Software Defined Networking (SDN) separates the control plane from the data plane within the network, allowing the intelligence and state of the network to be managed centrally while abstracting the complexity of the underlying physical network. Great strides have been made within the industry toward this goal with standardized protocols such as OpenFlow. However, greater collaboration leveraging open source development best practices will significantly accelerate real, deployable solutions for the industry at large. Similarly, by evolving network services from an appliance model to one that leverages virtual compute, storage, and networking, Network Functions Virtualization (NFV) promises to drastically improve both the agility of when and where to run network functions as well as the cost structure of doing so.
SDN and NFV are a new way of deploying network infrastructure. A software-defined network adapts to the requirements of applications deployed on the network. Current generation networks and architectures are statically configured and vertically integrated. New generation applications such as Hadoop, video delivery, and virtualized network functions require networks to be agile and to flexibly adapt to application requirements.
From a high level view, software defined networking is commonly described in layers.
Network Apps & Orchestration: The top layer consists of business and network logic applications that control and monitor network behavior. In addition, more complex solution orchestration applications needed for cloud and NFV thread services together and engineer network traffic in accordance with the needs of those environments.
Controller Platform: The middle layer is the framework in which the SDN abstractions can manifest, providing a set of common APIs to the application layer (commonly referred to as the northbound interface) while implementing one or more protocols for command and control of the physical hardware within the network (typically referred to as the southbound interface).
Physical & Virtual Network Devices: The bottom layer consists of the physical & virtual devices, switches, routers, etc., that make up the connective fabric between all endpoints within the network.
OpenDaylight is an open source project with a modular, pluggable, and flexible controller platform at its core. This controller is implemented strictly in software and is contained within its own Java Virtual Machine (JVM). As such, it can be deployed on any hardware and operating system platform that supports Java.
The controller exposes open northbound APIs which are used by applications. OpenDaylight supports the OSGi framework and bidirectional REST for the northbound API. The OSGi framework is used for applications that will run in the same address space as the controller while the REST (web based) API is used for applications that do not run in the same address space (or even necessarily on the same machine) as the controller. The business logic and algorithms reside in the applications. These applications use the controller to gather network intelligence, run algorithms to perform analytics, and then use the controller to orchestrate the new rules, if any, throughout the network.
The controller platform itself contains a collection of dynamically pluggable modules to perform needed network tasks. There are a series of base network services for such tasks as understanding what devices are contained within the network and the capabilities of each, statistics gathering, etc. In addition, platform oriented services and other extensions can also be inserted into the controller platform for enhanced SDN functionality.
The southbound interface is capable of supporting multiple protocols (as separate plugins), e.g. OpenFlow 1.0, OpenFlow 1.3, BGP-LS, etc. These modules are dynamically linked into a Service Abstraction Layer (SAL). The SAL exposes device services to which the modules north of it are written. The SAL determines how to fulfill the requested service irrespective of the underlying protocol used between the controller and the network devices.
The OpenDaylight Project is ever evolving based on the contributions of its developer community. For additional documentation on the different components that make up the OpenDaylight project, please visit the Developer Wiki.