Content for TR 26.941 Word version: 19.0.0

4.0 Assumptions 4.1 General 4.2 Network slicing architecture 4.3 Slice orchestration and management 4.4 Network slice capability exposure
...

0 Introduction p. 6

This document covers key issues, candidate solutions and potential requirements for supporting network slicing with 5GMS architecture. Aspects related to provisioning of media services, dynamic policy, and resolution of slice-specific AS instances while using network slicing for media streaming use cases are covered in this document.

1 Scope p. 7

The present document identifies standardization needs and potential standards gaps relevant to media streaming while using 5G network slicing. In specific, the following aspects are addressed in this document:

To identify relevant use cases that can be addressed using network slicing, and study collaboration scenarios and deployment architectures to support network slicing for media services.
To identify any missing provisioning aspects for configuring media services with one or more network slices including QoS configuration, reporting and dynamic policy.
To identify impact of network slicing on dynamic policy invocation APIs, including selection of appropriate network slices for dynamic policy requests, possible migration of UE application traffic flows between network slices due to dynamic policy procedures, discovery of dynamic policy AF, and necessary routing considerations.
To determine the need and describe methods for AF-to-AF communication to support interoperability if 5GMS AF instances from different vendors are deployed in the same 5GMS System.
To identify methods for deploying, supporting, and resolving slice-specific 5GMS AS instances.
To identify potential areas for normative work and communicate/align with SA2 as well as other potential 3GPP WGs (SA5, SA6) on relevant aspects related to the study.

2 References p. 7

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]

TR 21.905: "Vocabulary for 3GPP Specifications".

[2]

TR 26.804: "Study on 5G media streaming extensions".

[3]

TS 28.530: "Management and orchestration; Concepts, use cases and requirements".

[4]

TS 28.531: "Management and orchestration; Provisioning".

[5]

GSM Association NG.116, "Generic Network Slice Template", https://www.gsma.com/newsroom/wp-content/uploads//NG.116-v6.0.pdf

[6]

TR 23.700-40: "Study on enhancement of network slicing; Phase 2".

[7]

TS 23.501: "System architecture for the 5G System (5GS)".

[8]

TS 23.700-99: "Study in Network slice capability exposure for application layer enablement (NSCALE)".

[9]

TS 23.435: "Procedures for Network Slice Capability Exposure for Application Layer Enablement Service".

[10]

TS 28.541: "Management and orchestration; 5G Network Resource Model (NRM); Stage 2 and stage 3".

[11]

TS 28.542: "Management and orchestration of networks and network slicing; 5G Core Network (5GC) Network Resource Model (NRM); Stage 1".
→ to date, still a draft

[12]

TS 28.532: "Management and orchestration; Generic management services".

[13]

TS 28.545: "Management and orchestration; Fault Supervision (FS)".

[14]

TS 28.546: "Management and orchestration of networks and network slicing; Fault Supervision (FS); Stage 2 and stage 3".
→ to date, still a draft

[15]

TS 23.502: "Procedures for the 5G System (5GS)".

[16]

TS 23.503: "Policy and charging control framework for the 5G System (5GS); Stage 2".

[17]

TS 23.434: "Service Enabler Architecture Layer for Verticals (SEAL); Functional architecture and information flows ".

[18]

TS 27.007: "AT command set for User Equipment (UE)".

[19]

TS 29.520: "5G System; Network Data Analytics Services; Stage 3".

[20]

TS 26.501: "5G Media Streaming (5GMS); General description and architecture".

[21]

TS 26.512: "5G Media Streaming (5GMS); Protocols".

[22]

TS 28.552: "Management and orchestration; 5G performance measurements".

[23]

TS 28.554: "Management and orchestration; 5G end to end Key Performance Indicators (KPI)".

[24]

TS 23.558: "Architecture for enabling Edge Applications".

[25]

TR 28.809: "Study on enhancement of management data analytics".

[26]

TR 23.700-41: "Enhancement of Network Slicing Phase 3".

[27]

TS 22.261: "Service requirements for the 5G system".

[28]

5G Media Slice Definition, version 1.2: Joint outcome between New European Media and Networld2020 technology platforms, https://5genesis.eu/wp-content/uploads/2019/10/NEM_Networld2020-5GPPP-5G-Media-Slice-White-Paper-V1.pdf.

[29]

Commercializing 5G Network Slicing, 5G Americas White Paper: https://www.5gamericas.org/wp-content/uploads/2022/07/Commercializing-5G-Network-Slicing-Jul-2022.pdf, July 2022.

