ONOS architecture is strictly segmented into a protocol-agnostic system core tier and the protocol-aware providers tier as shown in the figure below:

The ONOS core is responsible for tracking information about the network environment and distributing it to the applications either synchronously via query or asynchronously via listener callbacks. The core is also responsible for persisting select state and synchronizing state among the cluster peers.

The protocol-aware providers are responsible for interacting with the network environment using various control and configuration protocols and supplying such sensory data to the core. Some providers may also need to accept control edicts from the core and apply them to the environment using the appropriate protocol-specific means.

The figure below provides a visual inventory of the various ONOS subsystems. The ones with the gray outline represent either work in progress features planned for release in 2015.

The following diagram describes the general structure of each ONOS subsystem:

For example, the device-subsystem comprises of a core DeviceManager, which exposes a north-bound DeviceService through which applications or other core components can learn about the global infrastructure device inventory and through which they can also subscribe for asynchronous DeviceEvent notifications via the DeviceListener mechanism. A set of administrative actions can be performed via DeviceAdminService, e.g. setting mastership role, removing a decommissioned device.

On the south-bound side, the core DeviceManager exposes a DeviceProviderRegistry through which any number of DeviceProvider entities can register and in turn obtain a DeviceProviderService. Device and port information can then be supplied to the core by each provider through the provider service issued to them. When a provider unregisters, its DeviceProviderService will be invalidated and can no longer be used for interacting with the core.

Within the core, the tasks of indexing, persisting and synchronizing the global device and port state with the cluster peers falls on the DeviceStore.

Similar structure applies to the link subsystem, host subsystem and others.

More information to come later...

