Ts 123501v150300p

ETSI TS 123 501 V15.3.0 (2018-09)
5G;
System Architecture for the 5G System
(3GPP TS 23.501 version 15.3.0 Release 15)
TECHNICAL SPECIFICATION

ETSI
ETSI TS 123 501 V15.3.0 (2018-09)13GPP TS 23.501 version 15.3.0 Release 15
Reference
RTS/TSGS-0223501vf30
Keywords
5G
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ETSI
Contents
Intellectual Property Rights................................................................................................................................2
Foreword.............................................................................................................................................................2
Modal verbs terminology....................................................................................................................................2
Foreword...........................................................................................................................................................11
1 Scope......................................................................................................................................................12
2 References..............................................................................................................................................12
3 Definitions and abbreviations.................................................................................................................14
3.1 Definitions........................................................................................................................................................14
3.2 Abbreviations ...................................................................................................................................................17
4 Architecture model and concepts ...........................................................................................................18
4.1 General concepts ..............................................................................................................................................18
4.2 Architecture reference model ...........................................................................................................................19
4.2.1 General........................................................................................................................................................19
4.2.2 Network Functions and entities ..................................................................................................................19
4.2.3 Non-roaming reference architecture ...........................................................................................................20
4.2.4 Roaming reference architectures.................................................................................................................23
4.2.5 Data Storage architectures ..........................................................................................................................25
4.2.6 Service-based interfaces .............................................................................................................................27
4.2.7 Reference points .........................................................................................................................................27
4.2.8 Support of non-3GPP access.......................................................................................................................29
4.2.8.1 General Concepts to Support Non-3GPP Access..................................................................................29
4.2.8.2 Architecture Reference Model for Non-3GPP Accesses.......................................................................30
4.2.8.2.1 Non-roaming Architecture for Non-3GPP Accesses .......................................................................30
4.2.8.2.2 LBO Roaming Architecture for Non-3GPP Accesses, N3IWF in same PLMN as 3GPP access....30
4.2.8.2.3 Home-routed Roaming Architecture for Non-3GPP Accesses, N3IWF in same PLMN as
3GPP access ....................................................................................................................................31
4.2.8.2.4 LBO Roaming Architecture for Non-3GPP Accesses, N3IWF in different PLMN from 3GPP
access...............................................................................................................................................32
4.2.8.2.5 Home-routed Roaming Architecture for Non-3GPP Accesses, N3IWF in different PLMN
from 3GPP access............................................................................................................................33
4.2.8.3 Non-3GPP Access Reference Points.....................................................................................................34
4.2.9 Network Analytics architecture ..................................................................................................................34
4.3 Interworking with EPC.....................................................................................................................................34
4.3.1 Non-roaming architecture...........................................................................................................................34
4.3.2 Roaming architecture..................................................................................................................................35
4.3.3 Interworking between 5GC via non-3GPP access and E-UTRAN connected to EPC................................37
4.3.3.1 Non-roaming architecture .....................................................................................................................37
4.3.3.2 Roaming architecture ............................................................................................................................38
4.3.4 Interworking between ePDG connected to EPC and 5GS ..........................................................................40
4.3.4.1 Non-roaming architecture .....................................................................................................................40
4.3.4.2 Roaming architectures...........................................................................................................................41
4.4 Specific services...............................................................................................................................................43
4.4.1 Public Warning System ..............................................................................................................................43
4.4.2 SMS over NAS ...........................................................................................................................................43
4.4.2.1 Architecture to support SMS over NAS................................................................................................43
4.4.2.2 Reference point to support SMS over NAS ..........................................................................................45
4.4.2.3 Service based interface to support SMS over NAS...............................................................................45
4.4.3 IMS support ................................................................................................................................................45
4.4.4 Location services ........................................................................................................................................46
4.4.4.1 Architecture to support Location Services ............................................................................................46
4.4.4.2 Reference point to support Location Services.......................................................................................46
4.4.4.3 Service Based Interfaces to support Location Services.........................................................................47
4.4.5 Application Triggering Services.................................................................................................................47
5 High level features..................................................................................................................................47

ETSI
5.1 General .............................................................................................................................................................47
5.2 Network Access Control ..................................................................................................................................47
5.2.1 General........................................................................................................................................................47
5.2.2 Network selection .......................................................................................................................................47
5.2.3 Identification and authentication.................................................................................................................47
5.2.4 Authorisation ..............................................................................................................................................48
5.2.5 Access control and barring .........................................................................................................................48
5.2.6 Policy control..............................................................................................................................................48
5.2.7 Lawful Interception.....................................................................................................................................48
5.3 Registration and Connection Management.......................................................................................................48
5.3.1 General........................................................................................................................................................48
5.3.2 Registration Management...........................................................................................................................48
5.3.2.1 General..................................................................................................................................................48
5.3.2.2 5GS Registration Management states....................................................................................................49
5.3.2.2.1 General ............................................................................................................................................49
5.3.2.2.2 RM-DEREGISTERED state............................................................................................................49
5.3.2.2.3 RM-REGISTERED state.................................................................................................................49
5.3.2.2.4 5GS Registration Management State models ..................................................................................50
5.3.2.3 Registration Area management.............................................................................................................50
5.3.2.4 Support of a UE registered over both 3GPP and Non-3GPP access .....................................................51
5.3.3 Connection Management ............................................................................................................................52
5.3.3.1 General..................................................................................................................................................52
5.3.3.2 5GS Connection Management states.....................................................................................................52
5.3.3.2.1 General ............................................................................................................................................52
5.3.3.2.2 CM-IDLE state................................................................................................................................53
5.3.3.2.3 CM-CONNECTED state.................................................................................................................53
5.3.3.2.4 5GS Connection Management State models ...................................................................................54
5.3.3.2.5 CM-CONNECTED with RRC Inactive state ..................................................................................54
5.3.3.3 NAS signalling connection management ..............................................................................................56
5.3.3.3.1 General ............................................................................................................................................56
5.3.3.3.2 NAS signalling connection establishment.......................................................................................56
5.3.3.3.3 NAS signalling connection Release.................................................................................................56
5.3.3.4 Support of a UE connected over both 3GPP and Non-3GPP access.....................................................57
5.3.4 UE Mobility................................................................................................................................................57
5.3.4.1 Mobility Restrictions.............................................................................................................................57
5.3.4.1.1 General ............................................................................................................................................57
5.3.4.1.2 Management of Service Area Restrictions ......................................................................................58
5.3.4.2 Mobility Pattern ....................................................................................................................................59
5.3.4.3 Radio Resource Management functions................................................................................................59
5.3.4.4 UE mobility event notification..............................................................................................................60
5.4 3GPP access specific aspects............................................................................................................................61
5.4.1 UE reachability in CM-IDLE......................................................................................................................61
5.4.1.1 General..................................................................................................................................................61
5.4.1.2 UE reachability allowing mobile terminated data while the UE is CM-IDLE......................................62
5.4.1.3 Mobile Initiated Connection Only (MICO) mode.................................................................................62
5.4.2 UE reachability in CM-CONNECTED.......................................................................................................62
5.4.3 Paging strategy handling.............................................................................................................................63
5.4.3.1 General..................................................................................................................................................63
5.4.3.2 Paging Policy Differentiation................................................................................................................63
5.4.3.3 Paging Priority ......................................................................................................................................64
5.4.4 UE Radio Capability handling....................................................................................................................64
5.4.4.1 UE radio capability information storage in the AMF............................................................................64
5.4.4.2 Void.......................................................................................................................................................65
5.4.4.2a UE Radio Capability Match Request ....................................................................................................65
5.4.4.3 Paging assistance information...............................................................................................................65
5.4.4a UE MM Core Network Capability handling...............................................................................................65
5.4.4b UE 5GSM Core Network Capability handling ...........................................................................................66
5.4.5 DRX (Discontinuous Reception) framework..............................................................................................66
5.4.6 Core Network assistance information for RAN optimization.....................................................................66
5.4.6.1 General..................................................................................................................................................66
5.4.6.2 Core Network assisted RAN parameters tuning....................................................................................66
5.4.6.3 Core Network assisted RAN paging information..................................................................................67

