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Versions: 00 01 02 03 04 05 06 07 08 09                                 
Network Working Group                                              K. Ma
Internet-Draft                                       Azuki Systems, Inc.
Intended status: Standards Track                        February 4, 2013
Expires: August 8, 2013


    Content Distribution Network Interconnection (CDNI) Capabilities
                               Interface
                     draft-ma-cdni-capabilities-01

Abstract

   The interconnection of Content Distribution Networks (CDNs) is
   predicated on the ability of downstream CDNs (dCDNs) to handle end-
   user requests in a functionally equivalent manner to the upstream CDN
   (uCDN).  The uCDN must be able to assess the ability of the dCDN to
   handle individual requests.  A CDN interconnection (CDNI) interface
   is needed to facilitate the advertisement of capabilities by the dCDN
   to the uCDN.  This document describes an approach to implementing a
   CDNI capabilities advertisement interface.

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 August 8, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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   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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Capabilities . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Delivery Protocol  . . . . . . . . . . . . . . . . . . . .  6
     2.2.  Acquisition Protocol . . . . . . . . . . . . . . . . . . .  7
     2.3.  Metadata Bundle  . . . . . . . . . . . . . . . . . . . . .  8
     2.4.  Redirection Mode . . . . . . . . . . . . . . . . . . . . .  9
   3.  Capability Advertisement . . . . . . . . . . . . . . . . . . . 11
     3.1.  Capability Update  . . . . . . . . . . . . . . . . . . . . 11
     3.2.  Capability Removal . . . . . . . . . . . . . . . . . . . . 13
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 15
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 15
   Appendix A.  Capability Aggregation  . . . . . . . . . . . . . . . 16
     A.1.  Downstream CDN Aggregation . . . . . . . . . . . . . . . . 16
     A.2.  Internal Request Router Aggregation  . . . . . . . . . . . 17
     A.3.  Internal Capability Aggregation  . . . . . . . . . . . . . 19
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 20

















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1.  Introduction

   The need for capabilities advertisement in CDNI is described in the
   CDNI requirements document [I-D.ietf-cdni-requirements].  Requirement
   REQ-2 describes the need to allow dCDNs to communicate capabilities
   to the uCDN.  The uCDN aggregates the capabilities information for
   all dCDNs for use in making request routing decisions.  Per
   requirement REQ-3, the uCDN should further use the aggregated
   capabilities in advertisements to CDNs further upstream.  This
   concept of aggregation can apply to both organizationally different
   dCDNs (e.g., other CDN providers, or different business units within
   a larger organization) or logical entities within the same CDN (e.g.,
   using multiple request routers for scalability reasons, to segregate
   surrogates based on specific protocol support, or to segregate
   surrogates based on software version or feature level, etc.).

   Appendix A contains more detailed descriptions of the different
   capabilities management scenarios, but it is important to note that
   it is the ability of the dCDN to service each request in a
   functionally equivalent manner as the uCDN that is important, not the
   physical layout of resources through which it services the request.
   The aggregation of resource knowledge by the dCDN into a simple set
   of capabilities which can be advertised to the uCDN enables efficient
   decision making at each delegation point in the CDN interconnection
   hierarchy.

   It is assumed that an authoritative request router in each CDN will
   be responsible for aggregating and advertising capabilities
   information in a dCDN, and receiving and aggregating capabilities
   information in the uCDN.  As there is no centralized CDNI controller
   defined in the CDNI architecture, the request router seems the most
   logical place for capabilities aggregation to occur, as it is the
   request router that needs such information to make delegation
   decisions.  The protocol defined herein may be implemented as part of
   an entity other than an authoritative request router, but for the
   purposes of this discussion, the authoritative request router is
   assumed to be the centralized capabilities aggregation point.

