Description
E-UTRA/EPC represents the standard and original system architecture for 4G LTE networks, where the Enhanced Universal Terrestrial Radio Access (E-UTRA) radio network is connected to the Evolved Packet Core (EPC). In this configuration, the LTE base station, known as the Evolved Node B (eNB), communicates with the EPC via the S1 interface. The S1 interface is split into the control plane (S1-MME), which connects the eNB to the Mobility Management Entity (MME) for signaling, and the user plane (S1-U), which connects the eNB to the Serving Gateway (S-GW) for data traffic. The EPC, comprising the MME, S-GW, Packet Data Network Gateway (P-GW), and Home Subscriber Server (HSS), manages mobility, session management, policy enforcement, and interconnection to external packet data networks (e.g., the internet). When a User Equipment (UE) attaches to the network, it performs an Attach procedure with the MME, which authenticates the subscriber via the HSS and establishes a default bearer through the S-GW and P-GW. All data packets are tunneled using the GPRS Tunneling Protocol (GTP) over the S1-U and S5/S8 interfaces. This architecture is fully IP-based and was designed for efficient packet-switched communication, supporting high data rates, low latency, and quality of service (QoS) differentiation through dedicated bearers. It forms the backbone of commercial LTE networks worldwide, providing the connectivity for mobile broadband services. The E-UTRA/EPC system is defined to work independently, but it also serves as the anchor for evolved system architectures like E-UTRA/5GC.
Purpose & Motivation
E-UTRA/EPC was created to establish a high-performance, all-IP mobile network architecture that could overcome the limitations of previous 3GPP systems. Prior 3G UMTS networks used a complex, hierarchical radio network controller (RNC) architecture and a core network that still supported circuit-switched voice, which was inefficient for the burgeoning data traffic. The primary problems addressed were high latency, architectural bottlenecks at the RNC, and the inability to scale cost-effectively for packet data. The E-UTRA/EPC architecture was motivated by the need for a simplified, flat network design that reduced the number of network elements in the data path, thereby lowering latency and operational costs. It was designed from the outset to support only packet-switched traffic, optimizing for the internet protocol and enabling seamless mobility and service continuity. This architecture allowed mobile operators to meet the explosive demand for mobile broadband driven by smartphones and applications, providing a significantly improved user experience over 3G. It set the standard for 4G and became the workhorse for global mobile connectivity for over a decade.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (16 CRs across 4 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the primary new introduction for the E-UTRA/EPC function was the foundational support for E-UTRA to connect to the 5G Core network (5GC), enabling new UE states like RRC_INACTIVE and procedures for this dual-core connectivity. This included specifying mobility procedures between E-UTRA/5GC and the legacy E-UTRA/EPC system. Furthermore, the release addressed detailed protocol corrections and clarifications for this new architecture, covering areas such as paging, system information provision in connected mode, and procedures for Unified Access Control (UAC).
- Capture NR agreements into 36.331 for E-UTRA connected to 5GC TS 36.331CR3475
- Miscellaneous corrections on E-UTRA connected to 5GCN TS 36.331CR3586
- Open issues on E-UTRA connected to 5GC for UAC TS 36.331CR3587
- Open issues on E-UTRA connected to 5GC for INACTIVE TS 36.331CR3588
- Corrections for E-UTRA connected to 5GC TS 36.331CR3653
- Correction for E-UTRA connected to 5GC Procedures TS 36.331CR3698
+ 3 more changes
In Release 16, a key new feature for E-UTRA/EPC was the introduction of an on-demand system information block (SIB) procedure for UEs in the RRC_CONNECTED state. This enhancement allowed connected mode UEs to request specific system information on demand, rather than relying solely on periodic broadcasts. The release included subsequent corrections and refinements to the procedural text for this new on-demand SIB mechanism.
In Release 17, the key new feature for E-UTRA/EPC was the introduction of support for User Plane (UP) IP for EPC-connected architectures using the NR Packet Data Convergence Protocol (PDCP). This enhancement allows the E-UTRA radio access to utilize the more advanced NR PDCP protocol layer while remaining connected to the legacy Evolved Packet Core, facilitating a more efficient user plane data path. This update integrates a core protocol from the 5G NR system into the 4G architecture to improve performance without requiring a full migration to the 5G Core.
In Release 18, changes for E-UTRA/EPC included a correction regarding the availability of flight path information specifically when a UE is connected to a 5G Core network. Furthermore, a correction was made concerning System Information reception procedures for a UE in the RRC_CONNECTED state. These updates clarified operational behaviors within the existing E-UTRA/EPC architecture without introducing new major features.
Explore further
Broader topics and technologies where E-UTRA/EPC plays a role.
Defining Specifications
3GPP specifications that define or reference E-UTRA/EPC, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |