ETSI TS 123 548 V18.10.0 (2025-07)

5G; 5G System Enhancements for Edge Computing; Stage 2 (3GPP TS 23.548 version 18.10.0 Release 18)

RTS/TSGS-0223548via0

General Information

• Status: Not Published
• Technical Committee: 3GPP SA 2 - Architecture
• Current Stage: 12 - Citation in the OJ (auto-insert)
• Completion Date: 21-Jul-2025

Standards Content (Sample)

TECHNICAL SPECIFICATION
5G;
5G System Enhancements for Edge Computing;
Stage 2
(3GPP TS 23.548 version 18.10.0 Release 18)

3GPP TS 23.548 version 18.10.0 Release 18 1 ETSI TS 123 548 V18.10.0 (2025-07)

Reference
RTS/TSGS-0223548via0
Keywords
5G
ETSI
650 Route des Lucioles
F-06921 Sophia Antipolis Cedex - FRANCE

Tel.: [phone]  Fax: [phone]

Siret N° 348 623 562 00017 - APE 7112B
Association à but non lucratif enregistrée à la
Sous-Préfecture de Grasse (06) N° w061004871

Important notice
The present document can be downloaded from the
ETSI Search & Browse Standards application.
The present document may be made available in electronic versions and/or in print. The content of any electronic and/or
print versions of the present document shall not be modified without the prior written authorization of ETSI. In case of any
existing or perceived difference in contents between such versions and/or in print, the prevailing version of an ETSI
deliverable is the one made publicly available in PDF format on ETSI deliver repository.
Users should be aware that the present document may be revised or have its status changed,
this information is available in the Milestones listing.
If you find errors in the present document, please send your comments to
the relevant service listed under Committee Support Staff.
If you find a security vulnerability in the present document, please report it through our
Coordinated Vulnerability Disclosure (CVD) program.
Notice of disclaimer & limitation of liability
The information provided in the present deliverable is directed solely to professionals who have the appropriate degree of
experience to understand and interpret its content in accordance with generally accepted engineering or
other professional standard and applicable regulations.
No recommendation as to products and services or vendors is made or should be implied.
No representation or warranty is made that this deliverable is technically accurate or sufficient or conforms to any law
and/or governmental rule and/or regulation and further, no representation or warranty is made of merchantability or fitness
for any particular purpose or against infringement of intellectual property rights.
In no event shall ETSI be held liable for loss of profits or any other incidental or consequential damages.

Any software contained in this deliverable is provided "AS IS" with no warranties, express or implied, including but not
limited to, the warranties of merchantability, fitness for a particular purpose and non-infringement of intellectual property
rights and ETSI shall not be held liable in any event for any damages whatsoever (including, without limitation, damages
for loss of profits, business interruption, loss of information, or any other pecuniary loss) arising out of or related to the use
of or inability to use the software.
Copyright Notification
No part may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm except as authorized by written permission of ETSI.
The content of the PDF version shall not be modified without the written authorization of ETSI.
The copyright and the foregoing restriction extend to reproduction in all media.

