Description
The Core Network (CN) constitutes the central switching and control infrastructure of a 3GPP mobile network, distinct from the Radio Access Network (RAN). It is responsible for the overall control, management, and routing of user data and signaling traffic. The CN authenticates subscribers, manages their sessions (establishment, modification, release), handles mobility (tracking and handovers between different areas), and provides connectivity to external packet data networks (PDNs) like the internet or private corporate networks. It acts as the anchor point for user services, ensuring service continuity and quality across the network.
Architecturally, the CN has evolved significantly. In 2G/3G (GSM/UMTS), it was split into the Circuit-Switched (CS) domain for voice and the Packet-Switched (PS) domain for data, with key nodes like the Mobile Switching Center (MSC) and Serving GPRS Support Node (SGSN). With the introduction of the IP Multimedia Subsystem (IMS) and the System Architecture Evolution (SAE) for 4G LTE, the CN transitioned to an all-IP, flat architecture. The 4G Evolved Packet Core (EPC) and 5G Core (5GC) are purely packet-based, separating the control plane (CP) and user plane (UP) functions. Key components include the Mobility Management Entity (MME), Serving Gateway (SGW), Packet Data Network Gateway (PGW) in EPC, and the Access and Mobility Management Function (AMF), Session Management Function (SMF), and User Plane Function (UPF) in 5GC.
The CN interfaces with the RAN (e.g., via S1, N2, N3 interfaces), with other CN nodes, and with external networks. It executes critical procedures like Attach, Tracking Area Update, PDU Session Establishment, and Handover. It also enforces policy and charging control (PCC), manages subscriber data in the Home Subscriber Server (HSS) or Unified Data Management (UDM), and provides lawful interception capabilities. In 5G, the CN is designed with cloud-native principles, using a service-based architecture (SBA) with network functions communicating via HTTP/2-based APIs, enabling network slicing, edge computing, and greater automation.
Purpose & Motivation
The Core Network exists to provide the centralized intelligence, control, and switching fabric for a mobile network, decoupling these functions from the radio-specific access layer. Its primary purpose is to enable reliable, secure, and feature-rich mobile services for subscribers. It solves the fundamental problems of user authentication, session and mobility management, service delivery, and interconnection with other networks (both fixed and mobile). Without a CN, the RAN would be a collection of isolated base stations with no ability to route calls, manage user identity, or provide continuous service as users move.
Historically, the CN evolved from telephony-centric circuit-switched networks for voice in 2G to support packet data in 2.5G/3G, leading to a dual-domain architecture. The limitations of this approach—complexity, inefficiency for IP traffic, and difficulty in introducing new services—motivated the move to an all-IP, flatter architecture with 4G EPC and 5G 5GC. The creation of the modern CN was driven by the need for higher data throughput, lower latency, support for a massive number of diverse devices (IoT), and the flexibility to deploy new services rapidly through network virtualization and softwarization.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (25 CRs across 4 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the Core Network introduced support for several legacy Circuit-Switched supplementary services within the IP Multimedia (IM) subsystem, including Flexible Alerting, Terminating Identification Presentation/Restriction, Completion of Communications services, and Advice of Charge. The release also specified enhancements to CN assistance information and clarified the description of CN Tunnel Info. Furthermore, it defined the inclusion of a CN type indicator in Access Stratum signalling and UE radio capability for paging information for New Radio and evolved LTE connected to the CN.
- Flexible Alerting (FA) using IP Multimedia (IM) Core Network (CN) subsystem TS 24.239CR0008
- Terminating Identification Presentation (TIP) and Terminating Identification Restriction (TIR) using IP Multimedia (IM) Core Network (CN) subsystem TS 24.608CR0029
- Completion of Communications to Busy Subscriber (CCBS) and Completion of Communications by No Reply (CCNR) using IP Multimedia (IM) Core Network (CN) subsystem TS 24.642CR0088
- Advice Of Charge (AOC) using IP Multimedia (IM) Core Network (CN) subsystem TS 24.647CR0030
- CN assistance information enhancement TS 23.501CR0068
- Updates to description of CN Tunnel Info TS 23.501CR0151
+ 3 more changes
In Release 16, the Core Network introduced new capabilities for CN Selection and Steering for CIoT, provided clarifications on assistance information and parameters sent to the RAN for tuning, and specified the configuration of Core Network components like the Packet Delay Budget (PDB) per uplink and downlink, including for Time-Sensitive Networking (TSN). The release also included detailed corrections and clarifications on procedures such as MICO mode operation during CN node changes and the allocation of CN tunnel information.
