5G Message Library

This 5G message library organizes protocol messages used across the radio access network, core network signalling, RAN split interfaces, inter-node mobility, and IMS services. Browse messages by protocol family such as NR RRC, 5G NAS, NGAP, F1AP, E1AP, XnAP, and IMS SIP to understand message direction, procedure role, key fields, and troubleshooting context.

Use this page as the starting point for finding 5G signalling messages used in registration, authentication, RRC setup, PDU session establishment, handover, paging, UE context management, CU-DU coordination, CU-CP/CU-UP coordination, Xn mobility, and VoNR/IMS call flows.

Protocol Family Cards

Choose the message family first, then drill into individual messages and procedures.

NR RRC MessagesUE-to-gNB radio control messages for setup, system information, security, reconfiguration, measurements, resume, reestablishment, release, sidelink, NTN, and MBS.3GPP TS 38.331 5G NAS MessagesUE-to-5GC NAS messages for registration, authentication, security mode, service request, deregistration, NAS transport, and PDU session management.3GPP TS 24.501 NGAP MessagesN2 signalling messages between NG-RAN and AMF for NAS transport, UE context, mobility, PDU sessions, paging, warning, trace, location, and radio capability procedures.3GPP TS 38.413 F1AP MessagesF1-C messages between gNB-CU and gNB-DU for F1 setup, DU configuration, UE context setup/modification/release, RRC transfer, paging, and system information.3GPP TS 38.473 E1AP MessagesE1 messages between gNB-CU-CP and gNB-CU-UP for E1 setup, bearer context setup, modification, release, inactivity, data usage reporting, and reset.3GPP TS 38.463 XnAP MessagesXn-C messages between NG-RAN nodes for Xn setup, handover preparation, SN status transfer, UE context release, paging coordination, and RAN configuration transfer.3GPP TS 38.423 IMS SIP MessagesIMS SIP requests and responses used in IMS registration, VoLTE, VoNR, call setup, early media, session update, messaging, supplementary services, and call release.3GPP TS 24.229 / RFC 3261

Browse By Signalling Area

Use these compact groups when you know the network area but not the exact protocol family.

UE Radio Access

Messages used by the UE during cell access, registration, RRC setup, security, session establishment, and mobility.

NR RRC Messages 5G NAS Messages

Core / RAN Control Plane

Messages used between NG-RAN, AMF, and UE for N2 signalling, NAS transport, registration, paging, PDU sessions, and UE context management.

NGAP Messages 5G NAS Messages

Split RAN Interfaces

Messages used inside split gNB architecture between CU/DU and CU-CP/CU-UP.

F1AP Messages E1AP Messages

Inter-RAN Mobility

Messages used for handover preparation, path switching, status transfer, UE context release, and inter-node mobility.

XnAP Messages NGAP Mobility Messages

IMS / VoNR / VoLTE

Messages used for IMS registration, voice/video session setup, early media, session update, and call release.

IMS SIP Messages IMS SIP Requests IMS SIP Responses

Most Used 5G Message Hubs

Fast paths to the protocol hubs engineers usually check first.

NR RRC Messages 5G NAS Messages NGAP Messages F1AP Messages E1AP Messages XnAP Messages IMS SIP Messages

Common 5G Procedure Paths

Typical cross-protocol paths for registration, session setup, mobility, split RAN, and IMS voice.

Registration and Access

NR RRC Setup -> Initial UE Message / NAS Registration Request -> Authentication -> Security Mode -> Registration Accept

5G Initial Registration

PDU Session Establishment

NAS PDU Session Establishment Request -> NGAP PDU Session Resource Setup Request -> RRC Reconfiguration

5G PDU Session Establishment

Handover

RRC Measurement Report -> NGAP/XnAP Handover Preparation -> Handover Command -> Handover Notify -> Path Switch Request

5G Connected Mode Handover 5G Xn Handover 5G N2 Handover

Split RAN UE Context

F1AP UE Context Setup -> E1AP Bearer Context Setup -> RRC Reconfiguration

5G User Plane Establishment 5G RRC Reconfiguration

VoNR / IMS Call

IMS REGISTER -> SIP INVITE -> 183 Session Progress / PRACK -> 200 OK -> ACK

VoNR Mobile Originated Call VoNR Mobile Terminated Call VoNR Call Flow Procedures

FAQ

What are 5G messages?

5G messages are protocol signalling messages used by the UE, NG-RAN, 5G Core, and IMS network to handle radio access, registration, authentication, session management, mobility, bearer setup, paging, warning, and voice service procedures.

Which protocols are included in the 5G message library?

The main protocol families are NR RRC, 5G NAS, NGAP, F1AP, E1AP, XnAP, and IMS SIP.

What is the difference between RRC, NAS, and NGAP?

RRC controls radio signalling between UE and gNB. NAS carries UE-to-core signalling between UE and AMF/SMF. NGAP carries control-plane signalling between NG-RAN and AMF over N2.

What is the difference between F1AP and E1AP?

F1AP runs between gNB-CU and gNB-DU on the F1-C interface. E1AP runs between gNB-CU-CP and gNB-CU-UP on the E1 interface.

What is XnAP used for?

XnAP is used between neighbouring NG-RAN nodes for Xn setup, handover preparation, status transfer, UE context release, paging coordination, and RAN configuration transfer.

Where are IMS SIP messages used in 5G?

IMS SIP messages are used for IMS registration, VoNR/VoLTE call setup, early media, session update, messaging, supplementary services, and call release.

Which 3GPP specifications define these message protocols?

NR RRC is defined in TS 38.331, NGAP in TS 38.413, F1AP in TS 38.473, E1AP in TS 38.463, XnAP in TS 38.423, and 5G NAS mainly in TS 24.501.