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Roles are discussed further in Cluster Coordination.
Network Discovery
As the subsystem charged with the management of a key model object, the Device subsystem is integral to network discovery, which includes link, topology, and host discovery.
Link Discovery
The Link Subsystem interfaces with the Device subsystem with a LLDPLinkProvider that subscribes to the DeviceService for DeviceEvents (i.e. by implementing a DeviceListener), and polling for information about OpenFlow-capable Devices. The LLDPLinkProvider allocates a LinkDiscovery object per discovered Device.
LinkDiscovery implements the actual mechanism for link discovery via LLDP and BDDP messages. Every proberate milliseconds (default 3000ms), a LinkDiscovery instance sends out probe messages containing LLDPs and BDDPs, as PacketOuts via the Device that it is paired with. A probe message intercepted at an adjacent switch is passed, as PacketIns, to their corresponding LinkDiscovery instance, which corresponds the sender and receiver of the probe message as the source and destination endpoints of a directed link.
Host Discovery
The Device Subsystem discovers network end-hosts via ARP and DHCP messages detected as PacketIns, and describes their locations in the network in terms of Device-Port pairs referred to as ConnectPoints. The HostLocationProvider implements this function by implementing a DeviceListener in a similar vein as the LLDPLinkProvider.
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Previous : Representing Networks
Next : Clustering
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