5G Slicing: Concepts, Architectures, and Challenges
Part 1: The beginning, what is slicing?
5G is expected to open up many new opportunities for service providers – of these we have talked in other blogs and articles. This blog series will focus on one of the most hyped and talked about technology enablers – Network Slicing. It is believed that network slicing will enable service providers to simultaneously accommodate the wide range of services, over a common network infrastructure.
Digitalization/softwarization of the network is one catalyst of network slicing. Technologies like Software-Defined Networking (SDN) and Network Function Virtualization (NFV), have already separated the data plane from the control plane. This separation of ‘elements’ provides the programmability, flexibility, and modularity that is required to create multiple logical (virtual) networks, each tailored for a given use case, on top of a common network. These logical networks are referred to as network slices.
Network slices is an end-to-end (E2E) logical networks running on a common underlying (physical or virtual) network, mutually isolated, with independent control and management, and which can be created, suspend and terminated on demand as well. Such self-contained, virtual networks must be flexible enough to simultaneously accommodate diverse business-driven use cases from multiple players, man or machine, across a variety of platforms.
But for proper slicing, one must first understand the basic facets of a network slices: Resources, Virtualization, Orchestration, Isolation and Autonomous Behaviour.
A network slice is composed of a collection of resources that, appropriately combined, meet the service requirements of the use case (or service) that the slice supports. One can differentiate between two types of resources:
- Network Functions (NFs): functional blocks that provide specific network capabilities to support and realize the particular service(s) each use case demands. Generally implemented as software instances running on infrastructure resources, NFs can be physical (a combination of vendor-specific hardware and software, defining a traditional purpose-built physical appliance) and/or virtualized (network function software is decoupled from the hardware it runs on).
- Infrastructure Resources: heterogeneous hardware and software for hosting and connecting NFs. They include computing hardware, storage capacity, networking resources (e.g. links and switching/routing devices enabling network connectivity) and physical assets for radio access.
Virtualization is key as it enables effective resource sharing among slices. To make these resources suitable for network slicing, the aforementioned resources and their attributes need to be abstracted and logically partitioned with virtualization mechanisms.
Resource abstraction is the representation of a resource in terms of attributes that match predefined selection criteria while hiding or ignoring aspects that are irrelevant to such criteria, in an attempt to simplify management. The resources to be virtualized can be physical or already virtualized, supporting a recursive pattern with different abstraction layers.
Just like in the case of VMs, network virtualization enables the creation of multiple isolated virtual networks that are completely decoupled from the underlying physical network, and can safely run on top of it.
The introduction of virtualization to the networking field has spawned new business models, new players with distinct business roles. Consider:
- Infrastructure Provider (InP): who owns and manages a given physical network and its constituent resources. Resources, such as WANs and/or data center (DCs), are virtualized and then offered to single or multiple tenants.
- Tenant: then leases virtual resources from one or more InPs. Usually in the form of a virtual network, with which the tenant can realize, manage and provide services to its end-users.
- End-user: consumes (part of) the services supplied by the tenant for his own needs.