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Generally, the concept of Software Defined Networking (SDN) is the result of efforts to make computer networks become more programmable (Nick Feamster, Rexford, & Zegura, 2013b). This term refers to the behavior of network devices and the flow control handled by software which operates independently from network hardware. As such, programmable network simplifies the network administration tasks by reprogramming a network infrastructure, instead of having to re-build it manually. To date, programmable networks approach has attracted the attention of the networking community, given its flexibility in terms of network management and network design. According to research (Gude et al., 2008), SDN introduces the idea of network operating system abstraction, which is markedly different from previous programmable networks. In this regard, the Open Networking Foundation (ONF) organization defines the term “Software Defined Networking” as:
The physical separation of the network control plane from the forwarding plane; and where a control plane controls several devices. (Open Networking Foundation, 2014)
ONF is a non-profit organization which is committed to accelerating the adoption of SDN. Interestingly, several companies have also developed a number of standards, such as OpenFlow Standard and the OpenFlow Configuration Management Protocol Standard. In fact, OpenFlow Standard is the first communication interface that enables the communication between the control plane and network devices in the data plane layer. Based on the definition given by ONF, the key idea of SDN is the separation of control function from hardware devices, with the control function being centralized in a software component known as the SDN controller. The details of the control plane and data plane are discussed in Section 4.
Figure 1.
Example of the SDN Network
Figure 1 shows the example of the SDN network, which clearly shows that the network control elements are removed or separated from the network devices by centralizing the former in the controller machine. Network administrator is programmed in the OpenFlow switch through the controller machine to specify how data will be forwarded in the network. Lately, the SDN paradigm has been introduced in the networking industry to improve the performance of current network architecture.