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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 8007

Network Working Group                                          R. Murray
Internet-Draft                                          B. Niven-Jenkins
Intended status: Standards Track                                   Nokia
Expires: November 20, 2016                                  May 19, 2016


                   CDNI Control Interface / Triggers
                  draft-ietf-cdni-control-triggers-15

Abstract

   This document describes the part of the CDN Interconnection Control
   Interface that allows a CDN to trigger activity in an interconnected
   CDN that is configured to deliver content on its behalf.  The
   upstream CDN can use this mechanism to request that the downstream
   CDN pre-positions metadata or content, or that it invalidates or
   purges metadata or content.  The upstream CDN can monitor the status
   of activity that it has triggered in the downstream CDN.

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 November 20, 2016.

Copyright Notice

   Copyright (c) 2016 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.  Model for CDNI Triggers . . . . . . . . . . . . . . . . . . .   4
     2.1.  Timing of Triggered Activity  . . . . . . . . . . . . . .   6
     2.2.  Scope of Triggered Activity . . . . . . . . . . . . . . .   6
       2.2.1.  Multiple Interconnected CDNs  . . . . . . . . . . . .   7
     2.3.  Trigger Results . . . . . . . . . . . . . . . . . . . . .   8
   3.  Collections of Trigger Status Resources . . . . . . . . . . .   8
   4.  CDNI Trigger Interface  . . . . . . . . . . . . . . . . . . .   9
     4.1.  Creating Triggers . . . . . . . . . . . . . . . . . . . .  10
     4.2.  Checking Status . . . . . . . . . . . . . . . . . . . . .  11
       4.2.1.  Polling Trigger Status Resource collections . . . . .  12
       4.2.2.  Polling Trigger Status Resources  . . . . . . . . . .  12
     4.3.  Cancelling Triggers . . . . . . . . . . . . . . . . . . .  12
     4.4.  Deleting Triggers . . . . . . . . . . . . . . . . . . . .  13
     4.5.  Expiry of Trigger Status Resources  . . . . . . . . . . .  14
     4.6.  Loop Detection and Prevention . . . . . . . . . . . . . .  14
     4.7.  Error Handling  . . . . . . . . . . . . . . . . . . . . .  15
     4.8.  Content URLs  . . . . . . . . . . . . . . . . . . . . . .  16
   5.  CI/T Object Properties and Encoding . . . . . . . . . . . . .  16
     5.1.  CI/T Objects  . . . . . . . . . . . . . . . . . . . . . .  16
       5.1.1.  CI/T Commands . . . . . . . . . . . . . . . . . . . .  16
       5.1.2.  Trigger Status Resource . . . . . . . . . . . . . . .  17
       5.1.3.  Trigger Collection  . . . . . . . . . . . . . . . . .  19
     5.2.  Properties of CI/T Objects  . . . . . . . . . . . . . . .  20
       5.2.1.  Trigger Specification . . . . . . . . . . . . . . . .  20
       5.2.2.  Trigger Type  . . . . . . . . . . . . . . . . . . . .  21
       5.2.3.  Trigger Status  . . . . . . . . . . . . . . . . . . .  22
       5.2.4.  PatternMatch  . . . . . . . . . . . . . . . . . . . .  23
       5.2.5.  Absolute Time . . . . . . . . . . . . . . . . . . . .  24
       5.2.6.  Error Description . . . . . . . . . . . . . . . . . .  24
       5.2.7.  Error Code  . . . . . . . . . . . . . . . . . . . . .  25
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  26
     6.1.  Creating Triggers . . . . . . . . . . . . . . . . . . . .  26
       6.1.1.  Preposition . . . . . . . . . . . . . . . . . . . . .  26
       6.1.2.  Invalidate  . . . . . . . . . . . . . . . . . . . . .  28



