Description
The Evolved Packet System (EPS) is the complete network system defined by 3GPP for Long-Term Evolution (LTE) wireless communication. It comprises two main domains: the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), consisting of evolved NodeBs (eNBs), and the Evolved Packet Core (EPC). The EPS architecture is a radical departure from previous 3GPP systems, adopting an all-IP, flat design with fewer network nodes to reduce latency and improve data throughput. Its primary function is to provide secure, seamless IP connectivity between User Equipment (UE) and external packet data networks (PDNs), such as the internet or private corporate networks.
At the heart of the EPC are several key logical entities. The Mobility Management Entity (MME) handles control-plane functions like NAS signaling, UE authentication, tracking area management, and bearer establishment. The Serving Gateway (S-GW) is the user-plane anchor during intra-LTE handovers and routes data packets between the eNB and the Packet Data Network Gateway (P-GW). The P-GW is the critical interface to external PDNs, performing IP address allocation, policy enforcement, charging, and packet filtering. Other essential components include the Home Subscriber Server (HSS) for subscriber data and the Policy and Charging Rules Function (PCRF) for quality-of-service (QoS) and charging policy. Connectivity is managed through EPS bearers—logical tunnels with specific QoS characteristics that extend from the UE to the P-GW.
The EPS works by establishing a default EPS bearer when a UE attaches to the network, providing always-on IP connectivity. This bearer is associated with an IP address and a default QoS profile. Dedicated bearers with guaranteed bit rates (GBR) can be established on-demand for services like VoIP or video streaming. The control plane (signaling) and user plane (data) are separated, with the S1 interface (S1-MME for control, S1-U for user) connecting E-UTRAN to EPC. The system supports mobility within LTE (via X2-based handovers between eNBs), mobility to/from legacy 2G/3G networks (via the S3/S4 interfaces to SGSN), and idle-mode mobility with tracking area updates. Security is provided by mutual authentication between UE and network using keys from the HSS and ciphering/integrity protection of signaling and data bearers.
Purpose & Motivation
The EPS was created as part of the 3GPP LTE project initiated around 2004 to address the exploding demand for mobile data and the limitations of the existing 3G UMTS/HSPA architecture. The UMTS core network (GPRS Core) was an evolution of GSM's circuit-switched design, with complex hierarchies and multiple tunneling protocols, leading to higher latency and suboptimal data efficiency. The industry needed a system optimized for packet-switched data from the ground up to support high-speed, low-latency services like mobile video, real-time gaming, and VoIP.
The primary purpose of the EPS was to simplify the network architecture, dramatically reducing the number of nodes involved in data transfer to lower cost and latency. It introduced a "flat" architecture where the eNB connects directly to the gateway (S-GW/P-GW), eliminating the Radio Network Controller (RNC) of 3G. This all-IP design simplifies transport, reduces operational expenses, and facilitates the introduction of new services. Furthermore, EPS was designed to seamlessly interwork with existing 3GPP (2G/3G) and non-3GPP (e.g., Wi-Fi, CDMA) access technologies, providing service continuity. It solved the problem of network complexity and latency, enabling the 4G mobile broadband experience. The EPS, with its EPC, formed the backbone for LTE services and later evolved to become the foundation integrated with the 5G Core (5GC) in 5G non-standalone (NSA) deployments.
Classification
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (346 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, key enhancements for the Evolved Packet System (EPS) included raising the maximum number of supported EPS bearers from eight to fifteen, requiring updates to UE and network NAS capabilities and bearer ID support. The release also introduced Early Data Transmission for Control Plane CIoT EPS optimization and refined inter-system mobility procedures with 5GS, including the handling of S-NSSAI and the establishment of mapped EPS security contexts. Furthermore, it extended the EPS QoS IE for higher maximum bitrates and provided clarifications for using more than eight EPS bearers.