   Though there is an obvious need for the ability to exchange and
   update capability information in real-time, it is assumed that
   capabilities do not change very often.  There is also an assumption
   that the capabilities are not by themselves useful for making
   delegation decisions.  Capability information is assumed to be input
   into business logic.  It is the business logic which provides the
   algorithms for delegation decision making.  The definition of
   business logic occurs outside the scope of CDNI and outside the
   timescale of capability advertisement.  It may be the case that the
   business logic anticipates and reacts to changes in dCDN



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   capabilities.  However, it may also be the case that business logic
   is tailored through offline processes as dCDN capabilities change.
   The capabilities interface is agnostic to the business processes
   employed by a given uCDN.  The capabilities that are advertised over
   the capabilities interface may be used by the uCDN at its leisure to
   implement delegation rules.  Setting proper defaults in the business
   logic should prevent any unwanted delegation from occurring when dCDN
   capabilities change, however, that is beyond the scope of this
   discussion.

1.1.  Terminology

   This document uses the terminology defined in section 1.1 of the CDNI
   Framework [I-D.ietf-cdni-framework] document.


2.  Capabilities

   There is a basic set of capabilities that must be advertised by the
   dCDN for the uCDN to be able to determine if the dCDN is functionally
   able to handle a given request.  Mandatory capabilities include:

   o  Delivery Protocol

   o  Acquisition Protocol

   o  Metadata Bundle

   o  Redirection Mode

   The following sections describe each of the capabilities in further
   detail, however, all of the capabilities can be described using the
   same general format.  A capability object can be described as:

      CapabilityObject:
        Name: Identifier for the capability
        Values: List of supported options for the capability
        Footprint: Optional list of footprint restrictions

   The list of valid capability options for a given capability will be
   specific to the given capability type.  Though the degenerate case
   may exist where the range of option values is a single value, it is
   anticipated that all capability types will have more than one
   capability option value.  For consistency in the model, all
   capability types are implemented with lists of values.  To optimize
   actions on the entire range of capability option values for a given
   capability type, the capability option value "ALL" is reserved and
   MUST be supported by all capability types.  For completeness, the



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   capability option value "NONE" is also reserved and MUST be supported
   by all capability types.  Reserved values SHOULD NOT be combined with
   any other valid capability option values for a given capability type.
   Reserved values MUST NOT be combined with each other for a given
   capability type.  The reserved values MUST be given precedence over
   all other capability option values for a given capability type, when
   specified in the same capabilities advertisement message, with NONE
   superceding ALL if both are specified.

   The footprint restriction list is optional.  Footprint restriction
   lists override in their entirety all previously advertised footprint
   restriction lists for the specified capability option values for the
   given capability type.  If no footprint restriction list is
   specified, it SHALL be understood that all of the capability option
   values specified have global reach, overriding any previous
   capability advertisements for the specified capability option values.
   The footprint restriction list supports either IP prefix or ASN
   values.  IP prefix and ASN restrictions MUST NOT be mixed within a
   given footprint list.  In the case of interconnecting private network
   CDNs, IP prefix or ASN-based footprint advertisement are the likely
   methods for describing coverage areas.

   [Ed. note: Though other methods exist for defining footprints (e.g.,
   GPS coordinates, country/zip/area codes, etc.), only IP prefix and
   ASN are considered here.  Need to evaluate use cases for other
   methods of footprint definition.]

   Note: Further optimization of the capabilities object to provide
   quality information for a given footprint is certainly possible,
   however, it is not critical to the basic interconnection of CDNs.
   The ability to transfer quality information in capabilities
   advertisements may be desirable and is noted here for completeness,
   however, the specifics of such mechanisms are outside the scope of
   this document.

   Multiple capability objects of the same capability type are allowed
   within a given capability advertisement message as long as the
   capability option values do not overlap, i.e., a given capability
   option value MUST NOT show up in multiple capability objects within a
   single capability advertisement message.  If multiple capability
   objects for a given capability type exist, those capability objects
   SHOULD have different footprint restrictions; capability objects of a
   given capability type with identical footprint restrictions SHOULD be
   combined.

   Note: The examples shown below use an XML representation, however,
   other representations (e.g., JSON) may also be acceptable.




