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Versions: 00

Network Working Group                                   B. Niven-Jenkins
Internet-Draft                                                 R. Murray
Intended status: Standards Track                               G. Watson
Expires: January 10, 2013                       Velocix (Alcatel-Lucent)
                                                            M. Caulfield
                                                                K. Leung
                                                           Cisco Systems
                                                            July 9, 2012


                       CDN Interconnect Metadata
                      draft-cjlmw-cdni-metadata-00

Abstract

   The CDNI Metadata Interface enables interconnected CDNs to exchange
   content distribution metadata in order to enable content acquisition
   and delivery.  The CDNI metadata associated with a piece of content
   provides a downstream CDN with sufficient information for the
   downstream CDN to service content requests on behalf of an upstream
   CDN.  This document describes both the core set of CDNI metadata and
   the protocol for exchanging that metadata.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 10, 2013.

Copyright Notice




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   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Design Principles  . . . . . . . . . . . . . . . . . . . . . .  5
   3.  CDNI Metadata Data Model . . . . . . . . . . . . . . . . . . .  5
     3.1.  HostIndex, HostMetdata & PathMetadata objects  . . . . . .  6
     3.2.  Remaining CDNI Metadata objects  . . . . . . . . . . . . .  9
     3.3.  Metadata Inheritance . . . . . . . . . . . . . . . . . . . 12
   4.  Encoding-Independent CDNI Metadata Object Descriptions . . . . 12
     4.1.  CDNI Metadata Data Object Descriptions . . . . . . . . . . 12
       4.1.1.  HostIndex  . . . . . . . . . . . . . . . . . . . . . . 13
       4.1.2.  HostMatch  . . . . . . . . . . . . . . . . . . . . . . 13
       4.1.3.  HostMetadata . . . . . . . . . . . . . . . . . . . . . 13
       4.1.4.  Acquisition  . . . . . . . . . . . . . . . . . . . . . 14
       4.1.5.  Delivery . . . . . . . . . . . . . . . . . . . . . . . 14
       4.1.6.  PathMatch  . . . . . . . . . . . . . . . . . . . . . . 15
       4.1.7.  PathMetadata . . . . . . . . . . . . . . . . . . . . . 15
       4.1.8.  ACL  . . . . . . . . . . . . . . . . . . . . . . . . . 15
       4.1.9.  ACLRule  . . . . . . . . . . . . . . . . . . . . . . . 16
       4.1.10. TimeWindow . . . . . . . . . . . . . . . . . . . . . . 16
       4.1.11. Location . . . . . . . . . . . . . . . . . . . . . . . 17
       4.1.12. Source . . . . . . . . . . . . . . . . . . . . . . . . 17
       4.1.13. Auth . . . . . . . . . . . . . . . . . . . . . . . . . 17
       4.1.14. Link . . . . . . . . . . . . . . . . . . . . . . . . . 18
     4.2.  CDNI Metadata Simple Data Type Descriptions  . . . . . . . 19
       4.2.1.  Protocol . . . . . . . . . . . . . . . . . . . . . . . 19
       4.2.2.  Endpoint . . . . . . . . . . . . . . . . . . . . . . . 19
       4.2.3.  IPRange  . . . . . . . . . . . . . . . . . . . . . . . 19
       4.2.4.  Pattern  . . . . . . . . . . . . . . . . . . . . . . . 20
       4.2.5.  PatternFlags . . . . . . . . . . . . . . . . . . . . . 20
       4.2.6.  URI  . . . . . . . . . . . . . . . . . . . . . . . . . 20
       4.2.7.  Time . . . . . . . . . . . . . . . . . . . . . . . . . 20
   5.  CDNI Metadata interface  . . . . . . . . . . . . . . . . . . . 21



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     5.1.  Transport  . . . . . . . . . . . . . . . . . . . . . . . . 21
     5.2.  Retrieval of CDNI Metadata resources . . . . . . . . . . . 22
     5.3.  Bootstrapping  . . . . . . . . . . . . . . . . . . . . . . 23
     5.4.  Encoding . . . . . . . . . . . . . . . . . . . . . . . . . 23
       5.4.1.  MIME Media Types . . . . . . . . . . . . . . . . . . . 23
       5.4.2.  JSON Encoding of Objects . . . . . . . . . . . . . . . 24
         5.4.2.1.  JSON Example . . . . . . . . . . . . . . . . . . . 25
       5.4.3.  XML Encoding of Objects  . . . . . . . . . . . . . . . 27
         5.4.3.1.  XML Example  . . . . . . . . . . . . . . . . . . . 28
     5.5.  Extensibility  . . . . . . . . . . . . . . . . . . . . . . 30
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 31
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 31
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 31
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 31
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 31
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 31
   Appendix A.  Relationship to the CDNI Requirements . . . . . . . . 32
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33

































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1.  Introduction

   CDNI enables a downstream CDN to service content requests on behalf
   of an upstream CDN.  In the simplest use case, a content request
   received by the downstream CDN provides sufficient information for
   sending a response.  More complex use cases require additional
   context, i.e. metadata.  The CDNI metadata associated with a piece of
   content (or with a set of contents) provides a downstream CDN with
   sufficient information for servicing content requests on behalf of an
   upstream CDN in accordance with the policies defined by the upstream
   CDN.

   The CDNI Metadata Interface is introduced by
   [I-D.ietf-cdni-problem-statement] along with three other interfaces
   that may be used to compose a CDNI solution (Control, Request Routing
   and Logging).  [I-D.davie-cdni-framework] expands on the information
   provided in [I-D.ietf-cdni-problem-statement] and describes each
   interface, and the relationships between them, in more detail.  The
   requirements for the CDNI metadata interface are specified in
   [I-D.ietf-cdni-requirements]

   This document focuses on the CDNI Metadata interface which enables a
   downstream CDN to obtain CDNI Metadata from an upstream CDN so that
   the downstream CDN can properly process and respond to:

   o  Redirection Requests received over the CDNI Request Routing
      protocol.
   o  Content Requests received directly from User Agents.

   Specifically this document proposes:

   o  A data structure for mapping content requests to CDNI Metadata
      properties (Section 3).
   o  An initial set of CDNI Metadata properties (Section 4.1 through
      Section 4.2).
   o  A RESTful web service for the transfer of CDNI Metadata
      (Section 5).

1.1.  Terminology

   This document reuses the terminology defined in
   [I-D.ietf-cdni-problem-statement].