- CIoT Introduction of CN Selection and Steering TS 23.501CR0896
- Clarification on MICO and eDRX during CN node changes TS 23.501CR1075
- Clarification on the CN PDB configured in each NG-RAN node TS 23.501CR1163
- Corrections to CN assisted RAN parameters tuning TS 23.501CR1256
- Clarifications on CN assistance information sent to the RAN TS 23.501CR1899
- CN component of the PDB is configured per UL and DL TS 23.501CR2015
+ 3 more changes
In Release 17, the Core Network introduced enhancements for Non-Terrestrial Networks, specifically enabling an NG-RAN node providing satellite access to select a CN node when the service area spans multiple countries. Furthermore, the specification increased the number of Core Network paging subgroups to improve efficiency.
In Release 18, the Core Network introduced new capabilities for handling Mobile-Terminated (MT) communication, specifically a defined **CN based MT communication capability** that can be indicated by the UE. The release also addressed the **co-existence of Small Data Transmission and CN based MT communication handling** for a UE in the RRC_INACTIVE state, alongside corrections for asynchronous type communication and CN Packet Delay Budget configuration in the NG-RAN related to this MT handling.
- CN based MT communication capability indication TS 23.501CR4081
- Co-existence of Small Data Transmission and CN based MT communication handling for UE in RRC_INACTIVE TS 23.501CR4218
- CN based MT communication capability TS 23.501CR4499
- Correction for Asynchronous Type Communication for CN based MT communication handling TS 23.501CR4569
- Correction on CN PDB configured in NG-RAN TS 23.501CR5225
Explore further
Broader topics and technologies where CN plays a role.
Defining Specifications
3GPP specifications that define or reference CN, 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 |
| TS 22.101 vk00 | Service Principles for PLMNs | Rel-20 |
| TS 22.228 vj00 | IP Multimedia Service Requirements | Rel-19 |
| TS 22.468 vj00 | Group Communication System Enabler Requirements | Rel-19 |
| TS 22.495 v1700 | NGN Requirements for IMS Services | Rel-7 |
| TS 22.519 vj00 | NGN Business Communication Requirements | Rel-19 |
| TS 22.801 vc00 | Study on Non-MTC Mobile Data Application Impacts | Rel-12 |
| TS 22.811 v1700 | Network Selection Mechanisms Overview | Rel-7 |
| TS 22.822 vg00 | Satellite Access in 5G Study | Rel-16 |
| TR 22.980 vj00 | Network Composition Feasibility Study | Rel-19 |
| TS 23.050 v1100 | UMTS Network Principles and Architecture | R99 |
| TS 23.107 vj00 | UMTS QoS Framework | Rel-19 |
| TS 23.110 vj00 | Access Stratum Services Specification | Rel-19 |
| TS 23.171 v1300 | LCS Stage 2 Specification for UMTS | Rel-4 |
| TS 23.207 vj00 | End-to-End QoS Framework for GPRS | Rel-19 |
| TS 23.221 vj00 | 3GPP System Architectural Requirements | Rel-19 |
| TS 23.228 vj50 | IMS Stage-2 Service Description | Rel-19 |
| TS 23.236 vj00 | Intra Domain Connection of RAN Nodes to Multiple CN Nodes | Rel-19 |
| TS 23.251 vj00 | Network Sharing Stage 2 Specification | Rel-19 |
| TS 23.271 vj00 | LCS Stage 2 Specification | Rel-19 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TR 23.758 vh00 | Study on Edge Application Architecture | Rel-17 |
