Author: Shaun

RAN slicing creates independent virtualized sub-networks that convert user requirements to different QoS requirements on the network. User requirements are service requirements as specified in CFSSpecs.
These requirements cover scenarios for creating RAN subnet slices and modifying RAN subnet slices as required by created or modified services.

One of the service requirements for creating or modifying a RAN subnet-slice relates to Quality of Service (QoS). QoS Profile allows mapping of packets flowing from UE to Data Network using QoS flows and Data Radio Bearers (DRBs). In 5GNR QoS flows represent logical streams of data packets that have specific QoS requirements.
Rules in the UE and in the RAN map QoS Flows to DRBs. Setting up QoS Profiles and mapping rules is part of the design time activity for the slice.

The following diagrams illustrate a logical diagram of QoS in RAN.

In the figure, each cell is identified by the radio beam and frequency of a Remote Radio Head (RRH) sector.
The Tracking Area Code identifies each cell in a Tracking area
TAI = PLMN ID + TAC
PLMN-ID = MCC + MNC

Ultimately the RAN subnet slice would have its QoS Profile defined at design time via the NST and then mapped to QoS definitions in the CFSSpec. These definitions abstract a specific QoS Profile in the RFSSpec representing the Slice Profile.

QoS characteristics are considered representative of service usage as they are relevant to dynamic decisions made during operations of QoS flow, such as using the priority level as a tiebreaker when two flows compete for resources.
There are many scenarios for QoS events, as seen in the 5G QoS Identifier, 5QI Table available from 3GPP and ETSI.

QoS ER and logical relationships are shown below.

From the figure, each RAN slice is associated with a specific set of QoS parameters that define the desired quality of the slice and its performance characteristics, such as latency, throughput, packet loss, and reliability. These parameters represent the requirements of the applications or services the slice supports and comprise the QoS Profile.

In this example, the slice consumes resources that are primarily radio resources in terms of physical resource blocks in a radio beam that makes up the sector of a cell.

Multiple QoS flows can be mapped to the same QoS Profile.
However, each QoS flow is associated with a single QoS Profile represented by 5QI. The 5QI value defines a set of QoS parameters, such as priority and packet error rate, that can be applied to multiple QoS flows, each identified by its unique QoS Flow Identifier. At runtime, the QoS characteristics work with a priority level.

Multiple QoS flows can be associated with a single RAN slice, as long as the QoS flows have similar QoS requirements that can be met by the same RAN slice. For example, multiple QoS flows carrying video streaming traffic with similar QoS requirements may be associated with a single RAN slice designed to support high data rates and low latency.

If we assume RAN slicing is at the MAC layer (does Qos Scheduling), the Physical Radio Blocks (PRBs) on the radio beams from RRH are allocated to a slice, performed dynamically depending on users allocated to the slice and traffic conditions.

The QoS scheduler determines the appropriate allocation of resources for the RAN slice. The QoS scheduler also assigns Dedicated Radio Bearers (DRBs) to the slice. DRBs are logical connections between the user equipment (UE) and the core network, enabling the transfer of data and control information. Each DRB is associated with specific QoS parameters and represents a dedicated channel for the slice to communicate with the network.

By allocating DRBs based on the QoS requirements, the QoS scheduler enables the identification and creation of different slices within the RAN. Each slice can have its own allocated resource set, including DRBs, allowing for the isolation and customization of services based on the associated QoS parameters.

Mapping of QoS flows to be discussed in future.

As illustrated by 3GPP standard TR 28.801 Study on management and orchestration of network slicing for next-generation network (Release 15), one Network Slice Instance can be consumed by many Communication Service Instances. And one Communication Service Instance can consume more than on NSI. This is as per the logical model shown in Figure 4.9.3.1 of 3GPP TR 28.801.

This relationship is shown in the Information model of Figure 4.2.2.1 of 3GPP TR28.801

A specific example of this is illustrated in my contributions to TMForum IG1224

The S-NSSAI is created during the 5G Network Slice Creation Process. The specific requirements for the slice (based on the service profile) are provided by the OSS/BSS system when ordering a slice from the Network Slice Management function (NSMF). This includes the S-NSSAI used to identify the appropriate Network Slice Instance based on Service Profile.

How the S-NSSAI is used depends on how the 5G slicing network is configured and available network functions like

• NSSF
• URSP
• pre-configured S-NSSAIs based on specific requirements of network slice
• default S-NSSAIs as defined by 3GPP for specific types of services and applications

The NSSF is not a mandatory 5G Core Network function and plays a role in 5G slicing either

a) when AMF cannot provide the requested NSSAI (made up of S-NSSAIs)

b) when there is more than one slice with the same NSSAI

Without an NSSF function in the network, the S-NSSAI would be pre-configured in the network. This would be part of the slice creation workflow. In this case, the S-NSSAI can be selected based on the preconfigured policies without needing an NSSF.

In cases where there is no NSSF function in the network and pre-configured policies have not been defined, the default N-SSAI is used.

Multiple consuming services on a slice

For the scenario in which more than one Communication Service Instance consumes one Networks Slice Instance, each Communication Service Instance would have its own Resource Facing Service Instance related to the NSI. Because the provisioning of the RFS uses parameters specific to the RFS and specified in the RFSSpec.