ETSI
5.4.7 NG-RAN location reporting .......................................................................................................................67
5.5 Non-3GPP access specific aspects ...................................................................................................................68
5.5.1 Registration Management...........................................................................................................................68
5.5.2 Connection Management ............................................................................................................................68
5.5.3 UE Reachability..........................................................................................................................................69
5.5.3.1 UE reachability in CM-IDLE................................................................................................................69
5.5.3.2 UE reachability in CM-CONNECTED.................................................................................................69
5.6 Session Management........................................................................................................................................69
5.6.1 Overview ....................................................................................................................................................69
5.6.2 Interaction between AMF and SMF ...........................................................................................................71
5.6.3 Roaming......................................................................................................................................................73
5.6.4 Single PDU Session with multiple PDU Session Anchors .........................................................................73
5.6.4.1 General..................................................................................................................................................73
5.6.4.2 Usage of an UL Classifier for a PDU Session.......................................................................................74
5.6.4.3 Usage of IPv6 multi-homing for a PDU Session...................................................................................75
5.6.5 Support for Local Area Data Network........................................................................................................76
5.6.6 Secondary authentication/authorization by a DN-AAA server during the establishment of a PDU
Session........................................................................................................................................................78
5.6.7 Application Function influence on traffic routing ......................................................................................79
5.6.8 Selective activation and deactivation of UP connection of existing PDU Session .....................................84
5.6.9 Session and Service Continuity ..................................................................................................................85
5.6.9.1 General..................................................................................................................................................85
5.6.9.2 SSC mode..............................................................................................................................................85
5.6.9.2.1 SSC Mode 1.....................................................................................................................................85
5.6.9.2.2 SSC Mode 2.....................................................................................................................................85
5.6.9.2.3 SSC Mode 3.....................................................................................................................................86
5.6.9.3 SSC mode selection...............................................................................................................................86
5.6.10 Specific aspects of different PDU Session types ........................................................................................87
5.6.10.1 Support of IP PDU Session type ...........................................................................................................87
5.6.10.2 Support of Ethernet PDU Session type .................................................................................................87
5.6.10.3 Support of Unstructured PDU Session type..........................................................................................88
5.6.11 UE presence in Area of Interest reporting usage by SMF...........................................................................89
5.6.12 Use of Network Instance.............................................................................................................................90
5.7 QoS model........................................................................................................................................................91
5.7.1 General Overview.......................................................................................................................................91
5.7.1.1 QoS Flow ..............................................................................................................................................91
5.7.1.2 QoS Profile............................................................................................................................................91
5.7.1.3 Control of QoS Flows ...........................................................................................................................92
5.7.1.4 QoS Rules .............................................................................................................................................92
5.7.1.5 QoS Flow mapping ...............................................................................................................................93
5.7.1.6 DL traffic...............................................................................................................................................94
5.7.1.7 UL Traffic .............................................................................................................................................95
5.7.1.8 AMBR/MFBR enforcement and rate limitation....................................................................................95
5.7.1.9 Precedence Value..................................................................................................................................95
5.7.2 5G QoS Parameters.....................................................................................................................................96
5.7.2.1 5QI ........................................................................................................................................................96
5.7.2.2 ARP.......................................................................................................................................................96
5.7.2.3 RQA......................................................................................................................................................96
5.7.2.4 Notification control...............................................................................................................................96
5.7.2.5 Flow Bit Rates.......................................................................................................................................97
5.7.2.6 Aggregate Bit Rates ..............................................................................................................................97
5.7.2.7 Default values .......................................................................................................................................98
5.7.2.8 Maximum Packet Loss Rate..................................................................................................................98
5.7.3 5G QoS characteristics................................................................................................................................98
5.7.3.1 General..................................................................................................................................................98
5.7.3.2 Resource Type.......................................................................................................................................99
5.7.3.3 Priority Level ........................................................................................................................................99
5.7.3.4 Packet Delay Budget.............................................................................................................................99
5.7.3.5 Packet Error Rate ..................................................................................................................................99
5.7.3.6 Averaging Window.............................................................................................................................100
5.7.3.7 Maximum Data Burst Volume ............................................................................................................100
5.7.4 Standardized 5QI to QoS characteristics mapping....................................................................................100

