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.

Scalability and network management

SDN is only just starting to gain traction in some of the massively scalable data centres of the world but all kinds of companies, from service providers to educational networks, could benefit from the ability to free the application layer from the limitations of the physical equipment.

This is because, in a typical hierarchical monolithic network, it is often very costly and time-consuming to make architectural changes. The network can also act as a bottleneck during massive spikes in traffic, because it does not have the ability to scale in the way that servers do thanks to virtualisation.

By managing the application layer independently of the physical network layer, companies can monetise their network investments much faster, according to Flemming Andersen, Director of Service Providers for EMEA at Brocade.

It also means that organisations can run their network infrastructure in hybrid mode. So they may use SDN for some of their requirements, where it is deemed to be the optimal method of routing traffic, and then use their traditional IP network for other services that are not quite ready to move onto an SDN infrastructure.

“If you imagine Royal Mail delivering a letter to you in your house, they're doing it in exactly the same way every single day – they're using the same infrastructure and there's very little flexibility,” said Anderson.

“But sometimes you need a package to arrive more urgently. So SDN is like the courier companies, where you can get them to come and pick up the package and they guarantee the delivery. So SDN gives you the ability to launch many more services of higher value.”

As well as reducing latency, SDN can also allow packets to be sent more securely. Anderson gave the example of the national research and education network in the US called Internet2, which is the equivalent of the JANET education network in the UK.

Internet2 has already launched an SDN using OpenFlow, because it has some data that needs to be kept secure. By creating an OpenFlow connection between the universities, members of Internet2 can share confidential documents without having to send them over the public internet.

Brocade recently announced that it is buying open source routing vendor Vyatta in order to further it’s SDN and network virtualisation strategy. But companies like Cisco, Brocade and Juniper tend to be cautious in their plans for SDN, as they do not want to undermine their existing hardware-defined networking businesses.

The same goes for the IT vendors offering integrated systems, like HP and Dell, which are starting to explore how SDN can become part of an end-to-end product portfolio. Dario Zamarian, general manager of Dell's networking division, said that what matters is having a network that can be simplified, programmed and changed dynamically.

“The emphasis is not just about whether you can have standards across a controller that talks to a switch. It's more important, when you combine the application layer with the controller layer with the switching, both physical and virtual – the combination of the three, it gives you a simpler, more manageable, programmable network for new ways to do things,” said Zamarian.

However, he dismissed the notion that any vendor expects to make money out of SDN in the next few years, suggesting instead that it is a way for vendors to show their customers that they are investing in the next generation of networking technology, and that they will continue to evolve.

'Bigger than server virtualisation'

Not everyone in the industry is so cautious. For companies that do not have a legacy hardware business to protect, such as network automation firm Infoblox, the drive towards SDN is picking up pace.

From this perspective the greatest attraction of SDN is the fact that it allows customers to buy low-cost commodity hardware and load industry-standard software on top of it.

Within the server industry, customers have been able to take advantage of commodity hardware economics for a long time – in fact, one of the major factors that led to the resurgence of the hypervisor around 2005 was the fact that servers were getting cheaper.

In the networking industry, however, the problem is very different. While spinning up 1,000 machines is not that different to spinning up 50,000 machines – because the machines operate independently from one another – networking boxes are all interconnected.

This means that enabling organisations to take advantage of cheap hardware in the networking business requires a different set of core competencies. However, the revolutionary potential of SDN is also much greater than server virtualisation, according to Infoblox founder and CTO Stu Bailey.

“It's much bigger than server virtualisation; it's way more disruptive than that; there's way more at stake in terms of change; the complexity profile of networks is much greater than that of server virtualisation, so that means the timing is probably less certain,” he said.

“Ultimately it's about a market correction for the networking business to get it back to something that's much more efficient, that's healthier for the consumer. They get more value out of every dollar they spend; every dollar sets them up for more strategic value in the future.”

He pointed to VMware's recent acquisition of Nicera as a sign that software-defined networking is about to take off. Given VMware's success in the server virtualisation space, “they are not messing about by acquiring Nicera,” he said.

He added that techniques like big data analytics assume very sophisticated networking infrastructure that simply doesn't exist today, so organisations either have to run a dedicated network, or use SDN to program the network so that it appears dedicated.

“Once you have a network that can make the public web feel like a dedicated network, the possibilities are endless,” he said. “Just as with the creation of the World Wide Web, installing the infrastructure for SDN could be the beginning of something fundamental.”

2013 is unlikely to be the year when SDN achieves mass market adoption – the technologies are still too nascent for that. But there is no harm in organisations starting to experiment with SDN in the context of their existing network environments, to find out how running a programmable network could transform their business processes in the years to come.