   Additionally, the following terms are used throughout this document
   and are defined as follows:
   o  Object - a collection of properties





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   o  Property - a key / value pair where the key is a property name and
      the value is the property value (possibly an object)


2.  Design Principles

   The proposed CDNI Metadata Interface aims to achieve the following
   design principles:

   1.  Cacheability of CDNI metadata objects
   2.  Deterministic mapping from content requests to CDNI metadata
       properties
   3.  Support for DNS redirection as well as application-specific
       redirection (for example HTTP redirection)
   4.  Minimal duplication of CDNI metadata
   5.  Leverage existing protocols

   Cacheability improves the latency of acquiring metadata and therefore
   improves the latency of serving content requests.  The CDNI Metadata
   Interface uses HTTP to achieve cacheability.

   Deterministic mappings from content requests to metadata properties
   eliminates ambiguity and ensures that the same policies are applied
   consistently by all downstream CDNs.

   Support for both HTTP and DNS redirection ensures that the CDNI
   Metadata Interface can be used for HTTP and DNS redirection and also
   meets the same design principles for both HTTP and DNS based
   redirection schemes.

   Minimal duplication of CDNI metadata provides space efficiency on
   storage in the CDNs, on caches in the network, and across the network
   between CDNs.

   Leveraging existing protocols avoids reinventing common mechanisms
   such as data structure encoding (e.g.  XML, JSON) and data transport
   (e.g.  HTTP).


3.  CDNI Metadata Data Model

   The CDNI Metadata Model describes a data structure for mapping
   content requests to metadata properties.  Metadata properties
   describe how to acquire, authorize, and deliver content from a
   downstream CDN.  The data model relies on the assumption that these
   metadata properties may be aggregated based on the authoritative
   hostname of the content and subsequently on the resource path of the
   content.  The data model associates a set of CDNI Metadata properties



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   with a Hostname to form a default set of metadata properties for
   content delivered for that Hostname.  That default set of metadata
   properties can be overridden by properties that apply to specific
   paths within a URI.

   Different Hostnames and URI paths will contain different sets of CDNI
   Metadata properties in order to describe the required behaviour when
   a dCDN surrogate is processing User Agent requests for content on
   that Hostname or URI path.  As a result of this structure,
   significant commonality may exist between the CDNI Metadata
   properties specified for different Hostnames, different URI paths
   within a Hostname and different URI paths on different Hostnames.
   For example the definition of which User Agent IP addresses should be
   treated as being grouped together into a single network or geographic
   location is likely to be common for a number of different Hostnames.
   Another example is that although a uCDN is likely to have several
   different policies configured to express geo-blocking rules, it is
   likely that a single geo-blocking policy would be applied to multiple
   Hostnames delivered through the CDN.

   In order to enable the CDNI Metadata for a given Hostname or URI Path
   to be decomposed into sets of CDNI Metadata properties that can be
   reused by multiple Hostnames and URI Paths the CDNI Metadata
   interface specified in this document splits the CDNI Metadata into a
   number of objects.  Efficiency is improved by enabling a single CDNI
   Metadata object (that is shared across Hostname and/or URI paths) to
   be retrieved by a dCDN once, even if it is referenced by the CDNI
   Metadata of multiple Hostnames.

   Section 3.1 introduces a high level description of the HostIndex,
   HostMetadata and PathMetadata objects and describes the relationships
   between those objects.

   Section 3.2 introduces a high level description of the remaining CDNI
   Metadata objects and describes the relationships between those
   objects as well as the relationships of those objects to HostMetadata
   and PathMetadata objects.

   Section 4.1 describes the specific properties of each object in more
   detail.

3.1.  HostIndex, HostMetdata & PathMetadata objects

   A HostIndex object contains a list of Hostnames that may be delegated
   to the downstream CDN.  The HostIndex is the starting point for
   accessing the uCDN's CDNI Metadata data store.  It enables surrogates
   in the dCDN to deterministically discover, on receipt of a User Agent
   request for content, which other CDNI Metadata objects it requires in



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   order to deliver the requested content.

   The HostIndex links end-user facing Hostnames to HostMetadata
   objects, which contain (or reference) the default CDNI Metadata
   required to serve content for that Hostname.  When looking up CDNI
   Metadata, the downstream CDN looks up the requested Hostname in the
   HostIndex, from there it can find HostMetadata which describes
   delivery rules for a Hostname and PathMetadata which may override
   those rules for given URI paths within the Hostname.

   As well as containing the default CDNI Metadata for the specified
   Hostname, HostMetadata and PathMetadata objects may also contain
   PathMatch objects which in turn contain PathMetadata objects.
   PathMatch objects override the CDNI Metadata in the HostMetadata
   object or one or more preceding PathMetadata objects with more
   specific CDNI Metadata that applies to content requests matching the
   pattern defined in that PathMatch object.

   For the purposes of retrieving CDNI Metadata all other required CDNI
   Metadata objects and their properties are discoverable from the
   appropriate HostMetadata, PathMatch and PathMetadata objects for the
   requested content.

   The relationships between the HostIndex, HostMatch, HostMetadata,
   PathMatch and PathMetadata objects are described in Figure 1.

+---------+     +---------+     +------------+
|HostIndex+---->|HostMatch|---->|HostMetadata+----------------+
+---------+     +---------+     +------+-----+                |
                                       |                      |
                                       V                      V
                                  +---------+      ************************
                             +--->|PathMatch|      *Other Metadata Objects*
                             |    +---------+      ************************
                             |         |                      ^
                             |         V                      |
                             |  +------------+                |
                             +--|PathMetadata+----------------+
                                +------------+

   Key: ----> = References

       Figure 1: Relationships between the HostIndex, HostMetadata &
                    PathMetadata CDNI Metadata Objects

   The table below describes the HostIndex, HostMetadata and
   PathMetadata objects in more detail.