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     6.2.  Examining Trigger Status  . . . . . . . . . . . . . . . .  29
       6.2.1.  Collection of All Triggers  . . . . . . . . . . . . .  29
       6.2.2.  Filtered Collections of Trigger Status Resources  . .  30
       6.2.3.  Individual Trigger Status Resources . . . . . . . . .  32
       6.2.4.  Polling for Change  . . . . . . . . . . . . . . . . .  34
       6.2.5.  Deleting Trigger Status Resources . . . . . . . . . .  37
       6.2.6.  Error Reporting . . . . . . . . . . . . . . . . . . .  38
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  39
     7.1.  CDNI Payload Type Parameter Registrations . . . . . . . .  40
     7.2.  CDNI CI/T Trigger Types Registry  . . . . . . . . . . . .  40
     7.3.  CDNI CI/T Error Codes Registry  . . . . . . . . . . . . .  40
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  41
     8.1.  Authentication, Authorization, Confidentiality, Integrity
           Protection  . . . . . . . . . . . . . . . . . . . . . . .  41
     8.2.  Denial of Service . . . . . . . . . . . . . . . . . . . .  42
     8.3.  Privacy . . . . . . . . . . . . . . . . . . . . . . . . .  43
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  43
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  43
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  43
     10.2.  Informative References . . . . . . . . . . . . . . . . .  44
   Appendix A.  Formalization of the JSON Data . . . . . . . . . . .  45
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  46

1.  Introduction

   [RFC6707] introduces the problem scope for CDN Interconnection (CDNI)
   and lists the four categories of interfaces that may be used to
   compose a CDNI solution (Control, Metadata, Request Routing,
   Logging).

   [RFC7336] expands on the information provided in [RFC6707] and
   describes each of the interfaces and the relationships between them
   in more detail.

   This document describes the "CI/T" interface, "CDNI Control interface
   / Triggers".  It does not consider those parts of the control
   interface that relate to configuration, bootstrapping or
   authentication of CDN Interconnect interfaces.  Section 4 of
   [RFC7337] identifies the requirements specific to the CI interface,
   requirements applicable to the CI/T interface are CI-1 to CI-6.

   o  Section 2 outlines the model for the CI/T Interface at a high
      level.

   o  Section 3 describes collections of Trigger Status Resources.

   o  Section 4 defines the web service provided by the dCDN.




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   o  Section 5 lists properties of CI/T Commands and Status Resources.

   o  Section 6 contains example messages.

1.1.  Terminology

   This document reuses the terminology defined in [RFC6707] and uses
   "uCDN" and "dCDN" as shorthand for "Upstream CDN" and "Downstream
   CDN", respectively.

2.  Model for CDNI Triggers

   A CI/T Command, sent from the uCDN to the dCDN, is a request for the
   dCDN to do some work relating to data associated with content
   requests originating from the uCDN.

   There are two types of CI/T Command: CI/T Trigger Commands, and CI/T
   Cancel Commands.  The CI/T Cancel Command can be used to request
   cancellation of an earlier CI/T Trigger Command.  A CI/T Trigger
   Command is of one of the following types:

   o  preposition - used to instruct the dCDN to fetch metadata from the
      uCDN, or content from any origin including the uCDN.

   o  invalidate - used to instruct the dCDN to revalidate specific
      metadata or content before re-using it.

   o  purge - used to instruct the dCDN to delete specific metadata or
      content.

   The CI/T interface is a web service offered by the dCDN.  It allows
   CI/T commands to be issued, and triggered activity to be tracked.
   The CI/T interface builds on top of HTTP/1.1 [RFC7230].  References
   to URL in this document relate to http/https URIs, as defined in
   [RFC7230] section 2.7.

   When the dCDN accepts a CI/T Command it creates a resource describing
   status of the triggered activity, a Trigger Status Resource.  The
   uCDN can poll Trigger Status Resources to monitor progress.

   The dCDN maintains at least one collection of Trigger Status
   Resources for each uCDN.  Each uCDN only has access to its own
   collections, the locations of which are shared when CDN
   interconnection is established.