© ETSI 2025.
All rights reserved.
ETSI
3GPP TS 23.548 version 18.10.0 Release 18 2 ETSI TS 123 548 V18.10.0 (2025-07)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The declarations
pertaining to these essential IPRs, if any, are publicly available for ETSI members and non-members, and can be
found in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to
ETSI in respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the
ETSI IPR online database.
Pursuant to the ETSI Directives including the ETSI IPR Policy, no investigation regarding the essentiality of IPRs,
including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not
referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become,
essential to the present document.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
DECT™, PLUGTESTS™, UMTS™ and the ETSI logo are trademarks of ETSI registered for the benefit of its
Members. 3GPP™, LTE™ and 5G™ logo are trademarks of ETSI registered for the benefit of its Members and of the
3GPP Organizational Partners. oneM2M™ logo is a trademark of ETSI registered for the benefit of its Members and of ®
the oneM2M Partners. GSM and the GSM logo are trademarks registered and owned by the GSM Association.
Legal Notice
This Technical Specification (TS) has been produced by ETSI 3rd Generation Partnership Project (3GPP).
The present document may refer to technical specifications or reports using their 3GPP identities. These shall be
interpreted as being references to the corresponding ETSI deliverables.
The cross reference between 3GPP and ETSI identities can be found at 3GPP to ETSI numbering cross-referencing.
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
ETSI
3GPP TS 23.548 version 18.10.0 Release 18 3 ETSI TS 123 548 V18.10.0 (2025-07)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 6
1 Scope . 7
2 References . 7
3 Definitions of terms, symbols and abbreviations . 7
3.1 Terms . 7
3.2 Abbreviations . 8
4 Reference Architecture and Connectivity Models . 8
4.1 General . 8
4.2 Reference Architecture for Supporting Edge Computing . 8
4.3 Connectivity Models . 10
5 Functional Description for Supporting Edge Computing . 11
5.1 EASDF . 11
5.1.1 Functional Description . 11
5.1.2 EASDF Discovery and Selection . 12
5.2 Edge DNS Client (EDC) Functionality . 12
5.2.1 Functional Description . 12
6 Procedures for Supporting Edge Computing . 13
6.1 General . 13
6.2 EAS Discovery and Re-discovery . 14
6.2.1 General . 14
6.2.2 EAS (Re-)discovery over Distributed Anchor Connectivity Model . 15
6.2.2.1 General . 15
6.2.2.2 EAS Discovery Procedure . 15
6.2.2.3 EAS Re-discovery Procedure at Edge Relocation . 15
6.2.2.4 Procedure for EAS Discovery with Dynamic PSA Distribution . 16
6.2.3 EAS (Re-)discovery over Session Breakout Connectivity Model . 18
6.2.3.1 General . 18
6.2.3.2 EAS Discovery Procedure . 18
6.2.3.2.1 General . 18
6.2.3.2.2 EAS Discovery Procedure with EASDF . 19
6.2.3.2.3 EAS Discovery Procedure with Local DNS Server/Resolver . 26
6.2.3.2.4 Select common DNAI with Local DNS Server/Resolver for a set of UEs . 28
6.2.3.2.5 Common EAS discovery with EASDF for a set of UEs . 28
6.2.3.2.6 EAS discovery corresponding to Common DNAI with EASDF for a set of UEs . 30
6.2.3.2.7 Coordination among SMFs for Common EAS/DNAI determination . 31
6.2.3.3 EAS Re-discovery Procedure at Edge Relocation . 32
6.2.3.4 EAS Deployment Information Management . 34
6.2.3.4.1 General . 34
6.2.3.4.2 EAS Deployment Information Provision from AF via NEF. 35
6.2.3.4.3 EAS Deployment Information Management in the SMF . 35
6.2.3.4.4 BaselineDNSPattern Management in the EASDF . 36
6.2.4 EDC Functionality based DNS Query to reach EASDF/DNS Resolver/DNS Server indicated by the
