The Evolution of Network Slicing: Enhancements in 3GPP Release 18

What is Network Slicing ?

Network Slicing is a key 5G Standalone (5GSA) feature that provides flexible deployment and operation of diverse communication services. A network slice is a combination of network functions, network resources & their interconnections that provides a logical network over shared network infrastructure. Logical networks can be used to provide customized services with very diverse requirements, for example, in terms of quality of service (QoS) or traffic isolation. This makes network slicing a key element of the 5G value proposition to enterprise customers and will help to grow operators’ B2B revenues.

With the help of Network Slicing, CSPs can create on-demand, programmable, isolated, and end-to-end logical networks. These networks can be established as needed and for the duration required, ensuring efficient use of network resources.

Key Benefits & Use Cases

Network slicing enables customized services for diverse enterprise needs, which can help operators grow their B2B revenues. Some potential use cases include:

Industrial Process Optimization: Autonomous guided vehicles (AGVs) and factory digital twins.

AR/VR Operations: Enhanced operations and maintenance.

Media and Entertainment: Remote broadcast and production, enhanced live event experiences.

Connected Vehicles: V2X support.

Utilities: Smart grid and metering solutions.

Public Safety: Communication support for disaster recovery and public safety organizations.

These are only a subset of a growing range of enterprise digitalization use cases that network slicing can support, representing both Industry 4.0 digital transformation and metaverse applications.

Evolution with 3GPP Releases

The development of network slicing has been guided by the 3GPP standards:

Rel-15: Introduced the baseline network slicing features, including identification of network slices, UE subscription support, and initial 4G interworking.

• Identification of network slices with single network slice selection assistance information (S-NSSAI)

• UE subscription and configuration support for individual network slices • Slice-aware UE network registration for proper network slice access

• Session management enhancements to support establishment of traffic sessions for particular network slices

• Initial 4G interworking and roaming support To help reduce the operational complexity of deploying network slicing in a multiservice network, the operations and management (OAM) specifications were also enhanced to support life-cycle management of the network slices.

Rel-16: Enhanced 4G interworking and introduced network slice-specific authentication and authorization (NSSAA).

Rel-17: Focused on optimization, including quotas and restrictions per network slice, and improved RAN performance with the introduction of frequency-band-specific network slices, which enable the network to steer a UE to a specific frequency band where the UE-requested slice is supported. The configuration and execution of RAN procedures like cell re-selection and random access were also made slice-aware to meet their slice-specific performance requirements.

Additionally, for performance analysis and service assurance, the network data analytics functions (NWDAF) and management data analytics (MDA) were also enhanced with network slice specific analytics capabilities.

Rel-17 enforced restrictions per network slice related to:

• The number of simultaneously connected UEs

• The number of allowed PDU sessions

• UE data rate limitations

• Overall data rate limitations.

Release 18 brings new features that help simplify the deployment and operation of network slices within a very small service area, typical of enterprise campuses and industrial settings, which require highly customized and localized services. In pre-Release 18 networks have the following limitations:

• Network slices have to be supported homogeneously across the whole TA (Tracking Area). Deploying network slices in an area served by only a few cells necessitates redefining the TAs. Rel-18 streamlines this process for network operators, enabling network slices to be deployed in a subset of cells within a TA. This subset of cells is then included in the Network Slice Area of Service (NS-AoS), and only the cells within this NS-AoS are configured with resources for the network slice. Conversely, no resources for this network slice are configured in cells outside the NS-AoS, even if those cells are within the same TA.

3GPP maintains that even if a network slice is configured with resources in only a subset of cells within the Tracking Area(s) - TA(s) - that are part of the Network Slice Area of Service (NS-AoS), the slice is still indicated as supported in the TA(s). This is because slice support is indicated at the TA level, while slice availability is determined at the cell level.

Additionally, the TA(s) are part of the Registration Area (RA) where the allowed network slice is supported. If a User Equipment (UE) indicates support for this Release 18 feature, the network signals to it the list of cells in the TA(s) where the slice is available, in addition to the list of TAs that form the RA.

• A key requirement for pre-Release 18 network slicing deployments is the homogeneous support of network slices throughout the Registration Area (RA) of a User Equipment (UE). The RA, comprising a set of Tracking Areas (TAs), is utilized by the network to monitor the UE’s location. For network slices with small coverage areas, this requirement imposes constraints on how the network can assign an RA to individual UEs. This often results in smaller RA assignments, leading to increased registration and location update signalling within the network. Release 18 introduces greater flexibility for operators by removing this constraint. It allows for the possibility that, in some TAs within the RA of a UE, the network slice may not be supported. To facilitate this new flexibility, the concepts of “partially allowed NSSAI” and “S-NSSAIs partially rejected” within the RA have been introduced.

When the UE registers on the network and indicates “partial support of a network slice in the RA,” the AMF accepts the registration. It then provides the UE with a list of network slices not uniformly supported across all TAs of the RA, along with a list of TAs where the network slice is supported.

Conversely, the AMF partially rejects the UE if the requested S-NSSAI is not supported in all TAs of the RA. The partially rejected S-NSSAI is associated with a list of TAs where the network slice is not supported. Both solutions enable the network to configure larger RAs for UEs and reduce frequent signalling between the UE and network entities for registration area updates. The AMF can indicate to a UE in the Registration Accept message the allowed network slices, partially allowed network slices, and network slices partially rejected in the RA.

These methods, introduced by 3GPP, allow efficient coexistence of customized network slices, such as enterprise slices, alongside more common network slices (e.g., eMBB and URLLC), even if the latter are widely deployed in the RA of the UE.

Enhanced Operator Control for Slice Quota Enforcement

In Rel-17, 3GPP introduced Network Slice Admission Control (NSAC) to enable network operators to set quotas on the maximum number of UEs that can connect to a network slice and the maximum number of PDU sessions that can be simultaneously associated with a network slice. This gives operators full control over the use of a network slice and allows them to limit the network resources used by a particular slice. This control is crucial for operators in terms of network resource utilization and the monetization of their networks. It ensures that resources are distributed among customers in the most efficient manner.

Dynamic Network Slices for Temporary Deployments

In enterprise and commercial environments, there is often a need to deploy network slices for limited periods, such as to support the communication requirements of special events or emergency services. To optimize signalling load and network resources for such deployments, 3GPP has introduced the concept of a validity timer associated with a specific network slice. Depending on the subscription, a network slice may be available to all UEs at all times or only for a specified duration.

The primary benefit of a validity timer for a network slice, accessible to both the UE and the network, is that it optimizes the allocated network resources based on the SLA and reduces signaling between the UE and the network. Network functions are configured with timing information related to individual network slices, where applicable, and this information is provided to the UE during registration for a particular network slice. Once the validity timer of a network slice expires, the UE is no longer permitted to utilize or establish any PDU sessions with that network slice. Additionally, any existing PDU sessions are automatically terminated by both the UE and the network without the need for additional signaling.

Abbreviations:

AR - Augmented Reality

AGV - Autonomous Guided Vehicle

eMBB - Enhanced Mobile Broadband

MDA - Management data analytics

NS-AoS - Network Slice Area of Service

NSAC - Network Slice Admission Control

NSSAA - Network Slice-specific Authentication & Authorization

NWDAF - Network data analytics functions

RA - Registration Area

TA - Tracking Area

URLLC - Ultra Reliable Low Latency Communication

VR - Virtual Reality

V2X - Vehicle to Everything