Network Working Group                                           L. Amini
Internet-Draft                                              IBM Research
Expires: August 20, 2001                                       S. Thomas
                                                         TransNexus, Inc
                                                           O. Spatscheck
                                                               AT&T Labs
                                                       February 19, 2001


       Distribution Peering Requirements for Content Distribution
                            Internetworking
                  draft-amini-cdi-distribution-reqs-00

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 20, 2001.

Copyright Notice

   Copyright (C) The Internet Society (2001). All Rights Reserved.

Abstract

   This document specifies requirements for interconnecting, or
   peering, the distribution systems of Content Distribution Networks
   (CDN). Distribution peering requires advertising the capabilities of
   a CDN offering distribution services, moving content from one CDN to
   another, and signaling requirements for consistent storage and
   delivery of content. This document does not address requirements for
   directing user agents to distributed content, nor for aggregating
   access information for distributed content.


Amini, et. al.          Expires August 20, 2001                 [Page 1]


Internet-Draft     Distribution Peering Requirements       February 2001


1. Introduction

   Content Distribution Internetworking (CDI) assumes an architecture
   wherein the resources of multiple CDNs are combined so as to achieve
   a larger scale, or reach, than any of the component CDNs could
   individually [3].  At the core of CDI are three principal
   architectural elements.  These elements are the Request Routing
   System, the Distribution Peering System and the Accounting Peering
   System. The focus of this document, the Distribution Peering System,
   is responsible for moving content from one Distribution CDN to
   another Distribution CDN.  Note that the original content provider
   is considered a degenerate case of a Distribution CDN.

   In any Distribution Peering arrangement, the relationships between
   Distribution CDNs can always be decomposed into one or more pairs of
   CDNs. Each CDN pair comprises one CDN which has, or has access to,
   content, and another CDN which has, or has access to, systems
   capable of providing distribution and/or delivery functions for
   content. The former CDN is referred to as the Content Source, while
   the latter is referred to as the Content Destination.

   This document describes the overall architectural structure and
   building blocks of the Distribution Peering System. It also defines
   the protocol requirements for interconnecting two or more
   Distribution CDNs via their respective Content Peering Gateways
   (CPG). Specifically, it defines the requirements for:

      Distribution Advertising: announcing the distribution
      capabilities of a Content Destination to potential Content
      Sources.

      Content Signaling: enabling consistent storage and delivery of
      content to user agents.

      Content Replication: moving content from a Content Source to a
      Content Destination.

   Although this document does not specifically address requirements
   for communicating within a CDN, it is plausible that protocols
   developed to meet inter-CDN requirements may also be well-suited for
   intra-CDN communications.

   Requirements for the remaining CDI architectural elements, the
   Request Routing System, which is responsible for directing user
   agents to the distributed content, and the Accounting System, which
   is responsible for aggregating information related to the access of
   distributed content, are detailed in [6], [7].




Amini, et. al.          Expires August 20, 2001                 [Page 2]


Internet-Draft     Distribution Peering Requirements       February 2001


1.1 Conventions used in this document

   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 [2].

   All other terms in ALL CAPS, except those qualified with explicit
   citations, are defined in [8].











































Amini, et. al.          Expires August 20, 2001                 [Page 3]


Internet-Draft     Distribution Peering Requirements       February 2001


2. Overview of Distribution Peering System

   In the Distribution Peering System architecture, even the most
   complex communication arrangements can be expressed in terms of
   simple interactions between a Content Source and a Content
   Destination. Figure 1, for example, shows a relationship between
   four different administrative authorities. CDN A operates a network
   of SURROGATES, and "CDN D" (actually the original content provider,
   or ORIGIN) has content to be distributed. CDN A communicates with
   CDN B, who communications with CDN C, who, in turn, communicates
   with CDN D.

      +------------+   +-----------+   +-----------+   +------------+
      |   CDN A    |   |   CDN B   |   |   CDN C   |   |  "CDN D"   |
      |(SURROGATES)|<->|  (agent   |<->|  (agent   |<->| (ORIGIN)   |
      |            |   |   for A)  |   |   for D)  |   |            |
      +------------+   +-----------+   +-----------+   +------------+

        CONTENT DST <-> CONTENT SRC
                        CONTENT DST <-> CONTENT SRC
                                        CONTENT DST <-> CONTENT SRC

      Figure 1: Distribution Peering System Components


   In each case, one of the parties in the communications has the role
   of Content Destination, while the other party is the Content Source.
   Note that a particular CDN's role may change, depending on the party
   with whom it is communicating. CDN B, for example, is a Content
   Source when communicating with CDN A, but a Content Destination when
   communicating with CDN C.