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2.1.  Delivery Protocol

   The delivery protocol refers to the protocol over which an end user
   (EU) has requested content.  If a dCDN does not support the protocol
   requested by the client, then the dCDN is not a viable candidate for
   delegation.

   Though the delivery protocol is specified in the URI scheme (as
   defined in RFC3986 [RFC3986]) of the client request URL, protocol
   feature subsets or augmented protocol feature sets MAY be defined and
   SHOULD correspond with the protocols supported by the ProtocolACL
   defined in the CDNI Metadata Interface [I-D.ietf-cdni-metadata]
   document.

   [Ed. note: A protocol identifier registry should be created to be
   able to consistently reference defined subsets of features for a
   given protocol (e.g., different HTTP methods, chunking, ranges, etc.)
   or augemented feature sets (e.g., from application layer protocols
   like HLS, DASH, etc.) which run over top of HTTP.]

   The delivery protocol capability object MUST support a list of
   protocols for a given footprint.  The delivery protocol capability
   SHOULD support optional footprint restriction information.  The
   following XML-encoded example shows two lists of protocols with
   different footprints.

      <Capabilities>
        <DeliveryProtocols>
          <Protocols>
            <Protocol>HTTP</Protocol>
            <Protocol>RTSP</Protocol>
            <Protocol>MMS</Protocol>
          </Protocols>
        </DeliveryProtocols>
        <DeliveryProtocols>
          <Protocols>
            <Protocol>RTMP</Protocol>
            <Protocol>HTTPS</Protocol>
          </Protocols>
          <Footprint>
            <Prefixes>
              <Prefix>10.1.0.0/16</Prefix>
              <Prefix>10.10.10.0/24</Prefix>
            </Prefixes>
          </Footprint>
        </DeliveryProtocols>
      </Capabilities>




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   In the above example, the three protocols HTTP, RTSP, and MMS are
   supported globally, while the protocols RTMP and HTTPS are only
   supported in a restricted footprint (in this case, specified by IP
   address prefix).

   A protocol MUST not appear in multiple delivery protocol lists,
   within a given capability advertisement message.  Redefinition of
   footprint restrictions in subsequent capability advertisement
   messages MAY occur and SHALL override all previous capability
   advertisements for the specified delivery protocol.

2.2.  Acquisition Protocol

   The acquisition protocol refers to the protocol over which the dCDN
   may acquire content from the uCDN.  If a dCDN does not support any of
   the protocols offered by the uCDN, then the dCDN is not a viable
   candidate for delegation.

   Though the acquisition protocol is disseminated to the dCDN in the
   URI scheme (as defined in RFC3986 [RFC3986]) of the URL provided by
   the uCDN via the CDNI Metadata Interface [I-D.ietf-cdni-metadata],
   protocol feature subsets or augmented protocol feature sets MAY be
   defined and SHOULD correspond with the protocols supported by the
   ProtocolACL defined in the CDNI Metadata Interface
   [I-D.ietf-cdni-metadata] document.

   [Ed. note: A protocol identifier registry should be created to be
   able to consistently reference defined subsets of features for a
   given protocol (e.g., different HTTP methods, chunking, ranges, etc.)
   or augemented feature sets (e.g., from application layer protocols
   like HLS, DASH, etc.) which run over top of HTTP.]

   The acquisition protocol capability object MUST support a list of
   protocols for a given footprint.  The acquisition protocol capability
   SHOULD support optional footprint restriction information.  The
   following XML-encoded example shows two lists of protocols with
   different footprints.














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      <Capabilities>
        <AcquisitionProtocols>
          <Protocols>
            <Protocol>HTTP</Protocol>
            <Protocol>FTP</Protocol>
          </Protocols>
        </AcquisitionProtocols>
        <AcquisitionProtocols>
          <Protocols>
            <Protocol>SFTP</Protocol>
            <Protocol>HTTPS</Protocol>
          </Protocols>
          <Footprint>
            <ASNs>
              <ASN>0</ASN>
              <ASN>65535</ASN>
            </ASNs>
          </Footprint>
        </AcquisitionProtocols>
      </Capabilities>

   In the above example, the two protocols HTTP and FTP are supported
   globally, while the protocols SFTP and HTTPS are only supported in a
   restricted footprint (in this case, specified by ASN).