   To trigger activity in the dCDN, the uCDN POSTs a CI/T Command to the
   collection of Trigger Status Resources.  If the dCDN accepts the CI/T
   Command, it creates a new Trigger Status Resource and returns its



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   location to the uCDN.  To monitor progress, the uCDN can GET the
   Trigger Status Resource.  To request cancellation of a CI/T Trigger
   Command the uCDN can POST to the collection of Trigger Status
   Resources, or simply DELETE the Trigger Status Resource.

   In addition to the collection of all Trigger Status Resources for the
   uCDN, the dCDN can maintain filtered views of that collection.  These
   filtered views are defined in Section 3 and include collections of
   Trigger Status Resources corresponding to active and completed CI/T
   Trigger Commands.  These collections provide a mechanism for polling
   the status of multiple jobs.

   Figure 1 is an example showing the basic message flow used by the
   uCDN to trigger activity in the dCDN, and for the uCDN to discover
   the status of that activity.  Only successful triggering is shown.
   Examples of the messages are given in Section 6.

      uCDN                                                   dCDN
       |    (1) POST https://dcdn.example.com/triggers/uCDN    |
      [ ] --------------------------------------------------> [ ]--+
       |                                                      [ ]  | (2)
       |    (3) HTTP 201 Response                             [ ]<-+
      [ ] <-------------------------------------------------- [ ]
       |     Loc: https://dcdn.example.com/triggers/uCDN/123   |
       |                                                       |
       .                           .                           .
       .                           .                           .
       .                           .                           .
       |                                                       |
       |   (4) GET https://dcdn.example.com/triggers/uCDN/123  |
      [ ] --------------------------------------------------> [ ]
       |                                                      [ ]
       |   (5) HTTP 200 Trigger Status Resource               [ ]
      [ ] <-------------------------------------------------- [ ]
       |                                                       |
       |                                                       |

              Figure 1: Basic CDNI Message Flow for Triggers

   The steps in Figure 1 are:

   1.  The uCDN triggers action in the dCDN by posting a CI/T Command to
       a collection of Trigger Status Resources,
       "https://dcdn.example.com/triggers/uCDN".  The URL of this was
       given to the uCDN when the CI/T interface was established.






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   2.  The dCDN authenticates the request, validates the CI/T Command
       and, if it accepts the request, creates a new Trigger Status
       Resource.

   3.  The dCDN responds to the uCDN with an HTTP 201 response status,
       and the location of the Trigger Status Resource.

   4.  The uCDN can poll, possibly repeatedly, the Trigger Status
       Resource in the dCDN.

   5.  The dCDN responds with the Trigger Status Resource, describing
       progress or results of the CI/T Trigger Command.

   The remainder of this document describes the messages, Trigger Status
   Resources, and collections of Trigger Status Resources in more
   detail.

2.1.  Timing of Triggered Activity

   Timing of the execution of CI/T Commands is under the dCDN's control,
   including its start-time and pacing of the activity in the network.

   CI/T invalidate and purge commands MUST be applied to all data
   acquired before the command was accepted by the dCDN.  The dCDN
   SHOULD NOT apply CI/T invalidate and purge commands to data acquired
   after the CI/T Command was accepted, but this may not always be
   achievable so the uCDN cannot count on that.

   If the uCDN wishes to invalidate or purge content then immediately
   pre-position replacement content at the same URLs, it SHOULD ensure
   the dCDN has completed the invalidate/purge before initiating the
   prepositioning.  Otherwise, there is a risk that the dCDN pre-
   positions the new content, then immediately invalidates or purges it
   (as a result of the two uCDN requests running in parallel).

   Because the CI/T Command timing is under the dCDN's control, the dCDN
   implementation can choose whether to apply CI/T invalidate and purge
   commands to content acquisition that has already started when the
   command is received.

2.2.  Scope of Triggered Activity

   Each CI/T Command can operate on multiple metadata and content URLs.