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   +--------------+----------------------------------------------------+
   | Data Object  | Description                                        |
   +--------------+----------------------------------------------------+
   | HostIndex    | A HostIndex object lists the Hostnames that an     |
   |              | upstream CDN can provide CDNI metadata for and the |
   |              | URIs to use for retrieving that CDNI Metadata.     |
   |              | For example, if "example.com" is a content         |
   |              | provider, the HostIndex object may include an      |
   |              | entry for "example.com" with the URI of the        |
   |              | associated HostMetadata object.  These hostnames   |
   |              | are contained inside a list of HostMatch objects.  |
   | HostMatch    | A HostMatch object defines a hostname to match     |
   |              | against a requested host, and contains or          |
   |              | references a HostMetadata object which contains    |
   |              | CDNI Metadata properties to be applied when a      |
   |              | content request matches against the hostname.      |
   | HostMetadata | A HostMetadata object contains (or references) the |
   |              | default CDNI Metadata properties for content       |
   |              | served from that hostname, i.e. the CDNI Metadata  |
   |              | properties for content requests that do not match  |
   |              | any of the PathMatch objects contained or          |
   |              | referenced by that HostMetadata object.  For       |
   |              | example, a HostMetadata object may describe the    |
   |              | metadata properties which apply to "example.com"   |
   |              | and may contain PathMatches for                    |
   |              | "example.com/movies/*" and "example.com/music/*"   |
   |              | which reference corresponding PathMetadata objects |
   |              | that contain the CDNI Metadata properties for      |
   |              | those specific URI paths.                          |
   | PathMatch    | A PathMatch object defines a pattern to match      |
   |              | against the requested path, and contains or        |
   |              | references a PathMetadata object which contains    |
   |              | (or references) the CDNI Metadata properties to be |
   |              | applied when a content request matches against the |
   |              | defined URI path pattern.                          |
















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   | PathMetadata | A PathMetadata object contains the CDNI Metadata   |
   |              | properties for content served with the associated  |
   |              | URI path (defined in a PathMatch object).  A       |
   |              | PathMetadata object may also contain PathMatch     |
   |              | objects in order to recursively define more        |
   |              | specific URI paths that require different (e.g.    |
   |              | more specific) CDNI Metadata to this one.  For     |
   |              | example, the PathMetadata object which applies to  |
   |              | "example.com/movies/*" may describe CDNI metadata  |
   |              | which apply to that resource path and may contain  |
   |              | a PathMatch object for "example.com/movies/hd/*"   |
   |              | which would reference the corresponding            |
   |              | PathMetadata object for the                        |
   |              | "example.com/movies/hd/" path prefix.              |
   +--------------+----------------------------------------------------+

      Table 1: HostIndex, HostMetadata and PathMetadata CDNI Metadata
                                  Objects

3.2.  Remaining CDNI Metadata objects

   The HostMetadata and PathMetadata objects contain or can reference
   other CDNI Metadata objects that contain properties which describe
   how User Agent requests for content should be processed, for example
   where to acquire the content, authorization rules that should be
   applied, delivery location restrictions and so on.  The properties
   associated with the processing of User Agent requests fall into two
   categories, Delivery and Acquisition.  Delivery properties, such as
   Location based restrictions, are contained or referenced within a
   Delivery object.  Acquisition properties, such as which Origin Server
   to use to acquire the content, are contained or referenced within an
   Acquisition Object.  Delivery and Acquisition objects contain or
   reference other CDNI Metadata objects to define the properties and
   rules which should be applied when processing requests for content.
   In some cases the rules that should be applied are complex but also
   likely to be reusable and repeated across many HostMetadata or
   PathMetadata objects.

   The relationships between the HostMetadata and PathMetadata objects
   and the other CDNI Metadata objects (Delivery object, Acquisition
   object, etc.) required for CDNI request routing and delivery are
   illustrated in Figure 2.









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                            +-------------+        +----------------+
   +--------------+    +--> | Acquisition | -----> |   Source       |
   | HostMetadata |    |    +-------------+        +----------------+
   |    - or -    | ---+
   | PathMetadata |    |    +-------------+        +----------------+
   +--------------+    +--> |  Delivery   | --+--> | TimeWindow ACL |
                            +-------------+   |    +----------------+
                                              |
                                              |    +----------------+
                                              +--> |  Location ACL* |
                                              |    +----------------+
                                              |
                                              |    +----------------+
                                              +--> |    Auth        |
                                                   +----------------+


   *example ACL

   +----------------+        +----------------+
   | Location ACL   |   =    |      ACL       |
   +----------------+        +----------------+
                                     |
                                     v
                             +----------------+
                             |   ACL Rules    |
                             +----------------+
                                     |
                                     v
                             +----------------+
                             |   Location     |
                             +----------------+

   Key: ----> = References

   Figure 2: Relationships between HostMetadata and PathMetadata and the
                        other CDNI Metadata Objects

   The table below describes the remaining CDNI Metadata objects that
   were not defined in Section 3.1.











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   +-------------+-----------------------------------------------------+
   | Data Object | Description                                         |
   +-------------+-----------------------------------------------------+
   | Acquisition | Container object for metadata that applies to       |
   |             | content acquisition.                                |
   | Delivery    | Container object for metadata that applies to       |
   |             | content delivery.                                   |
   | Source      | Information needed by a dCDN to acquire content.    |
   |             | For example the host to contact, the protocol to    |
   |             | use for acquisition and any authentication and      |
   |             | authorization methods that should be used.          |
   | ACL         | Contains or references a list of ACLRules that are  |
   |             | used to define any delivery restrictions that must  |
   |             | be applied e.g.  Location restrictions or Time      |
   |             | based restrictions.                                 |
   | ACLRule     | Contains or references a list of objects which      |
   |             | define to what the restrictions should be applied   |
   |             | e.g. an ACLRule may reference a Location Object if  |
   |             | a location based ACL is required.                   |
   | TimeWindow  | Start and end time used to specify windows of       |
   |             | availability or unavailability for the content.     |
   | Location    | Geographic or network location identified by        |
   |             | country code, BGP AS number, or subnet to which     |
   |             | content may (or may not) be delivered.              |
   | Auth        | Method and credentials for authentication and       |
   |             | authorization including URI-signing, token-base,    |
   |             | etc.                                                |
   +-------------+-----------------------------------------------------+

            Table 2: Content Distribution Metadata Data Objects

   The relationships in Figure 1 and Figure 2 are summarised in Table 3
   below and the properties of each object are described in Section 4.1.

   +--------------+----------------------------------------------------+
   | Data Object  | Objects it References                              |
   +--------------+----------------------------------------------------+
   | HostIndex    | 0 or more HostMetadata objects.                    |
   | HostMetadata | 0 or more PathMatch objects. 0 or 1 Delivery       |
   |              | objects. 0 or 1 Acquisition objects.               |
   | PathMatch    | 1 PathMetadata object.                             |
   | PathMetadata | 0 or more PathMatch objects. 0 or 1 Delivery       |
   |              | objects. 0 or 1 Acquisition objects.               |
   | Acquisition  | 0 or more Source objects.                          |
   | Delivery     | 0 or more ACL objects. 0 or more Auth objects.     |
   | ACL          | 0 or more ACLRule objects.                         |





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   | ACLRule      | 0 or more Location objects or 0 or more TimeWindow |
   |              | objects.                                           |
   +--------------+----------------------------------------------------+

           Table 3: Relationships between CDNI Metadata Objects

3.3.  Metadata Inheritance

   In the data model, a HostMetadata object may contain (or reference)
   multiple PathMetadata objects.  Each PathMetadata object may in turn
   contain (or reference) other PathMetadata objects.  These
   relationships form a tree.

