5G-Advanced: 3GPP Rel-18 SA2 Features

5G-Advanced in 3GPP SA2

On the 20th of December 2021, 3GPP SA TSG approved a total of 28 Work-/Study-Items (WIs/SIs) for the SA2 Rel-18 at the SA plenary meeting #94e (SP-94e). 3GPP Rel-18 is the first release of the 5G-Advanced standard. The approved projects include TSN, NW slicing, support for edge computing, NW automation, location services, AI and ML-based services, XR services to name a few. In this post, we elaborate on each of the approved WI/SI entering 5G-Advanced standardization.

Note: this is a follow-up article from the 5G-Advanced RAN features. Interested readers are recommended to take a look here: 3GPP Rel-18: 5G-Advanced RAN Features – RIMEDO Labs.

Note: This article deals with SA2 features (i.e. TSG SA WG2 – System Architecture and Services) for the full list on the other SA WGs, see [2].

3GPP Rel-18 SA2 Features

The current set of accepted WIs/SIs (Work Items/Study items) for 3GPP Rel-18 SA2 features is shown on the figure below. Those are discussed in detail in the following section. Note: After the description, the relevant reference to the particular Study- and Work-Item description document is provided in square brackets.

Fig. 1. 3GPP Rel-18 SA2 Approved Projects, as per [1]

WI/SIs to be led by SA2

SA2 is responsible for the specification of the overall 3GPP system architecture and services including User Equipment, Access Network, Core Network, and IP Multimedia Subsystem. SA2 defines the main entities of the system architecture, and how these entities are linked to each other. It also defines the main functionality and the information exchange between these entities. Within 5G-Advanced Rel-18 scope the following projects are to be covered by SA2:

  • SI: System Enabler for Service Function Chaining (SFC) – will study whether and how to define SFC policies, and investigate solutions and procedures for the 5G network with SFC capabilities to identify/detect/classify UP traffic and steer the traffic to a chain of ordered service functions for SFC processing in non-roaming and home routed roaming scenarios. Based on the outcome, this SI could specify possible enhancement to northbound APIs for allowing an AF to request network capability exposure functionalities, e.g. to request a SFC for a certain traffic flow. [3GPP SP-211594, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • WI: Multimedia Priority Service (MPS) when access to EPC/5GC is WLAN – aims at enhancing the existing procedures to convey 3GPP MPS subscription information to the WLAN/UE during attach/registration procedure; and to pass an MPS priority indication to the WLAN for 4G Bearers/5G QoS Flows of MPS for MMTEL voice/video calls, and for MPS for Data Transport Service sessions. This applies to the scenarios when the UE (or IoT device) has WLAN access to EPC/5GC. [3GPP SP-211595, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Generic group management, exposure and communication enhancements – will study the three following tasks: 5G capabilities exposure for industrial and automation applications (i.e. enhance group attribute management and group status event reporting; and study whether and how to enhance NEF exposure framework to enable capability exposure for  provisioning of traffic characteristics and monitoring of performance characteristics applicable to each UE of a given group); enhancements of 5G VN group communication (i.e. support group communication for a 5G VN which supports multiple SMFs, including support of SMF redundancy for reliability of the 5G VN group communication); additional mechanisms or enhancements that are needed and how to support group communication allowing UE to simultaneously send data to different groups, where each group has a different QoS policy. [3GPP SP-211603, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Access Traffic Steering, Switching and Splitting (ATSSS) support in the 5G system architecture; Phase 3 – aims at further enhancing and optimizing ATSSS by studying the following topics: how new steering functionalities can be supported that are able to steer/switch/split non-TCP traffic flows; how to support redundant traffic steering with regards to both GBR and non-GBR traffic; how an Multi-Access (MA) PDU Session can support more types of access paths; how a MA PDU Session can be supported with one 3GPP access path via 5GC and one non-3GPP access path via ePDG/EPC. [3GPP SP-211612, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Enhanced support of Non-Public Networks (NPN); Phase 2 – will investigate enhancements of 5GS to enable broader use cases in relation with NPN, including the support for: enhanced mobility by enabling support for idle and connected mode mobility between SNPNs without new network selection; non-3GPP access for SNPN; enabling Localized Services via a local hosting NPN; enabling UE to discover, select, access  the local hosting NPN and the localized services via the hosting NPN with proper authorization; and what, how and when services are accessed via a specific network e.g. via home network. [3GPP SP-211656, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Uncrewed Aerial System (UAS), Uncrewed Aerial Vehicle (UAV) and Urban Air Mobility (UAM); Phase 2 – aims at studying and identifying potential architecture and system level enhancements for 5GS and EPS to support additional scenarios and requirements for UAV and UAM including: study on how to transport Broadcast Remote Identification and C2 communications via the 3GPP system by identifying how and whether existing mechanisms can be re-used, and identifying architectural and functional modifications required; and identification on how and whether existing mechanisms can be re-used, and identify architectural and functional modifications required, in order to support aviation applications such as Detect And Avoid (DAA). [3GPP SP-211632, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Extensions to the Time Sensitive Communications (TSC) Framework to support Deterministic Networking (DetNet) – will investigate: whether and how to enable 3GPP support for DetNet (IP-based DetNet) such that a mapping is provided between the central DetNet controller and the 5G system. Mapping involves translation of DetNet traffic profile and flow specification to 5GS QoS parameters and TSCAI; information which needs to be exposed from the 5G system to the DetNet controller. [3GPP SP-211633, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: 5G Timing Resiliency and TSC & URLLC enhancements – aims at studying the following: how to report 5GS network timing synchronization status (such as divergence from UTC and 5GS network timing source degradation) to UEs and 3rd party applications (AFs); how to enable AFs to request time synchronization service in a specific coverage area and how to enforce the coverage area; how to control 5G time synchronization service based on subscription; how to enable an AF to explicitly provide PER to NEF/PCF; support for 5G Timing Resiliency requirements; and support for low latency. [3GPP SP-211634, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Enhanced support of NR RedCap with long eDRX for RRC INACTIVE State; RedCap Phase 2 – will investigate potential enhancements of 5GS to enable the support of RRC_INACTIVE state with extended DRX cycle longer than 10.24s and in particular: support the of eDRX cycle longer than 10.24s and up to 10485.76s for RRC_INACTIVE state for RAN paging (e.g. PTW and eDRX cycle values); and MT signalling and data handling for UE with long eDRX cycle in RRC_INACTIVE state. [3GPP SP-211635, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Architecture Enhancements for Vehicle Mounted Relays – will study architectural and system level enhancements for 5G system to support the operation of base station (BS) relays possibly mounted on vehicles, using NR for wireless access toward the UE and for wireless self-backhauling toward 5GC. This will capture the following objectives: efficient mobility and service continuity for UE or a group of UEs to efficiently deliver data during different mobility scenarios (including mobility of the mobile BS relays); provisioning, policies and mechanisms to e.g. manage relay configuration, geographic restrictions, QoS, authorize and control of UEs’ access via the mobile BS relay; and support for roaming of mobile BS relay (including the roaming of MT and DU components), support for regulatory requirements (e.g. emergency, priority services, public safety), and support for location services for UEs accessing mobile BS relay. [3GPP SP-211636, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Enhancement to the 5GC LoCation Services (LCS); Phase 3 – aims at investigations on: potential architectural enhancements to LCS (e.g. in scenarios like edge computing, and other), i.e. support Positioning Signalling via UP and reduction of LCS latency, signalling overhead and location estimate exposure; how the LCS can benefit from NWDAF reporting and how the