SMF . 37
6.3 Edge Relocation . 37
6.3.1 General . 37
6.3.2 Edge Relocation Involving AF Change . 38
6.3.3 Edge Relocation Using EAS IP Replacement . 38
6.3.3.1 EAS IP Replacement Procedures . 39
6.3.3.1.1 Enabling EAS IP Replacement Procedure by AF . 39
ETSI
3GPP TS 23.548 version 18.10.0 Release 18 4 ETSI TS 123 548 V18.10.0 (2025-07)
6.3.3.1.2 EAS IP Replacement Update upon DNAI and EAS IP Change . 40
6.3.3.1.3 Disabling EAS IP Replacement Procedure . 41
6.3.3.2 Enhancement to AF Influence . 41
6.3.4 AF Request for Simultaneous Connectivity over Source and Target PSA at Edge Relocation . 42
6.3.5 Packet Buffering for Low Packet Loss . 42
6.3.6 Edge Relocation Considering User Plane Latency Requirement . 44
6.3.7 Edge Relocation Triggered by AF . 44
6.4 Network Exposure to Edge Application Server. 45
6.4.1 General . 45
6.4.2 Network Exposure to Edge Application Server . 45
6.4.2.1 Usage of Nupf_EventExposure to Report QoS Monitoring results . 45
6.4.2.2 Local NEF Discovery . 47
6.5 Support of 3GPP Application Layer Architecture for Enabling Edge Computing . 47
6.5.1 General . 47
6.5.2 ECS Address Provisioning . 48
6.5.2.1 ECS Address Configuration Information . 48
6.5.2.2 ECS Address Configuration Information Provisioning to the UE. 48
6.5.2.3 ECS Address Provisioning by a 3rd Party AF . 49
6.5.2.4 ECS Address Provisioning by MNO . 49
6.5.2.5 Interworking with EPC . 49
6.5.2.6 ECS Address Provisioning in Roaming . 49
6.5.2.6.1 General . 49
6.5.2.6.2 ECS Address Configuration Information Provision from AF via NEF in VPLMN . 49
6.5.2.6.3 ECS Address Configuration Information Provision to the SMF in VPLMN . 50
6.6 Support of AF Guidance to PCF Determination of Proper URSP Rules . 51
6.7 Support of the local traffic routing in VPLMN for Home Routed PDU Session for roaming (HR-SBO) . 52
6.7.1 General . 52
6.7.2 Procedure . 52
6.7.2.1 General . 52
6.7.2.2 PDU Session establishment for supporting HR-SBO in VPLMN . 53
6.7.2.3 EAS Discovery Procedure with V-EASDF for HR-SBO . 56
6.7.2.4 EAS Discovery Procedure with Local DNS for HR-SBO . 58
6.7.2.5 EAS discovery procedure with V-EASDF/Local DNS Server using IP replacement mechanism
for supporting HR-SBO . 59
6.7.2.6 N2 Handover with V-SMF insertion/change/removal in HR-SBO case . 60
6.7.2.7 Inter V-SMF mobility registration update procedure in HR-SBO case . 64
6.7.2.8 N2 Handover without V-SMF change in HR-SBO case . 67
6.7.2.9 Xn Handover with V-SMF change in HR-SBO case . 68
6.7.2.10 Xn Handover without V-SMF change in HR-SBO case . 69
6.7.3 EAS Re-discovery and Edge Relocation Procedure . 69
6.7.3.1 General . 69
6.7.3.2 Network triggered EAS change in HR-SBO context . 70
6.7.4 AF request on PDU Sessions supporting HR-SBO. 71
6.8 Support for mapping between EAS address Information and DNAI . 72
6.8.1 General . 72
6.8.2 AF request for DNAI Procedures . 73
7 Network Function Services and Descriptions . 73
7.1 EASDF Services . 73
7.1.1 General . 73
7.1.2 Neasdf_DNSContext Service. 74
7.1.2.1 General . 74
7.1.2.2 Neasdf_DNSContext_Create Service Operation . 74
7.1.2.3 Neasdf_DNSContext_Update Service Operation . 74
7.1.2.4 Neasdf_DNSContext_Delete Service Operation . 74
7.1.2.5 Neasdf_DNSContext_Notify Service Operation . 75
7.1.3 Neasdf_BaselineDNSPattern Service . 75
7.1.3.1 General . 75
7.1.3.2 Neasdf_BaselineDNSPattern_Create Service Operation . 75
7.1.3.3 Neasdf_BaselineDNSPattern_Update Service Operation . 75
7.1.3.4 Neasdf_BaselineDNSPattern_Delete Service Operation . 75
ETSI
3GPP TS 23.548 version 18.10.0 Release 18 5 ETSI TS 123 548 V18.10.0 (2025-07)
Annex A (Informative): EAS Discovery Using 3rd Party Mechanisms . 76
Annex B (Informative): Application Layer based EAS (Re-)Direction . 77
