.. _link:

Link Object
-----------

The Link Object is a specialized form of a :ref:`Data packet <data>` packet, defined as follows::

    LinkObject ::= DATA-TLV TLV-LENGTH
                     Name
                     MetaInfo (.ContentType = LINK)
                     LinkContent
                     Signature

    LinkContent ::= CONTENT-TYPE TLV-LENGTH
                      Delegation+

    Delegation ::= LINK-DELEGATION-TYPE TLV-LENGTH
                     Preference
                     Name

    Preference ::= LINK-PREFERENCE-TYPE TLV-LENGTH
                     nonNegativeInteger


Link Object is a data packet, whose content contains a list of one or more name delegations: a pair of name and the associate priority.
The LinkObject can be used to derive the ``ForwardingHint`` guider of an Interest packet.

The list of delegations in ``LinkContent`` SHOULD be ordered by preference value in ascending order (i.e., the lowest value first).

In a LinkContent, each Delegation SHOULD have a distinct Name.


..
   Let’s assume that we have files that are published under /net/ndnsim, but are hosted under /att/user/alex/net/ndnsim and /verizon/user/alex/net/ndnsim. The structure of the Link would be the following:


   +-----------------+---------------------------------------------+--------------------------------------------------------------+
   | Link Field      | Value                                       | Description of the value                                     |
   +=================+=============================================+==============================================================+
   | Name            | /net/ndnsim/LINK                            | Name of the link (as a convention, the last NameComponent    |
   |                 |                                             | MAY be "LINK")                                               |
   +-----------------+---------------------------------------------+--------------------------------------------------------------+
   | MetaInfo        | ContentType = LINK                          | Field that identifies the actual data content                |
   +-----------------+---------------------------------------------+--------------------------------------------------------------+
   | Content         | (/verizon/user/alex/net/ndnsim, 10)         | Content in the form of (alias, preference) pairs             |
   |                 | (/att/user/alex/net/ndnsim, 100)            |                                                              |
   +-----------------+---------------------------------------------+--------------------------------------------------------------+
   | Signature       | Varying                                     | Signed by the publisher of the Link                          |
   +-----------------+---------------------------------------------+--------------------------------------------------------------+