[30]

Network Slicing, Technical White Paper: https://images.samsung.com/is/content/samsung/p5/global/business/networks/insights/white-paper/network-slicing/200420_Samsung_Network_Slicing_Final.pdf, April 2020

[31]

FCC Technological Advisory Council, 5G IOT Working Group: "5G Network Slicing Whitepaper", https://transition.fcc.gov/bureaus/oet/tac/tacdocs/reports/2018/5G-Network-Slicing-Whitepaper-Finalv80.pdf.

[32]

Applied Network Slicing Scenarios in 5G: https://www.ericsson.com/en/reports-and-papers/ericsson-technology-review/articles/applied-network-slicing-scenarios-in-5g.

[33]

5G Network Slicing: How to Secure the Opportunity: https://www.juniper.net/content/dam/www/assets/executive-briefs/us/en/5g-network-slicing-how-to-secure-the-opportunity.pdf.

[34]

Navigate the network slicing transformation journey: https://www.ericsson.com/en/network-slicing.

[35]

GSM Association: "5G Network Slicing", https://www.gsma.com/futurenetworks/ip_services/understanding-5g/network-slicing/.

[36]

Jose Ordonez-Lucena, Pablo Ameigeiras, Luis M. Contreras, Jesús Folgueira and Diego R. López: "On the Rollout of Network Slicing in Carrier Networks: A Technology Radar", National Library of Medicine, Sensors, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8659767/, December 2021.

[37]

Network Slicing using User Equipment Route Selection Policy (URSP): https://blog.3g4g.co.uk/2021/11/network-slicing-using-user-equipment.html, November 2021.

[38]

5G Network Slicing: Android documentation, https://source.android.com/docs/core/connect/5g-slicing.

[39]

Apple device support for private 5G and LTE networks: https://support.apple.com/guide/deployment/support-for-private-5g-and-lte-networks-depac6747317/web.

[40]

GSM Association: "Network Slicing: North America's Perspective (Current) Version 1.0", https://www.gsma.com/newsroom/wp-content/uploads//NG.130-White-Paper-Network-Slicing-NA-Perspective.pdf, August 2021.

[41]

TS 24.526: "User Equipment (UE) policies for 5G System (5GS); Stage 3".

[42]

TS 26.510: "Media delivery; interactions and APIs for provisioning and media session handling".

3 Definitions of terms, symbols and abbreviations p. 9

3.1 Terms p. 9

For the purposes of the present document, the terms given in TR 21.905 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.

3.2 Symbols p. 9

For the purposes of the present document, the following symbols apply:

3.3 Abbreviations p. 9

For the purposes of the present document, the abbreviations given in TR 21.905 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.

ANDSP

Access Network Discovery & Selection Policy

CSC

Communication Service Customer

CSP

Communication Service Provider

Data Network

DNN

Data Network Name

ECS

Edge Configuration Server

EEC

Edge Enabler Client

eMBB

Enhanced Mobile Broadband

EPC

Evolved Packet Core

GST

Generic Network Slice Template

MIoT

Massive Internet of Things

MPS

Multimedia Priority Service

MNO

Mobile Network Operator

MVNO

Mobile Virtual Network Operator

NEST

Network Slice Type

NOP

Network Operator

NRM

Network Resource Model

NSaaS

Network Slice as a Service

NSC

Network Slice Customer

NSCE

Network Slice Capability Enablement

NSI

Network Slice Instance

NSP

Network Slice Provider

NSSI

Network Slice Subnet Instance

NSSP

Network Slice Selection Policy

NWDAF

Network Data Analytics Function

PDU

Protocol Data Unit

ProSe

Proximity based Services

ProSeP

ProSe Policy

URSP

UE Route Selection Policy

V2X

Vehicle-to-Everything

V2XP

V2X Policy

4 Overview p. 10

4.0 Assumptions p. 10

The following assumptions apply to the present document:

Possible and efficient solutions based on network slicing are sought to support the use cases listed in clause 5 and many others that also require differentiated QoS for their application streams. Network slicing may not be the only solution to support these use cases, but is one possible solution.
Service requirements relating to network slicing specified in TS 22.261 and TR 23.700-99 are considered for studying possible issues in relation to 5G Media Streaming.

4.1 General p. 10

Clause 5.12 of TR 26.804 provides a brief overview of network slicing feature standardization in different 3GPP groups, areas of study related to 5G Media Streaming for specifying network slicing extensions, and potential open issues. This clause describes different slice management processes in a little more detail that are relevant for specifying the media streaming aspects of network slicing.