   Note that a Content Destination which peers directly with the
   Content ORIGIN, will interface with the ORIGIN just as it interfaces
   with any other Content Source.

   Although Figure 1 provides an example of multiple CDNs peered in
   series, a Distribution CDN may serve as the Content Source for
   multiple Content Destinations.  Likewise, a Distribution CDN may
   serve as the Content Destination for multiple Content Sources.

   Additionally, it is possible for the peering relationship between a
   single Source-Destination pair to be reciprocal for different
   content sets.  That is, CDN A may request distribution services from
   CDN B for Content Set A, while CDN B requests distribution services
   from CDN A for Content Set B.





Amini, et. al.          Expires August 20, 2001                 [Page 4]


Internet-Draft     Distribution Peering Requirements       February 2001


2.1 Relationship with other CDI components

   Figure 1 showed only the relationships among peered distribution
   systems, it did not show the relationship between these distribution
   systems and the other two CDI components.  The purpose of this
   section is to place the Distribution Peering System into the overall
   CDI context.

2.1.1 CDI Full Peering

   Figure 2 provides a simple example with each of three CDNs peering
   at each CDI layer.

   [Editor's note: I don't like the term "Full Peering," seeking
   suggestions ...Like-Component Peering, Layered Peering,...]



          CDN A                  CDN B                 CDN C
     +---------------+     +---------------+     +---------------+
     |Request Routing|<--->|Request Routing|<--->|Request Routing|
     |...............|     |...............|     |...............|
     | Distribution  |<--->| Distribution  |<--->| Distribution  |
     |...............|     |...............|     |...............|
     |   Accounting  |<--->|  Accounting   |<--->|  Accounting   |
     +---------------+     +---------------+     +---------------+

     Figure 2: CDI Full Peering Example



   As illustrated, the information exchanged between CDI components of
   the same type (denoted by arrows) are inter-CDN exchanges, and
   therefore, are specified by CDI.  However, all information that
   flows between the various CDI components within a given CDN is
   intra-CDN communication; its format is not specified by CDI.  For
   example, the format of information exchanged between the
   Distribution System and the Request Routing System of CDN A is not
   specified by CDI.

   An example of CDI Full Peering occurs when proxies [4] are
   configured to be in the communications path between ORIGIN servers
   and their CLIENTs.  Systems which follow this model are said to be
   "in-line" between the ORIGIN and their CLIENTs. The purpose of the
   proxy may be to cache content closer to the CLIENT (i.e., caching
   proxies) or dynamically export content to a preconfigured CDN.  The
   "dynamic exporter," because it recognizes content which is likely to
   benefit from the services of a CDN, initiates the export of that
   content to a CDN, and then rewrites references to that content so


Amini, et. al.          Expires August 20, 2001                 [Page 5]


Internet-Draft     Distribution Peering Requirements       February 2001


   clients will be directed to the CDN, is often referred to as a "URI
   rewriter."

   This example is a special, or limited, case because there are no
   Request Routing exchanges per se.  Instead, Request Routing is
   generally configured at the CLIENT and intermediate proxies.
   Further, accounting information may not be exchanged.  It is
   provided as an example because it is a well-known, relatively simple
   model of best-effort, implicit mechanisms for distribution
   "peering."  This is in spite of the fact there are currently no
   standardized protocols for the Content Destination to explicitly
   advertise distribution capabilities, for the Content Source to
   explicitly request replication, nor for the Content Source to
   explicitly signal content meta-data.

   In this example, an HTTP proxy identifies itself by inserting the
   "Via" general header into proxied requests [5].  However, this is
   for the purpose of for tracking message forwards, avoiding request
   loops, and identifying the protocol capabilities of senders along
   the request/response chain.  It does not identify the distribution
   capabilities of the intermediary.  HTTP replication is also implicit
   in that content may, or may not, be cached at an intermediary as it
   flows from ORIGIN to CLIENT.  HTTP also provides limited content
   signaling via expiration and cache control headers.