   The tree of HostMetadata objects and PathMetadata objects forms an
   inheritance tree.  Each node in the tree inherits the property values
   set by its parent.

   In the tree, a child may override any property value which has been
   set by its parent.  If a HostMetadata object sets the value of a
   property, that value may be overridden by a PathMetadata object (the
   child of the HostMetadata object).  If a PathMetadata object contains
   (or references) other PathMetadata objects as children, then those
   children PathMetadata objects may override the property values set by
   the parent PathMetadata object.

   If a child node overrides the value of a list, then the entire list
   is replaced with the value set by the child node.  If a child node
   overrides the value of an object, then the whole object is replaced
   with the value set by the child node.


4.  Encoding-Independent CDNI Metadata Object Descriptions

   This section provides the definitions of each object type declared in
   Section 3.  The definition of each object contains an unordered set
   of properties.  The type of some properties is another CDNI Metadata
   object and in those cases the value of the property can be either an
   object of that type (the object is embedded) or a Link object that
   describes a URI and relationship that can be dereferenced to retrieve
   the CDNI Metadata object that should be used as the value of that
   property.

4.1.  CDNI Metadata Data Object Descriptions

   Each of the sub-sections below describes the properties associated
   with the data objects defined in Table 2.





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4.1.1.  HostIndex

   The HostIndex object is the entry point into the CDNI Metadata
   hierarchy.  An incoming content request is matched against the list
   of hosts to find the HostMatch object which applies to the request.

      Property: hosts
         Description: List of HostMatch objects
         Type: List of HostMatch
         Mandatory: Yes.

4.1.2.  HostMatch

   The HostMatch object contains a hostname to match against and a
   metadata object to apply if a match is found.

      Property: hostname
         Description: String to match against the requested host.
         Type: String
         Mandatory: Yes
      Property: hostmetadata
         Description: CDNI Metadata to apply when delivering content
         that matches this pattern.
         Type: HostMetadata
         Mandatory: Yes

4.1.3.  HostMetadata

   The HostMetadata object contains both metadata that applies to
   content requests for a particular host and a list of pattern matches
   for finding more specific metadata based on the resource path in a
   content request.

      Property: acquisition
         Description: Container for content acquisition related
         metadata.
         Type: Acquisition
         Mandatory: No.  No default.
      Property: delivery
         Description: Container for content delivery related metadata.
         Type: Delivery
         Mandatory: No.  No default.
      Property: paths
         Description: Path specific rules.  First match applies.
         Type: List of PathMatch
         Mandatory: No.  Default apply the properties defined in this
         HostMetadata object to all paths.




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      Property: hostname
         Description: The end-user facing Hostname for this HostMetadata
         object.
         Type: Hostname
         Mandatory: Yes.

4.1.4.  Acquisition

   Metadata which provides the dCDN information about content
   acquisition e.g. how to contact an uCDN Surrogate or an Origin
   Server.  The sources are not necessarily the actual Origin Servers
   operated by the CSP but might be a set of Surrogates in the uCDN.

      Property: sources
         Description: Sources from which the dCDN can acquire content.
         Type: List of Source
         Mandatory: No.  Defaults to empty list.

4.1.5.  Delivery

   Metadata related to content delivery, e.g. delivery restrictions or
   content authorization methods.

      Property: locations
         Description: Access control list which applies restrictions to
         delivery based on client location.
         Type: ACL
         Mandatory: No.  Defaults is allow all locations.
      Property: times
         Description: Access control list which applies restrictions to
         delivery based on request time.
         Type: ACL
         Mandatory: No.  Defaults is allow all times.
      Property: auth
         Description: Options for authenticating content requests.  All
         options in the list are equally valid.
         Type: List of Auth
         Mandatory: No.  Defaults is no auth.
      Property: protocol
         Description: The delivery protocol to be used for content
         requests that match this HostMetadata object.
         Type: protocol
         Mandatory: Yes.
      Property: active
         Description: Enable or disable delivery from this host.
         Type: boolean





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         Mandatory: No.  Default yes.

4.1.6.  PathMatch

   The PathMatch object contains an expression to match against and a
   metadata object to apply if a match is found.

      Property: pattern
         Description: String to match against the requested path, i.e.
         against the [RFC3986] path-absolute.
         Type: Pattern
         Mandatory: Yes
      Property: patternflags
         Description: Flags to control the pattern match.
         Type: List of PatternFlags
         Mandatory: No.  Default Case-sensitive infix matching.
      Property: pathmetadata
         Description: CDNI Metadata to apply when delivering content
         that matches this pattern.
         Type: PathMetadata
         Mandatory: Yes

4.1.7.  PathMetadata

   A PathMetadata object contains the CDNI Metadata properties for
   content served with the associated URI path (defined in a PathMatch
   object).  Note that if CDNI metadata is used as an input to CDNI
   request routing and DNS-based redirection is employed, then any
   metadata at the PathMetadata level or below will be inaccessible at
   request routing time.

   PathMetadata objects may contain any of the properties of a
   HostMetadata object with the following exceptions:

   o  PathMetadata objects MUST NOT contain a hostname property.
   o  PathMetadata objects MUST NOT contain a protocol property.
   o  The presence of an sources property is OPTIONAL.

4.1.8.  ACL

   An ACL object contains or references a list of ACLRule objects which
   define a set of restrictions to apply to content delivery e.g.
   Location restrictions.  An ACL may reference or contain ACLRules
   referencing or containing Location or TimeWindow objects but not
   both.






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      Property: aclrules
         Description:
         Type: List of ACLRule
         Mandatory: No.  Default no rules.

4.1.9.  ACLRule

   An ACLRule contains or references a list of either TimeWindow or
   Location objects.  ACLRule objects are used to construct ACL to apply
   restrictions to content delivery.

   Note: Although both the allow and deny properties are optional, one
   and only one of them MUST be present in an ACLRule.  An ACLRule must
   also only refer to one of Location or TimeWindow but not both and
   should only refer to the objects relevant to the ACL type as defined
   by Delivery Metadata i.e. a Delivery Metadata object with an ACL with
   relationship of LocationACL must not reference TimeWindow objects
   further down in the Metadata hierarchy.

      Property: allow
         Description: List of either Locations (Location ACL) or Time
         Windows (TimeWindow ACL) which must be allowed.
         Type: List of Location or TimeWindow
         Mandatory: No.  Default implicit Allow.
      Property: deny
         Description: List of either Locations (Location ACL) or Time
         Windows (TimeWindow ACL) which must be denied.
         Type: List of Location or TimeWindow
         Mandatory: No.  Default implicit Deny.