4.2 Network slicing architecture p. 10

4.2.1 General p. 10

A Network Slice is a logical network with specific capabilities and characteristics as defined in clause 3.1 of TS 23.501. According to the supported features, functionalities and different groups of UEs, the multiple Network Slices can be deployed by the operator. More specifically, the network slice can support different functionality (e.g., priority, policy control), different performance requirements (e.g., latency, data rates), or different targeted users (e.g., MPS users, Public Safety users, corporate customers, roamers, or MVNO hosting users). For example, based on the operator's needs, there can be one network slice for MIoT services, one for supporting eMBB UEs and another one for V2X services.

A Network Slice instance is a set of Network Function instances and the required resources (e.g. compute, storage and networking resources) which form a deployed Network Slice. A slice instance includes both core network control plane and user plane network functions as defined in clause 5.15.1 of TS 23.501.

A UE can access multiple Network Slices simultaneously. Figure 4.2.1-1 below shows some illustrative scenarios. The occurrence of PDU Session Establishment in a Network Slice instance to a DN allows data transmission in that Network Slice instance.

The Network Slice Selection policies in the UE are used to associate an application with a specific network slice during PDU Session Establishment. A PDU Session belongs to one and only one specific Network Slice instance per PLMN. Therefore, different Network Slice instances do not share a PDU Session. But multiple PDU Sessions in different Network Slice instances may be associated with the same Data Network, identified by the same DNN.

Copy of original 3GPP image for 3GPP TS 26.941, Fig. 4.2.1-1: Mapping of PDU Sessions to Data Network Names and Network Slice instances

Figure 4.2.1-1: Mapping of PDU Sessions to Data Network Names and Network Slice instances
(⇒ copy of original 3GPP image)

In addition, enhancements to interworking between the EPC and the 5GC have been made to the 5G System, and network slice-specific authentication and authorization are also supported. For each network slice that is subject to Network Slice Admission Control, the monitoring and control of the number of registered UEs, the number of PDU Sessions and the slice-maximum bit rate are defined in order to ensure that the maximum resource of the network slice is not exceeded.

4.2.2 Network slicing for specific applications p. 11

Before application services are allowed to access specific network slices, a third-party Application Service Provider can negotiate with the MNO and the MNO may create or allocate the network slices based on the service requirements. For example, a cloud gaming service provider may interact with the MNO to reserve specific network slices supporting low latency, and high computing resources.

Afterwards, the Application Function, on behalf of the Application Service Provider, informs the 5GC that the target application service can use the specific network slices, i.e., by providing application guidance for UE Route Selection Policy (URSP) determination as defined in clause 4.15.6.10 of TS 23.502. Depending on the nature of the application guidance, the operator may update the Network Slice Selection policies in the URSP accordingly. As a consequence, the application service may be migrated to the new network slice/DNN duple based on the updated URSP rule.

The URSP rules in the UE, which are used to associate applications with usage of particular network slices, may be pre-configured or provided by the PCF as defined in TS 23.503. Each URSP rule is expressed as a traffic descriptor for application detection, e.g. IP descriptors, application descriptors, domain descriptors.

Once an application is started or detected on the UE, the following procedure is followed:

The UE evaluates its URSP rules in the order of Rule Precedence and determines whether the application matches the Traffic descriptor of any URSP rule.
1. When a URSP rule is determined to be applicable for a given application, the UE derives the suitable network slices based on the applicable URSP rule.
2. If the UE determines that there is more than one existing PDU Session which matches a given URSP rule, it is up to UE implementation (Operating System or modem layer) to select one of them to use. Otherwise, the UE tries to establish a new PDU Session using the derived network slices.
If there is no matching URSP rule (except the "match all" rule), the UE uses its own local configuration (if any) to determine which PDU Session to use.

NOTE:
The UE local configuration in this context is information about the associated application, such as application-specific parameters to set up a PDU Session or end user configuration for specific applications. This can be provisioned in the UE via the application layer, e.g. following interaction between the Edge Enabler Client (EEC) and the Edge Configuration Server (ECS), as defined in TS 23.558.
When URSP rules are updated, or when a particular URSP rule's validity changes, the association of existing applications to PDU Sessions may need to be re-evaluated.
Depending on UE implementation, the associations between applications and PDU Sessions may also be re-evaluated periodically, independent of any changes to URSP rules.

In the case where a network slice becomes unavailable (e.g. due to overload), the AMF is triggered, either by local configuration (e.g. trigger from OAM) or by a notification from the Access and Mobility Management PCF (AM PCF) or by the NSSF [26], to replace the current S-NSSAI with a previously chosen Alternative S-NSSAI. Using a suitable NAS procedure (e.g. UE Configuration Update) the AMF informs the UE about the Alternative S-NSSAI as well as providing the mapping between S-NSSAI(s) and Alternative S-NSSAI(s) in the Allowed NSSAI and/or in the Configured NSSAI.