2.1.2 CDI Component Peering

   Now consider a peering relationship in which ORG A is providing
   Accounting and Request Routing functions, but has no Distribution
   capabilities. Distribution functions are provided by peered
   Distribution CDNs, CDN A and CDN B. Within this Distribution Peering
   arrangement, CDN A is a Content Source and CDN B is a Content
   Destination.  This relationship is illustrated in Figure 3.


















Amini, et. al.          Expires August 20, 2001                 [Page 6]


Internet-Draft     Distribution Peering Requirements       February 2001


                            +-----------------------------+
    Request Routing System  |            ORG A            |
                            +-----------------------------+
                                  ^              ^
                                  |              |  (Content Advertisements)
                                  |              |
                            + - - - - - - - - - - - - - - +
                                +-----+       +-----+
    Peered Distribution     |   |CDN A|<----->|CDN B|     |
    System                      +-----+       +-----+
                            + - - - - - - - - - - - - - - +
                                  |              |
                                  |              |   (Access Information)
                                  v              v
                            +-----------------------------+
    Accounting System       |           ORG A             |
                            +-----------------------------+


    Figure 3: CDI Component Peering Example



   As in the previous example, CDN A and CDN B exchange Distribution
   Peering information (i.e., Distribution Advertisements, Content
   Signals and Content Replication) as defined by CDI.  Additionally,
   the CDN A and CDN B send information to the Request Routing and
   Accounting systems. Unlike the previous example, the information
   sent to the Request Routing and Accounting Systems in Figure 3 is
   inter-CDN communication. Content Advertisements are sent to the
   Request Routing System to indicate the content for which a
   particular Distribution CDN will accept requests.  Distribution CDNs
   send Access Information to the Accounting System to report usage and
   accounting events.

   An example of Component Peering occurs when a Content Provider
   relies on an RRS CDN using Layer-7 or DNS [6] redirection to direct
   CLIENTS to SURROGATES which are not in the same administrative
   domain. Current systems generally use proprietary extensions to
   existing protocols to implement CDI Component Peering.

2.2 CDN Peering Gateways for Distribution CDNs

   A Distribution CDN may be peered with other CDNs for Distribution,
   Request Routing (RR) and/or Accounting services. Communications
   between any two CDNs will occur via their respective CPGs.

   For example, Figure 4 illustrates the same relationships described
   for Figure 3, but adds the CPGs for clarity. This three-way peering


Amini, et. al.          Expires August 20, 2001                 [Page 7]


Internet-Draft     Distribution Peering Requirements       February 2001


   relationship is also detailed in [9].

   In Figure 4, only those links marked by an "*" carry inter-CDN
   exchanges. Further, the inter-CDN information exchanged with ORG A
   (by the CPG of either CDN A or CDN B) is Request Routing and
   Accounting information, and is not covered by this document.  Only
   the inter-CDN flow between the CPGs of CDN A and CDN B is a
   Distribution Peering System exchange. The protocol requirements for
   this flow of Distribution Peering information is addressed in this
   document.


          +---------------+
          |    ORG A      |
          |...............|     +--------------+
          |REQUEST ROUTING|<===>|              |
          |...............|     |    CDN       |
          |  ACCOUNTING   |<===>|  PEERING     |
          +---------------+     |  GATEWAY     |
                                |              |
                                +--------------+
                                  ^| ^|   ^| ^|
                                  // //   \\ \\
                                *// //*   *\\ \\*
      +---------------+         // //       \\ \\      +---------------+
      |    CDN A      |        |v |v        |v |v      |    CDN B      |
      |...............|   +---------+    +---------+   |...............|
      |REQUEST ROUTING|<=>|         |    |         |<=>|REQUEST ROUTING|
      |...............|   |   CDN   |  * |   CDN   |   |...............|
      | DISTRIBUTION  |<=>| PEERING |<==>| PEERING |<=>| DISTRIBUTION  |
      |...............|   | GATEWAY |    | GATEWAY |   |...............|
      |  ACCOUNTING   |<=>|         |    |         |<=>|  ACCOUNTING   |
      |---------------|   +---------+    +---------+   +---------------+
             | ^                                            | ^
             v |                                            v |
       +--------------+                               +--------------+
       |  SURROGATES  |                               |  SURROGATES  |
       +--------------+                               +--------------+
                    ^ \                               ^ /
                     \ \         +---------+         / /
                      \ \------->| CLIENTS |--------/ /
                       \---------|         |<--------/
                                 +---------+

