Over the past few decades, communication network has undergone a milestone development, software defined network (SDN) is a new network structure which sprang up in recent years, it uses OpenFlow technology to separate control planes and data planes from network equipment, thereby to achieve flexible control of network traffic, and provide an excellent platform for core network and application innovation. So, what on earth is software defined network (SDN)? What is the difference between software defined network (SDN) and traditional network? This article will give satisfied answers to these questions.

Brief introduction to traditional network structure

In traditional network structure, in order to connect the various terminal services of different services, various devices in the network are also forced to support both interfaces and protocols from both hardware and software. Data planes of the network equipment have to identify the types of each received data, and according to the results to find its corresponding forwarding rules and then forward it. At the control planes of equipment need to separately handle the protocol for each type of service to coordinate and control the forwarding behavior at the data planes. So that to form a stack of multiple business logic network in a physical network. As a result, with the growing number of service types, business logic network becomes increasingly, software and hardware is also becoming more complex, resulting in a decrease in the forwarding efficiency of the network and an increase in the development time of new services.

The components of SDN

In order to learn more about the Software Definition Network (SDN), this part will describe six components in detail.

Network Equipment

In SDN, network equipment refers to an actual physical or virtual switch of defining network forwarding platform. And a heterogeneous network may also include wireless AP, sensors, computer resources etc.

Southbound API (OpenFlow)

SDN controller is mainly uses Southbound API protocol to achieve the control of the network, which include link discovery, topology management, policy development, and issuance of entries etc. of which link discovery and topology management are mainly to control the uplink channel of the southbound interface to the unified monitoring and statistics for the underlying exchange of information; while policy development and issuance of entries are mainly to unified control of the network equipment via the downlink channel of the Southbound interface.

Controller

SDN controller is the central nervous of the entire network system, which control all physical and virtual network equipment. OpenDayLight and ONOS are two of the most popular open source software defined network (SDN) controllers.

Northbound API

Northbound API is an interface that is open to the upper business through the controller， which the target is to enable business applications to easily call the underlying network resources and capabilities. Network business developers can call various network resources with the form of software programming by using northbound interface; and the upper network resource management system can control the resource status of the whole network through the northbound interface of the controller and dispatch the resources uniformly.

Application and service layer

Application and service layer contains multiple services such as security, management, and cloud virtualization, the main function is that provide SLA, QoE, Security and Firewall etc. network services.

Orchestration

Orchestration is a system that automatically creates, initializes, coordinates, and manages the physical and virtual resources required to deliver cloud services.

 

Conclusion

The emergence of SDN decreases the dependency on expensive ASIC network hardware and associated pay-as-you-go (often leading to over-provisioning) and also provides higher programmability that makes it easier to extend network, design and manage system. In general, SDN enables enterprises to quickly deploy new infrastructures, applications, and servers, the speed is faster than traditional networks.