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OpenFlow is a well-known southbound API. OpenFlow defines the way the SDN Controller should interact with the forwarding plane to make adjustments to the network, so it can better adapt to changing business requirements. The Network Configuration Protocol (NetConf) uses Extensible Markup Language (XML) to install, manipulate and delete configuration to network devices. Other southbound APIs are: ¢ onePK: a Cisco proprietary SBI to inspect or modify the network element configuration without hardware upgrades. ¢ OpFlex: an open-standard, distributed control system. It send summary policy to network elements.