FEATURE: SDN
What is virtualisation
of networks?
By Arun Shankar
P
roduct development within the telecommunications
industry has traditionally followed rigorous
standards reflected by the term ‘carrier grade’.
While this model worked well in the past, it inevitably led
to long product cycles, a slow pace of development and
reliance on proprietary hardware.
Network function virtualisation is a network architecture
concept that uses IT technology to virtualise entire classes
of network node functions into building blocks that may
connect, or chain together, to create communication
services. Network function virtualisation relies upon, but
differs from, traditional server-virtualisation techniques.
A virtualised network function may consist of one or
more virtual machines running different software and
processes, on top of standard high-volume servers,
switches and storage devices, or even cloud computing
infrastructure, instead of having custom hardware
appliances for each network function. For example, a
virtual session border controller could be deployed to
protect a network without the cost and complexity of
installing physical network protection units.
Network function virtualisation framework consists of
three main components:
Virtualised network functions: These are software
implementations of network functions.
Network functions virtualisation infrastructure: This
is hardware and software components that build the
environment where virtualised network functions are
deployed.
To build more complex services, the notion of service
chaining is used, where multiple virtualised network
functions are used in sequence to deliver a service.
Another aspect of implementing network function
virtualisation is the orchestration process. To build
highly reliable and scalable services, network function
virtualisation requires that the network be able to initiate
virtualised network function instances, monitor them,
repair them, and most important for a service provider
business, bill for the services rendered. These attributes,
referred to as carrier-grade features, are allocated to an
orchestration layer in order to provide high availability
and security, and low operation and maintenance costs.
The initial perception of network function virtualisation
was that virtualised capability should be implemented
in datacentres. This approach works in many, but not
all cases. Network function virtualisation presumes
and emphasises the widest possible flexibility as to the
physical location of the virtualised functions.
Virtualised functions should be located where they are
the most effective and least expensive. That means
a service provider should be free to locate network
function virtualisation in all possible locations, from
the datacentre to the network node to the customer
premises. This approach is known as distributed network
function virtualisation.
Network functions virtualisation management
and orchestration architectural framework: This is
a collection of functional blocks, data repositories,
reference points, interfaces through which these blocks
exchange information for the purpose of orchestration. Network function virtualisation is a software platform
running on standard multi-core hardware and built using
open source software that incorporates carrier-grade
features. The network function virtualisation platform
software is responsible for dynamically reassigning
virtualised network functions due to failures and changes
in traffic load, and therefore plays an important role in
achieving high availability. There are numerous initiatives
underway to specify, align and promote network function
virtualisation carrier-grade capabilities.
The network function virtualisation platform
implements carrier-grade features to manage the
platform components, recover from failures and
provide effective security, all required for public carrier
networks. A service provider that follows the network
function virtualisation design implements one or more
virtualised network functions. A virtualised network
function by itself does not automatically provide a
usable product or service to the provider’s customers. Virtualisation is also changing the way availability is
measured in network function virtualisation solutions.
As virtualised network functions replace traditional
function-dedicated equipment, there is a shift from
equipment-based availability to a service-based, end-to-
end, layered approach. Virtualising network functions
breaks the explicit coupling with specific equipment,
therefore availability is defined by the accessibility of
virtualised network function services . ¡
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