- Per EPS bearer, RAN selection of DC (or non-DC) usage TS 23.401CR3258
- Feature definition for supporting 15 EPS bearers TS 23.401CR3396
- UE Capability for supporting 15 EPS bearers TS 23.401CR3419
- Introducing Early Data Transmission for Control Plane CIoT EPS optimization TS 23.401CR3436
- Handling of S-NSSAI and PDU session ID during mobility between EPS and 5GS TS 24.301CR2965
- Mode selection for inter-system change between EPS and 5GS TS 24.301CR2979
+ 86 more changes
In Release 16, the EPS saw enhancements for interworking with 5GS, including support for Multi-Access PDU sessions from a 5G-RG with and without the N26 interface. It introduced new capabilities such as Integrated CAPIF for network exposure, support for IAB nodes and RACS within the EPS architecture, and refined procedures for EPS bearer context activation and small data rate control parameter handling. Additional updates included enhancements for IoT, such as NIDD LI, and security improvements like UE capability protection using AS security.
- Integrated CAPIF with 3GPP EPS and 5GS network exposure TS 23.222CR0021
- EPS architecture supporting RACS TS 23.401CR3510
- Support for IAB in EPS TS 23.401CR3555
- Support for IAB indication and authorization in EPS TS 23.401CR3570
- Default EPS bearer context activation for accessing RLOS TS 24.301CR3194
- Small data rate control parameters received in EPS TS 24.301CR3245
+ 65 more changes
In Release 17, the primary enhancements to the Evolved Packet System (EPS) focused on introducing comprehensive support for Multi-USIM (MUSIM) devices. This included new procedures like the Service Request for removing paging restrictions, mechanisms for paging cause handling and paging rejection, and the introduction of an IMSI Offset to the Attach and TAU procedures. Additionally, the release introduced EPS User Plane Integrity Protection support indication with minimal core network changes.
- EPS User Plane Integrity Protection with minimal core network changes TS 23.401CR3645
- Paging Cause feature for EPS TS 24.301CR3503
- Using Service Request procedure for removing paging restrictions in EPS for a Multi-USIM UE TS 24.301CR3517
- Handling the paging cause in the UE for MUSIM mode in EPS TS 24.301CR3520
- Leaving procedure and Reject Paging Indication for Multi-USIM UEs in EPS TS 24.301CR3534
- Introducing IMSI Offset to Attach and TAU procedures for MUSIM handling in EPS TS 24.301CR3527
+ 86 more changes
In Release 18, the EPS saw the introduction of URSP (UE Route Selection Policy) provisioning procedures, enabling policy delivery to UEs over the 4G system. It also added support for enhanced discontinuous coverage, including capability negotiation and UE unavailability period reporting, and defined procedures for PCF-triggered UE mobility from 5GS to EPS. Furthermore, the release extended authorization and procedures for A2X direct C2 communications within the EPS architecture.
- Authorization of A2X Direct C2 Communications in EPS TS 24.301CR3881
- Authorization of A2X direct C2 communication in EPS - additional procedures TS 24.301CR3891
- Capability negotiation for enhanced discontinuous coverage - EPS TS 24.301CR3920
- URSP provisioning in EPS - procedures TS 24.301CR3897
- Overview of URSP provisioning in EPS TS 24.301CR3935
- URSP provisioning in EPS procedure TS 24.301CR3936
+ 41 more changes
In Release 19, EPS was enhanced to introduce support for Disaster Roaming, including specific call flows and handling within procedures like DETACH and REJECT. The release also added mechanisms for the Control of UE RAT utilization by EPS and introduced new capabilities such as the definition of an EPS update type and the inclusion of a Pending PDN Connection Restoration Indication during mobility to 5GS. Furthermore, features like initial paging with priority and the control of time reference information delivery were introduced to expand EPS functionality.
- Subscription control for time reference information delivery in EPS TS 23.401CR3796
- Introduction of Disaster roaming support in EPS(General clause) TS 23.401CR3945
- Introduction of Disaster roaming support in EPS(Call flows) TS 23.401CR3946
- Control of UE RAT utilization by EPS TS 24.301CR4077
- List of USS addresses in EPS TS 24.301CR4114
- No-transmit zone restriction in EPS TS 24.301CR4115
+ 38 more changes
Explore further
Broader topics and technologies where EPS plays a role.
