SDN - Software Defined Networking?
SDN is short for software defined networking. Software defined networking (SDN) is an approach to using open protocols, such as OpenFlow, to apply globally aware software control at the edges of the network to access network switches and routers that typically would use closed and proprietary firmware.
Benefits of Software Defined Networking
Software defined networking offers numerous benefits including on-demand provisioning, automated load balancing, streamlined physical infrastructure and the ability to scale network resources in lockstep with application and data needs. As noted on Enterprise Networking Planet, coupled with the ongoing virtualization of servers and storage, SDN ushers in no less than the completely virtualized data center, where end-to-end compute environments will be deployed and decommissioned on a whim.
SDN Challenges: Legacy Network Infrastructure
Legacy network infrastructure is typically a mix of vendor solutions, platforms and protocol solutions making the ultimate goal of an integrated network ecosystem a difficult process for many organizations. According to Enterprise Networking Planet, it is feasible, though perhaps not optimal, to implement software defined networking on existing physical infrastructure. Today, the enterprise and large customers look to build new SDN infrastructure from the ground up.
Source : http://www.webopedia.com/TERM/S/software_defined_networking.html