   A protocol MUST not appear in multiple acquisition protocol lists,
   within a given capability advertisement message.  Redefinition of
   footprint restrictions in subsequent capability advertisement
   messages MAY occur and SHALL override all previous capability
   advertisements for the specified acquisition protocol.

2.3.  Metadata Bundle

   Metadata bundles are groupings of one or more metadata definitions
   which the dCDN is capable of understanding.  There will be a core set
   of metadata defined in the CDNI Metadata Interface
   [I-D.ietf-cdni-metadata] document, which all CDNI implementations
   will be required to support, however, future revisions of CDNI may
   include additional mandatory to implement metadata, and some
   operators may require the use of vendor specific metadata.  If a dCDN
   is not capable of understanding a given piece of metadata which the
   uCDN feels is mandatory for delivery, then the dCDN is not a viable
   candidate for delegation.

   [Ed. note: A metadata bundle identifier registry should be created to
   be able to consistently reference defined sets of metadata types and
   any individual options within a given piece of metadata within a
   given bundle which may need to be advertised.



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   The metadata bundle capability object MUST support a list of
   protocols for a given footprint.  The metadata bundle capability
   SHOULD support optional footprint restriction information.  The
   following XML-encoded example shows two lists of bundles with
   different footprints.

      <Capabilities>
        <MetadataBundles>
          <Bundles>
            <Bundle>cdni.core.v1</Bundle>
          <Bundles>
        </MetadataBundles>
        <MetadataBundle>
          <Bundles>
            <Bundle>vendor.azuki.has.v1</Bundle>
            <Bundle>private.rw.color.v1</Bundle>
          <Bundles>
          <Footprint>
            <Prefixes>
              <Prefix>10.1.2.0/24</Prefix>
            </Prefixes>
          </Footprint>
        </MetadataBundles>
      </Capabilities>

   In the above example, core version 1 CDNI metadata cdni.core.v1 is
   supported globally, while the vendor specific metadata bundles
   vendor.azuki.has.v1 and private.rw.color.v1 are only supported in a
   restricted footprint (in this case, specified by IP Prefix).

   A bundle MUST not appear in multiple metadata bundle lists, within a
   given capability advertisement message.  Redefinition of footprint
   restrictions in subsequent capability advertisement messages MAY
   occur and SHALL override all previous capability advertisements for
   the specified metadata bundle.

2.4.  Redirection Mode

   The redirection mode refers to the method(s) employed by request
   routers to perform request redirection.  The CDNI framework
   [I-D.ietf-cdni-framework] document describes four possible request
   routing modes:

   o  DNS iterative (DNS-I)

   o  DNS recursive (DNS-R)





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   o  HTTP iterative (HTTP-I)

   o  HTTP recursive (HTTP-R)

   If a dCDN supports only a specific mode or subset of modes that does
   not overlap with the modes supported by the uCDN, then the dCDN is
   not a viable candidate for delegation.

   [Ed. note: A request routing mode identifier registry should be
   created to be able to consistently reference an extensible list of
   supported CDNI request routing modes.

   The redirection mode capability object MUST support a list of
   redirection modes for a given footprint.  The redirection mode
   capability SHOULD support optional footprint restriction information.
   The following XML-encoded example shows two lists of modes with
   different footprints.

      <Capabilities>
        <RedirectionModes>
          <Modes>
            <Mode>DNS-I</Mode>
            <Mode>HTTP-I</Mode>
          <Modes>
        </RedirectionModes>
        <RedirectionModes>
          <Modes>
            <Mode>DNS-R</Mode>
            <Mode>HTTP-R</Mode>
          <Modes>
          <Footprint>
            <ASNs>
              <ASN>64511</ASN>
            </ASNs>
          </Footprint>
        </RedirectionModes>
      </Capabilities>

   In the above example, iterative redirection is supported globally,
   while recursive redirection is only supported in a restricted
   footprint (in this case, specified by ASN).

