Introduction to Controller Architecture

Controller is a software program that runs on a separate server, implemented in an unspecified language, and can run on different operating systems. Currently, controllers are divided into two categories. The first category is the generalized Controller, also known as SDN Controller, which supports a variety of protocols. OpenFlow is one of them. This controller adheres to the SDN principle of control and forwarding separation, but it can control the forwarding device through other southward interface protocols, while opendayLight organizes and develops SDN Controller. The second type is the controller of the protocol, also called OpenFlow Controller. OpenFlow is the only protocol supported.

In the SDN market, major manufacturers are fighting for the right to define and control the controller more than the switch. This is because in the future, the network will be the main application, the final trend is that the underlying layer will be blocked, the network serves the application. Once the SDN is developed, the Controller is the core of the SDN and has a voice in the Controller, has a voice in the SDN market.

There are many properties of a Controller, and to analyze a controller, you need to analyze each of them:

North to the interface

Each Controller has a programming interface for user-oriented programs, that is, the north-facing interface. The north-facing interface has great differences. The simplest and most traditional north-facing interface is CLI,SNMP, and the REST API is popular at present

Integrated services and applications

Controller does not only provide programming interface, but also provides a variety of applications and services, such as routing protocol, access control, QOS, firewall and other rich network functions. Of course, there are simple controller only provide control interface. Usually, large manufacturers will provide some applications and services, which will be an important means to provide differentiated services, and also one of the important reasons why manufacturers want to control the market.

South to the interface

All OpenFlow Controllers naturally support OpenFlow, which is a southbound interface, while SDN Controller is different. Besides OpenFlow, it also supports other functions, such as SNMP, NetConf, doT-config, etc.

The control mode

Many people think of SDN is centralized control, so the controller is the centralized controller, actually otherwise, there was an obvious scalability problem of centralized controller, when the network size is larger, a controller is uncertain, so there must be a distributed controller, multiple controller work together to complete the network control, coordination between usually by global control logic for the server.