| TS 23.851 v1600 | Network Sharing Architecture for 3G Systems | Rel-6 |
| TR 23.910 v1400 | UMTS Circuit Switched Bearer Services Overview | Rel-5 |
| TR 23.923 v1300 | Mobile IP+ Feasibility Study for UMTS/GPRS | Rel-4 |
| TR 23.979 vj00 | PoC over 3GPP Systems Architectural Requirements | Rel-19 |
| TR 23.981 vj00 | IPv4 IMS Interworking and Migration Study | Rel-19 |
| TS 24.141 vj00 | Presence Service Protocol Details | Rel-19 |
| TS 24.147 vj00 | IMS Conferencing Protocol Details | Rel-19 |
| TS 24.166 vj00 | IMS Conferencing Management Object | Rel-19 |
| TS 24.167 vj00 | 3GPP IMS Management Object Specification | Rel-19 |
| TS 24.173 vj00 | Multimedia Telephony Service and Supplementary Services in IMS | Rel-19 |
| TS 24.186 vj60 | IMS Data Channel applications | Rel-19 |
| TS 24.196 vj00 | Enhanced Calling Name (eCNAM) Stage 3 Protocol | Rel-19 |
| TS 24.206 v1700 | Voice Call Continuity Between CS and IMS | Rel-7 |
| TS 24.216 vj00 | Communication Continuity Management Object | Rel-19 |
| TS 24.228 v1500 | IP Multimedia Call Control Signaling Flows | Rel-5 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 24.239 vj00 | Flexible Alerting Protocol for IMS | Rel-19 |
| TS 24.247 vj10 | IMS Messaging Service Protocol Details | Rel-19 |
| TS 24.259 vj00 | Personal Network Management (PNM) Protocol Details | Rel-19 |
| TS 24.292 vj00 | IMS Centralized Services (ICS) Protocol | Rel-19 |
| TS 24.323 vj00 | IMS Service Level Tracing Management Object | Rel-19 |
| TS 24.371 vj00 | WebRTC IMS Client Access Specification | Rel-19 |
| TS 24.391 vj00 | USSD over IMS Management Object Specification | Rel-19 |
| TS 24.408 v1700 | TIP/TIR Services Protocol Specification | Rel-7 |
| TS 24.417 vj00 | OIP/OIR Management Object Specification | Rel-19 |
| TS 24.447 v800 | Advice Of Charge (AOC) Service Protocol | Rel-8 |
| TS 24.508 v820 | TIP and TIR Service Protocol Description | Rel-8 |
| TS 24.523 vj00 | NGCN-NGN Interconnection Scenarios | Rel-19 |
| TS 24.608 vj00 | 3GPP TS 24608: TIP/TIR Services Protocol | Rel-19 |
| TS 24.642 vj00 | CCBS/CCNR/CCNL SIP Protocol Specification | Rel-19 |
| TS 24.647 vj00 | Advice of Charge (AOC) service protocol | Rel-19 |
| TS 24.819 v1700 | IMS Services via Fixed Broadband Access | Rel-7 |
| TS 24.841 v1600 | Presence Service IP Multimedia Subsystem | Rel-6 |
| TR 24.930 vj00 | IMS Session Setup Signalling Flows | Rel-19 |
| TS 25.301 vj00 | UE-UTRAN Radio Interface Protocol Architecture | Rel-19 |
| TS 25.302 vj00 | UTRA Physical Layer Services | Rel-19 |
| TS 25.304 vj00 | UTRA Idle Mode Procedures Specification | Rel-19 |
| TS 25.305 vj00 | UTRAN UE Positioning Stage 2 | Rel-19 |
| TS 25.321 vj00 | MAC Protocol Specification for UTRAN | Rel-19 |
| TS 25.322 vj00 | RLC Protocol Specification | Rel-19 |
| TS 25.331 vj00 | UTRAN RRC Protocol Specification | Rel-19 |
| TS 25.367 vj00 | Home NodeB Mobility Procedures | Rel-19 |
| TS 25.401 vj00 | UTRAN Overall Architecture | Rel-19 |
| TS 25.402 vj00 | UTRAN Synchronisation Mechanisms | Rel-19 |
| TS 25.410 vj00 | Iu Interface Introduction for UTRAN | Rel-19 |