      Figure 4: Accounting and Request Direction Across Multiple CDNs






Amini, et. al.          Expires August 20, 2001                 [Page 8]


Internet-Draft     Distribution Peering Requirements       February 2001


3. Replication Models

   Replication of content may take place using a push model, or a pull
   model, or a combination of both.

   o  Use-initiated replication, where SURROGATEs, upon getting a cache
      miss, retrieve CONTENT from the DISTRIBUTION SYSTEM, represents
      the pull model.  This model is currently used by caching proxies.

   o  ORIGIN-initiated replication of CONTENT to SURROGATEs represents
      the push model. This model is used to preposition CONTENT in
      anticipation of demand.

   Replication between the administrative domains of different
   Distribution CDNs will occur via CPGs. Replication within a single
   Distribution CDN is an intra-CDN communication and therefore, need
   not flow through CPGs.  Further, the replication model used within a
   single Distribution CDN need not be the same as the model used to
   replicate CONTENT between CDNs.

   For both ORIGIN- and use- initiated replication, the Content Source
   may use replication mechanisms beyond a simple transfer.  For
   example, it may be desirable to have the Content Destination join a
   multicast channel on which a set of content is pushed to all
   SURROGATES.

   Another example is for CONTINUOUS MEDIA.  In the case of live
   broadcasts, the data may not be cached on the SURROGATES.  Instead,
   replication takes the form of "splitting" the live stream at various
   points in the network. Splitting is also referred to as application
   layer multicast.

   Replication of CONTINUOUS MEDIA streams which are not live, and
   therefore may be stored on SURROGATES, also benefits from mechanisms
   beyond in-line replication. For example, CONTINUOUS MEDIA is often
   delivered to CLIENTS over an unreliable channel.  However, a CDN
   distributing this content to many CLIENTS should work with a full
   replica.  Existing proprietary replication protocols enable
   distribution of CONTINUOUS MEDIA objects in which a full or partial
   replica can be propagated, the data may be encrypted and/or
   authenticated, and the SURROGATE can support CONTINUOUS
   MEDIA-related services such as random access and stream
   insertion/splicing.

   It may be desirable to replicate content to a Distribution CDN which
   has no internal SURROGATES.  For example, a Distribution CDN may
   have servers at key exchange points within the network which only
   serve content to other distribution systems, and peer with other
   CDNs which provide SURROGATES which deliver content to CLIENTS.


Amini, et. al.          Expires August 20, 2001                 [Page 9]


Internet-Draft     Distribution Peering Requirements       February 2001


4. Distribution Peering Requirements

   This section details general requirements for exchange of
   inter-domain distribution information.

4.1 General Requirements

   The goal of the Distribution Peering System is to interconnect the
   Distribution Systems of multiple CDNs.  The intent of this
   interconnection is to effectively position content for fast,
   reliable access by CLIENTs. Generally this is accomplished by
   replicating content on SURROGATEs. While the communications path
   from ORIGIN to CLIENTs may traverse a number of links, some within a
   Distribution CDN and some between Distribution CDNs, the
   Distribution Peering System is concerned only with those
   communications between Distribution CDNs.

   The three main components of the Distribution Peering System are
   advertising, replication, and signaling.

   Advertising: Distribution CDNs SHOULD advertise their capabilities
      to potential Content Source CDNs.

   Replication: Distribution CDNs MUST be able to move content from a
      Content Source to a Content Destination.

   Content signaling: Distribution CDNs MUST be able to propagate
      content meta-data. This meta-data includes information such as
      the immediate expiration of content or a change in the expiration
      time of CONTENT.

   Note that these requirements do not necessarily translate directly
   into three distinct Distribution Peering protocols.

4.2 Advertising Requirements

   The following list specifies requirements to enable advertising of
   distribution capabilities.