Annex C (Informative): Considerations for EAS (re)Discovery . 78
C.1 General . 78
C.2 Impact of IP Addresses for DNS Resolver on UE . 78
C.3 UE Considerations for EAS Re-discovery . 78
C.4 UE Procedures for Session Breakout . 79
C.5 Split-UE Considerations for EAS (Re-)discovery . 79
C.6 Detection of UE not using 5GC provided DNS server . 79
Annex D (Informative): Examples of AF Guidance to PCF for Determination of URSP Rules . 81
Annex E (informative): EPS Interworking Considerations . 82
E.1 General . 82
E.2 Distributed Anchor . 82
E.3 Multiple Sessions . 82
E.4 Session Breakout . 82
Annex F (Informative): EAS Relocation on Simultaneous Connectivity over Source and Target
PSA . 83
Annex G (Informative): Change history . 86
History . 90
ETSI
3GPP TS 23.548 version 18.10.0 Release 18 6 ETSI TS 123 548 V18.10.0 (2025-07)
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
3GPP TS 23.548 version 18.10.0 Release 18 7 ETSI TS 123 548 V18.10.0 (2025-07)
1 Scope
The present document defines the Stage 2 specifications for enhancements of 5G System to support Edge Computing.
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 23.501: "System architecture for the 5G System (5GS); Stage 2".
[3] 3GPP TS 23.502: "Procedures for the 5G System; Stage 2".
[4] 3GPP TS 23.503: "Policy and Charging Control Framework for the 5G System; Stage 2".
[5] 3GPP TS 23.558: "Architecture for enabling Edge Applications (EA)".
[6] IETF RFC 7871: "Client Subnet in DNS Queries".
[7] 3GPP TS 24.301: "Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS);
Stage 3".
[8] 3GPP TS 24.526: "User Equipment (UE) policies for 5G System (5GS); Stage 3".
[9] 3GPP TS 29.500: "Technical Realization of Service Based Architecture; Stage 3".
[10] 3GPP TS 23.288: "Architecture enhancements for 5G System (5GS) to support network data
analytics services".
[11] 3GPP TS 24.501: "Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3".
[12] 3GPP TS 33.501: "Security architecture and procedures for 5G System".
3 Definitions of terms, symbols and abbreviations
3.1 Terms
For the purposes of the present document, the terms given in TR 21.905 [1], TS 23.501 [2] 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]
and TS 23.501 [2].
Central DNS resolver/server: A DNS resolver/server centrally deployed by the 5GC operator or 3rd party and is
responsible for resolving the UE DNS Queries into suitable Edge Application Server (EAS) IP address(es).
Edge Application Server: An Application Server resident in the Edge Hosting Environment.
Edge Hosting Environment: An environment providing support required for Edge Application Server's execution.
ETSI
3GPP TS 23.548 version 18.10.0 Release 18 8 ETSI TS 123 548 V18.10.0 (2025-07)
Local part of DN: The set of network entities of a DN that are deployed locally. The local access to the DN provides
access to the local part of DN.
Local DNS resolver/server: A DNS resolver/server that may be locally deployed by 5GC operator or 3rd parties within
the Local DN, and is responsible for resolving UE DNS Queries into suitable EAS IP address(es) within the local DN.
The L-DNS resolvers/servers may or may not have connectivity with C-DNS depending on the deployment.
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in TR 21.905 [1], TS 23.501 [2] 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] and TS 23.501 [2].
C-DNS Central DNS
C-NEF Central NEF
C-PSA UPF Central PSA UPF
EAS Edge Application Server
EASDF Edge Application Server Discovery Function
ECS Edge Configuration Server
EDC Edge DNS Client
EEC Edge Enabler Client
EES Edge Enabler Server
EHE Edge Hosting Environment
L-DN Local part of DN
L-DNS Local DNS
L-NEF Local NEF
L-PSA UPF Local PSA UPF
HR-SBO Home Routed Session BreakOut