   Multiple representations of an HTTP resource may share the same URL.
   CI/T Trigger Commands that invalidate or purge metadata or content
   apply to all resource representations with matching URLs.




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2.2.1.  Multiple Interconnected CDNs

   In a network of interconnected CDNs a single uCDN will originate a
   given item of metadata and associated content, it may distribute that
   metadata and content to more than one dCDN, which may in-turn
   distribute that metadata and content to further-downstream CDNs.

   An intermediate CDN is a dCDN that passes on CDNI metadata and
   content to further-downstream dCDNs.

   A diamond configuration is one where a dCDN can acquire metadata and
   content originated in one uCDN from that uCDN itself and an
   intermediate CDN, or via more than one intermediate CDN.

   CI/T commands originating in the single source uCDN affect metadata
   and content in all dCDNs but, in a diamond configuration, it may not
   be possible for the dCDN to determine which uCDN it acquired content
   from.  In this case a dCDN MUST allow each uCDN from which it may
   have acquired the content to act upon that content using CI/T
   Commands.

   In all other cases, a dCDN MUST reject CI/T Commands from a uCDN that
   act on another uCDN's data using, for example, HTTP "403 Forbidden".

   Security considerations are discussed further in Section 8.

   The diamond configuration may lead to inefficient interactions, but
   the interactions are otherwise harmless.  For example:

   o  When the uCDN issues an invalidate CI/T command, a dCDN will
      receive that command from multiple directly connected uCDNs.  The
      dCDN may schedule multiple those commands separately, and the last
      may affect content already revalidated following execution of the
      invalidate command scheduled first.

   o  If one of a dCDN's directly-connected uCDNs loses its rights to
      distribute content, it may issue a CI/T purge command.  That purge
      may affect content the dCDN could retain because it's distributed
      by another directly-connected uCDN.  But, that content can be re-
      acquired by the dCDN from the remaining uCDN.

   o  When the uCDN originating an item of content issues a CI/T purge
      followed by a preposition - two directly connected uCDNs will pass
      those commands to a dCDN.  That dCDN implementation need not merge
      those operations, or notice the repetition.  In which case the
      purge issued by one uCDN will complete before the other.  The
      first uCDN to finish its purge may then forward the preposition
      trigger, and content pre-positioned as a result might be affected



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      by the still-running purge issued by the other uCDN.  However, the
      dCDN will re-acquire that content as needed, or when it's asked to
      pre-position the content by the second uCDN.  A dCDN
      implementation could avoid this interaction by knowing which uCDN
      it acquired the content from, or it could minimize the
      consequences by recording the time at which the invalidate/purge
      command was received and not applying it to content acquired after
      that time.

2.3.  Trigger Results

   Possible states for a Trigger Status Resource are defined in section
   Section 5.2.3.

   The CI/T Trigger Command MUST NOT be reported as 'complete' until all
   actions have been completed successfully.  The reasons for failure,
   and URLs or Patterns affected, SHOULD be enumerated in the Trigger
   Status Resource.  For more detail, see section Section 4.7.

   If a dCDN is also acting as a uCDN in a cascade, it MUST forward CI/T
   Commands to any downstream CDNs that may be affected.  The CI/T
   Trigger Command MUST NOT be reported as 'complete' in a CDN until it
   is 'complete' in all of its downstream CDNs.  If a CI/T Trigger
   Command is reported as 'processed' in any dCDN, intermediate CDNs
   MUST NOT report 'complete', instead they MUST also report
   'processed'.  A CI/T Command MAY be reported as 'failed' as soon as
   it fails in a CDN or in any of its downstream CDNs.  A cancelled CI/T
   Trigger Command MUST be reported as 'cancelling' until it has been
   reported as 'cancelled', 'complete', or 'failed' by all dCDNs in a
   cascade.

3.  Collections of Trigger Status Resources

   As described in Section 2, Trigger Status Resources exist in the dCDN
   to report the status of activity triggered by each uCDN.