ETSI
5.7.5 Reflective QoS..........................................................................................................................................103
5.7.5.1 General................................................................................................................................................103
5.7.5.2 UE Derived QoS Rule ...................................................................................................................103
5.7.5.3 Reflective QoS Control.......................................................................................................................104
5.7.6 Packet Filter Set........................................................................................................................................105
5.7.6.1 General................................................................................................................................................105
5.7.6.2 IP Packet Filter Set..............................................................................................................................105
5.7.6.3 Ethernet Packet Filter Set....................................................................................................................106
5.8 User Plane Management.................................................................................................................................106
5.8.1 General......................................................................................................................................................106
5.8.2 Functional Description..............................................................................................................................106
5.8.2.1 General................................................................................................................................................106
5.8.2.2 UE IP Address Management...............................................................................................................107
5.8.2.2.1 General ..........................................................................................................................................107
5.8.2.2.2 Routing rules configuration...........................................................................................................108
5.8.2.2.3 The procedure of Stateless IPv6 Address Autoconfiguration........................................................108
5.8.2.3 Management of CN Tunnel Info .........................................................................................................109
5.8.2.3.1 General ..........................................................................................................................................109
5.8.2.3.2 Management of CN Tunnel Info in the SMF.................................................................................109
5.8.2.3.3 Management of CN Tunnel Info in the UPF .................................................................................109
5.8.2.4 Traffic Detection.................................................................................................................................109
5.8.2.4.1 General ..........................................................................................................................................109
5.8.2.4.2 Traffic Detection Information .......................................................................................................109
5.8.2.5 Control of User Plane Forwarding ......................................................................................................110
5.8.2.6 Charging and Usage Monitoring Handling .........................................................................................111
5.8.2.6.1 General ..........................................................................................................................................111
5.8.2.6.2 Activation of Usage Reporting in UPF..........................................................................................111
5.8.2.6.3 Reporting of Usage Information towards SMF .............................................................................112
5.8.2.7 PDU Session and QoS Flow Policing .................................................................................................112
5.8.2.8 PCC Related Functions .......................................................................................................................112
5.8.2.8.1 Activation/Deactivation of predefined PCC rules .........................................................................112
5.8.2.8.2 Enforcement of Dynamic PCC Rules............................................................................................113
5.8.2.8.3 Redirection ....................................................................................................................................113
5.8.2.8.4 Support of PFD Management........................................................................................................113
5.8.2.9 Functionality of Sending of "End marker"..........................................................................................114
5.8.2.9.0 Introduction ...................................................................................................................................114
5.8.2.9.1 UPF Constructing the "End marker" Packets ................................................................................114
5.8.2.9.2 SMF Constructing the "End marker" Packets................................................................................115
5.8.2.10 UP Tunnel Management .....................................................................................................................115
5.8.2.11 Parameters for N4 session management..............................................................................................115
5.8.2.11.1 General ..........................................................................................................................................115
5.8.2.11.2 N4 Session Context .......................................................................................................................116
5.8.2.11.3 Packet Detection Rule ...................................................................................................................116
5.8.2.11.4 QoS Enforcement Rule..................................................................................................................117
5.8.2.11.5 Usage Reporting Rule....................................................................................................................119
5.8.2.11.6 Forwarding Action Rule................................................................................................................121
5.8.2.11.7 Usage Report generated by UPF ...................................................................................................124
5.8.2.12 Reporting of the UE MAC addresses used in a PDU Session.............................................................124
5.8.3 Explicit Buffer Management.....................................................................................................................125
5.8.3.1 General................................................................................................................................................125
5.8.3.2 Buffering at UPF.................................................................................................................................125
5.8.3.3 Buffering at SMF ................................................................................................................................125
5.8.4 SMF Pause of Charging............................................................................................................................125
5.9 Identifiers .......................................................................................................................................................126
5.9.1 General......................................................................................................................................................126
5.9.2 Subscription Permanent Identifier ............................................................................................................126
5.9.2a Subscription Concealed Identifier.............................................................................................................126
5.9.3 Permanent Equipment Identifier...............................................................................................................126
5.9.4 5G Globally Unique Temporary Identifier ...............................................................................................126
5.9.5 AMF Name ...............................................................................................................................................127
5.9.6 Data Network Name (DNN).....................................................................................................................127
5.9.7 Internal-Group Identifier...........................................................................................................................127

ETSI
5.9.8 Generic Public Subscription Identifier......................................................................................................128
5.9.9 AMF UE NGAP ID ..................................................................................................................................128
5.10 Security aspects..............................................................................................................................................128
5.10.1 General......................................................................................................................................................128
5.10.2 Security Model for non-3GPP access .......................................................................................................128
5.10.2.1 Signalling Security..............................................................................................................................128
5.10.3 PDU Session User Plane Security.............................................................................................................128
5.11 Support for Dual Connectivity, Multi-Connectivity.......................................................................................130
5.11.1 Support for Dual Connectivity..................................................................................................................130
5.12 Charging.........................................................................................................................................................130
5.13 Support for Edge Computing..........................................................................................................................130
5.14 Policy Control ................................................................................................................................................131
5.15 Network slicing ..............................................................................................................................................131
5.15.1 General......................................................................................................................................................131
5.15.2 Identification and selection of a Network Slice: the S-NSSAI and the NSSAI ........................................132
5.15.2.1 General................................................................................................................................................132
5.15.2.2 Standardised SST values.....................................................................................................................133
5.15.3 Subscription aspects..................................................................................................................................133
5.15.4 UE NSSAI configuration and NSSAI storage aspects..............................................................................134
5.15.4.1 General................................................................................................................................................134
5.15.4.1.1 UE Network Slice configuration ...................................................................................................134
5.15.4.1.2 Mapping of S-NSSAIs values in the Allowed NSSAI and in the Requested NSSAI to the S-
NSSAIs values used in the HPLMN..............................................................................................135
5.15.4.2 Update of UE Network Slice configuration ........................................................................................136
5.15.5 Detailed Operation Overview ...................................................................................................................136
5.15.5.1 General................................................................................................................................................136
5.15.5.2 Selection of a Serving AMF supporting the Network Slices...............................................................136
5.15.5.2.1 Registration to a set of Network Slices..........................................................................................136
5.15.5.2.2 Modification of the Set of Network Slice(s) for a UE...................................................................139
5.15.5.2.3 AMF Re-allocation due to Network Slice(s) Support....................................................................140
5.15.5.3 Establishing a PDU Session in a Network Slice .................................................................................141
5.15.6 Network Slicing Support for Roaming .....................................................................................................142
5.15.7 Network slicing and Interworking with EPS ............................................................................................142
5.15.7.1 General................................................................................................................................................142
5.15.7.2 Idle mode aspects................................................................................................................................142
5.15.7.3 Connected mode aspects .....................................................................................................................143
5.15.8 Configuration of Network Slice availability in a PLMN..........................................................................143
5.16 Support for specific services ..........................................................................................................................144
5.16.1 Public Warning System ............................................................................................................................144
5.16.2 SMS over NAS .........................................................................................................................................144
5.16.2.1 General................................................................................................................................................144
5.16.2.2 SMS over NAS transport ....................................................................................................................144
5.16.3 IMS support ..............................................................................................................................................144
5.16.3.1 General................................................................................................................................................144
5.16.3.2 IMS voice over PS Session Supported Indication over 3GPP access .................................................145
5.16.3.2a IMS voice over PS Session Supported Indication over non-3GPP access ..........................................145
5.16.3.3 Homogeneous support for IMS voice over PS Session supported indication .....................................145
5.16.3.4 P-CSCF address delivery ....................................................................................................................146
5.16.3.5 Domain selection for UE originating sessions / calls..........................................................................146
5.16.3.6 Terminating domain selection for IMS voice......................................................................................146
5.16.3.7 UE's usage setting ...............................................................................................................................147
5.16.3.8 Domain and Access Selection for UE originating SMS......................................................................147
5.16.3.8.1 UE originating SMS for IMS Capable UEs supporting SMS over IP ...........................................147
5.16.3.8.2 Access Selection for SMS over NAS ............................................................................................147
5.16.3.9 SMF support for P-CSCF restoration procedure.................................................................................147
5.16.3.10 IMS Voice Service via EPS Fallback or RAT fallback in 5GS...........................................................147
5.16.4 Emergency Services..................................................................................................................................148
5.16.4.1 Introduction.........................................................................................................................................148
5.16.4.2 Architecture Reference Model for Emergency Services .....................................................................150
5.16.4.3 Mobility Restrictions and Access Restrictions for Emergency Services.............................................150
5.16.4.4 Reachability Management...................................................................................................................150
5.16.4.5 SMF and UPF selection function for Emergency Services .................................................................150