Defining Specifications
3GPP specifications that define or reference EPS, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TR 22.937 vd00 | FMC requirements for 3GPP-WLAN service continuity | Rel-13 |
| TS 23.003 vj50 | Numbering, addressing and identification in 3GPP | Rel-19 |
| TS 23.060 vj00 | GPRS Service Description Stage 2 | Rel-19 |
| TS 23.139 vj00 | 3GPP-Fixed Broadband Interworking Stage 2 | Rel-19 |
| TS 23.179 vd50 | MCPTT Functional Architecture | Rel-13 |
| TS 23.180 vj10 | MC services support in IOPS mode | Rel-19 |
| TS 23.221 vj00 | 3GPP System Architectural Requirements | Rel-19 |
| TS 23.222 vj80 | Common API Framework for 3GPP Northbound APIs | Rel-19 |
| TS 23.246 vj00 | MBMS Bearer Service Stage 2 Description | Rel-19 |
| TS 23.261 vj00 | IP Flow Mobility between 3GPP and WLAN | Rel-19 |
| TS 23.280 vk10 | Common Architecture for Mission Critical Services | Rel-20 |
| TS 23.286 vj00 | V2X Application Enabler Architecture | Rel-19 |
| TS 23.327 vd10 | 3GPP-WLAN Mobility Stage 2 Description | Rel-13 |
| TS 23.379 vk00 | MCPTT Functional Architecture | Rel-20 |
| TS 23.401 vj50 | Evolved Packet System (EPS) Stage 2 Description | Rel-19 |
| TS 23.402 vj00 | EPC for Non-3GPP Access (PMIP) | Rel-19 |
| TS 23.632 vj10 | 5G User Data Interworking and Migration | Rel-19 |
| TR 23.732 vg00 | User Data Interworking, Coexistence, Migration Study | Rel-16 |
| TS 23.795 vg10 | V2X Application Architecture Study | Rel-16 |
| TS 23.839 vc00 | Fixed-Mobile Convergence Architecture Study | Rel-12 |
| TS 23.857 vb00 | EPC Node Failure & Restoration Study | Rel-11 |
| TS 23.893 v800 | IMS Multimedia Session Continuity Study | Rel-8 |
| TS 23.894 va00 | IMS Local Breakout & Optimal Media Routing Study | Rel-10 |
| TS 23.896 vc00 | Policy & Charging Control for Fixed Broadband Convergence | Rel-12 |
| TR 23.973 vj00 | Separate HSS/UDM Deployment Scenarios & Solutions | Rel-19 |
| TS 24.171 vj00 | NAS Protocol for LCS in E-UTRAN | Rel-19 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 24.301 vj60 | NAS protocol for Evolved Packet System | Rel-19 |
| TS 24.302 vj00 | Access to EPC via non-3GPP networks; Stage 3 | Rel-19 |
| TS 24.303 vj00 | Dual-Stack MIPv6 Mobility Management | Rel-19 |
| TS 24.305 vj00 | Selective Disabling of 3GPP UE Capabilities | Rel-19 |
| TS 24.483 vj20 | Mission Critical Services Management Object | Rel-19 |
| TS 24.484 vj30 | MCS Configuration Management | Rel-19 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 24.623 vj00 | XCAP Protocol for Supplementary Services | Rel-19 |
| TS 24.801 v810 | CT1 SAE NAS Aspects for EPC | Rel-8 |
| TS 24.890 vg00 | 5G NAS Protocol for 5GS Stage 3 | Rel-16 |
| TS 26.501 vj30 | 5G Media Streaming (5GMS) Architecture | Rel-19 |
| TS 26.802 vj20 | Multicast Enhancements for 5G Media Streaming | Rel-19 |
| TS 26.804 vj10 | 5G Media Streaming Extensions Study | Rel-19 |
| TS 28.540 vk10 | 5G Network Resource Model (NRM) Management | Rel-20 |
| TS 28.631 vj00 | Inventory Management NRM IRP Requirements | Rel-19 |
| TS 28.707 vj00 | EPC NRM IRP Requirements | Rel-19 |
| TS 28.849 vj10 | CAPIF Phase2 Charging Study | Rel-19 |