| TS 25.413 vj00 | Radio Access Network Application Part (RANAP) | Rel-19 |
| TS 25.414 vj00 | UTRAN Iu Interface User Plane Transport Protocols | Rel-19 |
| TS 25.415 vj00 | Iu Interface User Plane Protocol | Rel-19 |
| TS 25.419 vj00 | Service Area Broadcast Protocol (SABP) | Rel-19 |
| TS 25.423 vj00 | UTRAN RNSAP Specification | Rel-19 |
| TS 25.444 vj00 | HNB User Data Transport Protocols | Rel-19 |
| TS 25.453 vj00 | PCAP Protocol Specification | Rel-19 |
| TS 25.468 vj00 | RANAP User Adaption (RUA) protocol specification | Rel-19 |
| TS 25.470 vj00 | PCAP User Adaption (PUA) protocol specification | Rel-19 |
| TS 25.705 vd00 | UMTS Small Data Transmission Enhancements Study | Rel-13 |
| TS 25.820 v820 | 3G Home NodeB Study Report | Rel-8 |
| TR 25.914 vj00 | 3G UE Radio Performance Test Methods | Rel-19 |
| TR 25.931 vj00 | UTRAN Signalling Procedures Examples | Rel-19 |
| TS 26.102 vj00 | Mapping of AMR and other codecs to interfaces | Rel-19 |
| TS 26.192 vj00 | AMR-WB Comfort Noise Requirements | Rel-19 |
| TS 26.202 vj00 | AMR-WB Speech Codec Mapping Specification | Rel-19 |
| TS 26.454 vj00 | EVS Codec Mapping for 3G CS Networks | Rel-19 |
| TR 26.919 vj00 | Study on 5G Conversational Media Handling | Rel-19 |
| TR 26.935 vj00 | Speech Codec Performance for Packet Switched Multimedia | Rel-19 |
| TR 26.937 vj00 | 3GPP PSS Characterization | Rel-19 |
| TS 28.535 vj00 | Closed Control Loop Assurance Management | Rel-19 |
| TS 28.621 vj00 | Generic Network Resource Model (NRM) IRP Requirements | Rel-19 |
| TS 28.652 vj00 | UTRAN Network Resource Model (NRM) IRP Information Service | Rel-19 |
| TS 28.671 vj00 | HNS Network Resource Model Requirements | Rel-19 |
| TS 28.701 vj00 | Core Network NRM IRP Requirements | Rel-19 |
| TS 28.702 vj00 | Core Network NRM IRP Information Service | Rel-19 |
| TS 28.705 vj00 | IMS NRM IRP Information Service | Rel-19 |
| TR 28.808 vh00 | 5G satellite integration management study | Rel-17 |
| TR 28.841 vi01 | Technical Report on IoT NTN Enhancements | Rel-18 |
| TS 29.229 vj10 | Diameter Protocol for Cx/Dx Interfaces | Rel-19 |
| TS 29.329 vj10 | Diameter Protocol for Sh Interface | Rel-19 |
| TS 29.332 vj00 | MGCF-IM-MGW Interface Protocol (Mn) | Rel-19 |
| TS 29.333 vj00 | MRFC-MRFP Mp Interface Protocol | Rel-19 |
| TS 29.412 v1810 | Trunking Gateway Control Procedures | Rel-8 |
| TS 29.414 vj00 | Nb Interface Bearer Transport & Control Protocols | Rel-19 |
| TS 29.415 vj00 | Nb User Plane Protocol Specification | Rel-19 |
| TS 29.424 v801 | H.248 Profile for Trunking Media Gateways | Rel-8 |
| TS 31.121 vi50 | UICC-terminal interface test specification | Rel-18 |
| TS 31.829 vd00 | ISIM Conformance Requirements Technical Report | Rel-13 |
| TS 32.102 vj00 | Telecom Management Physical Architecture Framework | Rel-19 |
| TS 32.103 vj00 | 3GPP Management IRP Overview | Rel-19 |
| TS 32.240 vj40 | Charging Management Architecture & Principles | Rel-19 |
| TS 32.404 vj00 | Performance Management Definitions & Template | Rel-19 |
| TS 32.405 vj00 | UTRAN Performance Measurements Specification | Rel-19 |
| TS 32.406 vj00 | Performance Management for CN PS Domain | Rel-19 |