ETSI
5.16.4.6 QoS for Emergency Services ..............................................................................................................151
5.16.4.7 PCC for Emergency Services..............................................................................................................151
5.16.4.8 IP Address Allocation .........................................................................................................................151
5.16.4.9 Handling of PDU Sessions for Emergency Services...........................................................................151
5.16.4.9a Handling of PDU Sessions for normal services for Emergency Registered UEs................................151
5.16.4.10 Support of eCall Only Mode...............................................................................................................151
5.16.4.11 Emergency Services Fallback .............................................................................................................152
5.16.5 Multimedia Priority Services....................................................................................................................152
5.16.6 Mission Critical Services..........................................................................................................................153
5.17 Interworking and Migration ...........................................................................................................................154
5.17.1 Support for Migration from EPC to 5GC..................................................................................................154
5.17.1.1 General................................................................................................................................................154
5.17.1.2 User Plane management to support interworking with EPS................................................................156
5.17.2 Interworking with EPC.............................................................................................................................156
5.17.2.1 General................................................................................................................................................156
5.17.2.2 Interworking Procedures with N26 interface ......................................................................................158
5.17.2.2.1 General ..........................................................................................................................................158
5.17.2.2.2 Mobility for UEs in single-registration mode................................................................................158
5.17.2.3 Interworking Procedures without N26 interface .................................................................................159
5.17.2.3.1 General ..........................................................................................................................................159
5.17.2.3.2 Mobility for UEs in single-registration mode................................................................................160
5.17.2.3.3 Mobility for UEs in dual-registration mode ..................................................................................161
5.17.2.3.4 Redirection for UEs in connected state .........................................................................................162
5.17.2.4 Mobility between 5GS and GERAN/UTRAN ....................................................................................162
5.17.3 Interworking with EPC in presence of Non-3GPP PDU Sessions............................................................162
5.17.4 Network sharing support and interworking between EPS and 5GS..........................................................163
5.18 Network Sharing ............................................................................................................................................163
5.18.1 General concepts.......................................................................................................................................163
5.18.2 Broadcast system information for network sharing ..................................................................................163
5.18.2a PLMN list handling for network sharing..................................................................................................164
5.18.3 Network selection by the UE ....................................................................................................................164
5.18.4 Network selection by the network ............................................................................................................164
5.18.5 Network Sharing and Network Slicing.....................................................................................................165
5.19 Control Plane Load Control, Congestion and Overload Control....................................................................165
5.19.1 General......................................................................................................................................................165
5.19.2 TNLA Load Balancing and TNLA Load Re-Balancing ...........................................................................165
5.19.3 AMF Load Balancing ...............................................................................................................................165
5.19.4 AMF Load Re-Balancing..........................................................................................................................165
5.19.5 AMF Control Of Overload .......................................................................................................................166
5.19.5.1 General................................................................................................................................................166
5.19.5.2 AMF Overload Control.......................................................................................................................166
5.19.6 SMF Overload Control .............................................................................................................................167
5.19.7 NAS level congestion control...................................................................................................................167
5.19.7.1 General................................................................................................................................................167
5.19.7.2 General NAS level congestion control................................................................................................167
5.19.7.3 DNN based congestion control ...........................................................................................................168
5.19.7.4 S-NSSAI based congestion control.....................................................................................................169
5.19.7.5 Group specific NAS level congestion control.....................................................................................170
5.20 External Exposure of Network Capability......................................................................................................170
5.21 Architectural support for virtualized deployments.........................................................................................170
5.21.0 General......................................................................................................................................................170
5.21.1 Architectural support for N2.....................................................................................................................171
5.21.1.1 TNL associations.................................................................................................................................171
5.21.1.2 NGAP UE-TNLA-binding..................................................................................................................171
5.21.1.3 N2 TNL association selection .............................................................................................................171
5.21.2 AMF Management....................................................................................................................................171
5.21.2.1 AMF Addition/Update ........................................................................................................................171
5.21.2.2 AMF planned removal procedure .......................................................................................................172
5.21.2.2.1 AMF planned removal procedure with UDSF deployed ...............................................................172
5.21.2.2.2 AMF planned removal procedure without UDSF..........................................................................173
5.21.2.3 Procedure for AMF Auto-recovery.....................................................................................................175
5.22 System Enablers for priority mechanism........................................................................................................176

