SDN Controllers are the “brains” of the network which manage flow control below to the southbound APIs and business logic to the northbound APIs for deploying networks. A controller uses application interfaces, like OpenFlow and open virtual switch database (OVSDB).

An SDN Controller has several “pluggable” modules for performing tasks of the network. The tasks include investigating the network and performing network statistics. The functionality of the network can be increased by inserting extensions. It is done by running different algorithms and rules for orchestration.

The famous protocols used for communication with routers by SDN Controllers are OpenFlow and OVSDB. While some others are also used that are YANG or NetConf. Some more established protocols are also designed in SDN environment which includes: the Internet Engineering Task Force (IETF)– the Interface to the Routing System (i2rs) – developed  OSPF, MPLS, BGP, and IS-IS.

The whole architecture of a network gets affected by the use of protocols, For instance, OpenFlow does packet-forwarding decisions, i2rs splits the decision making for execution of distributed routing. Routing decisions are also modified by i2rs.

History (SDN Controller Platforms)

NOX was the first SDN Controller by Nicira Networks. Then in 2008, Nicira Networks gave NOX to the SDN community.

Nicira then moved to develop ONIX with NTT and Google. ONIX became the base for the VMware Controller and also Google WAN Controller. ONIX was then converted to Open Source Platform.

The earliest famous controllers were POX and Beacon. While some others were Trema, Ryu, etc.

Beacon forked Floodlight which then formed the basis of commercial Controllers of Big switch networks. The first commercial SDN Controller was Note, NEC’s ProgrammableFlow Controller.

Afterwards Cisco, HP, IBM, VMWare, Lumina Networks, and Juniper offered their SDN Controllers which were based off beacon and now on OpenDaylight available in open source and commercial versions.

OpenDaylight

OpenDaylight SDN Controller which is java based and derived from Beacon was announced On April 8, 2013. It provides support to OpenFlow and southbound APIs for providing features, like high-availability and clustering.

An OpenDaylight Controller is kept inside Java Virtual Machine (JVM) and can be deployed to several network environments. It released two codes, Hydrogen, and helium for programming the SDN controls.

The latest code of OpenDaylight is Oxygen, having a P4 and a Kubernetes plug-in for VMs.

On. Lab created the Open Networking Operating System (ONOS) for challenging OpenDaylight and companies like AT&T, Dell EMC, Intel, Google, NTT, Ciena and Juniper Networks support it.