NWDAF use cases can benefit from LCS, e.g. enhanced accuracy in certain UE location or population flow statistics data that require UE locations smaller than TA/cell; enhancements to support low power positioning (e.g. for RedCap) including the requirements related to low power high accuracy positioning; enhancement to support the Flexible and Efficient Periodic and Triggered Location for UE power saving purpose; specific network functionality related to use of Positioning Reference Units (PRUs); enhancements to support the LCS continuity for UE mobility between EPS and 5GS; and LCS architectural enhancement to support network verified UE location and network controlled positioning for 5G satellite access. [3GPP SP-211637, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Enhancement of support for Edge Computing in 5G Core network; Phase 2 – will study the following items: improvements to roaming, to support access to EHE in a VPLMN; use cases that may benefit from exposure of additional data via the Local UPF/NEF including describing the characteristics of the data and data delivery to fulfil the use cases; solutions and their feasibility and suitability for improved network exposure of UE traffic related information to common Edge Application Server via Local UPF/NEF; solutions for supporting offload policies to match more granular sets of UE(s) without exposing operator-internal configurations to 3rd party AFs; solutions to influence of PSA-UPF and EAS (re)location for collection of UEs, e.g. in scenarios when UE(s) should use the same EAS and are not members of a pre-defined group; and solutions to avoid the UE to switch the EC traffic away from the EC PDU Session and 5GS altogether, due to conflicting connectivity preferences in the device. [3GPP SP-211638, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Support of Satellite Backhauling in 5GS – aims at investigating the following topics: architecture enhancements for support of a backhaul with changing delay, and/or limited bandwidth in case of a gNB with satellite backhaul only (including: policy/QoS control enhancements based on the detected packet delivery latency and/or bandwidth of the satellite backhaul on the UP path; exposure of backhaul information to AFs); and architecture enhancements for support of UPF deployed on GEO satellite with gNB on the ground (including: whether and how to enable satellite edge computing services via UPF on-board e.g., to reduce the latency for data transmission, and minimize the backhaul resources consumption; how to enhance local switch for UEs in a communication when they are served by UPF on-board). [3GPP SP-211639, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Support for 5G Wireless-Wireline Convergence (5WWC); Phase 2 – will enhance the works on 5WWC with the following items: improvements to the support of devices connecting behind 5G-RG (5G Residential Gateway) including providing differentiated service (e.g.  QoS and charging) for UE and Non-3GPP devices connected behind a 5G-RG; trusted/untrusted Non-3GPP access network (e.g. how to select a TNGF/N3IWF that supports the S-NSSAI(s) needed by the UE). [3GPP SP-211640, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Enhancement of Network Slicing; Phase 3 – will investigate the following further enhancements to Network Slicing: how to initiate a registration for a rejected S-NSSAI that was rejected in a first TA of the RA but may be available in another TA of the RA; enhancement the information available to the UE in roaming scenarios regarding the availability of network slices in VPLMNs available in the roaming country, in order to allow the UE to select and obtain services from the VPLMN supporting the network slices which UE would like to use; how to enhance the system to ensure network controlled behaviour of network slice usage including UE registration and PDU Session establishment; deployment considerations when a service provided has an area of service that does not overlap with the already deployed Tracking Areas and/or have a limited life time, and how existing mechanisms including network slicing can help support such scenarios; and how to enhance the support of NSAC when more than one NSACF is involved in enforcing a shared maximum allowed number of the UEs or PDU Sessions for a network slice in one PLMN or in roaming, in order to avoid fragmentation of the shared maximum allowed number. [3GPP SP-211641, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Enhancement of 5G AM Policy; Phase 2 – will work on the current mechanisms to provide Access and Mobility (AM) policy control when UE moves from/to 5GC to/from EPC and define enhancements in current mechanism if needed. [3GPP SP-211642, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Personal IoT Networks – is studying how the 5G System architecture can be enhanced to support Personal IoT Network (PIN). The following items are to be covered: potential architectural enhancements for supporting management of PIN, access of PIN via PIN Element with Gateway Capability (PEGC), communication of PIN, and identifycation of the PIN and the PIN Elements in the PIN; how to identify PIN and the PIN Elements in the PIN at 5GC level to serve for authentication/authorization; management of a PIN, e.g., create PIN, authorizing/de-authorizing PIN Elements, authorizing/de-authorizing PIN Elements with Management Capability (PEMC), authorizing/de-authorizing PIN Elements with Gateway Capability (PEGC), establishing duration of the PIN; and procedures for network discovery, PIN Element discovery, capability of PIN Element discovery, as well as availability and reachability discovery, e.g., assisted by a PIN Element with Management Capability. [3GPP SP-211643, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: System architecture for next generation real-time communication services (Evolution of IMS multimedia telephony service) – aims at investigating the system architecture solutions for the following aspects: how supporting the requirements from R18 eMMTEL impacts IMS architecture and functionalities to support AR telephony communication and to support 3rd party to verify via operator network that e.g. an employee is authorized to use or reference specific identity information; impact of IMS architecture and procedures to support Data Channel usage in IMS network, including whether and what functionalities are defined in IMS architecture for Data Channel server, with separate CP and media plane, and Data Channel application repository; and IMS media control interfaces that can be applied for service based architecture, besides Cx/Dx and Sh/Dh, supporting both existing and new capabilities for possible new applications and efficient media processing, considering backward compatibility and maintaining SIP as core IMS signalling protocol. [3GPP SP-211644, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Architectural enhancements for 5G multicast-broadcast services; Phase 2 – will evaluate further enhancements to 5G Multicast/Broadcast architecture to expand on the scope for MBS including end-to-end procedures/functionalities and architecture. The detailed objectives cover the following: support for and enhancement related to end-to-end MBS traffic delivery for, including