   1.  A common protocol for the Advertisement of distribution
       capabilities.

   2.  A common format for the actual distribution capabilities
       Advertisements in the protocol.

   3.  Security mechanisms.





Amini, et. al.          Expires August 20, 2001                [Page 10]


Internet-Draft     Distribution Peering Requirements       February 2001


4.3 Replication Requirements

   The following list specifies requirements to enable content
   replication.

   1.  A common protocol for the replication of content.

   2.  A common format for the actual content data in the protocol.

   3.  A common format for the content meta-data in the protocol.

   4.  Scalable distribution of the content.

   5.  Security mechanisms.

4.4 Content Signaling Requirements

   The following list specifies requirements to enable content
   signaling.

   1.  A common protocol for signaling content meta-data.

   2.  Signals for at least "add," "withdraw," and "expiration time
       update."

   3.  Scalable distribution of signals on a scale to enable
       Internet-wide peering.

   4.  Security mechanisms.






















Amini, et. al.          Expires August 20, 2001                [Page 11]


Internet-Draft     Distribution Peering Requirements       February 2001


5. Distribution Peering System Protocol Requirements

   This section defines protocol requirements for each of the
   advertising, replication and content signaling components of the
   Distribution Peering System.  Note that these requirements do not
   necessarily translate directly into either one converged or three
   distinct Distribution Peering protocols.

5.1 Overview of Distribution Peering Flow

   In a Distribution Peering arrangement, the following sequence of
   events is expected:

   1.  The Content Source will make a decision to request content
       distribution services from a Content Destination.  This decision
       may have been preceded by one or more Content Destinations
       sending distribution capabilities advertisements to the Content
       Source, negotiation of an off-line contractual agreement, or
       some combination.

   2.  The Content Source will send a content signal requesting
       distribution services.

   3.  The Content Destination will accept or reject the request; no
       partial acceptance or negotiation is defined.

       *  If the request is rejected, the error code SHOULD provide
          enough information for the Content Source to determine if it
          should send a request with modified service requirements.

       *  If the request is accepted, the Content Destination will
          prepare for distribution services. Generally, this
          preparation will entail:

          +  retrieving a copy of the object(s),

          +  joining the content update channel, and

          +  preparing to provide access information to the Accounting
             System

       *  Each of the above steps are according to the Content Source's
          specification, and to the Content Destination's policies and
          configuration.

   4.  Once the Content Destination is prepared, it will notify the
       Request Routing System of the content's availability.

   5.  The Content Destination will terminate service on first


Amini, et. al.          Expires August 20, 2001                [Page 12]


Internet-Draft     Distribution Peering Requirements       February 2001


       occurrence of either:

       *  the time frame specified in the Content Source's request for
          distribution services expires or

       *  a content signal requesting withdrawal of the content is
          received.

5.2 General Distribution Peering Protocol Requirements

   Protocols must be scalable, i.e., support Distribution Peering
   Systems on an Internet-wide scale.

   Protocols must prevent looping of advertisements, replication and
   content signaling.

   Protocols must support the ability to optionally conduct
   authenticated and/or encrypted exchanges.

   Protocols must support the ability to optionally exchange
   credentials.

5.3 Advertising Protocol Requirements

   1.  Distribution Peering protocols MUST enable a Content Destination
        to advertise the capabilities of its distribution service in a
        common format.

   2.  The advertisement protocol must be extensible with the
        restriction that implementation-specific capabilities may be
        safely ignored by Content Source.

   3.  Distribution Peering protocols MUST provide low-overhead,
        in-line advertising mechanism to support distribution
        advertising by in-line elements (e.g., proxies).

   4.  The CPG of a Content Destination MAY support Distribution
        Advertising.  That is, a Content Source may not require
        real-time advertisement of distribution capabilities in order
        to establish a Distribution Peering arrangement. Distribution
        capabilities may be communicated via Advertisements or some
        other agreed upon mechanism such as an off-line contract
        negotiated between the parties.

   5.  Advertised capabilities are those available to the peer,
        potentially based on some off-line contractual agreement, and
        may not necessarily reflect the total capacity of the Content
        Destination.



Amini, et. al.          Expires August 20, 2001                [Page 13]


Internet-Draft     Distribution Peering Requirements       February 2001


   6.  A Content Destination MUST be able to advertise multiple service
        profiles. Each profile MUST be specifiable by a profile
        identifier.  The profile identifier MAY encode Content Source
        or Content Destination specific information, but it has local
        significance only (i.e., it is strictly between the Content
        Source and Content Destination).

