Software defined networking (SDN) has been pegged as one of the major enterprise IT trends for the next few years, with analyst firm IDC predicting the worldwide market to grow from $360 million in 2013 to $3.7 billion by 2016.

But as interest grows around the technology, there is a risk that the term SDN will become something like the word cloud – which arguably has come to mean everything and nothing.

With this in mind, Techworld has been speaking to some of the big players in the market to try and pin down exactly what SDN means, both from a technical perspective and a business point of view.

The clearest definition of SDN has been provided by the Open Networking Foundation, which describes it as a separation of the control and data planes.

Most routers and switches today contain some fairly generic silicon, which sits in the network and provides the basic functionality, like forwarding of data using Layer 2 and Layer 3 tables. This is known as the data plane.

Within that switch or router you also have software that sits on top of the CPU element and creates those tables, using something like Spanning Tree Protocol or Open Shortest Path First (OSPF). In other words, it provides the intelligence within the product.

Within a network there will be multiple switches and routers, and the software elements in those switches and routers all talk to each other and share that information. This is known as the control plane.

What software-defined networking does is separate out the two planes, so rather than the software being locally within the switches and routers, it is hosted on a centrally located server that is typically referred to as a controller. The controller communicates with the agents (the dumb devices at the edge) using a communications protocol such as OpenFlow.

One advantage of this is that the controller is able to make intelligent decisions about how to route traffic. So for example, in the case of a financial exchange, where the number one priority is reducing latency, the controller is able to take a holistic view of the network and identify the most low-latency path to send the traffic over.

First steps to a software-defined network

While this sounds like a good idea, the reality is that there are very few organisations where this model has applicability today. The opportunity to do interesting things with SDN certainly exists, but the technology is still being defined and it is unlikely that many businesses will be deploying it in anger over the next two years.

Having said that, there are steps that organisations can take to put a toe in the water and find out what the benefits of SDN could be in the future.

Automation is also a good first step, allowing organisations to begin the transition from a hardware-defined legacy network into a software-defined business. This is particularly important for big cloud companies like Google and Amazon, that require IT to scale in line with their markets.

Cisco has come up with a strategy that allows customers to continue using their existing routers and switches, with the control and data plane located locally, but also presents them with application programming interfaces (APIs) so that all the information from the router or a switch is fed up the the controller, and the decisions are fed back down to the network.

In this way, they end up with a programmable network that has many of the properties of an SDN, but without giving up their existing distributed network architecture.

“The benefit of this approach is you continue to get the features and functionality distributed across the network,” said Ian Foddering, Chief Technology Officer and Technical Director for Cisco in the UK and Ireland.

“One argument that you could use against the traditional SDN approach is that you start to centralise everything into a couple of devices within the network, and you've got very dumb devices at the edge.”

Cisco also offers a “traditional” SDN approach, as well as a third stack that is effectively a combination of the two. So the customer has a centrally located controller and also continues to have the control plane and data plane at the edge, creating a virtual overlay.

“In terms of going forward, one of the skills and requirements that organisations will now need to start to consider from a networking point of view is how to integrate the two, and the write to those APIs,” said Foddering.