   A mode MUST not appear in multiple redirection mode lists, within a
   given capability advertisement message.  Redefinition of footprint
   restrictions in subsequent capability advertisement messages MAY
   occur and SHALL override all previous capability advertisements for
   the specified redirection mode.




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3.  Capability Advertisement

   The capabilities advertisement protocol is an HTTP-based protocol
   using the POST and DELETE methods.  Capability removal is
   distinguished from capability advertisement by the HTTP request
   method.  Capability advertisement uses the HTTP POST method, while
   capability removal uses the HTTP DELETE method.  The dCDN request
   router asynchronously issues capability advertisement messages to the
   uCDN request router (see Appendix A for detailed descriptions of
   authoritative request router capabilities aggregation scenarios).  It
   is assumed that the dCDN request router has been configured with the
   uCDN request router address either through the CDNI Control interface
   bootstrapping function, or through some other out-of-band
   configuration.

   Note: The examples shown below use an XML representation, however,
   other representations (e.g., JSON) are also acceptable.

3.1.  Capability Update

   A capabilities advertisement message may combine objects from one or
   more capability types.  On an initial advertisement, the dCDN SHOULD
   send a value for every capability type.




























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      POST /CDNI/RI/capabilities HTTP/1.1
      Host: rr0.u.example.com
      Accept: */*
      Content-Length: 530
      Content-Type: application/x-www-form-urlencoded

      <Capabilities>
        <DeliveryProtocols>
          <Protocols>
            <Protocol>HTTP</Protocol>
          </Protocols>
        </DeliveryProtocols>
        <AcquisitionProtocols>
          <Protocols>
            <Protocol>HTTP</Protocol>
            <Protocol>FTP</Protocol>
          </Protocols>
        </AcquisitionProtocols>
        <MetadataBundles>
          <Bundles>
            <Bundle>cdni.core.v1</Bundle>
            <Bundle>private.rw.color.v1</Bundle>
          <Bundles>
        </MetadataBundles>
        <RedirectionModes>
          <Modes>
            <Mode>HTTP-I</Mode>
          <Modes>
        </RedirectionModes>
      </Capabilities>

   In the above example, the dCDN issues a post to the uCDN request
   router rr0.u.example.com with a capability advertisement message
   specifying support for HTTP-based delivery, HTTP or FTP-based content
   acquisition, iterative HTTP redirection, and support for both core
   and color metadata.  A subsequent capabilities advertisement message
   may be used to update this information without respecifying all the
   fields.

   In the following example, the dCDN updates its ability to deliver
   content via HTTPS while restricting its previously advertised support
   for delivering content via HTTP to only its internal network.  All
   previous advertisements for acquisition protocol, metadata bundles,
   and redirection modes still are unaffected.







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      POST /CDNI/RI/capabilities HTTP/1.1
      Host: rr0.u.example.com
      Accept: */*
      Content-Length: 356
      Content-Type: application/x-www-form-urlencoded

      <Capabilities>
        <DeliveryProtocols>
          <Protocols>
            <Protocol>HTTPS</Protocol>
          </Protocols>
        </DeliveryProtocols>
        <DeliveryProtocols>
          <Protocols>
            <Protocol>HTTP</Protocol>
          </Protocols>
          <Footprint>
            <Prefixes>
              <Prefix>10.0.0.0/8</Prefix>
            </Prefixes>
          </Footprint>
        </DeliveryProtocols>
      </Capabilities>

3.2.  Capability Removal

   In the following example, the dCDN issues a DELETE command to the
   uCDN request router rr0.u.example.com with a capability advertisement
   message containing all four capability types specifying the reserved
   capability option value ALL.  This removes capabilities information
   for all capability options for all capability types, effectively
   allowing the dCDN to remove itself from delegation consideration.



















