Software Defined Networks – the future of networking?

Muhammad Rehan Sami, Senior Solution Architect, Business, Etisalat
Muhammad Rehan Sami, Senior Solution Architect, Business, Etisalat

SDN is a technology that promises to be the next big thing not only for IT organisations and networking vendors, but also for service providers, says Muhammad Rehan Sami, Senior Solution Architect, Business, Etisalat

Over the past few decades, routing and switching vendors have put all their efforts in developing the most intelligent piece of networking hardware. Multilayer switches, routers that can read packet information at layer 7 and networking equipment that can make decisions for better routing and switching based on intelligence that has been built into them. This evolution of networking technologies have resulted in today’s state of the art hardware that sits at WAN edges or at campus LANs and has made data and voice communication what it is in modern times. However, with ‘virtualisation’ being the buzzword in techno town, researchers and developers have not spared this very important piece of the puzzle aside.

In this article I take a closer look at the new virtualisation paradigm in town: software-defined networking, also known as network virtualisation. Whatever the name, it’s a technology that promises to be the next big thing not only for IT organisations, networking vendors and virtualisation vendors but also for service providers.

What is SDN?

In a software-defined network, switches and routers take some form of direction from a centralised software management system. Traditional networking equipment is mainly built on 2 logical functional elements: the control plane that makes decisions on how packets will be forwarded and the data forwarding plane that actually pushes the packets onto the wire. In the context of SDN, the control plane is abstracted from the data forwarding plane. A centralised controller, which maintains a real-time, holistic view of the network, defines network paths and distributes this data to individual switches and routers. With these data, the controller coordinates the forwarding of data across all network devices, enabling the automation and granularly manages dynamic provisioning necessary in virtualised environments and cloud networks.

The Trend

Industry & technology experts believe that the migration toward SDN will move faster than carriers’ migration to IP in the late 90s. They support their claims by the fact that vendors and network administrators are starting to embrace SDN, driven by the need for network operators to have more control over their infrastructures and be able to customise them more for their own needs.

Owners of data centre, enterprise, and service provider networks realise the promise of SDN and have been actively pursuing it. Some of the world’s largest network providers, including Deutsche Telekom, Facebook, Google, Microsoft, Verizon, and Yahoo!, have created the Open Networking Foundation (ONF), publicly launched in March 2011, to standardise and promote SDN interfaces and protocols including OpenFlow. Over 40 companies are now members of the Open Networking Foundation and 15 vendors demonstrated interoperable OpenFlow/SDN offerings.

With OpenFlow, a programmable controller is in charge of determining routes and priorities for a packet/stream to a particular destination in the network. The controller implements the network configuration and settings via flow tables that reside on the switches in the network. OpenFlow is the common protocol for communication between controllers and switches from various vendors.

However, the ONF is not the only player in this area. Other vendors, service providers and OTTs are working together to come up with SDN products. VMware, one of the leaders in virtualisation technologies, doesn’t want to miss out on the potentially huge market that SDN offers. Their recent collaboration with Stanford and Berkeley universities to create an industry consortium around SDNs, called the Open Networking Research Centre indicates the intent shown by research organisations and vendors alike. This consortium includes CableLabs, Cisco, Ericsson, Google, Hewlett-Packard, Huawei, Intel, Juniper, NEC, NTT Docomo and Texas Instruments as its founding sponsors. This ensures that VMware will have the technical support, collaboration and vendor interactions to create alternatives to OpenFlow.

Cisco recently announced their strategy and version of a completely programmable network. Termed as ‘Cisco ONE’ – Open Network Environment, it is designed to enable Cisco networks to be flexible and customisable to meet the needs of newer networking and IT trends such as cloud and mobility. Cisco’s approach, primarily based on APIs, agents and controllers, and overlay network technologies differs from more commonplace approaches to SDNs where OpenFlow is used as an API, agent and protocol to command switches from an external controller. Cisco ONE rather complements this approach by opening up areas above and below the control and forwarding planes addressed by OpenFlow. This enables networks to be programmable using a variety of protocols – not just OpenFlow.

SDN and Service Providers

Service providers today face major challenges in terms of the opportunity to provide value-added services (managed hosting, security, conferencing, cloud services etc.) and the overwhelming need to move to a business model that is ARPU-driven rather than subscriber-driven. An ARPU-driven business model would be based on bytes rather than minutes and could also leverage the wealth of subscriber data that is available within the service providers. Ideally, bandwidth would be sold as a utility, like electricity. These are all valid concepts but in general the industry does not have strategies to achieve them.

With the above as a reality, SDN can prove to be a paradigm shift in networking that allows for true innovation. The ability to remotely control network hardware, using central software, leads to real programmable networks. In addition, the decoupling of the control and data planes creates an abstraction and logical map of the overall topology. Moreover, vendor-independent interfaces to the hardware have the potential to change the way that service providers architect and build networks. It also promises to give network operators more control of their infrastructure, allowing customisation and optimisation, therefore reducing overall capital and operational costs.

So what are the business drivers for SDN, from the perspective of a service provider? The most important is cost (increasing APRU while minimising both CAPEX and OPEX), performance, security, compliance and the ability to innovate and grow.

Implementing SDNs using the OpenFlow technique requires a forklift upgrade as all devices along the path of a flow must support OpenFlow before the path is available. This approach is well suited, especially from a cost perspective, for closed environments such as data centres and campus networks. However, the complete upheaval of control plane function in the WAN, where IP routing and MPLS prevail, is not well suited for incumbent service providers where massive investments in network elements and legacy service requirements have been already made.

So is there a solution for service providers? The answer is “Yes”, and is “Path Computation Element – PCE”. SDN Migration with a PCE-based approach can be gradual and/or partial. With PCE, only the ingress node of a flow needs to be upgraded. Network elements that are not yet upgraded with PCE may still be used in paths and may also continue to function as ingress nodes using their existing path computation function. Moreover, the heavy investments carriers have made in IP routing and MPLS control plane technologies remain intact. For Telco/WAN environments, this approach is significantly less cost, less risk, and less disruptive than OpenFlow making it the preferred approach for SDN.

In summary, whatever the approach or whoever the vendor, the key message for leading service providers is to embrace the concept of a more flexible and programmable networking infrastructure. This is becoming all-important to keep up with new market trends and to come up to the expectation of today’s end user. The sooner service providers realise the importance of SDNs and start aligning their strategies accordingly, the quicker they can offer more customisable, easy to launch services to their subscribers which in turn will result in a hike in ARPU.

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