large number of UEs; support on demand multicast MBS session triggered by AF, and efficient resource utilization via 5GC choosing multicast and/or unicast delivery for a certain service; support group message delivery for capability-limited devices, including NEF enhancement, coexistence of existing power saving mechanisms and MBS; and indentyfy potential performance issues for high number of public safety UEs, and if found, study necessary enhancements to 5MBS for that scenario. [3GPP SP-211645, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Architecture enhancement for Extended Reality (XR) and media services – will study the system architecture aspects related to better support of advanced media services, e.g., High Data Rate Low Latency (HDRLL) services, AR/VR/XR services, and tactile/multi-modality communication services, including the following topics: enhancements for supporting multi-modality service; enhancements of network exposure to support interaction between 5GS and application; performing transmission of QoS and policy enhancements for XR service and media service; and enhancements of power management considering traffic pattern of media services. [3GPP SP-211646, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Architecture Enhancement to support Ranging based services and sidelink positioning – will study 5GC enhancements to support Ranging-based services and sidelink positioning for commercial, V2X and public safety use cases in in-coverage, partial coverage, and out-of-coverage of 5G network. The investigation will cover architecture enhancements to enable Ranging Service and sidelink positioning including: authorization and policy/parameter provisioning for a UE or a group of UEs; ranging device discovery and service operation procedures between two UEs, between one UE and multiple UEs or via the assistance of another UE; and ranging and sidelink positioning service exposure to a UE or an Application Server who has requested the service. [3GPP SP-211647, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: 5G System Support for AI/ML-based Services – aims at investigating AI/ML Services & Transmissions with 5GS assistance to support AI/ML model distribution, transfer, training for various applications, e.g. video/speech recognition, robot control, automotive, for the following types of AI/ML operations: AI/ML operation splitting between AI/ML endpoints, AI/ML model/data distribution and sharing over 5G system, and Distributed/Federated Learning (FL) over 5G system. The detailed objectives include: study the possible architectural and functional extensions to support the Application layer AI/ML operations; study possible QoS, Policy enhancements to support Application AI/ML operational traffic while supporting regular (non Application-AI/ML) 5GS user traffic; and study 5GS to provide assistance to AF and the UE for the AF and UE to manage the FL operation and model distribution/redistribution to facilitate collaborative Application AI/ML based Federated Learning operation between the application clients running on the UEs and the Application Servers. [3GPP SP-211648, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Enhancement of 5G UE Policy; Phase 2 – will investigate the following: UE Route Selection Policy (URSP) rule provisioning and updating procedures for home-routed and LBO roaming scenario, while keeping the existing framework of policy control based on HPLMN; optimization on UE Policy requesting and provisioning related aspects; enhancements for provisioning UE with consistent URSP across 5GC and EPC; and support for standardized and operator-specific traffic categories in the traffic descriptor of URSP. [3GPP SP-211649, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Enablers for Network Automation for 5G; Phase 3 – aim is to further investigate system enhancements for NWDAF to allow 5GS to support network automation. Specifically, this SI will focus on analytics for 5GC NFs with the target to support in their decision making. It will further study the necessary inputs to NWDAF and the necessary NWDAF outputs and to study the potential architecture enhancement, new scenarios and Rel-17 leftover for network data analytics. The specific topics will include: possible mechanisms for improved correctness of NWDAF analytics; identify how NWDAF can assist application detection; support data and analytics exchange in roaming case; data collection and data storage enhancements; enhancements to trained ML Model sharing for different vendors; interactions between NWDAF to leverage MDAS/MDAF functionality for data collection and analytics; and enhancements on QoS Sustainability analytics. [3GPP SP-211650, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: 5GC enhancement for satellite access; Phase 2 – will further study 5GC/EPC enhancements to support satellite access with the following architectural enhancements: support for discontinuous coverage for mobility enhancement (e.g. paging enhancement); considerations for prediction, awareness & notification of UE wake-up time, power saving optimizations. [3GPP SP-211651, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: UPF enhancement for Exposure And SBA – aims at studying support for better integration of UPF into the 5GC SBA and will cover the following: UPF event exposure service(s) registration/deregistration, and discovery via the NRF; UPF event exposure service(s) that would support, e.g. consumption of UPF exposure services by the PCF, NWDAF, CHF, NEF, Trusted AF and other NFs; and evaluation of usage of UPF event exposure service(s) considering the architectural impacts. [3GPP SP-211652, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: System enhancement for Proximity based Services in 5GS; Phase 2 – will study potential 5GS enhancements to support the following: support of single NR PC5 hop UE-to-UE Relay for unicast; service continuity when switching between two indirect network communication paths for UE-to-Network Relay (NR PC5 and NR Uu are used); support path switching between direct NR Uu communication path and direct NR PC5 communication path (i.e. non-relay case); service continuity when switching between direct network communication path and indirect network communication path for Layer-2 UE-to-Network Relay; multi-path transmission using only one direct network communication path and only one indirect network communication path for UE-to-Network Relay for improved reliability or data rates; and support for Emergency Services for Remote UE over UE-to-Network Relay. [3GPP SP-211653, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]
  • SI: Seamless UE context recovery – aims at investigating the possibility that an “unavailability period” is determined in 5GS for the UE. This addresses the need for co-ordination between UE and operator/application function in scenarios, when UEs becomes unavailable in the order of minutes due to e.g. Modem SW upgrades, OS upgrade, security patch update which are up to UE implementation. As UE become unavailable without prior knowledge of core network, it can impact the critical operations of application server if UE is responsible for it during the “unavailability period”. [3GPP SP-211654, 3GPP TSG SA Meeting #94e, Dec. 14 – 20, 2021]


