Next Generation Networks

Description

Within 3GPP, Next Generation Networks (NGN) represents the overarching architectural evolution from traditional, siloed telecommunication networks (PSTN, legacy mobile core) towards a unified, packet-based infrastructure capable of delivering a wide range of multimedia services. The core technical realization of NGN in 3GPP is the IP Multimedia Subsystem (IMS), defined as a subsystem within the packet-switched domain. IMS provides a standardized service delivery platform that uses Session Initiation Protocol (SIP) for session control and runs over IP transport, decoupling service logic from access technology.

NGN/IMS works by introducing a layered architecture. The transport layer provides IP connectivity, the control layer (comprising CSCF - Call Session Control Functions) handles SIP signaling for session establishment, modification, and termination, and the application layer hosts the actual service logic (Application Servers). Key components include the HSS (Home Subscriber Server) for user data, and various border control functions (P-CSCF, I-CSCF, S-CSCF) that manage network access and routing. This setup allows for the delivery of voice (VoIP), video, messaging, and other rich communication services with appropriate quality of service (QoS) and charging controls, independent of whether the user is on a GSM, WCDMA, LTE, or even fixed broadband access.

Its role expanded with later 3GPP releases to encompass the entire Evolved Packet Core (EPC) for LTE, which is the pure-IP core network for 4G. Here, NGN principles are fully realized with a flat, all-IP architecture supporting high-speed data and voice via IMS (VoLTE). The NGN framework ensures service continuity, interoperability with legacy systems, and a migration path for operators. It is the foundation for Fixed-Mobile Convergence (FMC), enabling seamless services across different access networks, and it paved the way for the fully cloud-native, service-based architecture of the 5G Core (5GC).

Purpose & Motivation

NGN was conceived to solve critical limitations of legacy telecom networks, which were built on dedicated, circuit-switched technology for each service (e.g., one network for voice, another for data). This model was inefficient, costly to scale, and inflexible for introducing new multimedia services. The primary problem was the inability to converge services onto a single, efficient infrastructure and the high operational cost of maintaining multiple parallel networks.

The motivation for NGN, and specifically IMS within 3GPP, was to leverage the ubiquity and efficiency of Internet Protocol (IP) to create a future-proof service platform. It aimed to enable rich, real-time multimedia communications (beyond simple voice) and to break down the barriers between fixed, mobile, and internet services. This addressed the operator's need to compete with Over-the-Top (OTT) service providers and to generate new revenue streams from bundled communication packages.

Historically, starting from 3GPP Release 5 (where IMS was first specified), NGN provided the strategic answer to the 'all-IP' transformation. It solved the problem of how to deliver carrier-grade voice and messaging over packet networks with the required reliability, security, and charging capabilities that best-effort internet services lacked. By standardizing IMS, 3GPP ensured global interoperability for multimedia services, facilitating the eventual sunset of circuit-switched networks and enabling the successful transition to 4G LTE and 5G, where all services, including voice, are delivered as data over IP.