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5.22.1 General......................................................................................................................................................176
5.22.2 Subscription-related Priority Mechanisms................................................................................................177
5.22.3 Invocation-related Priority Mechanisms...................................................................................................177
5.22.4 QoS Mechanisms applied to established QoS Flows................................................................................178
5.23 Supporting for Asynchronous Type Communication.....................................................................................179
5.24 3GPP PS Data Off..........................................................................................................................................179
5.25 Support of OAM Features ..............................................................................................................................179
5.25.1 Support of Tracing: Signalling Based Activation/Deactivation of Tracing ..............................................179
6 Network Functions ...............................................................................................................................180
6.1 General ...........................................................................................................................................................180
6.2 Network Function Functional description ......................................................................................................180
6.2.1 AMF..........................................................................................................................................................180
6.2.2 SMF ..........................................................................................................................................................181
6.2.3 UPF...........................................................................................................................................................182
6.2.4 PCF...........................................................................................................................................................183
6.2.5 NEF...........................................................................................................................................................183
6.2.5.1 Support for CAPIF..............................................................................................................................184
6.2.6 NRF ..........................................................................................................................................................184
6.2.7 UDM.........................................................................................................................................................185
6.2.8 AUSF........................................................................................................................................................185
6.2.9 N3IWF......................................................................................................................................................186
6.2.10 AF.............................................................................................................................................................186
6.2.11 UDR..........................................................................................................................................................186
6.2.12 UDSF........................................................................................................................................................187
6.2.13 SMSF........................................................................................................................................................187
6.2.14 NSSF.........................................................................................................................................................187
6.2.15 5G-EIR......................................................................................................................................................187
6.2.16 LMF..........................................................................................................................................................187
6.2.17 SEPP.........................................................................................................................................................187
6.2.18 Network Data Analytics Function (NWDAF) ..........................................................................................188
6.3 Principles for Network Function and Network Function Service discovery and selection ............................188
6.3.1 General......................................................................................................................................................188
6.3.2 SMF discovery and selection....................................................................................................................189
6.3.3 User Plane Function Selection..................................................................................................................190
6.3.3.1 Overview.............................................................................................................................................190
6.3.3.2 SMF Provisioning of available UPF(s) ...............................................................................................190
6.3.3.3 Selection of an UPF for a particular PDU Session..............................................................................191
6.3.4 AUSF discovery and selection..................................................................................................................191
6.3.5 AMF discovery and selection ...................................................................................................................192
6.3.6 N3IWF selection.......................................................................................................................................193
6.3.6.1 General................................................................................................................................................193
6.3.6.2 Stand-alone N3IWF selection .............................................................................................................194
6.3.6.3 Combined N3IWF/ePDG Selection ....................................................................................................194
6.3.7 PCF discovery and selection.....................................................................................................................195
6.3.7.0 General principles ...............................................................................................................................195
6.3.7.1 PCF discovery and selection for a UE or a PDU Session ...................................................................195
6.3.7.2 Providing policy requirements that apply to multiple UE and hence to multiple PCF........................195
6.3.7.3 Binding an AF request targeting an IP address to the relevant PCF ...................................................196
6.3.8 UDM discovery and selection...................................................................................................................196
6.3.9 UDR discovery and selection....................................................................................................................197
6.3.10 SMSF discovery and selection..................................................................................................................197
7 Network Function Services and descriptions .......................................................................................197
7.1 Network Function Service Framework...........................................................................................................197
7.1.1 General......................................................................................................................................................197
7.1.2 NF Service Consumer - NF Service Producer interactions.......................................................................198
7.1.3 Network Function Service discovery........................................................................................................199
7.1.4 Network Function Service Authorization .................................................................................................199
7.1.5 Network Function and Network Function Service registration and de-registration..................................199
7.2 Network Function Services ............................................................................................................................200
7.2.1 General......................................................................................................................................................200

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7.2.2 AMF Services ...........................................................................................................................................201
7.2.3 SMF Services............................................................................................................................................201
7.2.4 PCF Services.............................................................................................................................................201
7.2.5 UDM Services ..........................................................................................................................................202
7.2.6 NRF Services............................................................................................................................................202
7.2.7 AUSF Services..........................................................................................................................................203
7.2.8 NEF Services ............................................................................................................................................203
7.2.9 SMSF Services..........................................................................................................................................203
7.2.10 UDR Services ...........................................................................................................................................204
7.2.11 5G-EIR Services .......................................................................................................................................204
7.2.12 NWDAF Services .....................................................................................................................................204
7.2.13 UDSF Services..........................................................................................................................................204
7.2.14 NSSF Services ..........................................................................................................................................205
7.2.15 BSF Services.............................................................................................................................................205
7.2.16 LMF Services............................................................................................................................................205
7.2.17 CHF Services............................................................................................................................................205
7.3 Exposure.........................................................................................................................................................206
8 Control and User Plane Protocol Stacks...............................................................................................206
8.1 General ...........................................................................................................................................................206
8.2 Control Plane Protocol Stacks........................................................................................................................206
8.2.1 Control Plane Protocol Stacks between the 5G-AN and the 5G Core: N2 ...............................................206
8.2.1.1 General................................................................................................................................................206
8.2.1.2 AN - AMF...........................................................................................................................................207
8.2.1.3 AN - SMF ...........................................................................................................................................207
8.2.2 Control Plane Protocol Stacks between the UE and the 5GC...................................................................207
8.2.2.1 General................................................................................................................................................207
8.2.2.2 UE - AMF ...........................................................................................................................................209
8.2.2.3 UE – SMF ...........................................................................................................................................209
8.2.3 Control Plane Protocol Stacks between the network functions in 5GC....................................................210
8.2.3.1 The Control Plane Protocol Stack for the service based interface.......................................................210
8.2.3.2 The Control Plane protocol stack for the N4 interface between SMF and UPF..................................210
8.2.4 Control Plane for untrusted non 3GPP Access .........................................................................................210
8.3 User Plane Protocol Stacks.............................................................................................................................211
8.3.1 User Plane Protocol Stack for a PDU Session ..........................................................................................211
8.3.2 User Plane for untrusted non 3GPP Access..............................................................................................213
Annex A (informative): Relationship between Service-Based Interfaces and Reference Points...214
Annex B (normative): Mapping between temporary identities .....................................................216
Annex C (informative): Guidelines and Principles for Compute-Storage Separation...................217
Annex D (informative): Change history .............................................................................................218
History............................................................................................................................................................226

ETSI
Foreword
This Technical Specification has been produced by the 3rd Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.

ETSI
1 Scope
The present document defines the Stage 2 system architecture for the 5G System. The 5G System provides data
connectivity and services.
This specification covers both roaming and non-roaming scenarios in all aspects, including interworking between 5GS
and EPS, mobility within 5GS, QoS, policy control and charging, authentication and in general 5G System wide
features e.g. SMS, Location Services, Emergency Services.
ITU-T Recommendation I.130 [11] describes a three-stage method for characterisation of telecommunication services,
and ITU-T Recommendation Q.65 [12] defines Stage 2 of the method.
TS 23.502 [3] contains the stage 2 procedures and flows for 5G System and it is a companion specification to this
specification.
TS 23.503 [45] contains the stage 2 Policy Control and Charging architecture for 5G System and it is a companion
specification to this specification.
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.
[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TS 22.261: "Service requirements for next generation new services and markets; Stage 1".
[3] 3GPP TS 23.502: "Procedures for the 5G System; Stage 2".
[4] 3GPP TS 23.203: "Policies and Charging control architecture; Stage 2".
[5] 3GPP TS 23.040: "Technical realization of the Short Message Service (SMS); Stage 2".
[6] 3GPP TS 24.011: "Point-to-Point (PP) Short Message Service (SMS) support on mobile radio
interface: Stage 3".
[7] IETF RFC 7157: "IPv6 Multihoming without Network Address Translation".
[8] IETF RFC 4191: "Default Router Preferences and More-Specific Routes".
[9] IETF RFC 2131: "Dynamic Host Configuration Protocol".
[10] IETF RFC 4862: "IPv6 Stateless Address Autoconfiguration".
[11] ITU-T Recommendation I.130: "Method for the characterization of telecommunication services
supported by an ISDN and network capabilities of an ISDN".
[12] ITU-T Recommendation Q.65: "The unified functional methodology for the characterization of
services and network capabilities".
[13] 3GPP TS 24.301: "Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS):
Stage 3".
[14] IETF RFC 3736: "Stateless DHCP Service for IPv6".

