The research for a new paradigm for a better architecture of networking began in 2004. After several proposals and researches, the concept of software defined networking (SDN) emerged in 2008. In 2011, Open Networking Foundation was formed to take this concept to an executable level. The foundation consists of 69 members including Cisco, Juniper, HP, Dell and IBM.
Google, Yahoo, DT, Microsoft and Facebook serve as the Board of this foundation. One of the first SDN projects was AT&T’s GeoPlex. Some of the available commodity switches that are compliant with OpenFlow protocol of SDN are Hewlett-Packard (8200zl, 6600, 6200zl), Brocade (5400zl, 3500/3500yl) and IBM NetIron CES 2000 Series.
In traditional networks, most of the network functionality is implemented in hardware devices like switches and routers. In such systems, each appliance needs to be configured individually. Moreover, a router will treat all incoming packets equally and will follow the same protocols for all.
Inculcating such functionality is under the control of the device provider. So when a new technology, feature, update or application is introduced, all hardware devices need to be replaced. Thus, it has been found that traditional networking evolves slowly, is not dynamic and has limited functionality, as provided by the vendors. Being hardware-centric, it proves to be a huge challenge when the network is big and complex.
Software defined networking can be treated as a completely opposite architecture. Devicem level management is eliminated from networking. Here, the network administrator has the authority to shape the traffic from a centralised control console without configuring individual devices in the network. Unlike traditional networks, where the switch forwards all frames as per a pre-defined program, software defined networking has the provision to send the decision to switch through an application running on a server. Also, the switch can query the controller to provide information about the current traffic. This results in a highly-scalable, flexible and agile network.
Need for new architecture
There are several reasons why the traditional hardware-centric architecture needs to be replaced.
Increasing number of users
As shown in Fig. 1, advancement in technologies is leading to a drastic increase in the number of Internet users. Technologies and devices are becoming user-friendly. These have now become an inevitable part of our daily lives. This calls for a demand of upgrade in the technology to accommodate the increasing traffic.
Continuously varying traffic pattern
The number of users at any particular place is not always the same. Traffic pattern, thus, keeps changing continuously. There is a drastic change in the number of users at day time than at night time. Due to such variations in traffic pattern, there arises a demand for a flexible technology that should be capable of handling such traffic.
To eradicate vendor dependence
Traditional networking devices are functioned and programmed by technicians. The network administrator cannot modify the program or update the protocol. Thus, when any new algorithm or protocol is to be implemented in the network, altogether, the existing devices become useless.
Evolution of cloud technology
Companies are now moving towards cloud computing. Most of their data is stored on cloud servers for easy and quick access. Ultimately, it increases the burden on network architecture and increases traffic.
Increasing number of networking devices connected through the Internet
As shown in Fig. 2, researchers predict from the statistics that the number of connected networking devices may reach 50 billion by 2020.
Fig. 3 reveals the complexity of the network. To manage and control such a tremendous volume of traffic, appropriate architecture is required.
Evolution of the Internet of Things (IoT). As shown in Fig. 4, the IoT may connect 50.1 billion networking devices by 2020. The IoT market revenue is expected to grow from US$ 1.928 billion in 2013 to US$ 7.065 billion in 2020. Such a rapid evolution results in the demand for highly-reliable and agile networking architecture. Data-intensive services offered by the IoT like video surveillance, emergency services and uninterrupted monitoring demand a technology that supports the cause with excellent quality of service and high data rates.
Architecture components of SDN
Fig. 5 shows the various components of SDN architecture. The architecture comprises three planes, namely, data, control and application. Data plane includes the dedicated hardware and is responsible for the processing of packets as well as traffic forwarding.
In the controller plane, policies are configured to define the scope of control given to SDN application and to monitor system performance. Optimising resource allocation and checking network failure are also the roles of controllers. In both planes, security functions are considered to ensure secured intercommunication.
As demonstrated in Fig. 6, in traditional networking, each device has an embedded set of protocols that make the routing decision. Whereas in SDN (Fig. 7), there is a central network operating system (OS) that controls all devices in the network. All decision-making protocols and access-control algorithms are centrally managed by the control plane.