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Software Defined Networking (SDN) is getting a good deal of attention at the moment. So often it is reduced to the abstraction of the Control and Data Plane' with all that seems to promise, however, what is changing the world forever is cloud, not SDN. If we are discussing SDN in isolation, independent of its application within an orchestrated cloud solution, its value becomes murky at best and overhyped at worst. At its essence, in my view, SDN is an enabling function.

SDN is actually a confusing term as networking has always been defined by software. In the current context though, SDN is an umbrella term covering two environments. The first refers to underlay networking solutions that address network hardware evolution through the centralisation of the control plane for multiple network elements, in a common controller. In contrast, the second refers to overlay networking solutions that are agnostic to the underlying network hardware infrastructure.

Any discussion that takes place concerning rip and replace actually relates to SDN underlay network solutions. Rip and replace implementations are not likely to be widespread. A cap and grow strategy using next generation hardware and leveraging SDN will be much more pervasive. Even with cap and grow, SDN in the underlay will be far from ubiquitous in the near term. The promise of inexpensive white box switches that allow enterprises to dramatically reduce CAPEX is becoming a reality. The option to dramatically reduce data centre switching CAPEX with commodity hardware has been an option for years, however only a few vendors continue to dominate the market with premium priced hardware. The reason is straightforward - networking has always been defined by software.

So if SDN won't rapidly transform the network hardware infrastructure of the world's data centres then what is the big deal about SDN anyway? The big deal is the overlay. Overlay SDN solutions allow the networking of the cloud to be in software, using any networking hardware infrastructure as a bearer path. As enterprises look to move workloads to the cloud, they need to be able to operate the cloud and its applications without needing to manipulate the underlay network hardware of the cloud service provider (CSP). In other words, they need the networking of their applications, including functions like load balancing and firewalls, to be in the cloud software, not the networking hardware elements.

SDN overlay solutions, which IBM often refers to as 'cloud networking', allow operators to build virtual, software based networking solutions in the cloud. Bearer path still traverses the physical network infrastructure, but networking design and control for the virtual network is in the cloud software. More importantly, virtual networking can be integrated with the cloud orchestration layer via standard APIs.

In the orchestration layer, all elements of cloud infrastructure, including compute, storage and networking, can be brought into a single integrated system. Our clients are facing substantial growth in management requirements driven by big data, analytics and mobile. Marketing and sales organisations are demanding faster time to market for new applications, and IT professionals are trying to meet these business requirements in an environment of restrictive IT budgets. As a result, clients are increasingly turning to an operational model based on orchestrated cloud that allows for rapid deployment of new applications and a tighter coupling of investment to business benefit through pay as you play cloud business models. This is what is currently changing the world.

Early in my career, a great engineer and mentor told me that anything can be built with speed, quality, or affordability: pick two. The world has changed however, and cloud must deliver all three. Within cloud networking, SDN is simply a functional component which allows that to happen.