ETSI
[15] 3GPP TS 23.228: "IP Multimedia Subsystem (IMS); Stage 2".
[16] 3GPP TS 22.173: "IMS Multimedia Telephony Service and supplementary services; Stage 1".
[17] 3GPP TS 23.122: "Non-Access-Stratum (NAS) functions related to Mobile Station in idle mode".
[18] 3GPP TS 23.167: "3rd Generation Partnership Project; Technical Specification Group Services
and Systems Aspects; IP Multimedia Subsystem (IMS) emergency sessions".
[19] 3GPP TS 23.003: "Numbering, Addressing and Identification".
[20] IETF RFC 7542: "The Network Access Identifier".
[21] 3GPP TS 23.002: "Network Architecture".
[22] 3GPP TS 23.335: "User Data Convergence (UDC); Technical realization and information flows;
Stage 2".
[23] 3GPP TS 23.221: "Architectural requirements".
[24] 3GPP TS 22.153: "Multimedia priority service".
[25] 3GPP TS 22.011: "Service Accessibility".
[26] 3GPP TS 23.401: "General Packet Radio Service (GPRS) enhancements for Evolved Universal
Terrestrial Radio Access Network (E-UTRAN) access".
[27] 3GPP TS 38.300: "NR; NR and NG-RAN Overall Description".
[28] 3GPP TS 38.331: "NR; Radio Resource Control (RRC); Protocol Specification".
[29] 3GPP TS 33.501: "Security architecture and procedures for 5G system".
[30] 3GPP TS 36.300: "Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal
Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2".
[31] 3GPP TS 37.340: "Evolved Universal Terrestrial Radio Access (E-UTRA) and NR; Multi-
connectivity; Stage 2".
[32] 3GPP TS 23.214: "Architecture enhancements for control and user plane separation of EPC nodes;
Stage 2".
[33] 3GPP TS 22.101: "3rd Generation Partnership Project; Technical Specification Group Services
and Systems Aspects; Service aspects; Service principles".
[34] 3GPP TS 38.413: "NG-RAN; NG Application Protocol (NGAP)".
[35] 3GPP TS 33.126: "Lawful Interception Requirements".
[36] 3GPP TS 23.682: "Architecture enhancements to facilitate communications with packet data
networks and applications".
[37] 3GPP TS 22.280: "Mission Critical Services Common Requirements (MCCoRe); Stage 1".
[38] 3GPP TS 23.379: "Functional architecture and information flows to support Mission Critical Push
To Talk (MCPTT); Stage 2".
[39] 3GPP TS 23.281: "Functional architecture and information flows to support Mission Critical
Video (MCVideo); Stage 2".
[40] 3GPP TS 23.282: "Functional architecture and information flows to support Mission Critical Data
(MCData); Stage 2".
[41] 3GPP TS 32.240: "Charging management; Charging architecture and principles".
[42] 3GPP TS 38.401: "NG-RAN Architecture description".
[43] 3GPP TS 23.402: "Architecture enhancements for non-3GPP accesses".

ETSI
[44] IETF RFC 4960: "Stream Control Transmission Protocol".
[45] 3GPP TS 23.503: "Policy and Charging Control Framework for the 5G System".
[46] 3GPP TS 23.041: "Public Warning System".
[47] 3GPP TS 24.501: "Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3".
[48] 3GPP TS 24.502: "Access to the 5G System (5GS) via non-3GPP access networks; Stage 3".
[49] 3GPP TS 29.500: "5G System; Technical Realization of Service Based Architecture; Stage 3".
[50] 3GPP TS 38.304: "NR; User Equipment (UE) procedures in idle mode".
[51] 3GPP TS 36.331: "Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource
Control (RRC); Protocol specification".
[52] 3GPP TS 36.304: "Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE)
procedures in idle mode".
[53] IETF RFC 1027: "Using ARP to Implement Transparent Subnet Gateways".
[54] IETF RFC 4861: "Neighbor Discovery for IP version 6 (IPv6)".
[55] 3GPP TS 23.271: "Functional stage 2 description of Location Services (LCS)".
[56] 3GPP TS 23.060: "General Packet Radio Service (GPRS); Service description; Stage 2".
[57] IETF RFC 4555: "IKEv2 Mobility and Multihoming Protocol (MOBIKE)".
[58] 3GPP TS 29.510: "5G System: Network function repository services; Stage 3".
[59] 3GPP TS 29.502: "5G System: Session Management Services: Stage 3".
[60] IETF RFC 7296: "Internet Key Exchange Protocol Version 2 (IKEv2) ".
[61] 3GPP TS 23.380: "IMS Restoration Procedures".
[62] 3GPP TS 24.229: "IP multimedia call control protocol based on Session Initiation Protocol (SIP)
and Session Description Protocol (SDP); Stage 3".
[63] 3GPP TS 23.292: "IP Multimedia Subsystem (IMS) centralized services; Stage 2".
[64] 3GPP TS 23.222: "Functional architecture and information flows to support Common API
Framework for 3GPP Northbound APIs".
[65] 3GPP TS 29.244: "Interface between the Control Plane and the User Plane Nodes; Stage 3".
[66] 3GPP TS 32.421: "Telecommunication management; Subscriber and equipment trace; Trace
concepts and requirements".
[67] 3GPP TS 32.290: "5G system; Services, operations and procedures of charging using Service
Based Interface (SBI)".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in TR 21.905 [1] and the following apply. A
term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905 [1].
5G Access Network: An access network comprising a NG-RAN and/or non-3GPP AN connecting to a 5G Core
Network.
5G Core Network: The core network specified in the present document. It connects to a 5G Access Network.