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      DELETE /CDNI/RI/capabilities HTTP/1.1
      Host: rr0.u.example.com
      Accept: */*
      Content-Length: 442
      Content-Type: application/x-www-form-urlencoded

      <Capabilities>
        <DeliveryProtocols>
          <Protocols>
            <Protocol>ALL</Protocol>
          </Protocols>
        </DeliveryProtocols>
        <AcquisitionProtocols>
          <Protocols>
            <Protocol>ALL</Protocol>
          </Protocols>
        </AcquisitionProtocols>
        <MetadataBundles>
          <Bundles>
            <Bundle>ALL</Bundle>
          <Bundles>
        </MetadataBundles>
        <RedirectionModes>
          <Modes>
            <Mode>ALL</Mode>
          <Modes>
        </RedirectionModes>
      </Capabilities>


4.  IANA Considerations

   This memo includes no request to IANA.

   [Ed. note: Need to reference registry for protocol identifiers?]

   [Ed. note: Need to reference registry for metadata bundle
   identifiers?]

   [Ed. note: Need to reference registry for request routing mode
   identifiers?]

   [Ed. note: Need to define a registry for capability names?]


5.  Security Considerations

   There are a number of security concerns associated with the



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   capabilities interface.  As the capabilities interface essentially
   provides configuration information which the uCDN uses to make
   request routing decisions.  Injection of fake capability
   advertisement messages, or interception and discard of real
   capability advertisement messages may be used for denial of service
   (e.g., by falsely advertising or deleting capabilities or preventing
   capability advertisements from reaching the uCDN). dCDN capability
   advertisements MUST be authenticated by the uCDN to prevent
   unauthorized capability advertisement message injection. uCDN request
   router capability interface servers MUST be authenticated by the dCDN
   to prevent unauthorized interception of capability advertisement
   messages.  TLS with client authentication SHOULD be used for all
   capability interface implementations.  Deployments in controlled
   environments where physical security and IP address white-listing is
   employed MAY choose not to use TLS.


6.  Acknowledgements

   The authors would like to thank Ray van Brandenburg, Gilles Bertrand,
   and Scott Wainner for their timely reviews and invaluable comments.


7.  References

7.1.  Normative References

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

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

7.2.  Informative References

   [I-D.ietf-cdni-framework]
              Peterson, L., Ed. and B. Davie, Ed., "Framework for CDN
              Interconnection draft-ietf-cdni-framework-02",
              December 2012.

   [I-D.ietf-cdni-metadata]
              Niven-Jenkins, B., Murray, R., Watson, G., Caulfield, M.,
              Leung, K., and K. Ma, "CDN Interconnect Metadata
              draft-ietf-cdni-metadata-00", October 2012.

   [I-D.ietf-cdni-requirements]
              Leung, K. and Y. Lee, "Content Distribution Network



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              Interconnection (CDNI) Requirements
              draft-ietf-cdni-requirements-04", December 2012.


Appendix A.  Capability Aggregation

   The following sections show examples of three aggregation scenarios.
   In each case, CDN-U is the ultimate uCDN and CDN-P is the penultimate
   CDN which must perform capabilities aggregation.

A.1.  Downstream CDN Aggregation

   Figure A1 shows five organizationally different CDNs: CDN-U, CDN-P,
   and CDNS A, B, and C, the dCDNs of CDN-P which are being aggregated.
   Given the setup shown in Figure A1, we can construct a number of use
   cases, based on the coverage areas of each dCDN (i.e., CDNs P, A, B,
   and C).  Note: In all cases, the reachability of the uCDN (i.e.,
   CDN-U) is a don't care as it is assumed that the uCDN knows its own
   coverage area and is likely to favor itself in most situations, and
   if it has decided that it needs to delegate to a dCDN, then the only
   relevant question is if the dCDN can handle the request.