Summing up the above, Rel-18 set of features from the SA2 perspective could be grouped into several main topics like:

  • Enhanced Services, including: XR, Enhanced IMS, MBS, Priority Services, Ranging-based Services, LCS;
  • Advanced IoT Use Cases, including: UAS/UAV, RedCap, Satellite, Personal IoT, TSC, DetNet;
  • Architectural Aspects, including: Satellite backhaul, NPN, SFC, ProSe enhancements, Sidelink Positioning, Mobile Relays, Wireless-Wireline Convergence;
  • Automation and Optimization, including: AI/ML in CN, Edge computing, NW Automation, NW Slicing.

In those topics, you could find enhancements to the already settled functionality, as well as new topics, which provides further advancements to the 5G system. Those of course complement the aspects to be covered within 5G-Advanced by TSG RAN. If you’re interested in RAN features for Rel-18, see this post: 3GPP Rel-18: 5G-Advanced RAN Features – RIMEDO Labs


[1] SP-211655, „List of Approved 3GPP SA WG2 Study and Work Items”, 3GPP TSG SA Meeting #94e, Dec. 6 – 17, 2021
[2] Release 18 (3gpp.org)
[3] 3GPP TR 21.900
[4] 3GPP Features and Study Items

Author Bio

Marcin Dryjanski received his Ph.D. (with distinction) from the Poznan University of Technology in September 2019. Over the past 12 years, Marcin served as an R&D engineer and consultant, technical trainer, technical leader, advisor, and board member. Marcin has been involved in 5G design since 2012 when he was a work-package leader in the FP7 5GNOW project. Since 2018, he is a Senior IEEE Member. He is a co-author of many articles on 5G and LTE-Advanced Pro and a co-author of the book „From LTE to LTE-Advanced Pro and 5G” (M. Rahnema, M. Dryjanski, Artech House 2017). From October 2014 to October 2017, he was an external advisor at Huawei Technologies Sweden AB, working on algorithms and architecture of the RAN network for LTE-Advanced Pro and 5G systems.​ Marcin is a co-founder of Grandmetric, where he served as a board member and wireless architect between 2015 and 2020. Currently, he serves as CEO and principal consultant at Rimedo Labs.

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