4.1.10.  TimeWindow

   A TimeWindow object describes a time range which may be applied by an
   ACLRule, e.g.  Start 09:00AM 01/01/2000 End 17:00PM 01/01/2000.

      Property: start
         Description: The start time of the window.
         Type: Time
         Mandatory: Yes
      Property: end
         Description: The end time of the window.
         Type: Time
         Mandatory: Yes







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4.1.11.  Location

   A Location object describes a Location which may be applied by an
   ACLRule, e.g. a Location may be an IPv4 address range or a geographic
   location.

      Property: iprange
         Description: A set of IP Addresses.
         Type: List of IPRange.
         Mandatory: Yes

   [Ed: Location as specified above only supports the Class 1a names
   described in [I-D.jenkins-cdni-names].  Need to add support for Class
   1b names to a later version.]

4.1.12.  Source

   A Source object describes the Source which should be used by the dCDN
   for content acquisition, e.g. a Surrogate within the uCDN or an
   alternate Origin Server, the protocol to be used and any
   authentication method.

      Property: auth
         Description: Authentication method to use when requesting
         content from this source.
         Type: Auth
         Mandatory: No.  Default is no authentication.
      Property: endpoints
         Description: Origins from which the dCDN can acquire content.
         Type: List of EndPoint
         Mandatory: Yes.
      Property: protocol
         Description: Protocol to use for content acquisition.
         Type: Protocol
         Mandatory: Yes.

4.1.13.  Auth

   An Auth object defines authentication and authorization methods to be
   used during content delivery and content acquisition, e.g. methods
   such as tokenization and URL Signing.

      Property: type
         Description: A string containing the authentication type "url-
         signing", "url-token", "http-basic", or "http-digest".  The
         type dictates which optional fields are present and valid in
         the rest of the object.  The "url-signing" type refers to URL
         signing authentication.  The "url-token" type refers to token-



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         based authentication.  The "basic" and "digest" types refer to
         HTTP Basic and Digest access authentication.
         Type: String
         Mandatory: Yes.
      Property: algo
         Description: A string containing the signature algorithm (e.g.
         "md5", "sha-1", etc.).
         Type: String
         Mandatory: Yes, if type is "url-signing".
      Property: symmetric
         Description: A boolean if true, URL signing uses symmetric
         keys, otherwise asymmetric.
         Type: boolean
         Mandatory: Yes, if type is "url-signing".
      Property: key
         Description: A hex-encoded number containing the public key for
         verifying signatures, only valid if "symmetric" field is set to
         false.
         Type: boolean
         Mandatory: Yes, if type is "url-signing".
      Property: username
         Description: A string containing the username for "basic" and
         "digest" types.
         Type: String
         Mandatory: Yes, if type is "basic" or "digest".
      Property: password
         Description: A string containing the password for "basic" and
         "digest" types.
         Type: String
         Mandatory: Yes, if type is "basic" or "digest".

4.1.14.  Link

   A link object may be used in place of any of the objects described
   above.  Links can be used to avoid duplication if the same metadata
   information is repeated within the metadata tree.  When a link
   replaces an object, its href property is set to the URI of the
   resource, its rel property is set to the name of the property it is
   replacing, and its type property is set to the type of the object it
   is replacing.

      Property: href
         Description: The URI of the of the addressable object being
         referenced.
         Type: URI
         Mandatory: Yes





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      Property: rel
         Description: The Relationship between the referring object and
         the object it is referencing.
         Type: String
         Mandatory: Yes
      Property: type
         Description: The type of the object being referenced.
         Type: String
         Mandatory: Yes

4.2.  CDNI Metadata Simple Data Type Descriptions

   This section describes the simpler data types that are used for
   properties of CDNI Metadata objects.

4.2.1.  Protocol

   This type only appears in Links.  Links with this type are not
   machine readable but rather represent particular feature sets of a
   protocol defined in a specification and implemented in code.  The URI
   contained in the link needs to be defined for each delivery protocol
   with an associated interoperable feature set.

   The following examples are illustrative:

   o  http://url.cdni.ietf.example/protocol/delivery/http/rfcABCD
   o  http://url.cdni.ietf.example/protocol/delivery/rtmp/rfcEFGH
   o  http://url.vendorY.ietf.example/protocol/delivery/rtmp/releaseP.Q

   [Editor's Note: It may be more appropriate to use the 'tag' URI
   scheme [RFC4151] for these URIs.]

4.2.2.  Endpoint

   A hostname (with optional port) or an IP address (with optional
   port).

   Note: Client implementations MUST support IPv4 addresses encoded as
   specified by the 'IPv4address' rule in Section 3.2.2 of [RFC3986] and
   MUST support all IPv6 address formats specified in [RFC4291].  Server
   implementations SHOULD use IPv6 address formats specified in
   [RFC5952].

4.2.3.  IPRange

   One of:





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   o  A range of consecutive IP addresses (IPv4 or IPv6) expressed as
      Address1-Address2 which does not have to be to power of two
      aligned, for example the range 192.0.2.1-192.0.2.10 is valid.  The
      first Address in the range MUST be 'lower' than the final address
      in the range.
   o  A valid IP subnet (IPv4 or IPv6) expressed using CIDR notation.
   o  A single IP address (IPv4 or IPv6).

   Note: Client implementations MUST support IPv4 addresses encoded as
   specified by the 'IPv4address' rule in Section 3.2.2 of [RFC3986] and
   MUST support all IPv6 address formats specified in [RFC4291].  Server
   implementations SHOULD use IPv6 address formats specified in
   [RFC5952].

4.2.4.  Pattern

   A pattern for string matching paths.  The string may contain the
   wildcards * and ?.

   o  * matches any sequence of characters (including the empty string).
   o  ? matches exactly one character.

   Escaping: The three literals \ , * and ? should be escaped as \\, \*
   and \?

4.2.5.  PatternFlags

   A set of flags indicating how a pattern match is made.  The flags
   are:

   o  Case-insensitive - Perform a case insensitive match (absence
      indicates case-sensitive match).
   o  Prefix - Match against the start of the string (absence indicates
      that a match may start anywhere in the string).
   o  Suffix - Match against the end of the string (absence indicates
      that a match may end anywhere in the string).

   Absence of both Prefix and Suffix results in a match against any part
   of the string (infix).

4.2.6.  URI

   A URI as specified in [RFC3986].

4.2.7.  Time

   A time value expressed in seconds since Unix epoch in the UTC
   timezone.