                               ,---,---,---.
                            ,-'             `-.
                           ( rr0.u.example.com )
                            `-.    CDN-U    ,-'
                               `---'-+-'- --'
                                     |
                               ,---,-+-,---.
                            ,-'             `-.
                           ( rr0.p.example.com )
                            `-.    CDN-P    ,-'
                               `---'-+-'---'
                                     |
               +---------------------+---------------------+
              /                      |                      \
       ,---,-+-,---.           ,---,-+-,---.           ,---,-+-,---.
    ,-'             `-.     ,-'             `-.     ,-'             `-.
   ( rr0.a.example.com )   ( rr0.b.example.com )   ( rr0.c.example.com )
    `-.    CDN-A    ,-'     `-.    CDN-B    ,-'     `-.    CDN-C    ,-'
       `---'---'---'           `---'---'---'           `---'---'---'

              Figure A1: CDNI dCDN Request Router Aggregation

   o  None of the four dCDNs (CDNs P, A, B, and C) have global
      reachability.  In this case, each CDN is likely to advertise
      footprint information with its capabilities, specifying its
      reachability.  When CDN-P advertises capabilities to CDN-U, it may



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      advertise the aggregate footprint of itself and CDNs A, B, and C.
      Note: CDN-P MAY exclude any dCDN, and consequently its footprint,
      per its own internal aggregation decision criteria.

   o  All four dCDNs (CDNs P, A, B, and C) have global reachability.  In
      this case, none of the CDNs is likely to advertise any footprint
      information as none have any footprint restrictions.  When CDN-P
      advertises capabilities to CDN-U, the aggregate of all global
      reachability is global reachability.

   o  Some of the four dCDNs (CDNs P, A, B, and C) have global
      reachability and some do not.  In this case, even though some
      dCDNs do not have global reachability, the aggregate of some dCDNs
      having global reachability and some not should still be global
      reachability (for the given capability).  When CDN-P advertises
      capabilities to CDN-U, CDN-P may advertise capabilities for which
      at least one dCDN has global reach as being supported with global
      reachability.  It is up to the CDN-P request router to properly
      select a dCDN to process individual client requests and not choose
      a dCDN whose restricted footprint makes it unsuitable for
      delivering the requested content.

A.2.  Internal Request Router Aggregation

   Figure A2 shows CDN-U and CDN-P where CDN-P internally has four
   request routers: the authoritative request router rr0, and three
   other request routers rr1, rr2, and rr3.  The use of multiple request
   routers may be used to distribute request routing load across
   resources, possibly in different geographic regions covered by CDN-P.
   Similar to Figure A1, the setup shown in Figure A2 requires the
   authoritative request router rr0 in CDN-P to aggregate capabilities
   information from downstream request routers rr1, rr2, and rr3.  The
   primary difference between the scenario is that the request routers
   in Figure A2 are logically within the same CDN-P organization.  The
   same reachability scenarios apply to Figure A2 as with Figure A1.
















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                               ,---,---,---.
                            ,-'             `-.
                           ( rr0.u.example.com )
                            `-.    CDN-U    ,-'
                               `---'-+-'---'
                                     |
                    ,---,---,---,--,-+-,--,---,---,---.
                   (                                   )
                 ,-'       +-------------------+       `-.
                (          | rr0.p.example.com |          )
              ,-'          +---------+---------+          `-.
             (                       |                       )
           ,-'            +----------+----------+            `-.
          (              /           |           \              )
           )  +---------+---------+  |  +---------+---------+  (
          (   | rr1.p.example.com |  |  | rr3.p.example.com |   )
           `. +-------------------+  |  +-------------------+ ,'
            (                        |                        )
             `-.           +---------+---------+           ,-'
               (           | rr2.p.example.com |           )
                `-.        +-------------------+        ,-'
                  (                CDN-P                )
                   `---'---'---'---'---'---'---'---'---'

              Figure A2: Local CDN Request Router Aggregation

   o  None of the four CDN-P request routers have global reachability.
      In this case, each request router is likely to advertise footprint
      information with its capabilities, specifying its reachability.
      When rr0 advertises capabilities to CDN-U, it may advertise the
      aggregate footprint of itself and rr1, rr2, and rr3.