In the case where there is no existing PDU Session in the unavailable slice and the UE is trying to establish a new one to support a 5G Media Streaming session, the UE may provide both the Alternative S-NSSAI and the current S-NSSAI in the PDU Session Establishment message, in which case the AMF provides both S-NSSAI values to the SMF for the PDU Session establishment. The SMF proceeds with the PDU Session Establishment using the Alternative S-NSSAI. As a result, the new PDU Session is established over the Alternative S-NSSAI with a new IP address.
In the case where an ongoing 5G Media Streaming session is already being carried over the PDU Session associated with the unavailable slice, the AMF informs the SMF responsible for the PDU Session that it is to be transferred to the Alternative S-NSSAI. Then, depending on the Session and Service Continuity (SSC) mode of the existing PDU Session, either:
- SSC mode 1: The SMF further updates the network slices in the UE/RAN/UPF via the PDU Session Modification procedure. In this case, the IP address of the PDU Session remains the same.
- SSC mode 2 or 3: The SMF triggers the modification/release of the PDU Session and re-establishment of the PDU Session in the Alternative S-NSSAI. In this case, a new IP address is allocated during the PDU Session re-establishment procedure and the ongoing 5G Media Streaming session at reference point M4 and M5 needs to be migrated to the new PDU Session.

When the AMF is notified that the replaced network slice has become available again (e.g., congestion has been mitigated), the AMF reconfigures the UE (e.g., by using the UE Configuration Update procedure or else as a matter of course when the UE next registers with the network) to use the replaced S-NSSAI if it has already configured the UE to use the Alternative S-NSSAI when the S-NSSAI became unavailable. Furthermore, if a PDU Session was established in the Alternative S-NSSAI when the replaced S-NSSAI became unavailable, the AMF triggers transfer of that PDU Session to the replaced S-NSSAI when the S-NSSAI becomes available again by updating the SMF(s) of the PDU Session using the Nsmf_PDUSession_UpdateSMContext service operation described in clause 5.2.8.2.6 of TS 26.502.

4.2.3 Service continuity for media streaming sessions migrated between Network Slices p. 13

4.2.3.1 Background p. 13

TR 28.809 is the result of a feasibility study that looked into aspects of management data analytics. Clause 6 of TR 28.809 specifies use cases, potential requirements and possible solutions for management data analytics. One of the issues relating to service-level specifications documented in clause 6.3.2 of TR 28.809 is the issue of network slice load analysis, described as follows:

Network slice load may vary over time. Therefore, network resources allocated initially could not always satisfy the traffic requirements, for example, the network slice may be overloaded or underutilized. Various factors may impact the network slice load, e.g. number of UEs accessing the network, number of PDU sessions, service types and the end users distribution. Overload of signalling in control plane and/or user data congestion in user plane will lead underperforming network. Besides, allocating excessive resources for network slice with light load will decrease resource efficiency.

From the above, it is understood that a Network Slice can become overloaded from time to time, and that consequently the slice cannot satisfy the traffic requirements, and therefore may fail to meet its SLA.

Clause 5.1 of TR 23.700-41 describes a related key issue "Key Issue#1: Support of Network Slice Service Continuity" in terms similar to the issue described above in TR 28.809 above. Specifically, aspects related to service continuity are being studied for two scenarios - a "no mobility" scenario and an "inter-RA mobility" scenario - in the case when a Network Slice or Network Slice instance in the Core Network (CN) or target CN is overloaded or undergoing planned maintenance (e.g., Network Slice termination), and the network performance of the Network Slice cannot meet the SLA.

As described in clause 4.2.2 of the present document, SA2 is in the process of specifying a method where an alternative slice is identified in advance, with the aim of migrating application traffic from the PDU Session in the current slice to the existing PDU Session or a new one in that alternative slice.

4.2.3.2 Moving application flows to different Network Slices p. 13

The 5G System provides generic support for moving application flows to different slices. As described in clause 5.15.5.2.2 of TS 23.501 on determining whether ongoing traffic can be routed over existing PDU Sessions in other Network Slices:

The UE uses either the URSP rules (which includes the NSSP) or the UE Local Configuration as defined in clause 6.1.2.2.1 of TS 23.503 to determine whether ongoing traffic can be routed over existing PDU Sessions belonging to other Network Slices or establish new PDU Session(s) associated with same/other Network Slice.

