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Junxiao Shi, 02/10/2014 08:58 PM

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# NFD Notification mechanism
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NFD Notification mechanism notifies applications about events happening inside NFD.
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## Naming
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* A stream of notifications is published under a certain Name prefix.
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* A notification is a Data packet under this Name prefix with a sequence number.
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  * The sequence numbers of notifications in the same stream should be consecutive and increasing.
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  * Each notification is limited to one Data packet.
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Example:
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    ndn:/localhost/nfd/faces/events/%01 // first notification
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    ndn:/localhost/nfd/faces/events/%02 // second notification
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## Notification publisher
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Notifications from NFD are Data packets generated and signed by NFD.
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These Data packets enter forwarding system via the InternalFace, and are subject to regular forwarding pipelines.
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They should be admitted into the ContentStore.
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## Notification subscriber
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The subscriber should typically request the Name of notification stream (`ndn:/localhost/nfd/faces/events` in the example) with ChildSelector=1 and Exclude=\<Any>\<Component>*seq*\</Component>, where *seq* is the version number of the latest received notification.
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* If no new notification has been generated after *seq*, this Interest will stay in the PIT, and be satisfied when a new notification is generated.
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* If one or more new notifications have been generated after *seq*, the Interest will be satisfied from the ContentStore, and the latest notification is returned.  
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  The subscriber can retrieve missing notifications between *seq* and the returned latest notification by expressing additional Interests.