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SDN: Introduction, Working, Architecture

3. SDN Architecture

SDN architecture consists of three major layers:

  • Application Layer: It is responsible for developing and managing networking applications.Application layer deals with end-user business applications that utilizes the SDN services. Business application such as energy efficient networking, security monitoring, network virtualization etc.
  • Control Layer: The control layer is also referred as control plane that comprises a set of software-enabled SDN controllers. This layer allows the network administrator to apply custom policies to the physical layer devices. It is responsible for routing packets to their respective destination while applying different rules and policies.
  • Infrastructure Layer: This layer consists of forwarding devices like the physical switch, router, etc. Software switches which can be accessible via open interfaces, also part of this layer. This layer is considered as forwarding layer since it allows packet switching and for- warding.
SDN Architecture

4. Working

The networking applications are built and deployed on the top of the application layer and these applications communicate with Network Operating System (NOS) through Application Programming Interfaces (APIs) which are called “Northbound APIs”. NOS communicates and implements the routing rules and policies on forwarding devices via “Southbound APIs”. The end devices are connected to these forwarding devices for executing the task of communication through packets.

Interfaces of the controller

The SDN controller can interact with three layers through some standard open interfaces which are explained below.

Southbound interface: Southbound interface creates a channel to interact with the controller and underlying forwarding devices. OpenFlow is the standard-ized protocol supported by ONF, is the widely used southbound interface , which establishes a secured link between the controller and forwarding devices.

Northbound interface: The north bound APIs are interfaces between the controller and the applications application layer.This interface helps the application developers to manage the network through the program.

East-west Bridge: In practice, a large scale enterprise network is partitioned into sub-networks, where each sub-network is handled by a different controller. In this multi-controller based architecture, each network has the global network view to communicate with the other domain and exchange topology among the sub-domains. Direct intra domain communication is not possible without the help of a proper interface. East-west protocols solve this problem by exchanging network view among the controllers.

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