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Revision 3 (Junxiao Shi, 08/15/2018 06:17 PM) → Revision 4/10 (Junxiao Shi, 08/21/2018 01:46 PM)

# Prefix Announcement Protocol 

 The **prefix announcement protocol** allows registering prefixes using a *prefix announcement object*. It is an alternative to NFD [[RibMgmt|RIB Management protocol]]'s `rib/register` verb. 

 ## 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 `prefix-announcement` generic name component, followed by a version component and a segment component as defined by the NDN Naming Conventions. In this specification revision, segment number is always zero. 
 * ContentType is 5 (prefix announcement). "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 will be ignored. 

 **Validity period** of a prefix announcement object is given in 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 ValidityPeriod and ExpirationPeriod are present, the most restricted constraint applies. 

 Trust model of prefix announcement is to be defined by the application. 

 ### Example 

 ``` 
 Data 
   Name /net/example/32=PA/%FD%01/%00%00 /net/example/prefix-announcement/%FD%01/%00%00 
   MetaInfo 
     ContentType 5 (prefix announcement) "prefix announcement" 
   Content 
     ValidityPeriod 
       NotBefore 20181030T000000Z 
       NotAfter    20181124T235959Z 
     ExpirationPeriod 3600000 
   SignatureInfo 
   SignatureValue  
 ``` 

 This prefix announcement object announces the prefix `/net/example`. 
 It is valid for one hour since receipt, within the date range 30OCT2018 and 24NOV2018. 

 ## Command Verbs 

 ### 'announce' 

 This command announces a prefix using a prefix announcement object. 
 NFD-RIB accepts this command as a [[ndn-cxx:CommandInterest|Command Interest]] with the following syntax: 

 ``` 
 /localhost/nfd/rib/announce/<params-sha256>/<command-interest-components> 
 /localhop/nfd/rib/announce/<params-sha256>/<command-interest-components> 
 ``` 

 The Interest's Parameters element carries the prefix announcement object. 

 NFD-RIB converts this command into an equivalent `rib/register` command. Route *origin* is set to "prefix announcement" (number 129). 
 Response is the same as `rib/register` command. 

 ### 'unannounce' 

 There is no 'unannounce' command. Instead, use `rib/unregister` command.