ETSI
5G QoS Flow: The finest granularity for QoS forwarding treatment in the 5G System. All traffic mapped to the same
5G QoS Flow receive the same forwarding treatment (e.g. scheduling policy, queue management policy, rate shaping
policy, RLC configuration, etc.). Providing different QoS forwarding treatment requires separate 5G QoS Flow.
5G QoS Identifier: A scalar that is used as a reference to a specific QoS forwarding behaviour (e.g. packet loss rate,
packet delay budget) to be provided to a 5G QoS Flow. This may be implemented in the access network by the 5QI
referencing node specific parameters that control the QoS forwarding treatment (e.g. scheduling weights, admission
thresholds, queue management thresholds, link layer protocol configuration, etc.).
5G System: 3GPP system consisting of 5G Access Network (AN), 5G Core Network and UE.
Allowed NSSAI: NSSAI provided by the Serving PLMN during e.g. a Registration procedure, indicating the S-NSSAIs
values the UE could use in the Serving PLMN for the current registration area.
Allowed Area: Area where the UE is allowed to initiate communication as specified in clause 5.3.2.3.
AMF Region: An AMF Region consists of one or multiple AMF Sets.
AMF Set: An AMF Set consists of some AMFs that serve a given area and Network Slice(s). AMF Set is unique within
an AMF Region and it comprises of AMFs that support the same Network Slice(s). Multiple AMF Sets may be defined
per AMF Region.
Application identifier: An identifier that can be mapped to a specific application traffic detection rule.
AUSF Group ID: This refers to one or more AUSF instances managing a specific set of SUPIs.
Configured NSSAI: NSSAI provisioned in the UE applicable to one or more PLMNs.
DN Access Identifier (DNAI): Identifier of a user plane access to one or more DN(s) where applications are deployed.
Emergency Registered: A UE is considered Emergency Registered over an Access Type in a PLMN when in limited
service state and registered for emergency services only over this Access Type in this PLMN.
Endpoint Address: An address used by a NF service consumer to access the NF service (i.e. to invoke service
operations) provided by a NF service provider. An Endpoint Address is represented in the syntax of Uniform Resource
Identifier (e.g. part of Resource URI of the NF service API).
Expected UE Behaviour: Set of parameters provisioned by an external party to 5G network functions on the foreseen
or expected UE behaviour, see clause 5.20.
Forbidden Area: An area where the UE is not allowed to initiate communication as specified in clause 5.3.2.3.
GBR QoS Flow: A QoS Flow using the GBR resource type or the Delay-critical GBR resource type and requiring
guaranteed flow bit rate.
Initial Registration: UE registration in RM-DEREGISTERED state as specified in clause 5.3.2.
Local Area Data Network: a DN that is accessible by the UE only in specific locations, that provides connectivity to a
specific DNN, and whose availability is provided to the UE.
Local Break Out (LBO): Roaming scenario for a PDU Session where the PDU Session Anchor and its controlling
SMF are located in the serving PLMN (VPLMN).
Mobility Pattern: Network concept of determining within the AMF the UE mobility parameters as specified in
clause 5.3.2.4.
Mobility Registration Update: UE re-registration when entering new TA outside the TAI List as specified in
clause 5.3.2.
MPS-subscribed UE: A UE having a USIM with MPS subscription.
NGAP UE association: The logical per UE association between a 5G-AN node and an AMF.
NGAP UE-TNLA-binding: The binding between a NGAP UE association and a specific TNL association for a given
UE.

ETSI
Network Function: A 3GPP adopted or 3GPP defined processing function in a network, which has defined functional
behaviour and 3GPP defined interfaces.
NOTE 2: A network function can be implemented either as a network element on a dedicated hardware, as a
software instance running on a dedicated hardware, or as a virtualised function instantiated on an
appropriate platform, e.g. on a cloud infrastructure.
Network Instance: Information identifying a domain. Used by the UPF for traffic detection and routing.
Network Slice: A logical network that provides specific network capabilities and network characteristics.
Network Slice instance: A set of Network Function instances and the required resources (e.g. compute, storage and
networking resources) which form a deployed Network Slice.
Non-GBR QoS Flow: A QoS Flow using the Non-GBR resource type and not requiring guaranteed flow bit rate.
NSI ID: an identifier for a Network Slice instance.
NF instance: an identifiable instance of the NF.
NF service: a functionality exposed by a NF through a service based interface and consumed by other authorized NFs.
NF service instance: an identifiable instance of the NF service.
NF service operation: An elementary unit a NF service is composed of.
NG-RAN: A radio access network that supports one or more of the following options with the common characteristics
that it connects to 5GC:
1) Standalone New Radio.
2) New Radio is the anchor with E-UTRA extensions.
3) Standalone E-UTRA.
4) E-UTRA is the anchor with New Radio extensions.
Non-Allowed area: Area where the UE is allowed to initiate Registration procedure but no other communication as
specified in clause 5.3.2.3.
Non-Seamless Non-3GPP offload: The offload of user plane traffic via non-3GPP access without traversing either
N3IWF or UPF.
PDU Connectivity Service: A service that provides exchange of PDUs between a UE and a Data Network.
PDU Session: Association between the UE and a Data Network that provides a PDU connectivity service.
PDU Session Type: The type of PDU Session which can be IPv4, IPv6, IPv4v6, Ethernet or Unstructured.
Periodic Registration Update: UE re-registration at expiry of periodic registration timer as specified in clause 5.3.2.
(Radio) Access Network: See 5G Access Network.
Requested NSSAI: NSSAI provided by the UE to the Serving PLMN during registration.
Service based interface: It represents how a set of services is provided/exposed by a given NF.
Service Continuity: The uninterrupted user experience of a service, including the cases where the IP address and/or
anchoring point change.
Service Data Flow Filter: A set of packet flow header parameter values/ranges used to identify one or more of the
packet (IP or Ethernet) flows constituting a Service Data Flow.
Service Data Flow Template: The set of Service Data Flow filters in a policy rule or an application identifier in a
policy rule referring to an application detection filter, required for defining a Service Data Flow.
Session Continuity: The continuity of a PDU Session. For PDU Session of IPv4 or IPv6 or IPv4v6 type "session
continuity" implies that the IP address is preserved for the lifetime of the PDU Session.