   7.  A Content Destination MUST be able to advertise multiple
        services profiles to the same or different potential Content
        Sources.

   8.  A Content Destination with regional capabilities SHOULD
        advertise capabilities on a per region basis.  A Content
        Destination which advertises regional capabilities MUST
        minimally be able to identify regions by network
        addresses/prefixes.

   9.  By default, advertisements are advisory. A Content Destination
        SHOULD be able to specify whether the capabilities are advisory
        or binding.

   10.  The protocol MUST provide the ability to specify distribution
        capabilities in terms of one or more of the following
        attributes:

        Profile ID: Profile Identifier for this advertisement to be
           used by the Content Source when requesting service.  This
           attribute is required for all advertisements.  The value
           need not be unique across Distribution CDNs, and may be used
           in advertisements to multiple Content Sources.

        FootPrint: The areas served by the CDN. Minimally, a Content
           Destination should support expressing footprint according to
           IP network addresses/prefixes.

        Content Type: The type of content (e.g. static Web pages,
           streaming media, etc.) that the CDN is able to distribute.

        Capacity: The storage capacity that the CDN can provide.

        Bandwidth: Maximum outbound bandwidth available from the CDN.

        Object Bandwidth: Maximum outbound bandwidth supported for a
           single object.

        Distribution Method: The distribution methods that the CDN
           supports; one or more of push, pull, and alm. "alm" refers
           to application layer multicast, or splitting, of CONTINUOUS
           MEDIA; if specified, supported protocols must also be


Amini, et. al.          Expires August 20, 2001                [Page 14]


Internet-Draft     Distribution Peering Requirements       February 2001


           specified.

              [ Editor's Note: Specifying support for splitting
              requires refinement. ]

        Request Routing Type: Type(s) of Component Peering supported
           for CDI Request Routing Systems.

        Accounting System Format: Supported protocol(s) and format(s)
           for sending accounting and access feedback to a specified
           CDI Accounting System.

        Time Frame: Time frame for which this advertisement is valid.

        Distribution Fee: Indicates the fee charged for distribution
           services.  The value may be expressed in Mbps
           (megabits/second) or in MB (megabytes of storage).

        Advertisement Type: Indicates whether the advertisement is
           advisory or binding.  By default, all advertisements are
           advisory.

        Private Extensions: Additional metrics that the communicating
           parties may agree to use, but are not part of the IETF
           standard. Extensions must be defined such that if not
           understood by the Content Source, they can be safely
           ignored.

5.3.1 Advertising Examples

   To be provided.

5.4 Replication Protocol Requirements

   1.  A common (base) replication protocol MUST be defined which is
       supported by all CPGs, for any content type which can be used to
       transport meta-data and a full replica of content data.

   2.  In-line replication MUST be supported. I.e., it must be possible
       for a Content Source to send a Content Signal which includes the
       data to be distributed.  This mechanism is expected to be used
       only for small objects.

   3.  Replication MUST support the ability for a Content Source to
       specify a replication channel from which content may be
       retrieved.

       1.  [ Editors Note: I am using channel as a generic term which
           would provide a contact point and protocol, and any


Amini, et. al.          Expires August 20, 2001                [Page 15]


Internet-Draft     Distribution Peering Requirements       February 2001


           additional info required to establish a connection.  E.g.
           wcips://invalidation.com/content_set for signaling;  will
           provide clarification later ]

   4.  Replication MUST enable specifying optionally supported,
       alternative replication protocols which may be better suited
       than the common base protocol for specific content types or
       configuration scenarios.

   5.  A Content Source SHOULD be able to specify an authoritative
       source for content as well alternative distribution points.

   6.  The protocol MUST enable replication that is secured (encrypted)
       across the communications channel, as well as content which has
       been source encrypted.

5.4.1 Replication Examples

   To be provided.

5.5 Content Signaling Protocol Requirements

   1.  A Content Source MUST be able to request distribution services
       for one or more content objects.

   2.  A Content Destination MUST explicitly accept or reject a request
       for distribution services.

   3.  A Content Source MUST be able to withdraw (cancel) a request for
       content services for one or multiple content objects.

