Reference Guide

 Maintaining information about the state of all OpenFlow ports on connected switches
 Conforming to protocol rules for sending messages back to switches
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To provide a modular framework for controller sub-components, facilitating extensibility of the
core controller.
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To provide an elegant, yet simple, API for Network Service components and SDN
Applications to access the core services.
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To provide a certain degree of “sandboxing” of applications to protect them (and the
controller itself) from ill-performing applications.
Design Choices
Some specific design choices were made to establish the underlying principles of the
implementation, to help meet the goals specified above.
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The controller will use the OpenFlow Message Library to encode / decode OpenFlow
messages; all APIs will be defined in terms of OpenFlow Java rich data-types.
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All OpenFlow messages and structures passed into and out of the controller must be
immutable.
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Services and Applications may register as listeners to be notified of events such as:
 Datapaths connecting or disconnecting
 Messages received from datapaths
 Packets received from datapaths (packet-in processing)
 Flows being added to or removed from datapaths
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The controller will decouple incoming connection events and message events from the
consumption of those events by listeners, using bounded event queues.
 This will provide some level of protection for the controller and for the listeners, from an
ill-performing listener implementation.
 It is up to each listener to consume events fast enough to keep pace with the rate of
arrival.
− In the event that the listener is unable to do so, an out-of-band “queue-full” event will
be posted, and event queuing for that listener will be suspended.
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Services and Applications will interact with the controller via the ControllerService API.
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The controller will be divided into several modules, each responsible for specific tasks:
 Core Controller—listens for connections from, and maintains state information about,
OpenFlow switches (datapaths).
 Packet Sequencer—listens for Packet-In messages, orchestrates the processing and
subsequent transmission of Packet-Out replies.
 Flow Tracker—provides basic management of flow rules, meters, and groups.
Controller Service
The ControllerService API provides a common façade for consumers to interact with the controller.
The implementing class (ControllerManager) delegates to the appropriate sub-component or to the
core controller. The following sections briefly describe the API methods, with some code examples –
see the Javadocs for more details.
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