ETSI
Subscribed S-NSSAI: S-NSSAI based on subscriber information, which a UE is subscribed to use in a PLMN
UDM Group ID: This refers to one or more UDM instances managing a specific set of SUPIs.
UDR Group ID: This refers to one or more UDR instances managing a specific set of SUPIs.
UPF Service Area: The area within which PDU Session associated with the UPF can be served by (R)AN nodes via a
N3 interface between the (R)AN and the UPF without need to add a new UPF in between or to remove/re-allocate the
UPF.
Uplink Classifier: UPF functionality that aims at diverting Uplink traffic, based on filter rules provided by SMF,
towards Data Network.
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in TR 21.905 [1] and the following apply. An
abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in
TR 21.905 [1].
5GC 5G Core Network
5GS 5G System
5G-AN 5G Access Network
5G-EIR 5G-Equipment Identity Register
5G-GUTI 5G Globally Unique Temporary Identifier
5G-S-TMSI 5G S-Temporary Mobile Subscription Identifier
5QI 5G QoS Identifier
AF Application Function
AMF Access and Mobility Management Function
AS Access Stratum
AUSF Authentication Server Function
BSF Binding Support Function
CAPIF Common API Framework for 3GPP northbound APIs
CP Control Plane
DL Downlink
DN Data Network
DNAI DN Access Identifier
DNN Data Network Name
DRX Discontinuous Reception
ePDG evolved Packet Data Gateway
EBI EPS Bearer Identity
FAR Forwarding Action Rule
FQDN Fully Qualified Domain Name
GFBR Guaranteed Flow Bit Rate
GMLC Gateway Mobile Location Centre
GPSI Generic Public Subscription Identifier
GUAMI Globally Unique AMF Identifier
HR Home Routed (roaming)
LADN Local Area Data Network
LBO Local Break Out (roaming)
LMF Location Management Function
LRF Location Retrieval Function
MCX Mission Critical Service
MDBV Maximum Data Burst Volume
MFBR Maximum Flow Bit Rate
MICO Mobile Initiated Connection Only
MPS Multimedia Priority Service
N3IWF Non-3GPP InterWorking Function
NAI Network Access Identifier
NEF Network Exposure Function
NF Network Function
NGAP Next Generation Application Protocol
NR New Radio
NRF Network Repository Function

ETSI
NSI ID Network Slice Instance Identifier
NSSAI Network Slice Selection Assistance Information
NSSF Network Slice Selection Function
NSSP Network Slice Selection Policy
NWDAF Network Data Analytics Function
PCF Policy Control Function
PDR Packet Detection Rule
PEI Permanent Equipment Identifier
PER Packet Error Rate
PFD Packet Flow Description
PPD Paging Policy Differentiation
PPF Paging Proceed Flag
PPI Paging Policy Indicator
PSA PDU Session Anchor
QFI QoS Flow Identifier
QoE Quality of Experience
(R)AN (Radio) Access Network
RQA Reflective QoS Attribute
RQI Reflective QoS Indication
SA NR Standalone New Radio
SBA Service Based Architecture
SBI Service Based Interface
SD Slice Differentiator
SEAF Security Anchor Functionality
SEPP Security Edge Protection Proxy
SMF Session Management Function
SMSF Short Message Service Function
S-NSSAI Single Network Slice Selection Assistance Information
SSC Session and Service Continuity
SSCMSP Session and Service Continuity Mode Selection Policy
SST Slice/Service Type
SUCI Subscription Concealed Identifier
SUPI Subscription Permanent Identifier
TNL Transport Network Layer
TNLA Transport Network Layer Association
TSP Traffic Steering Policy
UDM Unified Data Management
UDR Unified Data Repository
UDSF Unstructured Data Storage Function
UL Uplink
UL CL Uplink Classifier
UPF User Plane Function
URSP UE Route Selection Policy
VID VLAN Identifier
VLAN Virtual Local Area Network
4 Architecture model and concepts
4.1 General concepts
The 5G System architecture is defined to support data connectivity and services enabling deployments to use techniques
such as e.g. Network Function Virtualization and Software Defined Networking. The 5G System architecture shall
leverage service-based interactions between Control Plane (CP) Network Functions where identified. Some key
principles and concept are to:
- Separate the User Plane (UP) functions from the Control Plane (CP) functions, allowing independent scalability,
evolution and flexible deployments e.g. centralized location or distributed (remote) location.
- Modularize the function design, e.g. to enable flexible and efficient network slicing.

ETSI
- Wherever applicable, define procedures (i.e. the set of interactions between network functions) as services, so
that their re-use is possible.
- Enable each Network Function to interact with other NF directly if required. The architecture does not preclude
the use of an intermediate function to help route Control Plane messages (e.g. like a DRA).
- Minimize dependencies between the Access Network (AN) and the Core Network (CN). The architecture is
defined with a converged core network with a common AN - CN interface which integrates different Access
Types e.g. 3GPP access and non-3GPP access.
- Support a unified authentication framework.
- Support "stateless" NFs, where the "compute" resource is decoupled from the "storage" resource.
- Support capability exposure.
- Support concurrent access to local and centralized services. To support low latency services and access to local
data networks, UP functions can be deployed close to the Access Network.
- Support roaming with both Home routed traffic as well as Local breakout traffic in the visited PLMN.
4.2 Architecture reference model
4.2.1 General
This specification describes the architecture for the 5G System. The 5G architecture is defined as service-based and the
interaction between network functions is represented in two ways.
- A service-based representation, where network functions (e.g. AMF) within the Control Plane enables other
authorized network functions to access their services. This representation also includes point-to-point reference
points where necessary.
- A reference point representation, shows the interaction exist between the NF services in the network functions
described by point-to-point reference point (e.g. N11) between any two network functions (e.g. AMF and SMF).
Service-based interfaces are listed in clause 4.2.6. Reference points are listed in clause 4.2.7.
Network functions within the 5GC Control Plane shall only use service-based interfaces for their interactions.
NOTE 1: The interactions between NF services within one NF are not specified in this Release of the specification.
NOTE 2: UPF does not provide any services in this Release of the specification, but can consume services provided
by 5GC Control Plane NFs.
4.2.2 Network Functions and entities
The 5G System architecture consists of the following network functions (NF). The functional description of these
network functions is specified in clause 6.
- Authentication Server Function (AUSF)
- Access and Mobility Management Function (AMF)
- Data Network (DN), e.g. operator services, Internet access or 3rd party services
- Unstructured Data Storage Function (UDSF)
- Network Exposure Function (NEF)
- Network Repository Function (NRF)
- Network Slice Selection Function (NSSF)
- Policy Control Function (PCF)
- Session Management Function (SMF)

ETSI
- Unified Data Management (UDM)
- Unified Data Repository (UDR)
- User Plane Function (UPF)
- Application Function (AF)
- User Equipment (UE)
- (Radio) Access Network ((R)AN)
- 5G-Equipment Identity Register (5G-EIR)
- Security Edge Protection Proxy (SEPP)
- Network Data Analytics Function (NWDAF)
4.2.3 Non-roaming reference architecture
Figure 4.2.3-1 depicts the non-roaming reference architecture. Service-based interfaces are used within the Control
Plane.
UE (R)AN UPF
AF
AMF SMF
PCF UDM
DNN6
NRFNEF
N3
N2 N4
AUSF
Nausf Namf Nsmf
NpcfNnrfNnef Nudm Naf
NSSF
Nnssf
N9
Figure 4.2.3-1: 5G System architecture
Figure 4.2.3-2 depicts the 5G System architecture in the non-roaming case, using the reference point representation
showing how various network functions interact with each other.

Ts 123501v150300p

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