   4.  Rejected requests for distribution services MUST include error
       codes. Partial rejections or negotiations are not supported.  A
       Content Source may follow a rejection with a request for
       distribution services under alternate service requirements.

   5.  A Content Source MUST be able to signal consistency meta-data.
       Minimally, Content Sources SHOULD support weak consistency
       mechanisms.  Content Sources MAY support mechanisms for strong
       consistency.

   6.  Content signaling SHOULD include mechanisms to aggregate content
       information.

   7.  Content Signaling SHOULD be decoupled from the content ORIGIN.
       I.e., a Content Source should be able to specify a content
       signaling channel.

   8.  The following attributes are defined for content signals:


Amini, et. al.          Expires August 20, 2001                [Page 16]


Internet-Draft     Distribution Peering Requirements       February 2001


       Content ID: A unique identifier for this specific content, so
          that future references (e.g. to modify the content or to
          withdraw it from distribution) may be resolved. This value
          can also be used to avoid loops. The Content ID MUST be
          global and unique, i.e., a given content set MUST have the
          same Content ID across all distribution CDNs in a
          Distribution Peering System, and this ID MUST be unique
          across *all* Distribution Peering Systems.

       URI: The uniform resource identifier for the content. It
          identifies how CLIENTS will request delivery services from
          the Distribution CDN.  This attribute can support an atomic
          unit of content or it can be used to generally specify a URI
          path. For pull distribution, a URI path serves as pattern
          (e.g. http://origin/images/*) to qualify which content should
          receive the specified service. For push distribution, only
          URIs which identify an atomic unit of content may be used.

           [Ed: The editor would prefer further discussion on whether
             this attribute must uniquely identify an atomic unit of
             content or whether it can more generally specify a URI
             path. Allowing paths may significantly reduce the size of
             any protocol transfers, but, there are some attributes
             (e.g. size, content type) that do not apply as cleanly to
             paths, and some distribution methods (e.g. pull) cannot be
             easily accommodate paths.]

       Authoritative Source: Identifies the channel where the
          authoritative copy of the content may be retrieved. In the
          case of live CONTINUOUS MEDIA, this channel may represent
          where the Content Destination may retrieve meta-data required
          to provide application layer multicasting services.

       Distribution Method: Push, pull, on-demand, alm or withdraw.
          Specifies how the Content Destination should retrieve the
          content. Withdraw is a special case that indicates a Content
          Destination should cease distribution of previously accepted
          content.

       Service Profile ID: Identifies the service profile to be
          associated with this request.  The Service Profile ID may
          have been provided by a Content Destination advertisement or
          some other means (e.g. contractual agreement negotiated
          off-line). The identifier MAY encode Content Source or
          Content Destination specific information, but it has local
          significance only (i.e., it is strictly between the Content
          Source and Content Destination).

       Size: Size of the content.


Amini, et. al.          Expires August 20, 2001                [Page 17]


Internet-Draft     Distribution Peering Requirements       February 2001


       Time Frame: The period of time for which the Content Source
          requests distribution.

       Request Routing Type: Type of Request Routing requested for this
          content. Depending on the Request Routing type, an RRS
          channel may also be supplied.

        [ Editor's Note: Request Routing Types to be defined according
          to [6]. ]

       Accounting Format: Format for sending accounting and access
          feedback.

       Accounting Type: Accounting/access feedback type desired.
          Depending on the type requested, an Accounting channel may
          also be supplied. The information conveyed with this
          attribute should also indicate whether the Content
          Destination is required to provide this feedback.

        [ Editor's Note: Accounting Formats and Types to be defined
          according to [7]. ]

       Distribution Authority: Indicates whether the Content
          Destination can serve as the Authoritative Source for this
          content set or if the Authoritative Source attribute must be
          treated as a global attribute. By default, the Content
          Destination can serve as Authoritative Source to Content
          Destinations for which it is the Content Source.

       Mirrors: Alternate channels for retrieving the content.

       Update Channel: Alternate channels for receiving consistency
          signals.  The information conveyed in this attribute should
          also indicate whether the Content Destination is required to
          subscribe to this channel.

       Content Data: The actual content data to be distributed; this is
          expected to be used for small objects only.

       Expires: Indicates the date/time after which this version of the
          content is considered stale.