   o  All four CDN-P request routers have global reachability.  In this
      case, none of the request routers is likely to advertise any
      footprint information as none has any footprint restrictions.
      When rr0 advertises capabilities to CDN-U, the aggregate of all
      global reachability is global reachability.

   o  Some of the four CDN-P request routers have global reachability
      and some do not.  In this case, even though some request routers
      do not have global reachability, the aggregate of some request
      routers having global reachability and some not should still be
      global reachability (for the given capability).  When rr0
      advertises capabilities to CDN-U, CDN-P may advertise capabilities
      for which at least one request router has global reach as being
      supported with global reachability.  It is up to the authoritative
      request router rr0 to properly select from the other request
      routers for any given request, and not choose a request router



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      whose restricted footprint makes it unsuitable for delivering the
      requested content.

A.3.  Internal Capability Aggregation

   Figure A3 shows CDN-U and CDN-P where the delivery network of CDN-P
   is segregated by delivery protocol (e.g., RTSP, HTTP, and RTMP).
   Figure A3 differs from Figures A1 and A2 in that request router rr0
   of CDN-P is not aggregating the capabilities advertisements of
   multiple other downstream request routers, but rather it is managing
   the disparate capabilities across resources within its own local CDN.
   Though not every delivery node has the same protocol capabilities,
   the aggregate delivery protocol capabilities advertised by CDN-A may
   include all delivery protocols.  Note, Figure A3 should not be
   construed to imply anything about the coverage areas for each
   delivery protocol.  They may all support the same delivery footprint,
   or they may have different delivery footprints.  It is the
   responsibility of the request router rr0 to properly assign protocol-
   appropriate delivery nodes to individual content requests.  If
   certain protocols have limited reachability, CDN-P may advertise
   footprint restrictions for each protocol.

   It should be noted that though the delivery protocol capability was
   selected for this example, the concept of internal capability
   aggregation applies to all capabilities as discussed below.

                               ,---,---,---.
                            ,-'             `-.
                           ( rr0.u.example.com )
                            `-.    CDN-U    ,-'
                               `---'-+-'---'
                                     |
                    ,---,---,---,--,-+-,--,---,---,---.
                   (                                   )
                 ,-'       +-------------------+       `-.
                (          | rr0.p.example.com |          )
              ,-'          +---------+---------+          `-.
             (                       .                       )
           ,-'            .......................            `-.
          (              .           .           .              )
           )  +-------------------+  .  +-------------------+  (
          (   |rtsp.p.example.com |  .  |rtmp.p.example.com |   )
           `. +-------------------+  .  +-------------------+ ,'
            (                        .                        )
             `-.           +-------------------+           ,-'
               (           |http.p.example.com |           )
                `-.        +-------------------+        ,-'
                  (                CDN-A                )



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                   `---'---'---'---'---'---'---'---'---'

                Figure A3: Local CDN Capability Segregation

   Another situation in which physical footprint may not matter in an
   aggregated view has to do with feature support (e.g., new CDNI
   metadata features or new redirection modes).  Situations often arise
   when phased roll-out of software upgrades, or staging network
   segregation result in only certain portions of a CDN's resources
   supporting the new feature set.  The dCDN has a few options in this
   case:

   o  Enforce atomic update: The dCDN does not advertise support for the
      new capability until all resources have been upgraded to support
      the new capability.

   o  Transparent segregation: The dCDN advertises support for the new
      capability, and when requests are received that require the new
      capability, the dCDN request router properly selects a resource
      which supports that capability.

   o  Advertised segregation: The dCDN advertises support for the new
      capability with a footprint restriction allowing the uCDN to make
      delegation decisions based on the dCDN's limit support.

   The level of aggregation employed by the dCDN is likely to vary as
   business relationships dictate, however, the capability interface
   should support all possible modes of operation.


Author's Address

   Kevin J. Ma
   Azuki Systems, Inc.
   43 Nagog Park
   Acton, MA  01720
   USA

   Phone: +1 978-844-5100
   Email: kevin.ma@azukisystems.com











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