SDN: Introduction, Working, Architecture
8. SDN Terminologies
Network Operating System:Network Operating System (NOS) is used for routing packets. In the SDN paradigm, NOS is called the controller because it consists of a control plane. An SDN controller is the central component where dissected intelligence of conventional networking devices is merged. There are different SDN controllers built on the stack of different programming languages.
OpenFlow:OpenFlow is the core protocol of SDN architecture. The controllers use OpenFlow protocol for communicating with the switches (forwarding devices). OpenFlow is not a vendor-specific protocol which infers that the controller can communicate with every switch, irrespective of the vendors.
SDN Switches:The SDN switches are different from conventional switches and this is why it is better to refer SDN switches as forwarding devices because SDN switches are equipped with only data planes. SDN switches can either be in hardware form or software. Open vSwitch (OVS) is the more popular virtual switch that is used in the SDN paradigm for connecting end devices.
SDN Simulation Tools Mininet is the first open source simulator for Openflow networks. It is an inexpensive and quickly configurable network testbed. It is the most well known tool for SDN OpenFlow network research. The virtual switches in Mininet are a kind of software OpenFlow switches called “Open vSwitch”  With mininet the entire network can be packaged as a virtual machine so that others can download, run, examine and modify it. The major strengths of mininet
SDN has gained significant momentum in both the research community and in the industry. It is going to become the new approach for networking. Although SDN has its own limitations and challenges, it offers other significant benefits and cost savings such as its programmability, providing a global view of the whole network, providing more flexibility & control to researchers & network administrators, network equipment vendor independency and eliminating middleboxes. Future work can involve improving security of SDN and enhancing the controller design for scalability, resilience and robustnes