Software-defined networks

Does SDN mean a whole new world for operators – or just a more efficient and flexible one?

The quiet revolution

The concept of software-defined networks may once have seemed impossible in a hardware-defined and dominated world. Today SDNs are redefining network architectures in markets around the world. Simon Fletcher, CTO of wireless advisory firm Real Wireless* explains why.

IFIRST BECAME seriously involved in software defined networks (SDNs) more than 10 years ago. At the time I was working with product and standards development teams influencing an ETSI** policy document looking at SDN and network function virtualisation (NFV) as separate, but highly interdependent trends. The plan was to turn what was then a trial concept into a commercial reality.

While often mentioned in the same breath, SDN and NFV play different roles in redefining network architectures.

On the one hand, the main driver behind SDN is to separate the network control plane (essentially the routing that determines how data is sent from one place to another) from the transport layer. And this encapsulates the conceptual underpinning for SDN – to move from a vertical to a horizontal separation of the control and transport layers in mobile networks.

NFV, on the other hand, is about abstracting network functions from the hardware on which it runs. Theoretically, you could have SDN without NFV – a software-defined network with static hardware.

The reason this work was – and remains –important is that service providers always want to get away from operational and architectural inflexibility and vendor ‘lock in’.

Before the concept of SDN, networks were hardware-defined and the hardware market was dominated by two or three very big players that sold vertically integrated appliances that, while operationally robust, provided limited choice and offered very little operational flexibility.

To address this, the mobile industry borrowed standards and interfaces like OpenFlow from the IT world to enable secure and efficient access to and manipulation of network routers and switches. These devices could be either physical or virtual.

The proof of concept was established through a small-scale Stanford trial that demonstrated mobile network functionality over Wi-Fi using an SDN. This encouraged the support of pioneering operators like BT and Telefonica and led to the ETSI initiative.

Today SDNs are becoming mainstream. It’s true that there have been some bumps along the way, not least because switch vendors and some of the big equipment suppliers felt they could make more money in the short term by maintaining the status quo. There is also the issue of squeezing the most out of (costly) legacy hardware.

But the programmability of networks has become increasingly important to service providers. As data usage over mobile networks continues to surge, more granular resource management becomes a priority. The flexible, efficient end-to-end management of data flows has become business-critical to operators – and SDNs hold one of the keys to making it happen.

SDNs mean that the management plane can be separated from the data flow and that these aspects of network functionality can be sourced from different suppliers. This is partly about reducing capex by making it possible, for example, for operators to source hitherto expensive switches and routing gear from white box suppliers without compromising the integrity of network operations. But it is also about improving network efficiency by having more control