1 © Nokia 2016

End to End Network Slicing in 5G System

3GPP Standards Perspective

Sankaran Balasubramaniam

2 © Nokia 2016

Slicing in 5GS An Overview

Key Concepts

Slicing in 5GS -Procedures

Table of contents

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Network Slicing - Introduction

Formal Definitions• Network Slice

• A logical network that provides specific network capabilities and network characteristics• Network Slice instance

• A set of NF instances and the required resources (e.g. compute, storage and networking resources) which form a deployed Network Slice.

• A NS instance spans across the 5GC, 5G-RAN and the UE

Considerations in Network Slice Deployment• Network slices may differ for supported features and network functions optimisations• Network slices may offer the same service, but for different sets of users

Need for Network Slices in 5GS• Very wide set of use cases/services that require different/incompatible network characteristics• Early realization during Rel-15 – a single network cannot meet all these requirements

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E2E Network Slicing – Legacy vs 5GS

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Network Slice – What Could It Mean?

E2E Network Slice

Signaling

3GPP Specified

Negotiation/Assignment of NSSAI within the 5GS

Multiple Interfaces Involved (NR-Uu, N1, N2, Nsmf, Nnssf, F1, E1, Xn

etc.,)

Architecture

3GPP Enabled

Flexibility through Cloud Native Architecture

RAC/RAU & MMF/SMF Functional Split

Component S/W Architecture

Introduction of NSSF

Resource Management

3GPP Enabled

QoS Enforcement

RRM

Proprietary L1/L2 algorithms

Transport Optimizations

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RAN Slice – Resource Management Possibilities

• Multiple implementations possible

• The option itself is not mandated in the standards

• The standards define a framework where any of these could be realized

• Typical considerations• Service

characteristics

• Network deployment

• Commercial aspects

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RAN Slices – Example

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Slicing in 5GS An Overview

Key Concepts

Slicing in 5GS -Procedures

Table of contents

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Slicing in 5GS – Key Concepts

Slice Identity Management

Slice Awareness

Selection Functions

Resource Management

Slice Availability in the 5G Network

Support of Multiple Slices

UE Slice Validation

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Slice Identity ManagementS-NSSAI – Single Network Slice Selection Assistance Information• Identifies a Network Slice across the 5GC, 5G-RAN and the UE• Composed of

• Mandatory SST (Slice/Service Type) - 8 bits• Optional SD (Slice Differentiator) - differentiates slices with same SST - 24 bits

• Standardized S-NSSAI has only SST and no SD• Non-Standard S-NSSAI can be defined as either SST alone (Non-standard) or SST + SD

Standardized SST Values

SST SST Value

eMBB 1

URLLC 2

MIoT 3

Types of NSSAIs• Subscribed S-NSSAIs

• Stored in the UDM -> 5GC uses this as a default when the UE doesn’t send a Requested NSSAI• Configured NSSAI

• The PLMN may configure a UE with 1 or more configured NSSAIs – UE uses this as its default NSSAI• Could be the same as the Subscribed S-NSSAIs

• Allowed NSSAI• The value assigned by the 5GC & valid in a Registration Area or the PLMN over a given access type

• Requested NSSAI• Can be either Configured or Allowed NSSAI or a combination thereof• The UE sends this in both RRC and NAS signalling as part of registration• RAN uses this for AMF selection and provisional handling before getting Allowed NSSAI• 5GC use this for slice selection, validation etc., and returns the Allowed NSSAI

• Rejected NSSAI• Can be rejected in the Registration Area (or) for the entire PLMN• UE shouldn’t attempt this NSSAI again in that RA or in the PLMN

• NSSAIs could be mapped – across PLMNs for example

NSSAIs are managed at the Tracking area level in the 5G-RAN and Registration Area level in the 5GC

NSSAI is a collection of S-NSSAIs

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Key Concepts - DescriptionE2E Slice Awareness- Differentiated Traffic Handling within the 5GS- QoS Differentiation within a slice

- Different QoS profiles can be applied for non-GBR bearers within a slice- DRB profile can be different for the same 5QI flow type in different slices

- Granularity of Slice Awareness is at the level of a PDU session- Traffic Separation at Transport : L2VPN via VLANs or L3VPN via MPLS labels

Selection Functions- RAN Slice Selection based on Requested/Allowed NSSAI- AMF Selection based on Requested NSSAI & NSSF interaction -> can lead to

change in AMF

Resource Management- RRM policy enforcement across slices

- Slice specific Radio Admission Control policies- Resource Isolation across slices

- Failure in one slice not affecting the others

Traffic Separation = f(5QI, NSSAI & PLMN)

Cloud Architecture & Slice specific dimensioning

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Key Concepts – Description - Continued

Multiple Slices Support- A single UE could have PDU sessions corresponding to 8 slices at the maximum at any point- However, a single signalling connection (with the associated RRC state) is maintained for a given

UE- A common, logical AMF instance supports all the slices of a given UE (the SMF/UPF instances could

be multiple)

UE Slice Validation- Comparison of the UE’s Requested NSSAI vs Subscribed NSSAI done by the 5GC- 5G-RAN plays the slave here, getting the validated slice information in the ICS/PDU Session Request

