Author: Shaun

SD-WAN service orchestration and control allows managing the life-cycle of SD-WAN services as available with API, automation tools, and eco-systems from SD-WAN providers.

There is a need to operationalize SD-WAN services using existing IT systems in CSPs that have customer data.

The key capabilities of SD-WAN are as follows.

SD-WAN includes secure overlay connectivity that uses IP packet forwarding and routing based on policies for end-user applications and their traffic demand.

SD-WAN has multiple options for Transport underlay and is independent of it.

Service assurance is automated for each SD-WAN connection (as a virtual tunnel). SD-WAN Orchestrators and Controllers centralize management, orchestration and control of SD-WAN services.

Services are highly available; this helps automate deployments of specific SD-WAN offerings from SD-WAN vendors.

Operationalization via IT systems integration

Integration with these systems would depend on a few factors – at least three.

1. Whether the CSP SD-WAN solutions include multiple SD-WAN vendors
2. Whether the deployment is on a large scale, especially at the Telco Edge
3. How well any automation loop can be closed with the operational stack’s downward-facing service fulfilment and the operational stack’s upward-facing service assurance

All of these factors call for the introduction of a NaaS layer to allow IT systems to use the SD-WAN deployment systems.

Options for such a NaaS layer can be implemented

• Using standards as described in TMForum NaaS
• Using Hyperscalers
• Using a Customized in-house adaptation of Vendor offering

Using TMForum NaaS

This is described in TMForum IG1224, and the application of NaaS to SD-WAN has my contribution to IG1224 with my SD-WAN PSR model (Product-Service-Resource) model as peer reviewed and approved in Appendix A.

Using Hyperscalers

Using compute, storage and network from hyperscalers increases the cost as management and orchestration endpoints at the edge increase. Large-scale edge deployments with virtualized CPEs may not scale cost-wise on hyper-scalers.

In-house

Using a customised in-house adaptation of Vendor offering depends on CSP’s existing system and capabilities.

Finally, for any SD-WAN service, aligning with the performance and capacity of the underlying transport layer is required for closed-loop automation.

The existing performance monitoring solution and its closed loop will ensure that SD-WAN services meet their SLAs.

Traditional Enterprise WAN connectivity requires L2/L3 (L2.5) type protocols like MPLS to guarantee bandwidth between sites. The speeds selected from product offers for MPLS were guaranteed by the network based on QoS settings in the network. A form of security is provided by the MPLS network in the sense that the network is separate from the Internet and forms a VPN between enterprise sites.

However, maintaining such networks is costly for Enterprise Business, and SD-WAN has emerged as a possible less costly alternative. With SD-WAN, the control and data plane are separated, with the routing decisions centralized in the controller and forwarding done at the edge.

SD-WAN has been described extensively by MEF, and the service components there have been identified as

• SD-WAN Edge – SD-WAN provider to SD-WAN subscriber interface
• SD-WAN Controller – For Service Management
• Service Orchestrator – which I consider a Domain Orchestrator Orchestrator
• SD-WAN Gateway – for interconnect of transport service
• Subscriber – web Portal – for Service Management and Service Operations

While the service and service management models have been described extensively, the “operate” model that connects to IT systems has also to be considered.

In a similar vein as such operate models are being considered for 5G slicing, an “operate” model of SD-WAN is considered here. Additional details are in my contribution to TMForum IG1224 for NaaS.

The following figures are based on the MEF models and illustrate

A logical representation of the SD-WAN net,

And a logical representation of SD-WAN related circuits.

The “operate” model utilizes this by exposing SD-WAN services to the IT layer, which is the core commerce layer in TMForum’s open digital architecture.

Such a model is described in detail in my contribution to IG1224 Release 13 (currently in draft).

5G Slicing enables the partitioning of physical 5G core and RAN Networks into one or more logical networks. 

Each network slice is isolated end-to-end and tailored to fulfil diverse requirements that a particular service requests. This technology allows multiple 5G services to use one or many 5G slices, and one 5G service can use multiple 5G slices, depending on the specific needs of the service.

In the era of 5G, diverse use cases and services have different requirements in terms of latency, reliability, bandwidth, security, and quality.

