NFD

# Status Dataset

**Status Dataset** is a mechanism of [[Management|NFD Management protocol]].

This document defines how status information about a collection of entities is encoded, segmented, and published as Data packets.

**Status Dataset** is used by:

* [[FaceMgmt|FaceManager]]: to publish the description of all active faces and their counters

* [[FibMgmt|FibManager]]: to publish FIB entries and nexthop records

## Specification

**Encoding**

Status information of each entity is represented by a TLV block.

Those TLV blocks are concatenated into a BLOB.

**Segmentation**

The BLOB is segmented into one or more Data packets, such that each Data packet does not exceed the size limit.

Segmentation does not consider the boundary between TLV blocks.

**Data Naming**

A status dataset is publish under a certain Name prefix.

Every Data packet has Name ndn:/*prefix*/*version*/*segment*

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

This component starts with a 0xFD marker, followed by a nonNegativeInteger.

The version number is monotonic increasing during the lifetime of the producer;

it could be but is not necessarily a timestamp.

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

This component starts with a 0x00 marker, followed by a nonNegativeInteger.

The first segment has segment number zero.

An example Name is: `ndn:/example/dataset/%FD%00%00%01G%BB%82%CB%A8/%00%01`.

This represents the second segment (segment number 1) in version 1407600217000 of a dataset at `ndn:/example/dataset`.

*FinalBlockId* field contains the *segment* component of the last segment.

This field MUST appear in the last segment, and MAY appear in other segments.

## Operations

To request a status dataset, the consumer:

1. send an Interest `ndn:/example/dataset`, ChildSelector=rightmost, MustBeFresh=yes  

    * if the consumer has a previous version of this dataset and wish to request a new version,

      set Exclude=Any..*last-known-version*

2. wait for a Data; if no Data arrives, fail

3. take note of *version* in the arriving Data Name

4. send Interest(s) ndn:/example/dataset/*version*/*segment* to retrieve other segments

5. repeat step 4 until all segments are retrieved

6. sort segments in order, concatenate the Content of all segments to obtain the BLOB

7. parse the BLOB into a series of TLV blocks each represents the status information of an entity

To publish a status dataset, the producer:

1. listen on prefix `ndn:/example/dataset`

2. upon receiving an Interest, if the Interest Name is longer than `ndn:/example/dataset` (it contains version and/or segment), don't respond and abort these steps

    * these Interests should be satisfied by the ContentStore

3. generate a new version number

4. collect status TLV blocks, concatenate into the BLOB, and segment it into Data packets

5. put all Data packets

    * the first Data packet (preferably the first segment) satisfies the Interest

    * other Data packets are admitted to the ContentStore as unsolicited Data