Packet Switched Public Data Network

Description

A Packet Switched Public Data Network (PSPDN) is a generic telecommunications term adopted within 3GPP to denote any public network infrastructure that offers data transmission services using packet-switching technology. Unlike circuit-switched networks dedicated to voice, a PSPDN breaks data into packets that are routed independently across the network. In the architecture of 2G (GPRS), 3G, and evolved packet core (EPC) networks, the PSPDN represents the external data network destination. The mobile operator's core network acts as an access gateway, connecting the mobile subscriber to this external PSPDN.

The connection is facilitated by specific gateway nodes within the mobile core. In 2G/3G GPRS networks, the Gateway GPRS Support Node (GGSN) serves as the interface between the mobile packet core and external PSPDNs. In the 4G EPC and 5G Core (5GC), the Packet Data Network Gateway (PGW) and User Plane Function (UPF) fulfill a similar role, respectively. When a mobile device activates a Packet Data Protocol (PDP) context or establishes a Protocol Data Unit (PDU) Session for internet access, it is essentially requesting a connection to a specific PSPDN, often identified by an Access Point Name (APN). The gateway node manages the user's IP address allocation, performs routing of IP packets between the mobile network and the PSPDN, and enforces policy and charging rules.

The PSPDN itself is largely outside the scope of 3GPP standardization, as it is the external network. 3GPP specifications define how the mobile network interfaces with it. The PSPDN can be the public Internet, a private corporate network, or an Internet Service Provider's (ISP) network. The mobile network provides the 'access' service to this network. Key protocols involved include IP at the network layer, and the gateway nodes implement functions like firewall, Deep Packet Inspection (DPI), and traffic shaping at the border between the trusted mobile domain and the external PSPDN. The concept is fundamental to the data service offering of any mobile operator.

Purpose & Motivation

The concept of the PSPDN was integral to the development of mobile data services, beginning with GPRS in 2G networks. Its purpose was to formally define the destination for mobile data traffic, separating the mobile operator's access and core transport responsibilities from the services provided by external data networks. Before widespread packet data, mobile networks were primarily circuit-switched for voice, with limited, proprietary data capabilities. The PSPDN model acknowledged that the value of mobile data was in connecting to existing, vast packet-based networks like the Internet.

This separation solved critical architectural and business problems. It allowed mobile network operators to focus on providing reliable, billable access and mobility management without needing to become content or application providers themselves. It enabled a clear demarcation point for billing, security, and policy enforcement. The gateway node (GGSN/PGW) became the policy enforcement point between the operator's controlled network and the untrusted PSPDN. This model facilitated the explosive growth of mobile internet, as users could access the same Internet services from their mobile devices as from fixed lines. The PSPDN remains a core concept, even in 5G, where 'Data Network' (DN) is the analogous term, highlighting the continued architectural principle of connecting mobile users to external packet-based services.

Key Features

• External destination network for mobile data sessions (e.g., Internet)
• Connected via gateway nodes (GGSN, PGW, UPF) in the mobile core
• Identified by an Access Point Name (APN) during session establishment
• Uses standard Internet Protocol (IP) for data transport
• Demarcation point for operator policy, charging, and security controls
• Fundamental to the architecture of mobile packet data services from 2G to 5G

Evolution Across Releases

Defining Specifications