NFD

# Notification Stream

**Notification Stream** is a mechanism of [[Management|NFD Management protocol]].

It is a way to get updates about events happening in the forwarder. This mechanism is useful for monitoring the forwarder's state.

## Naming

* A stream of notifications is published under a certain Name prefix.

* A notification is a Data packet under this Name prefix with a sequence number.

  * The sequence number component is a `NameComponentWithMarkerAndNumber`, as defined in [NDN Naming Conventions (rev 1)](http://named-data.net/doc/tech-memos/naming-conventions.pdf).

    This component starts with a `0xFE` marker, followed by a `NonNegativeInteger`.

  * The sequence numbers of notifications in the same stream should be consecutive and increasing.

  * Each notification is limited to one Data packet.

Example:

    ndn:/localhost/nfd/faces/events/%FE%00 // first notification

    ndn:/localhost/nfd/faces/events/%FE%01 // second notification

## Notification publisher

Notifications from NFD are Data packets generated and signed by NFD.

FreshnessPeriod should be set to a minimum value (typically 1 ms) to facilitate subscriber operations.

The management dispatcher keeps them in an in-memory cache, ready for retrieval by subscribers.

## Notification subscriber

The subscriber should initially request the Name of the notification stream with CanBePrefix and MustBeFresh elements.

After a notification is received, the subscriber can send an Interest for the next anticipated sequence number, without CanBePrefix and MustBeFresh elements.

In both cases, InterestLifetime should be set to a long duration, e.g., 1 minute.

If any Interest times out (because no notification is delivered within InterestLifetime), the subscriber should restart with the initial request.