       Subscription Fee: Specifies the fee charged by the Content
          Source for providing content to the Distribution CDN.

           [ Editor's Note: Subscription Fee was proposed in the
             context of a Distributor model, i.e., the Content Source
             'sells' the content to the Distributor and the Distributor
             is responsible for clients relationship.  My concern is


Amini, et. al.          Expires August 20, 2001                [Page 18]


Internet-Draft     Distribution Peering Requirements       February 2001


             whether this single attribute is enough to help with this
             syndication model -- seeking comments. ]

        [ Editor's Note: Next Hop has also been proposed as an
          attribute, but the editor lacks sufficient understanding to
          describe it; clue injections are solicited. ]

   9.  The following table specifies the relationship between content
       signal types and the defined attributes.


    Attribute                       Add            Update            Withdrawal
    ---------------------           --------      ---------         -----------
    Content ID                      required       required          required
    URI                             required       optional          unsupported
    Service Profile ID              optional       optional          optional
    Authoritative Source            required       optional          unsupported
    Distribution Method             required       optional          unsupported
    Time Frame                      required       optional          required
    Request Routing Type            required       optional          unsupported
    Accounting Format               required       optional          unsupported
    Accounting Type                 required       optional          unsupported
    Mirrors                         optional       optional          unsupported
    Distribution Authority          optional       optional          unsupported
    Update Channel                  optional       optional          unsupported
    Content Data                    optional       optional          unsupported
    Expires                         optional       required          unsupported
    Subscription Fee                optional       optional          unsupported



5.5.1 Content Signaling Examples

   To be provided.

















Amini, et. al.          Expires August 20, 2001                [Page 19]


Internet-Draft     Distribution Peering Requirements       February 2001


6. Security Considerations

   To be provided.
















































Amini, et. al.          Expires August 20, 2001                [Page 20]


Internet-Draft     Distribution Peering Requirements       February 2001


References

   [1]  Bradner, S.O., "The Internet Standards Process -- Revision 3",
        RFC 2026, BCP 9, October 1996.

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

   [3]  Green, M., Cain, B., Tomlinson, G. and S. Thomas, "CDN Peering
        Architectural Overview", January 2001.

   [4]  Cooper, I., Melve, I. and G. Tomlinson, "Internet Web
        Replication and Caching Taxonomy", January 2001.

   [5]  Fielding, R., Gettys, J., Mogul, J., Nielsen, H. and T.
        Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", January
        2001.

   [6]  Cain, B., Spatscheck, O., May, M. and A. Barbir, "Request
        Routing Requirements for Content Internetworking", January 2001.

   [7]  Gilletti, D., Nair, R., Scharber, J. and J. Guha, "Accounting
        Requirements for CDN Internetworking", January 2001.

   [8]  Day, M., Cain, B. and G. Tomlinson, "A Model for Content
        Distribution Internetworking", January 2001.

   [9]  Day, M., Cain, B. and G. Tomlinson, "Content Distribution
        Network Peering Scenarios", January 2001.


Authors' Addresses

   Lisa D. Amini
   IBM Research
   30 Saw Mill River Road
   Hawthorne, NY  10532
   US

   Phone: +1 914 784 7366
   EMail: aminil@us.ibm.com










Amini, et. al.          Expires August 20, 2001                [Page 21]


Internet-Draft     Distribution Peering Requirements       February 2001


   Stephen Thomas
   TransNexus, Inc
   430 Tenth Street NW Suite N204
   Atlanta, GA  30318
   US

   Phone: +1 404 872 4887
   EMail: stephen.thomas@transnexus.com


   Oliver Spatscheck
   AT&T Labs
   180 Park Ave, Bldg 103
   Florham Park, NJ  07932


   Phone:
   EMail: spatsch@research.att.com

































Amini, et. al.          Expires August 20, 2001                [Page 22]


Internet-Draft     Distribution Peering Requirements       February 2001


Appendix A. Acknowledgements

   To be provided.
















































Amini, et. al.          Expires August 20, 2001                [Page 23]


Internet-Draft     Distribution Peering Requirements       February 2001


Full Copyright Statement

   Copyright (C) The Internet Society (2001). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC editor function is currently provided by the
   Internet Society.



















Amini, et. al.          Expires August 20, 2001                [Page 24]