   A collection of Trigger Status Resources is a resource that contains
   a reference to each Trigger Status Resource in that collection.

   The dCDN MUST make a collection of a uCDN's Trigger Status Resources
   available to that uCDN.  This collection includes all of the Trigger
   Status Resources created for CI/T Commands from the uCDN that have
   been accepted by the dCDN, and have not yet been deleted by the uCDN,
   or expired and removed by the dCDN (as described in section
   Section 4.4).  Trigger Status Resources belonging to a uCDN MUST NOT
   be visible to any other CDN.  The dCDN could, for example, achieve
   this by offering different collection URLs to each uCDN, and by




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   filtering the response based on the uCDN with which the HTTP client
   is associated.

   To trigger activity in a dCDN, or to cancel triggered activity, the
   uCDN POSTs a CI/T Command to the dCDN's collection of the uCDN's
   Trigger Status Resources.

   In order to allow the uCDN to check the status of multiple jobs in a
   single request, the dCDN MAY also maintain collections representing
   filtered views of the collection of all Trigger Status Resources.
   These filtered collections are optional-to-implement but, if
   implemented, the dCDN MUST include links to them in the collection of
   all Trigger Status Resources.  The filtered collections are:

   o  Pending - Trigger Status Resources for CI/T Trigger Commands that
      have been accepted, but not yet acted upon.

   o  Active - Trigger Status Resources for CI/T Trigger Commands that
      are currently being processed in the dCDN.

   o  Complete - Trigger Status Resources representing activity that
      completed successfully, and 'processed' CI/T Trigger Commands for
      which no further status updates will be made by the dCDN.

   o  Failed - Trigger Status Resources representing CI/T Commands that
      failed or were cancelled by the uCDN.

4.  CDNI Trigger Interface

   This section describes an interface to enable an upstream CDN to
   trigger activity in a downstream CDN.

   The CI/T interface builds on top of HTTP, so dCDNs may make use of
   any HTTP feature when implementing the CI/T interface.  For example,
   a dCDN SHOULD make use of HTTP's caching mechanisms to indicate that
   a requested response/representation has not been modified, reducing
   the uCDN's processing needed to determine whether the status of
   triggered activity has changed.

   All dCDNs implementing CI/T MUST support the HTTP GET, HEAD, POST and
   DELETE methods as defined in [RFC7231].

   The only representation specified in this document is JSON,
   [RFC7159].  It MUST be supported by the uCDN and by the dCDN.

   The URL of the dCDN's collection of all Trigger Status Resources
   needs to be either discovered by, or configured in, the uCDN.  The




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   mechanism for discovery of that URL is outside the scope of this
   document.

   CI/T Commands are POSTed to the dCDN's collection of all Trigger
   Status Resources.  If a CI/T Trigger Command is accepted by the dCDN,
   the dCDN creates a new Trigger Status Resource and returns its URI to
   the uCDN in an HTTP 201 response.  The triggered activity can then be
   monitored by the uCDN using that resource and the collections
   described in Section 3.

   The URI of each Trigger Status Resource is returned to the uCDN when
   it is created, and URIs of all Trigger Status Resources are listed in
   the dCDN's collection of all Trigger Status Resources.  This means
   all Trigger Status Resources can be discovered by the uCDN, so dCDNs
   are free to assign whatever structure they desire to the URIs for CI/
   T resources.  Therefore uCDNs MUST NOT make any assumptions regarding
   the structure of CI/T URIs or the mapping between CI/T objects and
   their associated URIs.  URIs present in the examples in this document
   are purely illustrative and are not intended to impose a definitive
   structure on CI/T interface implementations.

4.1.  Creating Triggers

   To issue a CI/T Command, the uCDN makes an HTTP POST to the dCDN's
   collection of all of the uCDN's Trigger Status Resources.  The
   request body of that POST is a CI/T Command, as described in
   Section 5.1.1.

