higher capacity and data rates, and a native packet-switched core to efficiently handle bursty IP data, moving beyond the circuit-switched data services of GSM. This release set the stage for the mobile data revolution, enabling the first viable mobile web browsing, video calling, and corporate data access services.
Key Features
- Introduction of UTRAN with WCDMA (UTRA FDD) air interface using 5 MHz bandwidth
- Split core network with Circuit-Switched (MSC) and Packet-Switched (SGSN/GGSN) domains
- Support for theoretical peak data rates of 384 kbps in the downlink
- Definition of the Iu interface (Iu-CS and Iu-PS) between UTRAN and core, using ATM transport
- Enhanced security with mutual authentication and stronger ciphering algorithms
- Four QoS classes: Conversational, Streaming, Interactive, and Background
Evolution Across Releases
Although the specifications are labelled 'Release 1999,' the formal publication and functional freeze occurred in early 2000, and it is often catalogued under the 3GPP Release 4 series. The initial architecture defined the complete UTRAN (Node B, RNC) and the split CS/PS core network. It established all fundamental protocols for radio resource control (RRC), radio link control (RLC), medium access control (MAC), and the core network interfaces like Iu, Gn, and Gi, creating a fully functional 3G system specification ready for commercial deployment.
Defining Specifications
| Specification | Title |
|---|---|
| TS 21.905 | 3GPP TS 21.905 |