4 Reference Architecture and Connectivity Models
4.1 General
Edge Computing enables operator and 3rd party services to be hosted close to the UE's access point of attachment, so as
to achieve an efficient service delivery through the reduced end-to-end latency and load on the transport network.
5GS supports Edge Hosting Environment (EHE) deployed in the DN beyond the PSA UPF. An EHE may be under the
control of either the operator or 3rd parties.
The Edge Computing features defined in this specification are applicable to PLMN(s) and to SNPN(s).
The Local part of the DN in which EHE is deployed may have user plane connectivity with both a centrally deployed
PSA and locally deployed PSA of same DNN. Edge Computing enablers as described in clause 5.13 of TS 23.501 [2],
e.g. local routing and traffic steering, session and service continuity, AF influenced traffic routing, are leveraged in this
specification.
Edge Computing in the serving network (e.g. for Local Break Out roaming scenario in case of PLMN access or Home
Routed with Session Breakout roaming scenario) is supported. For AF guidance to PCF determination of URSP rules in
the HR-SBO scenario, the Serving network (e.g. VPLMN or serving SNPN) has no control on URSP, so cannot
influence UE in selecting a specific Edge Computing related DNN and S-NSSAI.
4.2 Reference Architecture for Supporting Edge Computing
The reference architectures for supporting Edge Computing are based on the reference architectures specified in
clause 4.2 of TS 23.501 [2]. The following reference architectures for non-roaming, LBO roaming and HR with Session
Breakout (HR-SBO) roaming scenarios further depict the relationship between the 5GS and a DN where Edge
Application Servers (EASs) are deployed in an EHE.
ETSI
3GPP TS 23.548 version 18.10.0 Release 18 9 ETSI TS 123 548 V18.10.0 (2025-07)
Figure 4.2-1 depicts 5GS architecture for non-roaming scenario supporting Edge Computing with UL CL/BP.
NRF PCF AF UDM
Nudm
Nnrf Npcf Naf
Nsmf Nnef Neasdf
Namf
AMF SMF NEF EASDF
N1 N2 N4 N4 N4
UPF UPF
N3 N9 N6
DN
UE AN
(UL CL/ BP) (C-PSA)
UPF
EAS
N6
(L-PSA)
Local part of DN
Figure 4.2-1: 5GS providing access to EAS with UL CL/BP for non-roaming scenario
Figure 4.2-2 depicts 5GS architecture for non-roaming scenario supporting Edge Computing without UL CL/BP.
UDM
NRF PCF AF
Nnrf Nudm
Npcf Naf
Nsmf Nnef Neasdf
Namf
AMF SMF NEF EASDF
N1 N2 N4
UPF EAS
N3 N6
UE AN
(PSA) Local part of DN
Figure 4.2-2: 5GS providing access to EAS without UL CL/BP for non-roaming scenario
Figure 4.2-3 depicts 5GS architecture for LBO roaming scenario supporting Edge Computing with UL CL/BP.
NRF PCF AF PCF
Nnrf Npcf Naf
Npcf
Nsmf Nnef Neasdf
Namf Nudm
AMF SMF NEF EASDF UDM
N1 N2 N4 N4 N4
UPF UPF
N3 N9 N6
DN
UE AN
(UL CL/ BP) (C-PSA)
UPF EAS
N6
VPLMN HPLMN
(L-PSA) Local part of DN
Figure 4.2-3: 5GS providing access to EAS with UL CL/BP for LBO roaming scenario
ETSI
3GPP TS 23.548 version 18.10.0 Release 18 10 ETSI TS 123 548 V18.10.0 (2025-07)
Figure 4.2-4 depicts 5GS architecture for LBO roaming scenario supporting Edge Computing without UL CL/BP.
NRF PCF AF PCF
Nnrf
Npcf Naf Npcf
Namf Nsmf Nnef Neasdf Nudm
AMF SMF NEF EASDF UDM
N1 N2 N4
UPF
EAS
N3 N6
UE AN
(PSA)
Local part of DN
VPLMN HPLMN
Figure 4.2-4: 5GS providing access to EAS without UL CL/BP for LBO roaming scenario
Figure 4.2-5 depicts 5GS architecture for HR-SBO roaming scenario supporting Edge Computing with UL CL/BP.
NRF PCF AF PCF
Naf
Npcf
Nnrf Npcf
Neasdf
Nnef Nsmf Nudm
Namf Nsmf
EASDF
NEF SMF UDM
AMF SMF
N4
N1 N4 N4
N2
N6
N3 N9
UPF
UE UPF DN
AN
(ULCL/BP)
EAS
UPF
EAS
N6
(L-PSA)
Local part of DN
VPLMN HPLMN
Figure 4.2-5: 5GS providing access to EAS with UL CL/BP for HR-SBO roaming scenario
NOTE 1: Only some of the 5GS NFs are shown in the above reference architecture figures. In the above figures, the
split between the UPF acting as UL CL/BP and the UPF acting as local PSA is illustrative.
NOTE 2: Only the control plane of EASDF is depicted in the figure, the user plane between the EASDF and the
UPF (i.e. over which the DNS messages are exchanged) is part of N6. Additionally, the EADSF may have
direct connectivity with the local parts of one or more Data Networks.
NOTE 3: For the HR-SBO roaming scenario, there can be other UPF(s) located in VPLMN between the UPF acting
UL CL/BP and the UPF acting as remote PSA in HPLMN.
4.3 Connectivity Models
5GC supports the following connectivity models to enable Edge Computing:
- Distributed Anchor Point: For a PDU Session, the PSA UPF is in a local site, i.e. close to the UE location. The
PSA UPF may be changed e.g. due to UE mobility and using SSC mode 2 or 3.