   The dCDN validates the CI/T Command.  If the command is malformed or
   the uCDN does not have sufficient access rights, the dCDN MUST either
   respond with an appropriate 4xx HTTP error code and not create a
   Trigger Status Resource, or create a 'failed' Trigger Status Resource
   containing an appropriate error description.

   When a CI/T Trigger Command is accepted, the uCDN MUST create a new
   Trigger Status Resource which will convey a specification of the CI/T
   Command and its current status.  The HTTP response to the dCDN MUST
   have status code 201 and MUST convey the URI of the Trigger Status
   Resource in the Location header field.  The HTTP response SHOULD
   include the content of the newly created Trigger Status Resource.
   This is particularly important in cases where the CI/T Trigger
   Command has completed immediately.

   Once a Trigger Status Resource has been created the dCDN MUST NOT re-
   use its URI, even after that Trigger Status Resource has been
   removed.





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   The dCDN SHOULD track and report on progress of CI/T Trigger Commands
   using a Trigger Status Resource, Section 5.1.2.  If the dCDN is not
   able to do that, it MUST indicate that it has accepted the request
   but will not be providing further status updates.  To do this, it
   sets the status of the Trigger Status Resource to "processed".  In
   this case, CI/T processing should continue as for a "complete"
   request, so the Trigger Status Resource MUST be added to the dCDN's
   collection of Complete Trigger Status Resources.  The dCDN SHOULD
   also provide an estimated completion time for the request, by using
   the "etime" property of the Trigger Status Resource.  This will allow
   the uCDN to schedule prepositioning after an earlier delete of the
   same URLs is expected to have finished.

   If the dCDN is able to track the execution of CI/T Commands and a CI/
   T Command is queued by the dCDN for later action, the status property
   of the Trigger Status Resource MUST be "pending".  Once processing
   has started the "status" MUST be "active".  Finally, once the CI/T
   Command is complete, the status MUST be set to "complete" or
   "failed".

   A CI/T Trigger Command may result in no activity in the dCDN if, for
   example, it is an invalidate or purge request for data the dCDN has
   not yet acquired, or a pre-position request for data it has already
   acquired and which is still valid.  In this case, the "status" of the
   Trigger Status Resource MUST be "processed" or "complete", and the
   Trigger Status Resource MUST be added to the dCDN's collection of
   Complete Trigger Status Resources.

   Once created, Trigger Status Resources can be cancelled or deleted by
   the uCDN, but not modified.  The dCDN MUST reject PUT and POST
   requests from the uCDN to Trigger Status Resources by responding with
   an appropriate HTTP status code, for example 405 "Method Not
   Allowed".

4.2.  Checking Status

   The uCDN has two ways to check progress of CI/T Commands it has
   issued to the dCDN, described in sections Section 4.2.1 and
   Section 4.2.2.

   To allow the uCDN to check for change in status of a Trigger Status
   Resource or collection of Trigger Status Resources without re-
   fetching the whole Resource or Collection, the dCDN SHOULD include
   Entity Tags for the uCDN to use as cache validators, as defined in
   [RFC7232].






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   The dCDN SHOULD use the cache control headers for responses to GETs
   for Trigger Status Resources and Collections to indicate the
   frequency at which it recommends the uCDN should poll for change.

4.2.1.  Polling Trigger Status Resource collections

   The uCDN can fetch the collection of its Trigger Status Resources, or
   filtered views of that collection.

   This makes it possible to poll status of all CI/T Trigger Commands in
   a single request.  If the dCDN moves a Trigger Status Resource from
   the Active to the Completed collection, the uCDN can fetch the result
   of that activity.

   When polling in this way, the uCDN SHOULD use HTTP Entity Tags to
   monitor for change, rather than repeatedly fetching the whole
   collection.  An example of this is given in section Section 6.2.4.