Slice Availability in the 5G System- Some slices may be available only in a part of the network- A given Registration Area (ie the list of Tracking Areas within an RA) shall support a common set of slices

13 © Nokia 2016

Slicing in 5GS An Overview

Key Concepts

Slicing in 5GS -Procedures

Table of contents

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E2E Network Slicing in 5GS – High Level Architecture

AMFSMF

UPF

Slice B

SMF

UPF

Slice C

NG-RAN

UE

SMF

UPF

Slice A

The UE can use multiple network slices at the same time

RAN slice instance(s): Serving one or multiple slices (S-NSSAIs)

PDU sessions are slice specific

RAN selects the RAN slice instance and AMF for the UE based on Requested NSSAI

N3

N3

Nsmf

NsmfN2

Not Standardized

3GPP Standardized

AMF is unique per UE and common to all network slice instances serving a UE

Slice specific Network Functions

Single RRC per UE

Transport Functions distinguish NW slices

DN-1

DN-2

N3

NSSF

Nsmf N4

N4

N4

Nnssf

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Slice Allocation in 5GS

gNB-1

TAI-1 : NSSAI-1 & NSSAI-2TAI-2 : NSSAI-1 & NSSAI-3gNB-3

TAI-5: NSSAI-1, NSSAI-2 & NSSAI-4

gNB-2

TAI-3 : NSSAI-1 & NSSAI-4TAI-4 : NSSAI-1 & NSSAI-2

gNB-4

TAI-6 : NSSAI-1TAI-7 : NSSAI-1 & NSSAI-4

NSSAI-1, NSSAI-2, NSSAI-3 and NSSAI-4gNB-1, gNB-2, gNB-3 and gNB-4

PLMN-1

PLMN-1

gNB gNB

gNBgNB

gNB-1

RAI-1 : TAI-1 & TAI-2UE-1 : NSSAI-1UE-2 : NSSAI-1 & NSSAI-3

gNB-3

RAI-3 : TAI-5UE-4 : NSSAI-1 & NSSAI-2

gNB-2

RAI-2 : TAI-3 & TAI-4UE-3 : NSSAI-1 & NSSAI-4

gNB-4

RAI-4 : TAI-6 & TAI-7UE-5 : NSSAI-1 & NSSAI-4UE-6 : NSSAI-1

UE Registration

gNB-1RAI-1 : TAI-1 & TAI-2UE-1 : NSSAI-1 (PDU-1)UE-2 : NSSAI-1 (PDU-2) & NSSAI-3 (PDU-3)

gNB-3RAI-3 : TAI-5UE-4 : NSSAI-1 (PDU-6) & NSSAI-2 (PDU-7)

gNB-2

RAI-2 : TAI-3 & TAI-4UE-3 : NSSAI-1(PDU-4) & NSSAI-4 (PDU-5)

gNB-4RAI-4 : TAI-6 & TAI-7UE-5 : NSSAI-1 (PDU-8) & NSSAI-4 (PDU-9)UE-6 : NSSAI-1 (PDU-10)

NG Setup

PDU Sessions

PLMN-1

PLMN-1

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RAN Slice & AMF Selection

(1)

(2)

1) During NG Setup with AMF-1 & AMF-2• gNB and AMFs exchange their

supported NSSAI lists• gNB -> NSSAIs per TAC• AMF -> NSSAIs in the PLMN

2) In the RRC Setup Complete message• UE optionally provides the

Requested NSSAI along with the PDU session to be established

• Provisional RAN slice selection & AMF selection done based on this

3) gNB forwards the NAS Registration Request to the selected AMF instance

4) AMF validates the Requested NSSAI using Subscribed NSSAI

(2)

(3)

(4)

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Slice Aware Initial Context Setup

4) AMF responds with NAS Registration Accept in the ICS Request

• Includes the Allowed NSSAI• gNB may have to update the

policies based on the Allowed NSSAI

(4)

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Slice Aware PDU Session Handling

5) UE initiates PDU Session Establishment• Includes the Allowed NSSAI

assigned during the registration

6) AMF sets up the PDU Session with the gNB

• Includes the Allowed NSSAI that has been validated for the PDU Session

• Used by the gNB to map the PDU session to the appropriate slice instance

(6)

(5)NAS : PDU Session Setup Request

NAS : PDU Session Setup Accept

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Slice Aware Xn Based Mobility Handling

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Looking Forward – Rel 16

Improvements Being Studied

• Security Enhancements – Slice level Authentication & Authorization post the general procedure

• Network Slicing Enhancement to interwork with EPC in Idle/Connected modes

• Handling cases where 5GS is not able to support all possible combination of S-NSSAIs for the UE

• Isolation impacts among slices

• Business role models for network slicing

• Trust relationships between MNOs and slice tenants under various business role models

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Challenges in Network Slicing

• Complexity in the specification – multiple domains need to work together to implement E2E slicing

• Many aspects are not standardized – choice among solution options

• Acceptance of cloud architecture

• Service infrastructure

• Security considerations

• Commercial aspects

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References

• 3GPP TS 38.300 – 5G RAN Architecture

• 3GPP TS 23.501 – 5GS Architecture

• 3GPP TS 23.502 – 5GS Procedures

• Google Books : 5G System Design: Architectural and Functional Considerations and Long Term Research