- Session Breakout: A PDU Session has a PSA UPF in a central site (C-PSA UPF) and one or more PSA UPF in
the local site (L-PSA UPF). The C-PSA UPF provides the IP Anchor Point when UL Classifier is used. The
ETSI
3GPP TS 23.548 version 18.10.0 Release 18 11 ETSI TS 123 548 V18.10.0 (2025-07)
Edge Computing application traffic is selectively diverted to the L-PSA UPF using UL Classifier or multi-
homing Branching Point mechanisms. The L-PSA UPF may be changed due to e.g. UE mobility.
- Multiple PDU Sessions: Edge Computing applications use PDU Session(s) with a PSA UPF(s) in local site(s).
The rest of applications use PDU Session(s) with PSA UPF(s) in the central site(s). Any PSA UPF may be
changed due to e.g. UE mobility and using SSC mode 3 with multiple PDU Sessions.
URSP rules, for steering the mapping between UE applications and PDU Sessions, can be used for any connectivity
model and they are required for the Multiple PDU Sessions model.
These three connectivity models are illustrated in Figure 4.3-1:
UE UPF
DN
Distributed Anchor Point
UE UPF UPF
DN
Session Breakout
DN
UPF
UE
DN
UPF
Multiple PDU Sessions
DN
Radio Local Central
Sites Sites Sites
IP Anchor Point
UL CL/BP and Local PSA UPF
Figure 4.3-1: 5GC Connectivity Models for Edge Computing
5 Functional Description for Supporting Edge
Computing
5.1 EASDF
5.1.1 Functional Description
The Edge Application Server Discovery Function (EASDF) includes one or more of the following functionalities:
- Registering to NRF for EASDF discovery and selection.
- Providing DNS security information to SMF.
- Handling the DNS messages according to the instruction from the SMF, including:
- Receiving DNS message handling rules and/or BaselineDNSPattern from the SMF.
- Exchanging DNS messages from the UE.
- Forwarding DNS messages to C-DNS or L-DNS for DNS Query.
- Adding EDNS Client Subnet (ECS) option into DNS Query for an FQDN.
- Reporting to the SMF the information related to the received DNS messages.
- Buffering/Discarding DNS messages from the UE or DNS Server.
ETSI
3GPP TS 23.548 version 18.10.0 Release 18 12 ETSI TS 123 548 V18.10.0 (2025-07)
- Providing a DNS response with a specific IP address to a DNS query.
- Constructing and sending DNS Query messages with specific FQDN and ECS option.
- Terminates the DNS security, if used.
The EASDF has direct user plane connectivity (i.e. without any NAT) with the PSA UPF over N6 for the transmission
of DNS signalling exchanged with the UE. The deployment of a NAT between EASDF and PSA UPF is not supported.
Multiple EASDF instances may be deployed within a PLMN.
The interactions between 5GC NF(s) and the EASDF take place within a PLMN.
5.1.2 EASDF Discovery and Selection
The EASDF discovery and selection is defined in clause 6.3 in TS 23.501 [2].
5.2 Edge DNS Client (EDC) Functionality
5.2.1 Functional Description
The Edge DNS Client (EDC) functionality is a 3GPP functionality in the UE that ensures that DNS requests from
applications are sent to the DNS Server's (e.g. EASDF/DNS resolver) IP address received from the SMF in the ePCO.
The EDC functionality in the UE is a UE capability that ensures the usage of the EAS discovery and re-discovery
functionalities defined in clause 6.2.
NOTE 1: A UE without EDC functionality can use the EAS (re-)discovery functionalities provided by EASDF, but
the usage of the EASDF cannot be ensured since it may use a different DNS server from the DNS server
provided by the operator.
Figure 5.2-1 depicts the Edge DNS Client (EDC) functionality in the UE.
UE
EDC
consumer
EDC
functionality
Figure 5.2-1: EDC functionality in the UE
NOTE 2: Whether EDC functionality is provided to the consumer directly or via/by the UE's operating system is
implementation specific. The APIs between EDC consumer and EDC functionality are out of scope of
3GPP.
A UE that hosts the EDC functionality indicates its capability in the PCO during the PDU Session Establishment and
the PDU Session Modification procedures. The EDC functionality includes the following functionalities:
- Configures the DNS Client with the DNS Server's configuration (IP address and, conditionally, DNS security
information of the EASDF/DNS resolver; see TS 24.501 [11] and TS 33.501 [12]) received from the SMF in the
ePCO according to TS 23.501 [2] clause 5.6.10.1.
ETSI
3GPP TS 23.548 version 18.10.0 Release 18 13 ETSI TS 123 548 V18.10.0 (2025-07)
- DNS Client:
- Provides the capability to the consumer in the UE to resolve FQDN using DNS Queries towards the DNS
Server (e.g., EASDF/DNS resolver) indicated by the SMF.
- Sends DNS Queries towards the DNS Server indicated by the SMF via the related PDU session.