| TS 29.061 vj00 | Packet Domain Interworking for PLMN | Rel-19 |
| TS 29.168 vj00 | SBc-AP Protocol Specification | Rel-19 |
| TS 29.274 vj50 | GTPv2-C Control Plane Protocol Specification | Rel-19 |
| TS 29.305 vj00 | Interworking Functions for EPS-Legacy Systems | Rel-19 |
| TS 29.507 vj40 | 5G Access & Mobility Policy Control Service | Rel-19 |
| TS 29.513 vj40 | 5G PCC Signalling Flows & QoS Mapping | Rel-19 |
| TS 29.525 vj40 | 5G UE Policy Control Service Stage 3 | Rel-19 |
| TS 29.805 v800 | IWF for MAP-Diameter Interworking | Rel-8 |
| TS 31.102 vj40 | USIM Application Specification | Rel-19 |
| TS 31.111 vj30 | USIM Application Toolkit (USAT) Specification | Rel-19 |
| TS 31.121 vi50 | UICC-terminal interface test specification | Rel-18 |
| TS 32.240 vj40 | Charging Management Architecture & Principles | Rel-19 |
| TS 32.251 vj00 | PS Domain Charging Management | Rel-19 |
| TS 32.252 vc00 | 3GPP WLAN Interworking Charging | Rel-12 |
| TS 32.273 vj00 | MBMS Charging Management | Rel-19 |
| TS 32.295 vj00 | 3GPP Charging: CDR Transfer via GTP' Protocol | Rel-19 |
| TS 32.296 vj00 | Online Charging System (OCS) Architecture | Rel-19 |
| TS 32.297 vj00 | Charging Data Record File Transfer | Rel-19 |
| TS 32.404 vj00 | Performance Management Definitions & Template | Rel-19 |
| TS 32.425 vj00 | E-UTRAN Performance Measurements | Rel-19 |
| TS 32.450 vj00 | E-UTRAN Key Performance Indicators (KPI) Definitions | Rel-19 |
| TS 32.451 vj00 | KPI Requirements for E-UTRAN | Rel-19 |
| TS 32.641 vb00 | UTRAN Network Resources IRP Requirements | Rel-11 |
| TR 32.847 vi00 | Technical Report | Rel-18 |
| TS 33.107 vj00 | Lawful Interception Architecture & Functions | Rel-19 |
| TS 33.108 vj00 | LI Handover Interface Specification | Rel-19 |
| TS 33.401 vj10 | EPS Security Architecture | Rel-19 |
| TS 33.402 vj00 | Security for non-3GPP access to EPS | Rel-19 |
| TS 33.501 vk00 | 5G Security Architecture and Procedures | Rel-20 |
| TS 33.820 v1830 | Home NodeB/eNodeB Security Architecture | Rel-8 |
| TR 33.853 vh00 | Study on User Plane Integrity Protection | Rel-17 |
| TS 33.856 vg10 | Security for 5G to 3G Voice Continuity | Rel-16 |
| TS 33.859 vb10 | UTRAN Key Hierarchy Enhancement Study | Rel-11 |
| TS 33.863 ve20 | Security for Battery-Efficient IoT Device to Enterprise | Rel-14 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
| TS 36.304 vj00 | UE Idle Mode Procedures in E-UTRA | Rel-19 |
| TS 36.323 vj00 | PDCP Protocol Specification | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 36.401 vj00 | E-UTRAN Overall Architecture Description | Rel-19 |
| TS 36.410 vj00 | S1 Interface: General Aspects and Principles | Rel-19 |
| TS 36.413 vj10 | S1 Application Protocol (S1AP) | Rel-19 |
| TS 36.456 vj00 | SLm Interface Introduction | Rel-19 |
| TS 36.509 vh40 | EPC Special UE Conformance Testing Functions | Rel-17 |
| TS 36.887 vc00 | Energy Saving Enhancement for E-UTRAN Study | Rel-12 |
| TR 37.901 vf10 | UE Application Layer Data Throughput Performance | Rel-15 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TS 43.129 vj00 | PS Handover in GERAN A/Gb and GAN Modes | Rel-19 |
| TS 48.008 vj00 | BSS-MSC Interface Layer 3 Procedures | Rel-19 |