Package	Description
org.onlab.graph	Graph abstractions and graph path finding algorithms.
org.onlab.junit	Utilities to assist in developing JUnit tests.
org.onlab.metrics	Misc utils for various performance metrics.
org.onlab.osgi	Facilities for building testable components in OSGi independent fashion.
org.onlab.packet	Utilities for decoding and encoding packets of various network protocols and encapsulations.
org.onlab.packet.dhcp	Utilities for decoding and encoding DHCP options.
org.onlab.packet.ipv6	Utilities for decoding and encoding IPv6 extension headers.
org.onlab.packet.lacp	Utilities for decoding and encoding LACP packets.
org.onlab.packet.ndp	Utilities for decoding and encoding packets of Neighbor Discovery Protocol for IPv6 (RFC 4861).
org.onlab.packet.pim	Utilities for managing PIM packets.
org.onlab.rest	Facilities for building JAX-RS web resources.
org.onlab.rest.exceptions	Various exception mappers to map errors to proper response status codes.
org.onlab.util	Miscellaneous domain-agnostic utilities.
org.onosproject.alarm	Abstractions for interacting with alarms.
org.onosproject.app	Set of abstractions for managing network control applications.
org.onosproject.cfg	Set of abstractions for centrally managing component configurations.
org.onosproject.cli	Administrative console command-line extensions.
org.onosproject.cli.app	CLI commands for managing distributed inventory of applications.
org.onosproject.cli.cfg	CLI commands for managing centralized component and network configurations.
org.onosproject.cli.net	Administrative console command-line extensions for interacting with the network model & services.
org.onosproject.cli.net.completer	Completers for karaf CLI.
org.onosproject.cli.security	CLI commands for managing security permissions.
org.onosproject.cluster	Set of abstractions for dealing with controller cluster related topics.
org.onosproject.codec	Base JSON codec abstraction and a service for tracking various JSON codecs.
org.onosproject.common	Miscellaneous common facilities used for construction of various core and app subsystems.
org.onosproject.common.app	Common facilities for construction of application management subsystem.
org.onosproject.common.net	Set of common network core facilities.
org.onosproject.component	Component management system.
org.onosproject.core	ONOS Core API definitions.
org.onosproject.cpman	An application that manages the control plane.
org.onosproject.cpman.message	Service for looking up control message stats.
org.onosproject.dhcp	Sample application that assigns and manages DHCP leases.
org.onosproject.event	Local event delivery subsystem interfaces & supporting abstractions.
org.onosproject.mastership	Set of abstractions for dealing with controller mastership related topics.
org.onosproject.net	Constants for OSGi properties in the core/net components.
org.onosproject.net.behaviour	Abstractions of various device configuration or device adaptation behaviours; counterpart to the device driver subsystem.
org.onosproject.net.behaviour.protection	Protection behaviour and related classes.
org.onosproject.net.behaviour.trafficcontrol	Traffic control behaviors and related classes.
org.onosproject.net.config	Subsystem for tracking network environment configuration.
org.onosproject.net.config.basics	Various basic builtin network configurations.
org.onosproject.net.config.inject	Network configurations for "inject" provider.
org.onosproject.net.device	Infrastructure device model & related services API definitions.
org.onosproject.net.domain	Domain intent package.
org.onosproject.net.driver	Set of facilities to allow the platform to be extended with device specific behaviours and to allow modeling device (and other entity) behaviours while hiding details of specific driver implementations.
org.onosproject.net.edge	Service for interacting with network edge.
org.onosproject.net.flow	Flow rule model & related services API definitions.
org.onosproject.net.flow.criteria	Traffic selection criteria model.
org.onosproject.net.flow.instructions	Traffic treatment model.
org.onosproject.net.flow.oldbatch	Flow rule model & related services API definitions.
org.onosproject.net.flowobjective	Abstractions for objective-based flow programming of data plane without requiring device pipeline structure awareness. This subsystem is experimental and its interfaces will change in the upcoming release.
org.onosproject.net.group	Abstractions for interacting with device port groups.
org.onosproject.net.host	End-station host model & related services API definitions.
org.onosproject.net.intent	Set of abstractions for conveying high-level intents for treatment of selected network traffic by allowing applications to express the what rather than the how.
org.onosproject.net.intent.constraint	Definitions of constraints used to refine intent specifications.
org.onosproject.net.intent.util	Package supports intent northbound apis providing utility classes.
org.onosproject.net.intf	Interface Service.
org.onosproject.net.key	Device key data model and services.
org.onosproject.net.link	Infrastructure link model & related services API definitions.
org.onosproject.net.mcast	External model entities of the multicast RIB.
org.onosproject.net.meter	Flow meter model and related services.
org.onosproject.net.neighbour	Neighbour message (ARP, NDP) handling.
org.onosproject.net.packet	Mechanism for processing inbound packets intercepted from the data plane and for emitting outbound packets onto the data plane.
org.onosproject.net.packet.packetfilter	Packet filter classifier for various Packet types.
org.onosproject.net.pi.model	Model abstractions of a protocol-independent packet processing pipeline.
org.onosproject.net.pi.runtime	Classes abstracting entities for runtime control of a protocol-independent packet processing pipeline.
org.onosproject.net.pi.runtime.data	Classes abstracting data that can be used for runtime operations of a protocol-independent pipeline.
org.onosproject.net.pi.service	Service abstractions for runtime control of a protocol-independent pipeline.
org.onosproject.net.provider	Base abstractions related to network entity providers and their brokers.
org.onosproject.net.proxyarp	Base abstractions related to the proxy arp service.
org.onosproject.net.region	Subsystem for tracking inventory of network control regions.
org.onosproject.net.resource	Generic network resource model and services for resource allocation and resource tracking.
org.onosproject.net.statistic	Service for looking up statistics on links.
org.onosproject.net.topology	Network topology model & related services API definitions.
org.onosproject.net.utils	Utility classes.
org.onosproject.persistence	Persistence service and builders.
org.onosproject.rest	Base abstractions and utilities for developing REST APIs.
org.onosproject.routing	API for routing libraries.
org.onosproject.routing.config	Routing configuration interfaces.
org.onosproject.security	Application security constructs.
org.onosproject.store	Stores used by the core of ONOS.
org.onosproject.store.app	Implementation of distributed application store.
org.onosproject.store.atomix	Subsystem for tracking controller cluster nodes.
org.onosproject.store.cfg	Implementation of distributed component configuration store.
org.onosproject.store.cluster.messaging	Cluster messaging APIs for the use by the various distributed stores.
org.onosproject.store.flow	Definitions of events and messages pertaining to replication of flow entries.
org.onosproject.store.primitives	Interfaces for creating various distributed primitives.
org.onosproject.store.serializers	Various Kryo serializers for use in distributed stores.
org.onosproject.store.serializers.custom	Distributed store serializers.
org.onosproject.store.service	Distributed core state management services.
org.onosproject.ui	Mechanism for managing dynamically registered user interface extensions.
org.onosproject.ui.chart	Facilities for creating chart models of data for the Web UI.
org.onosproject.ui.lion	Facilities for handling localization of the UI.
org.onosproject.ui.model	Server-side modeling of UI entities.
org.onosproject.ui.model.topo	Server-side modeling of Topology View UI entities.
org.onosproject.ui.table	Facilities for creating tabular models of data for the GUI.
org.onosproject.ui.table.cell	Set of table cell renderers and comparators for use by GUI apps.
org.onosproject.ui.topo	Mechanism for dynamically extending topology view with information and behaviour overlays.
org.onosproject.upgrade	Abstractions for managing software upgrades.
org.onosproject.utils	Miscellaneous common facilities used for construction of various core and app subsystems.