From the above, it is clear that either the URSP rules delivered to the UE or the UE local configuration determine how ongoing application traffic can be routed over existing PDU Sessions belonging to other Network Slices.

Clause 4.2.2 of the present document describes how the URSP rules are used to route application traffic through appropriate network slices.

For UE Local Configuration, clause 6.1.2.2.1 of TS 23.503 describes UE policy control, and specifies that among the four policy objects - Access Network Discovery & Selection Policy (ANDSP), UE Route Selection Policy (URSP), V2X Policy (V2XP), and ProSe Policy (ProSeP) - only ANDSP and URSP may be pre-configured in the UE.

4.3 Slice orchestration and management p. 14

TS 28.530 and TS 28.531 specify general concepts related to network slicing and slice life cycle management including specification of roles related to network slicing such as the CSC, CSP, NOP, NSC, and NSP. A network operator can perform both the roles of a CSP and NSP. A request from a CSC or NSC to the CSP or the NSP respectively for setting up a network slice is in the form of a set of slice attributes that represents the service requirements for the service that the customer intends to provide to its users.

The GSM Association describes a GST template [5] which specifies a set of attributes that characterize a given type of network slice/service. The slice customer prepares a NEST based on GST attributes and forwards it to the NSP for slice orchestration. A NEST is a GST filled with values. A study on GST attributes is specified in TR 23.700-40, and a reference to GST attributes is included in clause 5.15.2.2 of TS 23.501. GST attributes and NEST are also discussed in study on network slice capability exposure for application enablement (NSCALE) in TR 23.700-99. The normative specification for this work is being specified in TS 23.435.

GST attributes, as defined in [5], are categorized into two types:

Character attributes: These attributes typically characterize a slice (e.g., throughput, latency, APIs etc.). The character attributes can be further classified as relating to performance, function, or control and management
Scalability attributes: These attributes provide information about the scalability of a slice (e.g., number of UEs)

The CSP/NSP translates the NEST to service requirements for a set of subnets (e.g., core, transport network, RAN) using the slice NRM as described in TS 28.530, TS 28.541, TS 28.542 [11]. Based on individual slice subnet requirements, slice subnet resources are provisioned using slice orchestration operations for creating and managing NSI and NSSI resources as defined in TS 28.531. Such operations include:

Creation/modification/termination of NSI instances.
Creation/modification/termination of NSSI instances.
Creation/modification/termination of 3GPP NF instances.

Management and orchestration concepts such as provisioning management services, fault supervision management services, and performance assurance management services in addition to management service specification on the above slice resources are specified in TS 28.532. TS 28.545 and TS 28.546 [14] describe fault supervision aspects of management and orchestration of networks and network slicing.

TS 23.501 and TS 23.502 specify control plane architecture and procedures on enabling the connection of the UE to the above provisioned network slices including establishment of PDU sessions through those slices to the intended DNN. TS 23.503 describes the data model for URSP rules and NSSP policies that enable UE application traffic to be routed through the provisioned network slices to the respective DNNs.

In addition, a study on network slice capability exposure for application layer enablement is described in TR 23.700-99. The application layer enablement architecture in TS 23.700-99 is based on the Service Enabler Architecture Layer for Verticals (SEAL) whose functional architecture and information flows are specified in TS 23.434.

One of the key issues under study in TS 23.700-99 is whether a more concise approach to managing the lifecycle of network slices exposed to the application layer with additional functionality for verticals can be defined. One of the solutions being studied in clause 6.1.1 of TS 23.700-99 is to interface the network slice capability enablement server with the 5G system in order to perform all the network slice lifecycle management operations defined in TS 28.530 and TS 28.531. With this capability, applications of different verticals can interface with the network slice capability enablement server for all network slice related operations.

TS 27.007, in clause 10.1, describes how via AT commands the UE is able to set network slice preferences.

4.4 Network slice capability exposure p. 15

TR 23.700-99 documents several key issues and candidate solutions in addition to enabling network slice lifecycle management operations using the network slice capability enablement server. Some of the key issues relevant to that study are the following:

Discovery and registration aspects for management service exposure.
Network slice fault management capability.
Communication service management exposure.
Application layer QoS verification capability enablement.
Network slice related performance and analytics exposure.
Network slice capability exposure in the edge data network.
Delivery of existing network slice information to the trusted third party.
Network slice creation to the third party and UE.

In addition to the above information available at the network slice capability enablement server, TS 29.520 specifies the stage-3 definition of NWDAF Services of the 5G System and provides a data model for network slice information that NWDAF can provide to authorized customers. Such information can also be used as network slice capability information.