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5.  CDNI Metadata interface

   This section specifies an interface to enable a Downstream CDN to
   retrieve CDNI Metadata objects from an Upstream CDN.

   The interface can be used by a Downstream CDN to retrieve CDNI
   Metadata objects either dynamically as required by the Downstream CDN
   to process received requests (for example in response to receiving a
   CDNI Request Routing request from an Upstream CDN or in response to
   receiving a request for content from a User Agent) or in advance of
   being required.

   The CDNI Metadata interface is built on the principles of RESTful web
   services.  This means that requests and responses over the interface
   are built around the transfer of representations of hyperlinked
   resources.  A resource in the context of the CDNI Metadata interface
   is any object in the Data Model (as described in Section 3 through
   Section 4.1).

   In the general case a CDNI Metadata server makes each instance of an
   addressable CDNI Metadata object available via a unique URI that
   returns a representation of that instance of that CDNI Metadata
   object.  When an object needs to reference another addressable CDNI
   Metadata object (for example a HostIndex object referencing a
   HostMetadata object) it does so by including a link to the referenced
   object.

   CDNI Metadata servers are free to assign whatever structure they
   desire to the URIs for CDNI Metadata objects and CDNI Metadata
   clients MUST NOT make any assumptions regarding the structure of CDNI
   Metadata URIs or the mapping between CDNI Metadata objects and their
   associated URIs.  Therefore any URIs present in the examples below
   are purely illustrative and are not intended impose a definitive
   structure on CDNI Metadata interface implementations.

5.1.  Transport

   The CDNI Metadata interface uses HTTP as the underlying protocol
   transport.

   The HTTP Method in the request defines the operation the request
   would like to perform.  Servers implementing the CDNI Metadata
   interface MUST support the HTTP GET and HEAD methods.

   The corresponding HTTP Response returns the status of the operation
   in the HTTP Status Code and returns the current representation of the
   resource (if appropriate) in the Response Body.  HTTP Responses from
   servers implementing the CDNI Metadata interface that contain a



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   response body SHOULD include an ETag to enable validation of cached
   versions of returned resources.

   The CDNI Metadata interface specified in this document is a read-only
   interface.  Therefore support for other HTTP methods such as PUT,
   POST and DELETE etc. is not specified.  Server implementations of
   this interface SHOULD reject all methods other than GET and HEAD.

   As the CDNI Metadata interface builds on top of HTTP, CDNI Metadata
   servers may make use of any HTTP feature when implementing the CDNI
   Metadata interface, for example a CDNI Metadata server may make use
   of HTTP's caching mechanisms to indicate that the returned response/
   representation can be reused without re-contacting the CDNI Metadata
   server.

5.2.  Retrieval of CDNI Metadata resources

   In the general case a CDNI Metadata server makes each instance of an
   addressable CDNI Metadata object available via a unique URI and
   therefore in order to retrieve CDNI Metadata, a CDNI Metadata client
   first makes a HTTP GET request for the URI of the HostIndex which
   provides the CDNI Metadata client with a list of Hosts (along with
   their public facing hostnames) that the upstream CDN may delegate to
   the downstream CDN.

   In order to retrieve the CDNI Metadata for a particular request the
   CDNI Metadata client processes the received HostIndex object and
   finds the corresponding HostMetadata entry (by matching the hostname
   in the request against the hostnames in the HostIndex).  The CDNI
   metadata client then makes a GET request for the URI specified in the
   href key of that Host's entry in the HostIndex.

   In order to retrieve the most specific metadata for a particular
   request, the CDNI metadata client inspects the HostMetadata for
   references to more specific PathMetadata objects.  If any
   PathMetadata match the request, the CDNI metadata client makes
   another GET request for the PathMetadata.  Each PathMetadata object
   may also include references to yet more specific metadata.  If this
   is the case, the CDNI metadata client continues requesting
   PathMetadata recursively.

   Where a downstream CDN is interconnected with multiple upstream CDNs,
   the downstream CDN must decide which upstream CDN's metadata should
   handle a particular User Agent request.

   In the case of where application level redirection (e.g.  HTTP 302
   redirects) is being used between CDNs, it is expected that the
   downstream CDN will be able to determine the upstream CDN that



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   redirected a particular request from information contained in the
   received request (e.g. via the URI in case of HTTP redirection across
   CDNs).  With knowledge of which upstream CDN routed the request, the
   downstream CDN can choose the correct metadata server.

   In the case of DNS redirection there is not sufficient information
   carried in the DNS request from User Agents to determine the upstream
   CDN that redirected a particular request and therefore downstream
   CDNs may have to apply local policy when deciding which upstream
   CDN's metadata to apply.

5.3.  Bootstrapping

   The URI for the HostIndex object of a given upstream CDN needs to be
   either discovered by or configured in the downstream CDN.  All other
   objects/resources are then discoverable from the HostIndex object by
   following the links in the HostIndex object and the referenced
   HostMetadata and PathMetadata objects.

   If the URI for the HostIndex object is not manually configured in the
   downstream CDN then the HostIndex URI could be discovered via the
   CDNI Control interface.  An upstream CDN would advertise the URI of
   the HostIndex object to the downstream CDN via the CDNI Control
   Interface.

5.4.  Encoding

   Object are resources that may be:

   o  Addressable, where the object is a resource that may be retrieved
      or referenced via its own URI.
   o  Embedded, where the object is contained (or inlined) within a
      property of an addressable object.

   In the descriptions of objects we use the term "X contains Y" to mean
   either Y is directly embedded in X or that Y is linked to by X. It is
   generally a deployment choice for the uCDN implementation to decide
   when and which CDNI Metadata objects to embed and which are
   separately addressable.

5.4.1.  MIME Media Types

   All MIME types are prefixed with "application/cdni."  The MIME type
   for each object matches the type name of that object as defined by
   this document.Table 4 lists a few examples of the MIME Media Type for
   each object (resource) that is retrievable through the CDNI Metadata
   interface.  The MIME type suffix depends on the metadata encoding,
   either "+xml" or "+json".



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             +--------------+-------------------------------+
             | Data Object  | MIME Media Type               |
             +--------------+-------------------------------+
             | HostIndex    | application/cdni.HostIndex    |
             | HostMatch    | application/cdni.HostMatch    |
             | HostMetadata | application/cdni.HostMetadata |
             | PathMatch    | application/cdni.PathMatch    |
             | PathMetadata | application/cdni.PathMetadata |
             +--------------+-------------------------------+

           Table 4: MIME Media Types for CDNI Metadata resources

   See http://www.iana.org/assignments/media-types/index.html for
   reference.

