Evolved Packet Core Routed

Description

EPC-routed refers to user plane traffic that traverses the Evolved Packet Core (EPC) through a Packet Data Network Gateway (PDN GW or P-GW) as part of a PDN Connection. This routing model is fundamental to the 3GPP Evolved Packet System (EPS) architecture, where the P-GW serves as the anchor point for IP address allocation, policy enforcement, and charging. The term distinguishes EPC-routed traffic from other routing paradigms, such as traffic that might be offloaded locally or routed via non-3GPP access without traversing the EPC. It applies uniformly across non-roaming scenarios, roaming with home-routed traffic (where the P-GW resides in the home network), and roaming with local break-out (where the P-GW is in the visited network).

The technical operation of EPC-routed traffic relies on the establishment of a PDN Connection, which is a logical link between the User Equipment (UE) and the P-GW. When the UE attaches to the network, it requests a PDN Connection, and the Serving Gateway (S-GW) forwards user plane packets between the E-UTRAN and the P-GW. The P-GW then routes the packets to external Packet Data Networks (PDNs) such as the Internet or IMS. This architecture ensures that all traffic passes through a consistent anchor point, enabling mobility management, lawful interception, and QoS differentiation. The routing decision is based on the Access Point Name (APN) and subscription policies, and the P-GW applies bearer-level QoS parameters as defined in 3GPP TS 23.203.

Key components involved in EPC-routed traffic include the PDN GW, which acts as the gateway to external networks and allocates IP addresses; the Serving GW, which handles user plane tunneling and mobility anchoring within the EPC; and the Mobility Management Entity (MME), which manages session and mobility signaling. The Policy and Charging Rules Function (PCRF) provides QoS and charging policies to the P-GW, ensuring that EPC-routed traffic adheres to operator-defined rules. This architecture supports multiple access technologies, including E-UTRAN, UTRAN, and non-3GPP accesses, as long as they interface with the EPC.

EPC-routed traffic is crucial for enabling seamless mobility, as the P-GW maintains the IP address and session continuity even when the UE moves between different access networks or base stations. It also facilitates roaming by allowing operators to route traffic either back to the home network (home-routed) or through the visited network (local break-out), depending on business agreements. The term is defined in 3GPP specifications such as TS 23.139 (3GPP system - Fixed Broadband Access interworking), TS 23.203 (Policy and charging control architecture), and TS 23.896 (Technical Report on the support of Fixed Broadband Access interworking). Its consistent definition across releases from Rel-11 to Rel-19 underscores its stable role in the EPS architecture.

Purpose & Motivation

EPC-routed traffic exists to provide a standardized, scalable, and policy-controlled method for delivering IP connectivity to mobile users. Before the introduction of the EPC in Release 8, networks like GPRS and UMTS used a more complex and less efficient gateway architecture (GGSN and SGSN) that struggled to handle the explosive growth of mobile data. The EPC introduced a flatter, all-IP architecture with separate control and user plane functions, and the concept of EPC-routed traffic ensured that all user data flows through a centralized anchor point (the P-GW) for consistent IP address management, charging, and lawful interception. This model simplified roaming and interworking with non-3GPP networks, enabling operators to offer seamless services across diverse access technologies.

The term 'EPC-routed' was formalized in Release 11 as part of efforts to define interworking with fixed broadband access and to clarify routing scenarios for roaming. It addressed the need to distinguish between traffic that stays within the EPC and traffic that might be offloaded locally (e.g., via SIPTO or LIPA) or routed through non-EPC paths. By specifying that EPC-routed traffic applies to non-roaming, home-routed roaming, and local break-out scenarios, 3GPP provided a clear framework for operators to manage traffic routing, ensuring that QoS and charging policies are applied consistently regardless of the user's location. This clarity is essential for supporting emerging services like VoLTE and mission-critical communications, which require guaranteed QoS and lawful interception capabilities.