Introduction to SDN Terminology

The SDN is the new feature which is currently used in various service providers so that they can separate the Control and Data plane, so which means one box is not using both the planes, then whats new in this and how it works.

In short : There is SDN controller where Control and Management plane is there and devices like Router and Switches are only processing the Data plane and real traffic will be routed or switched on the basis of Control plane instruction which is send by SDN Controller in the network.

The Open Network Foundation (ONF) defines SDN as a decoupling of the control plane and the data plane. Traditional network devices have an integrated control plane and data plane. In this classic SDN architecture, however, network intelligence is logically centralized in a controller, and there is a physical separation between control plane and the data plane. Open Flow is the protocol that specifies the interactions between the control plane running in the controller and the infrastructure

The intent of this architecture is agility, automation, and a decrease in overall costs of the network. 
While the classic SDN approach may hold promise for some customer segments and use cases, it may not be the best fit for others, and is not without its limitations.

This complete separation of the entire control plane from the data plane in a classic SDN model, removing it from the network to a centralized controller, is a radical departure from the design and operation of most networks today.The classic SDN approach to network architecture introduces potential challenges in availability, performance, scale, and security.

When all control plane functionality is moved to a central controller, the controller must be highly available. The performance should meet the rapid requests and extreme load conditions on the network.The controller must be able to scale to very large networks, with thousands of nodes. Finally, it must be highly secure, with only approved applications able to modify or change the underlying network.

Fig 1.1- SDN Architecture
While the traditional SDN model takes benefit of community programmability, SDN isn't always a demand for programmability. community devices can be uncovered to the application layer via utility programming interfaces (APIs).This hybrid method to network programmability and SDN deployments can take gain of hardware intelligence as well as current characteristic sets within the network running gadget.

This can be performed with out a whole decoupling of the manage aircraft and the information plane. furthermore, in a classic SDN model, one need to forgo the functions of the local operation device, as those capabilities need to be re-created in a controller.

The hybrid SDN version permits the various benefits of a conventional SDN model with a centralized controller, whilst nevertheless permitting users to benefit from the current community talents many have come to rely on. in many cases, the network working machine can actually be upgraded, in preference to a whole improve of the network infrastructure.This permits an evolutionary technique to network programmability, as opposed to the innovative approach of a classic SDN model.

This evolutionary method permits users to choose which programs and capabilities are migrated out of the community tool and onto a controller or software server. subsequently, a hybrid version lets in customers to apply their present fault control or network control systems.


The hybrid SDN model is capable of minimize a number of the capacity demanding situations that face a traditional SDN method to network structure.The lack of a global view of traffic, topology, costs, and policy continues to create complexity as interaction with the network requires detailed knowledge of networking protocols and an awareness of each vendor’s implementation.Profitability and business viability are further threatened by slow revenue growth. As is the case with WAN costs poor information flows and manual steps are impairing service providers’ abilities to respond to rapidly changing competitive threats.

Software program defined networking (SDN) within the WAN gives the possibility to drive down charges thru expanded operational efficiency network usage especially expanded service introduction speed, and differentiated and customized community services. mainly,SDN and automation are utilized in a hybrid centralized manage and automation answer to enhance WAN utilization and create and supply profitable new services. 

SDN accomplishes those commercial enterprise goals by means of converging the control of network and application offerings into centralized, extensible orchestration platforms that could automate the provisioning and configuration of the complete infrastructure. commonplace centralized IT rules carry collectively disparate IT organizations and workflows.The end result is a current infrastructure that could deliver new programs and offerings in mints, instead of days or weeks required inside the past. 

SDN delivers speed and agility when deploying new applications and business services. Flexibility, policy, and programmability are the hallmarks of Cisco's SDN solutions, with a platform capable of handling the most demanding networking needs of today and tomorrow.

Conclusion 
Inside the protection and intelligence communities, the network is challenge-vital. Software program-described networking affords a new architecture for this network, an structure that brings the application layer and the networking layer nearer collectively. it's far a shift in generation so one can alternate the networking landscape by means of providing greater automation and orchestration of the network material, and through allowing dynamic, utility-led configuration of networks and offerings. 

SDN allows the community to respond to requests from an software in actual time, based totally upon the contemporary state and circumstance at the network. it's far this agility with the intention to transform networks as we recognize them.