Network slicing allows the creation of dedicated network resources tailored to various business customers, paving the way for the provisioning of specialized services.

Example of 5G Service and 5G Slice Relationship

To illustrate the relationship between 5G services and 5G slices, let’s consider three main types of 5G services that use network slicing: Enhanced Mobile Broadband (eMBB), Massive Machine-Type Communications (mMTC), and Ultra-Reliable Low-Latency Communications (URLLC) 

1. .eMBB: This service focuses on providing high data rates and improved broadband experiences for users. A network slice tailored for eMBB would prioritize high bandwidth and capacity to support data-intensive applications like video streaming and virtual reality.
2. mMTC: This service is designed to support a massive number of connected devices, such as IoT sensors and smart meters. A network slice for mMTC would prioritize the efficient handling of a large number of connections with lower data rates and power consumption.
3. URLLC: This service aims to deliver secure communications with ultra-low latency, high reliability, and minimal data packet loss. A network slice for URLLC would prioritize low latency and high reliability, making it suitable for applications like autonomous vehicles and remote surgery.

In this example, each 5G service has unique requirements, and network slicing allows the creation of dedicated network resources tailored to these needs. A single 5G service may use multiple slices to meet its requirements, or multiple 5G services may share a single slice if their requirements align. This flexibility in resource allocation enables efficient utilization of network resources and ensures that diverse services can coexist on the same physical network infrastructure.

One such example is the use of slicing to broadcast a sporting event like the Tour de France. The PSR (Product, Service, Resource) model for this is as follows. 

How this PSR relates to the CFS/RFS model was presented logically in a previous post to be described further in the next post.

As described in TMF IG1224, 3GPP identifies services requiring 5G slices as Communication Services (3GPP Term). An example of a communication service would be a service modelled with technology-neutral Customer Facing Service Specifications (CFSSpec). The service model is instantiated as a service instance (end-to-end) of the corresponding Customer Facing Service Specifications and their relationships. The service instance represents the connected flow of traffic in the network, which flow is the actual network service delivering customer traffic from source to destination.

Modelling such a service requires defining the service technically in terms of its service parameters that must meet service quality requirements defined by SLOs. Service parameters are specified in CFSSpecs, and the definition and relationship between CFSSpecs of an end-to-end service evolve from service dependencies within the Service Topology model. The Service Topology model is built from the Network Topology Model, and related Network Traffic flows for the service.

Network Topology model is a resource model that represents a technical domain. (e.g. Carrier Ethernet, DWDM etc). Service Models are models representing services L2 Services (e.g., L2 VPNs, L2 Access) and L3 Services (e.g., L3 VPNs, Service Tunnels) that are ultimately abstracted as technology-neutral before providing to customers. This makes the lifecycle of the service presented to the customer independent of the realization of the services via the lifecycle of the resources and technologies.

In addition, the modelling of such services also needs to consider the management and operations of such services and how tasks that control such services are orchestrated. Such as service creation, modification and termination.

Finally, the modelling of such services also needs to consider the lifecycle of the service itself, how the service specification is created, what its requirements are, how it would be designed and assigned, and how it would be configured and provisioned.

This makes up the CFS-RFS relationship, as I have specified in IG1224 for 5G splicing. To be elaborated on in future posts.

This post relates to my contributions to TMForum IG224 NaaS Transformation Document.

A 5G Network Slice supports communication (and connectivity) services offered by the Production layer (of TMForum’s ODA Framework) using Network-as-a-Service (NaaS) APIs.

Examples of such communication services and fulfilment of the same are described in TMFIG1224 Appendix A.

The communication and connectivity services offered by NaaS are exposed as technology-neutral services to the Core Commerce Layer of ODA.

This means the Information-model of this connectivity service should map TMForums SID model to the RFS models of 3GPP’s NetworkSlice.

The data model requires mapping

• the communication and connectivity services exposed by NaaS
• each customer’s or tenant’s use of this connection as a flow within the communication service
• technology service exposed by 3GPP

Assurance

Assurance in 5G is dynamic, with various levels of closed loops. The assurance approach and standards are described in TMF IG1224 Appendix A.

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.