NFD

# Prefix Announcement Object

The **prefix announcement object** is a Data packet that represents an application's intent of registering a prefix toward itself. A Data packet that satisfies the following requirements is a prefix announcement object:

* Name starts with the announced prefix, followed by a fixed `32=PA` keyword name component, followed by a version component and a segment component as defined by the [NDN Naming Conventions](https://named-data.net/publications/techreports/ndn-tr-22-ndn-memo-naming-conventions/). In the current revision of this specification, the segment number MUST be zero.

* ContentType MUST be 5 (prefix announcement).

* Content contains a sequence of TLV elements, including at least an ExpirationPeriod element. Ordering of these TLV elements is insignificant. Unrecognized non-critical TLV elements are permitted and MUST be ignored.

The **validity period** of a prefix announcement object is given in the ExpirationPeriod and ValidityPeriod elements in its Content.

* ExpirationPeriod gives the duration for which the prefix announcement remains valid. The duration begins when a node or program receives the prefix announcement. This element is required.

* ValidityPeriod gives the absolute time range in which the prefix announcement remains valid. It is ignored if the receiving node does not have a UnixTime clock. This element is optional.

* When both ExpirationPeriod and ValidityPeriod are present, the most restrictive constraint applies.

The trust model of a prefix announcement is to be defined by the application.

## Example

```

Data

  Name /net/example/32=PA/v=0/seg=0

  MetaInfo

    ContentType 5 (prefix announcement)

  Content

    ExpirationPeriod 3600000

    ValidityPeriod

      NotBefore 20181030T000000

      NotAfter  20181124T235959

  SignatureInfo

  SignatureValue 

```

This prefix announcement object announces the prefix `/net/example`. It is valid for one hour from its receipt, between the dates 2018-10-30 and 2018-11-24 (included).