5G network slicing

5G Network slicing is a network architecture that consists in the multiplexing of virtualized and independent logical networks deployed on the same physical network infrastructure . Each network slice is an isolated end-to-end network tailored and customized to fullfill diverse requirements requested by a particular application. For this reason, this technology assumes a central role in the 5G mobile networks that are designed to efficiently embrace a plethora of services with very different service level requirements (SLA). The realization of this service-orieneted view of the network leverages on the concepts software-defined networking (SDN) and network function virtualization (NFV) that allow the implementation of flexibile and scalable network slices sharing the resources provided by physical network infrastructure.

From a business model perspective, each network slice is administraed by a virtual mobile network operator. The infrastructure provider (the owner of the telecommuications infrastructure) lease its physical resources to the mobile virtual network operators (MVNO) (known also as tenants) sharing the underlying physical network. According to the availability of the assigned resources, each MVNO can dynamically deploy several network slice istances to accomodate different service requests.

History

The history of network slicing can be tracked back in the late 80s with the introduction of overlay networks that provided a first form of service-oriented network. Each slice combined resources coming from different network domains, but lacked in programmability. In late 2000, PlanetLab introduced virtualization framework that allowed user to deploy isolated slice based on their application requirements. The flexibility introduced by the advent of SDN technologies in 2009 enabled the implementation of fully configurable and scalable network slices.

In the domain of mobile networks, the concept of network slicing was initially introduced as RAN sharing in the firsts releases of LTE standard in 2010. Examples of such technology are multi-operator radio access networks (MORAN) and multi-operator core networks (MCNO) which allow network operators to share common LTE resources.

Key concepts

Network slicing concept assumes an essential role to accomodate different QoS required by heterogeous services like machine-type communication, ultra reliable low latency communication and enhancend multi-broadbnd content delivery. The "one-size-fits-all" network paradigm currently employed in past mobile telecommunications system is no longer suited to address this new market model.

Architecture overview

Although there are different proposal of network slice architectures, it is possible to define a general architecture that maps the common elements of each solution into a general and unified framework. From a high-level perspective, the network slicing architecture can be considered as composed by two mains blocks, one dedicated to the actual slice implementation and the other dedicated to the slice management and configuration. The former is designed as a multi-tier architecture composed by three layers (service layer, network function layer, infrastructure layer), each one contributing to the slice definition and deployment with distinct tasks. The latter is designed as centralized network entity generically denoted as network slice controller that monitors and manages the functionalities between the three layers in order to efficiently coordinate the coexistence of multiple slices owned by different business entities.

Service layer

The service layer is the upper layer that interface directly with user application. It is composed by the set of services requested by different business entities (like mobile operators or 3rd party service providers) that share the underlying physical network. Each service is formally represented as service instance, which embeds all the network characteristics in the form of SLA requirements that are expected to be fully satisfied by a suitable slice creation.

Network Function layer

The network function layer is the middle-level layer that is in charge of the creation of each network slice in order to fully accommodate the diverse service instance requests coming from the upper layer. It composed by a set of network functions that embodies specific and well-defined behaviours and interfaces. Multiple network functions are placed over the virtual network infrastructure and chained together to create and end-to-end network slice instance reflecting the network characteristics requested by the service. The configuration of the network functions employed by the slice is enabled by a set of network operations that allows to manage their full life cycle (from their placement to their de-allocation when the service provided is no longer needed). To increase the resource usage efficiency, the same network function can be simultaneously shared by different slices at the cost of an increase in the complexity of operations management. Conversely, a one-to-one coupling between each network function and each slice eases the configuration procedures, but it could lead to poor and inefficient resource usage.

Infrastructure layer

The infrastructure layer is the bottom layer and it defines the actual physical network topology upon which the network slices are multiplexed. In addition, it provides the physical network resources to host the several network functions composing each slice. The network domain of the provided resources ranges a heterogeneous set of infrastructure components like data centers (e.g. storage and computation capacity resources), devices enabling network connectivity such as routers (e.g. networking resources) and base stations composing the RAN (e.g. radio bandwidth resources).

Network slice controller

The network slice controller is defined as a network orchestrator that interfaces with the various functionalities performed by each layer to coherently manage each slice request. The benefit of such network element is that it enable an efficient and flexibile slice creation that can be reconfigured during its life-cycle. Operationally, the network slice controller is in charge of several tasks that support a more effective coordination betweem the network slice layers:

• End-to-end service management: mapping of the various service instances expressed in terms SLA requirements with suitable network functions capable of satisfying the service constraints.
• Virtual resources definition: virtualized abstraction of the physical network resources in order to simplify the resources management operations performed to allocate the network functions.
• Slice life-cycle management: performance monitoring across all three layers in order to dynamically reconfigure each slice to accomodate SLA requirements modifications.

Due to the complexity of the performed tasks that address different purposes, the network slice controller can be composed by multiple orchestrators that indendently manage a subset of functinalities in each layer. To fullfil the service requirements, the various orchestration entites coordinate each other by exchanging high-level information about the configuration of the network processes involved in the slice creation and management.