, IBM, NEC, Ref. Switch Ref. Switch OpenFlow Pronto, Juniper.. and many more PCEngine switches OpenWRT WiFi / Open vSwitch Figure 4.2 SDN components and examples. which the control plane software is distributed across all the data plane devices in the network. Figure 4.3 shows the transition from today's integrated box view to the separation view. In this design, the centralized control enables deployment of new services and applica- tions that are not possible or are very difficult in traditional distributed networks. The deployment of new services is much faster compared to upgrading a whole networking device as it is done by current vendors. The separation of control and data planes enables independent and parallel optimizations of the two planes. We envision that this path 4.1 SDN Overview Control software Specialized forwarding hardware Network operating system Southbound interface Control software Control software Specialized Specialized Simple forwarding forwarding forwarding hardware hardware hardware Simple forwarding Simple forwarding hardware hardware Control software Simple forwarding Specialized forwarding hardware hardware Figure 4.3 SDN comparison. will lead to highly specialized and cost-effective high-performance packet-forwarding data plane devices and control plane servers, thus reducing the CAPEX of service providers significantly. And finally, since network information, applications, and services are concen- trated at a centralized location in SDN, operations such as network orchestration and monitoring become much easier and cost-effective by avoiding individual software upgrades at multiple device locations prevalent in current distributed networks. 4.1.2.2 Northbound Open APIs Open APIs enable developers to exploit the centrally available network information and the mechanisms to securely program the underlying network resources [78]. They not only enable rapid development and deployment of both in-house and third-party applications and services but also provide a standard mechanism to int