- Forwards EAS IP addresses and other relevant information included in the DNS responses received from the
DNS Server to the consumer in the UE.
- Provision of DNS settings (Optional):
- Provides to the consumer in the UE the configuration of the DNS Server (IP address and, conditionally, DNS
security information of the EASDF/DNS resolver; see TS 24.501 [11] and TS 33.501 [12]) received from the
SMF. The consumer in the UE can explicitly request the DNS Server's configuration and/or can
subscribe/unsubscribe to receive updates of the DNS Server's configuration.
When the UE performs an FQDN resolution request for an application, the UE shall use the EDC functionality to
perform the DNS resolution in one of the following cases:
- the application mapped onto the PDU Session explicitly requests the use of the EDC functionality and the SMF
indicated, at PDU Session Establishment or at PDU Session Modification, that the use of the EDC functionality
is allowed for that PDU session; or
- the SMF indicated, at PDU Session Establishment or at PDU Session Modification, that the use of the EDC
functionality is required for the PDU Session for the specific DNN. In this case, the UE shall use the EDC
functionality for all the applications mapped onto that PDU Session.
NOTE 3: Whether the specific DNN(s) is applied is based on the agreement between the MNO and the application
provider.
NOTE 4: User preferences at OS level related to the use of DNS server do not apply when the EDC functionality is
used.
NOTE 5: It is subject to local regulatory requirements whether the MNO can force the UE to use EDC
functionality.
6 Procedures for Supporting Edge Computing
6.1 General
Edge Computing enables operator and 3rd party services to be hosted in EAS close to the UE's point of attachment. The
traffic to EAS can be routed based on the UE position and EAS availability "near to" that position.
The subsequent clauses describe the procedures for supporting Edge Computing in 5G System considering different
connectivity models, including:
- EAS discovery and re-discovery.
- Edge relocation.
- Network exposure to Edge Application Server.
- Support of 3GPP application layer architecture defined in TS 23.558 [5].
- Support of AF guidance to PCF determination of proper URSP rules.
ETSI
3GPP TS 23.548 version 18.10.0 Release 18 14 ETSI TS 123 548 V18.10.0 (2025-07)
6.2 EAS Discovery and Re-discovery
6.2.1 General
In Edge Computing deployment, an application service may be served by multiple Edge Application Servers typically
deployed in different sites. These multiple Edge Application Servers that host service may use a single IP address
(anycast address) or different IP addresses. To start such a service, the UE needs to know the IP address(es) of the
Application Server(s) serving the service. The UE may do a discovery to get the IP address(es) of a suitable Edge
Application Server (e.g. the closest one), so that the traffic can be locally routed to the Edge Application Server and
service latency, traffic routing path and user service experience can be optimized.
EAS discovery is the procedure by which a UE discovers the IP address(es) of a suitable Edge Application Server(s)
using Domain Name System (DNS). EAS Re-discovery is the EAS Discovery procedure that takes place when the
previously discovered Edge Application Server cannot be used or may have become non-optimal (e.g. at edge
relocation).
The DNS server to be used for EAS (re-)discovery may be deployed in different locations in the network as Central
DNS (C-DNS) server or as Local DNS (L-DNS) resolver/server.
NOTE 1: The C-DNS servers and/or L-DNS resolvers/servers can use an anycast address.
NOTE 2: The C-DNS servers or L-DNS resolvers/servers can contact any other DNS servers for recursive queries,
which is out of scope of this specification.
NOTE 3: This specification describes the discovery procedure based on 5GS NFs as to ensure the UE is served by
the application service closest to the UE's point of attachment. However, this does not exclude other
upper layer solution that can be adopted by operator or service provider, like the EAS Discovery
procedure defined in TS 23.558 [5], or other alternatives shown in Annex A and Annex B. How those
other solutions work, or whether they are able to guarantee the closest application service for the UE, is
out of the scope of this specification.
In order to provide a translation of the FQDN of an EAS into the address of an EAS as topologically close as possible to
the UE, the Domain Name System may use following information:
- The source IP address of the incoming DNS Query; and/o
...