5.4.2.  JSON Encoding of Objects

   One possible encoding for a CDNI Metadata object is a JSON object
   containing a dictionary of (key,value) pairs where the keys are the
   property names and the values are the associated property values.

   The keys of the dictionary are the names of the properties associated
   with the object and are therefore dependent on the specific object
   being encoded (i.e. dependent on the MIME Media Type of the returned
   resource).  Likewise, the values associated with each key are
   dependent on the specific object being encoded (i.e. dependent on the
   MIME Media Type of the returned resource).

   Dictionary keys in JSON are case sensitive and therefore any
   dictionary key defined by this document (for example the names of
   CDNI Metadata object properties) MUST always be represented in
   lowercase.

   In addition to the properties of the object, the following three
   additional keys defined below may be present in any object.

      Key: base
         Description: Provides a prefix for any relative URLs in the
         object.  This is similar to the XML base tag [XML-BASE].  If
         absent, all URLs in the remainder of the document must be
         absolute URLs.
         Type: URI
         Mandatory: No

      Key: links
         Description: The links of this object to other addressable
         objects.  Any property may be replaced by a link to an object
         with the same type as the property it replaces.



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         Type: List of Link
         Mandatory: Yes

5.4.2.1.  JSON Example

   A downstream CDN may request the HostIndex and receive the following
   object of type "application/cdni.HostIndex+json":

   {
     "host": [
       {
         "hostname": "video.example.com",
         "links": [
           {
             "rel": "hostmetadata",
             "type": "HostMetadata",
             "href": "http://metadata.ucdn.com/video"
           }
         ]
       },
       {
         "hostname": "images.example.com",
         "links": [
           {
             "rel": "hostmetadata",
             "type": "HostMetadata",
             "href": "http://metadata.ucdn.com/images"
           }
         ]
       }
     ]
   }

   If the incoming request has a Host header with "video.example.com"
   then the downstream CDN would fetch from the next metadata object
   from "http://metadata.ucdn.com/video" expecting a MIME type of
   "application/cdni.HostMetadata+json":

   {
     "hostname": "video.example.com",
     "acquisition": {
       "source": [
         {
           "links": [{
             "rel": "auth",
             "type": "Auth",
             "href": "http://metadata.ucdn.com/auth1234"
           }],



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           "endpoint": "acq1.ucdn.com",
           "protocol": "ftp"
         },
         {
           "links": [{
             "rel": "auth",
             "type": "Auth",
             "href": "http://metadata.ucdn.com/auth1234"
           }],
           "endpoint": "acq2.ucdn.com",
           "protocol": "http"
         }
       ]
     },
     "delivery": {
       "location": {
         "aclrule": {
           "deny": { "iprange": "192.168.0.0/16" }
         }
       },
       "auth": {

       },
       "protocol": "http",
       "active": "true"
     },
     "path": [
       {
         "pattern": "/videos/trailers/*",
         "patternflags": "prefix",
         "links": [{
           "rel": "pathmetadata",
           "type": "PathMetadata",
           "href": "http://metadata.ucdn.com/videos/trailers"
         }]
       },
       {
         "pattern": "/videos/movies/*",
         "patternflags": "prefix",
         "links": [{
           "rel": "pathmetadata",
           "type": "PathMetadata",
           "href": "http://metadata.ucdn.com/videos/movies"
         }]
       }
     ]
   }




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   Suppose the path of the requested resource matches the "/video/
   movies/*" pattern, the next metadata requested would be for
   "http://metadata.ucdn.com/video/movies" with an expected type of
   "application/cdni.PathMetadata":

   {
     "delivery": {
       "auth": {

       }
     },
     "path": {
       "pattern": "/videos/movies/hd/*",
       "patternflags": "prefix",
       "links": [{
         "rel": "pathmetadata",
         "type": "PathMetadata",
         "href": "http://metadata.ucdn.com/videos/movies/hd"
       }]
     }
   }

   Finally, if the path of the requested resource also matches the
   "/videos/movies/hd/*" pattern, the downstream CDN would also fetch
   the following object from "http://metadata.ucdn.com/videos/movies/hd"
   with MIME type "application/cdni.PathMetadata":

   {
     "delivery": {
       "time": {
         "aclrule": {
           "allow": {
             "start": "1213948800",
             "end": "1327393200"
           }
         }
       }
     }
   }

5.4.3.  XML Encoding of Objects

   Another possible encoding for a CDNI Metadata object is an XML
   document containing elements with tag names which match property
   names and values which match the associated property values.

   Tag names of elements are the names of the properties associated with
   the object and are therefore dependent on the specific object being



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   encoded (i.e. dependent on the MIME Media Type of the returned
   resource).  Likewise, the values associated with each element are
   dependent on the specific object being encoded (i.e. dependent on the
   MIME Media Type of the returned resource).

   Lists are encoded by repeating the singular form of a property name.
   For example the "hosts" property is a list of "HostMatch" objects.
   This list would be encoded as multiple "host" elements.

   Link objects are a special case.  If a Link object replaces a
   property then a "link" element replaces the expected element.  The
   properties of the Link object are encoded as XML attributes.  The
   type attribute is set to the MIME type of the target object.  The
   href attribute is set to the URI of the target object.  The rel
   attribute is set to the name of the element being replaced.

5.4.3.1.  XML Example

   A downstream CDN may request the HostIndex and receive the following
   object of type "application/cdni.HostIndex+json":

   <HostIndex>
     <host>
       <hostname>video.example.com</hostname>
       <link rel="hostmetadata" type="HostMetadata"
         href="http://metadata.ucdn.com/video"/>
     </host>
     <host>
       <hostname>images.example.com</hostname>
       <link rel="hostmetadata" type="HostMetadata"
         href="http://metadata.ucdn.com/images"/>
     </host>
   </HostIndex>

   If the incoming request has a Host header with "video.example.com"
   then the downstream CDN would fetch from the next metadata object
   from "http://metadata.ucdn.com/video" expecting a MIME type of
   "application/cdni.HostMetadata+json":













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   <HostMetadata>
     <hostname>video.example.com</hostname>
     <acquisition>
       <source>
         <link rel="auth" type="Auth"
           href="http://metadata.ucdn.com/auth1234"/>
         <endpoint>acq1.ucdn.com</endpoint>
         <protocol>ftp</protocol>
       </source>
       <source>
         <link rel="auth" type="Auth"
           href="http://metadata.ucdn.com/auth1234"/>
         <endpoint>acq2.ucdn.com</endpoint>
         <protocol>http</protocol>
       </source>
     </acquisition>
     <delivery>
       <location>
         <aclrule>
           <deny>
             <iprange>192.168.0.0/16</iprange>
           </deny>
         </aclrule>
       </location>
       <auth></auth>
       <protocol>http</protocol>
       <active>true</active>
     </delivery>
     <path>
       <pattern>/videos/trailers/*</pattern>
       <patternflags>prefix</patternflags>
       <link rel="pathmetadata" type="PathMetadata"
         href="http://metadata.ucdn.com/videos/trailers"/>
     </path>
     <path>
       <pattern>/videos/movies/*</pattern>
       <patternflags>prefix</patternflags>
       <link rel="pathmetadata" type="PathMetadata"
         href="http://metadata.ucdn.com/videos/movies"/>
     </path>
   </HostMetadata>