| TS 32.407 vj00 | PM; CN CS Domain; UMTS/GSM measurements | Rel-19 |
| TS 32.408 vj00 | UMTS/GSM Performance Management Measurements | Rel-19 |
| TS 32.409 vj00 | IMS Performance Management Measurements | Rel-19 |
| TS 32.410 vj00 | 3GPP TS 32.410: Key Performance Indicators (KPI) | Rel-19 |
| TS 32.452 vj00 | PM Measurements for Home Node B Subsystem | Rel-19 |
| TS 32.453 vj00 | PM for Home eNodeB Subsystem (HeNS) | Rel-19 |
| TS 32.602 vj00 | Basic Configuration Management IRP Information Service | Rel-19 |
| TS 32.622 vb10 | Generic Network Resources IRP NRM | Rel-11 |
| TS 32.631 vb00 | Core Network Resources IRP Requirements | Rel-11 |
| TS 32.632 vb00 | Core Network Resources IRP: Network Resource Model | Rel-11 |
| TS 32.642 vb50 | UTRAN Network Resource Model for Configuration Management | Rel-11 |
| TS 32.662 vj00 | Configuration Management (CM); Kernel CM IRP | Rel-19 |
| TS 32.731 vb00 | IMS Network Resource Model IRP Requirements | Rel-11 |
| TS 32.732 vb00 | IMS Network Resource Model IRP: Information Service | Rel-11 |
| TS 32.741 vb00 | STN Interface NRM IRP Requirements | Rel-11 |
| TS 32.771 vb00 | HNS Network Resource Model IRP Requirements | Rel-11 |
| TS 32.808 v1800 | Common User Profile Storage Framework | Rel-8 |
| TS 33.859 vb10 | UTRAN Key Hierarchy Enhancement Study | Rel-11 |
| TS 34.114 vc20 | Radiated Performance Test Procedure for UE/MS | Rel-12 |
| TS 36.413 vj10 | S1 Application Protocol (S1AP) | Rel-19 |
| TS 36.887 vc00 | Energy Saving Enhancement for E-UTRAN Study | Rel-12 |
| TS 36.896 ve00 | Study on Flexible eNB-ID and Cell-ID in E-UTRAN | Rel-14 |
| TR 36.978 vd20 | Antenna Test Function for MIMO OTA Testing | Rel-13 |
| TS 37.320 vj00 | Minimization of Drive Tests (MDT) Overview | Rel-19 |
| TS 37.473 vj00 | W1 Application Protocol (W1AP) Specification | Rel-19 |
| TS 37.483 vj10 | E1 Application Protocol (E1AP) | Rel-19 |
| TS 37.544 vg70 | UE Radiated Performance Test Procedures | Rel-16 |
| TS 37.870 vd00 | Study on Multi-RAT Joint Coordination | Rel-13 |
| TR 37.902 vj00 | OTA TRP/TRS Measurement for LTE Terminals | Rel-19 |
| TS 38.304 vj00 | UE RRC_IDLE and RRC_INACTIVE Procedures | Rel-19 |
| TS 38.410 vj10 | NG Interface Introduction for NG-RAN to 5GC | Rel-19 |
| TS 38.463 vj00 | E1 Application Protocol (E1AP) | Rel-19 |
| TS 38.473 vj10 | 5G F1 Application Protocol (F1AP) | Rel-19 |
| TR 38.913 vj00 | Next Gen Access Tech Scenarios & Requirements | Rel-19 |
| TS 43.051 vj00 | GERAN Stage 2 Service Description | Rel-19 |
| TS 43.055 vj00 | Dual Transfer Mode (DTM) for GSM/GPRS | Rel-19 |
| TS 43.129 vj00 | PS Handover in GERAN A/Gb and GAN Modes | Rel-19 |
| TS 43.130 vj00 | Iur-g Interface Overview | Rel-19 |
| TS 43.318 vj00 | Generic Access Network (GAN) Stage 2 | Rel-19 |
| TR 43.901 vj00 | Generic Access to A/Gb Interface Feasibility Study | Rel-19 |
| TR 43.902 vj00 | GAN Enhancements Feasibility Study | Rel-19 |
| TS 44.060 vj00 | GERAN RLC/MAC Protocol Specification | Rel-19 |
| TS 44.160 vg00 | GERAN Iu Mode RLC/MAC Protocol Specification | Rel-16 |
| TS 44.318 vj00 | Generic Access Network (GAN) Interface Procedures | Rel-19 |
| TS 45.820 vd10 | CIoT for Internet of Things | Rel-13 |