As shown below multiple RFSs relate to one NSI.

Consuming service requires multiple slices

For the scenario where one Communication Service needs more than one NSI, then the CFS would decompose to multiple RFSs, with each RFS instance related to its respective NSI.

RFS instance tracks service usage and characteristics of service usage per slice consumer.

3GPP 28.541 shows relationships between Network Slice, Service Profile, Network Slice Subnet, Slice Profile and Network Service. This is replicated from the same spec as below.

As per Section 6 of 28.541, the properties for the requirement of a Network Slice Instance are specified in the Service Profile. And the properties for the requirement of a Network Slice Subnet Instance are specified in the Slice Profile.

The template for a Service Profile specifies the requirement for a Network Slice identified by the S-NSSAI (Single Network Slice Selection Assitance Information).

As mentioned above, a Service Profile instantiated from the Service Profile template is the requirement of the Network Slice Instance.
A Slice Profile instantiated from the Slice Profile template is the requirement of the Network Slice Subnet Instance.

These requirements have to be met by finding a suitable NST and NSST to create the Network Slice Instance and Network Slice Subnet Instance.

As per 3GPP 28.801 the Network Slice is described by the Network Slice Template (NST). The Network Slice Instance(NSI) is created using the NST and instance-specific information.

In this context, the Network Slice reperesents a logical network with a particular set of characteristics such as service type, QoS along with security requirements. The Network Slice is identified by the S-NSSAI. It is assigned to NSI when NSI is created from NST of Network Slice.

Because of this relationship, a Network Slice Instance (NSI) can be related to one or more S-NSSAIs. And a single S-NSSAI can be related to one or more Network Slice Instances.

Where there are two slices with the same S-NSSAI then the NSI-id is used. It is returned by the NSSF (3GPP core function) for specific S-NSSAI.

The next topic covers creation of S-NSSAIs and use of the same.

The Communication Service Management Function as per 3GPP (28.801, 28.805) translates the communication service-related requirements to network slice-related requirements. It also provides an interface to OSS/BSS layers.

For communication services offered to customers, the offerings can span B2C, B2B, and B2B2X. And such communication services must be supported in an optimized way by the 5G Network Slice Instance (NSI). In this way a communication service is associated with a network slice; an example of communication services using network slices. The Network Slice deployment offers communications services to UEs or Systems in B2C and B2B.

According to 3GPP, the communication service could also be the 3GPP service that makes up the NSI. An example could be customised network slices made available to customers. In this case, the native support for 5G slicing is also usable in the communication service. The amount of 5G slice management control provided to the customer is decided by the Network Slice Provider. This model describes Network Slice as a Service (NSaaS).

Relationship to Network Slice Instance

A Communication Service Instance is realized or instantiated by one or more Network Slice Instances as described by the Network Slice Information Object Class of 3GPP Spec 28.541.

The following diagram illustrates the relationship.

One Communication Service Instance (acting as Customer Facing Service = CFS) is specified by one Communication Service Profile (= CFSSpec). The CFS represents one of the service requirements of the 5G slice tenant, on the 5G slice.

Therefore the CFS is related to one Resource Facing Service (RFS), which in turn manifests the tenant’s service requirement in the Service Profile Instance. The Service Profile Spec (= RFSSpec) acts like a Service Profile Template for the Service Profile Instance.

Additional requirements on the 5G slice from the same 5G slice tenant will each require an additional CFS, instantiated from either the same, or different CFSSpec (= Communication Service Profile Template). In this way many CFSSpecs are related to one RFSSpec.

However, one CFS instance is related to one RFS instance and this CFS-RFS combination makes up the service requirement on the Network Slice Instance. As there can be many service requirements on a single Network Slice Instance (NSI), many RFSs (Service Profiles) can be related to one NSI.

The next post describe identification and management of the ids of NSIs.

5G slicing is a resource management capability of 5G networks that allows the separation of such mobile networks into multiple logical subnetworks. It is part of the 5G architecture and isolates user traffic for specific types of communication services. These communication services are specific to the required behaviour of the network traffic that delivers them from user/end devices to application services and other devices. The required behaviour of such network traffic could be lower latency, higher bandwidth, or increased connectivity access. Accordingly, slices are defined by ITU as types urLLC, emBB and iOT. ITU-R Rec M.2083 identifies applications that produce/consume such network traffic.
An example is as follows

These defined slice types support specific use cases and services that are enabled by dedicated network slices created by the service-based 5G SA core.
In a service-based architecture, the core network functions are divided into modular services that can be flexibly combined and orchestrated to create custom network slices. This means that different network slices can be created for different types of services, such as high-speed mobile broadband, mission-critical IoT, or ultra-low latency applications.

By using network slicing, service providers can offer a more customized and efficient service to their customers, as well as enable the development of new, innovative use cases that require specific network characteristics. With 5G slicing, service providers can allocate resources more efficiently, reduce network complexity, and improve overall network performance. While network complexity is reduced, the complexity in orchestrating and enabling 5G slices is increased compared to 5G services. To be disucssed in subsequent posts.