   Suppose the path of the requested resource matches the "/video/
   movies/*" pattern, the next metadata requested would be for
   "http://metadata.ucdn.com/video/movies" with an expected type of
   "application/cdni.PathMetadata":





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   <PathMetadata>
     <delivery>
       <auth></auth>
     </delivery>
     <path>
       <pattern>/videos/movies/hd/*</pattern>
       <patternflags>prefix</patternflags>
       <link rel="pathmetadata" type="PathMetadata"
         href="http://metadata.ucdn.com/videos/movies/hd"/>
     </path>
   </PathMetadata>

   Finally, if the path of the requested resource also matches the
   "/videos/movies/hd/*" pattern, the downstream CDN would also fetch
   the following object from "http://metadata.ucdn.com/videos/movies/hd"
   with MIME type "application/cdni.PathMetadata":

   <PathMetadata>
     <delivery>
       <time>
         <aclrule>
           <allow>
             <start>1213948800</start>
             <end>1327393200</end>
           </allow>
         </aclrule>
       </time>
     </delivery>
   </PathMetadata>

5.5.  Extensibility

   The set of metadata properties may be extended with proprietary and /
   or custom properties.  New properties may be added to any existing
   object.

   The names of such properties MUST begin with an "x-" prefix.  If a
   property is vendor specific, then "x-vendor-" SHOULD be used as the
   name prefix, where the "vendor" string is replaced by the name of the
   vendor.

   The values of new properties MAY include an "ignorable" property with
   a boolean type.  If "ignorable" is set to true, then request routers
   and surrogates in any interconnected CDN MAY safely ignore the new
   property.  If "ignorable" is set to false, then a CDN which does not
   understand the property MUST NOT service a request for the
   corresponding content.




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6.  IANA Considerations

   This document requests the registration of the "application/cdni"
   MIME type.


7.  Security Considerations

   The CDNI Metadata Interface is expected to be secured as a function
   of the transport protocol (e.g.  HTTP authentication).

   If a malicious metadata server is contacted by a downstream CDN, the
   malicious server may provide metadata to the downstream CDN which
   denies service for any piece of content to any user agent.  The
   malicious server may also provide metadata which directs a downstream
   CDN to a malicious origin server instead of the actual origin server.

   A malicious metadata client could request metadata for a piece of
   content from an upstream CDN.  However, given the current set of
   metadata properties, no useful information would be compromised.


8.  Acknowledgements

   The authors would like to thank David Ferguson and Francois le
   Faucheur for their valuable comments and input to this document.


9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952, August 2010.

9.2.  Informative References

   [I-D.davie-cdni-framework]
              Davie, B. and L. Peterson, "Framework for CDN
              Interconnection", draft-davie-cdni-framework-00 (work in
              progress), July 2011.




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   [I-D.ietf-cdni-problem-statement]
              Niven-Jenkins, B., Faucheur, F., and N. Bitar, "Content
              Distribution Network Interconnection (CDNI) Problem
              Statement", draft-ietf-cdni-problem-statement-03 (work in
              progress), January 2012.

   [I-D.ietf-cdni-requirements]
              Leung, K. and Y. Lee, "Content Distribution Network
              Interconnection (CDNI) Requirements",
              draft-ietf-cdni-requirements-02 (work in progress),
              December 2011.

   [I-D.zyp-json-schema]
              Zyp, K. and G. Court, "A JSON Media Type for Describing
              the Structure and Meaning of JSON Documents",
              draft-zyp-json-schema-03 (work in progress),
              November 2010.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC4151]  Kindberg, T. and S. Hawke, "The 'tag' URI Scheme",
              RFC 4151, October 2005.

   [RFC4287]  Nottingham, M., Ed. and R. Sayre, Ed., "The Atom
              Syndication Format", RFC 4287, December 2005.

   [XML-BASE]
              Marsh, J., Ed. and R. Tobin, Ed., "XML Base (Second
              Edition) - http://www.w3.org/TR/xmlbase/", January 2009.


Appendix A.  Relationship to the CDNI Requirements

   Section 6 of [I-D.ietf-cdni-requirements] lists the requirements for
   the CDNI Metadata Distribution interface.  This section outlines
   which of those requirements are met by the CDNI Metadata interface
   specified in this document.

   All metadata requirements are met either directly or indirectly by
   the CDNI Metadata Interface described in this document.  The
   following paragraphs describe notable exceptions.

   Requirements related to pre-positioning of metadata are not met
   directly by this document.  Triggering metadata pre-positioning is
   beyond the scope of the CDNI Metadata interface.  However, the
   interface as described by this document supports pulling metadata on-



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   demand for the purpose of pre-positioning.

   Requirement META-13 relating to feedback from the downstream CDN to
   the upstream CDN with respect to metadata is not directly supported
   by the pull-based interface described in this document.  As an
   alternative, the downstream CDN may use the CDNI Logging interface to
   convey error conditions related to metadata.

   Requirement META-18 relating to surrogate cache behavior parameters
   is supported via extensibility.  However, the example parameters in
   META-18 are not described in this document.


Authors' Addresses

   Ben Niven-Jenkins
   Velocix (Alcatel-Lucent)
   3 Ely Road
   Milton, Cambridge  CB24 6AA
   UK

   Email: ben@velocix.com


   Rob Murray
   Velocix (Alcatel-Lucent)
   3 Ely Road
   Milton, Cambridge  CB24 6AA
   UK

   Email: rmurray@velocix.com


   Grant Watson
   Velocix (Alcatel-Lucent)
   3 Ely Road
   Milton, Cambridge  CB24 6AA
   UK

   Email: gwatson@velocix.com











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   Matt Caulfield
   Cisco Systems
   1414 Massachusetts Avenue
   Boxborough, MA  01719
   USA

   Phone: +1 978 936 9307
   Email: mcaulfie@cisco.com


   Kent Leung
   Cisco Systems
   3625 Cisco Way
   San Jose  95134
   USA

   Phone: +1 408 526 5030
   Email: kleung@cisco.com

































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