Software-defined Networking (SDN) Controller

All traditional networking devices like router and switches uses distributed control plane. But newer model of networking i.e., Software-defined Networking (SDN) uses centralized control plane. Distributed control plane means that control plane of all networking devices lies within the device itself. 

Each device have their own control plane to control data plane. In Centralized control plane system, there is a device which contains control plane of all devices. This device control the activities of data plane of all networking devices simultaneously. This device is called Controller or SDN controller. 

The following figure shows a model of controller based networking. 

Figure- Controller based network model

1. Southbound Interface : 
   In SDN, all networking devices must be connected to controller so that it can regulate data planes of all devices. When drawing architecture of network, usually the network architect places networking devices below controller. Now according to map conventions, interface between controller and networking devices lies to south of controller. Hence, these interfaces are called Southbound Interface. 

   Southbound interface is an interface between a program on controller and a program on networking device. Note that these interfaces we are discussing are software interface not physical one. 

    

2. Northbound Interface : 
   Controller need to know many information regarding network so that it can control data plane of networking devices All these information are provided by Network Programmer. Network Programmer provide essential information to controller through various software or script about what functions it has to do. Again these softwares/scripts are placed above controller in network architecture. This placement of software/script makes interfaces between controller and software in north direction, according to map conventions. Hence, Interfaces between controller and softwares are called Northbound Interface. These interfaces enable programmability of network. 

   All interfaces we discussed above are program based interfaces. These interfaces in a broader sense are called Application Program Interface (API). An API is an interface through which two program can exchange data between them. 
    

Let us understand- what is the importance of SDN and where SDN is used?

Preface

In the last two decades, the traffic demand and monitoring for networks have increased, since sales, customer service, internal communications, and documents are increasingly relying on network connectivity. Networking defined by software is a key technology needed to meet these new demands, coupled with the virtualization of network functions. SDN is just one piece of the jigsaw puzzle, and each offers network operators a new way of designing, deploying, and managing an SDN architecture and its service.

The basic principle of SDN is “to automate network supply, management and control through centralised policy/control engines based on software, that control network enabling endpoints”.

Organizations can make innovation with SDN possible by creating in a record amount of time and with fewer complications than before new applications, services, and business models. With dynamic applications and a more efficient workflow, companies can create new services and paths to revenue. Network features can be executed with cheaper off-shelf hardware that reduces CAPEX levels. By supporting automation and algorithm control, companies can reduce the OPEX of IT services via the enhanced programming of network features, making it simple to design, deploy, manage and expand networks.

In short, it can be said that- SDN acts a “A Bigger Umbrella or a HUB” where rest other networking technologies come and sit under that umbrella and get merged with other platform to bring out the best of best outcome by decreasing the traffic rate and by increasing the efficiency of data flow.

Where is SDN used?

Enterprises use SDN, the most widely used method for application deployment, to deploy applications faster while lowering overall deployment and operating costs. SDN allows IT administrators to manage and provision network services from a single location.

Cloud networking software-defined uses white-box systems. Cloud providers often use generic hardware so that the Cloud data center can be changed and the cost of CAPEX and OPEX saved.