Software Defined Networking is on a roll: it's a real game changer. The game it's changing is the closed, proprietary world of networking with its vertically integrated hardware, slow innovation and artificially high margins. A world that hasn't changed much for decades.
There is nothing new about the concept of a software-defined network. It goes back to the early '90s when Cabletron prototyped a secure VPN solution, and more recently when HP was proposing an Adaptive Edge Architecture. The difference this time comes from the enabling OpenFlow/OpenStack protocols, which are de facto standards, and from the Open Networking Foundation (see "How Software Defined Networking Will Change Communications").
Let's start with a widely accepted definition of an SDN. It's one in which "the control and data planes are decoupled, network intelligence and state are logically centralized, and the underlying network infrastructure is abstracted from the applications" (source opennetworking.org).
Sounds good, but what does it mean? What does it bring to the enterprise table? Well, if you change "abstracted" to "virtualized," maybe you can spot the beginning of the business case.
Quoting from a Dell white paper:
"The introduction of server virtualization led to a revolution among enterprises that has consumed the focus around IT infrastructure for the past decade. Virtualization changed the entire operational model around server infrastructure in such a profound way that it laid the foundation for a complete re-imagining of enterprise IT. Prior to virtualization, IT services were encumbered by the realities of the physical world, but when empowered by virtualization, the deployment of a new server could become as simple as the touch of a button."
The ability to virtualize computing and storage resources is something we take for granted. But somehow the ability to add, drop and change network resources and profiles in the same way sounds like black magic: something that sounds too good to be true, possibly because networking has been stuck in a proprietary rut for 40 years.
OpenStack enables orchestration. This is an open source cloud operating system. It controls large pools of computing, storage, and networking resources. Schematic courtesy HP. 
As illustrated, a key business benefit is the ability to orchestrate network resources via a portal. The network devices are powerful OpenFlow-compliant switches having relatively limited intelligence--limited because most of the network smarts reside in the OpenFlow controller, which manages a distributed set of network devices as a single virtual switch. Most OpenFlow controllers expose an API to the applications.
OpenStack enables orchestration. This is an open source cloud operating system. It controls large pools of computing, storage, and networking resources. Schematic courtesy HP.
SDN's 3-layer architecture provides open, standards-based access to the infrastructure. The control layer separates the control and data planes, which enables multiple devices to be abstracted down to one. And the application layer delivers open, programmable interfaces to automate the orchestration of network services. SDN has the potential to shape traffic flow in order to meet specific business or security needs, e.g., the need to abide by OECD guidelines on the protection of privacy and trans-border flow of personal data.
This structure facilitates the ability to quickly create and deploy new applications and services. For example, the CERN logo (at top right of the schematic above) indicates the joint development of a distributed load balancing application that delivers advanced traffic characterization and orchestration. The objective was to optimize traffic distribution, with synchronization across load balancers. This SDN capability is particularly useful to CERN because its Large Hadron Collider experiments generate an enormous amount of data that needs to be transported to various universities and institutions around the world--hence the need for this advanced network application. It runs on an HP Virtual Applications Networks SDN controller.
OpenFlow and OpenStack
OpenFlow is a Layer 2 communications protocol that gives access to the forwarding plane of a network switch or router over the network. It allows the path of network packets through the network of switches to be determined by software running on multiple routers. This separation of the control from the forwarding allows for more sophisticated traffic management.
OpenStack is an open source cloud operating system designed to deliver high-performance virtualized network infrastructure that transitions customers to the cloud.
An Automated Model
Using the command line interface (CLI) to program the individual switches is something that Cisco and Cisco-trained IT staff had to do in order to meet customer requests for policy changes. However, this is an expensive, time-consuming task and SDN can provide a model that automates networking provisioning. Therefore, IT departments won't need to jump through such high-tech hoops in future: instead untrained staff can employ the model to develop self-service clouds. SDN also removes router/switch lock-in: switches and routers are now abstracted, which allows enterprises to swap between vendors.
This need is obvious, but how is this task realized? HP's model is built on top of the company's Virtual Application Network SDN controller. The APIs used to communicate between the layers of the SDN stack are grouped based on their function in the architecture: Northbound OpenStack APIs communicate between controllers and applications, and southbound OpenFlow APIs communicate between controller and infrastructure. Automation of the network configuration process is based on the policy-driven decisions built into the network applications.
The Big Picture
As the cloud era takes shape, technology continues to play an increasing role in all aspects of business, and its role is shifting from operational support to becoming core to product & service delivery and customer interaction. Data Centers in private or secure third party clouds are becoming the manufacturing floor of the information era. SDN allows IT to take a more proactive role in delivering cloud services and applications, which in turn will drive next-generation user experiences.
That is the real value of SDN. It is not a specific killer feature: instead it's a platform that removes many of the critical limitations of the traditional networking model: one that is set to create entirely new networking possibilities.
The big picture: the shape of the emerging cloud era. Virtual computing and storage resources employed over a virtual network and topped off with next-generation business applications and services. Schematic courtesy Dell.