4.2.2.  Polling Trigger Status Resources

   The uCDN has a URI provided by the dCDN for each Trigger Status
   Resource it has created, it may fetch that Trigger Status Resource at
   any time.

   This can be used to retrieve progress information, and to fetch the
   result of the CI/T Command.

   When polling in this way, the uCDN SHOULD use HTTP Entity Tags to
   monitor for change, rather than repeatedly fetching the Trigger
   Status Resource.

4.3.  Cancelling Triggers

   The uCDN can request cancellation of a CI/T Trigger Command by
   POSTing a CI/T Cancel Command to the collection of all Trigger Status
   Resources.

   The dCDN is required to accept and respond to the CI/T Cancel
   Command, but the actual cancellation of a CI/T Trigger Command is
   optional-to-implement.

   The dCDN MUST respond to the CI/T Cancel Command appropriately, for
   example with HTTP status code 200 "OK" if the cancellation has been
   processed and the CI/T Command is inactive, 202 "Accepted" if the
   command has been accepted but the CI/T Command remains active, or 501
   "Not Implemented" if cancellation is not supported by the dCDN.





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   If cancellation of a "pending" Trigger Status Resource is accepted by
   the dCDN, the dCDN SHOULD NOT start processing of that activity.
   Issuing a CT/T Cancel Command for a "pending" Trigger Status Resource
   does not however guarantee that the corresponding activity will not
   be started, because the uCDN cannot control the timing of that
   activity.  Processing could, for example, start after the POST is
   sent by the uCDN but before that request is processed by the dCDN.

   If cancellation of an "active" or "processed" Trigger Status Resource
   is accepted by the dCDN, the dCDN SHOULD stop processing the CI/T
   Command.  However, as with cancellation of a "pending" CI/T Command,
   the dCDN does not guarantee this.

   If the CI/T Command cannot be stopped immediately, the status in the
   corresponding Trigger Status Resource MUST be set to "cancelling",
   and the Trigger Status Resource MUST remain in the collection of
   Trigger Status Resources for active CI/T Commands.  If processing is
   stopped before normal completion, the status value in the Trigger
   Status Resource MUST be set to "cancelled", and the Trigger Status
   Resource MUST be included in the collection of failed CT/T Trigger
   Commands.

   Cancellation of a "complete" or "failed" Trigger Status Resource
   requires no processing in the dCDN.  Its status MUST NOT be changed
   to "cancelled".

4.4.  Deleting Triggers

   The uCDN can delete Trigger Status Resources at any time, using the
   HTTP DELETE method.  The effect is similar to cancellation, but no
   Trigger Status Resource remains afterwards.

   Once deleted, the references to a Trigger Status Resource MUST be
   removed from all Trigger Status Resource collections.  Subsequent
   requests to GET the deleted Trigger Status Resource SHOULD be
   rejected by the dCDN with an HTTP error.

   If a "pending" Trigger Status Resource is deleted, the dCDN SHOULD
   NOT start processing of that activity.  Deleting a "pending" Trigger
   Status Resource does not however guarantee that it has not started
   because the uCDN cannot control the timing of that activity.
   Processing may, for example, start after the DELETE is sent by the
   uCDN but before that request is processed by the dCDN.

   If an "active" or "processed" Trigger Status Resource is deleted, the
   dCDN SHOULD stop processing the CI/T Command.  However, as with
   deletion of a "pending" Trigger Status Resource, the dCDN does not
   guarantee this.



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   Deletion of a "complete" or "failed" Trigger Status Resource requires
   no processing in the dCDN other than deletion of the Trigger Status
   Resource.

4.5.  Expiry of Trigger Status Resources

   The dCDN can choose to automatically delete Trigger Status Resources
   some time after they become "complete", "processed", "failed" or
   "cancelled".  In this case, the dCDN will remove the Trigger Status
   Resource and respond to subsequent requests for it with an HTTP
   error.

   If the dCDN does remove Trigger Status Resources automatically, it
   MUST report the length of time after which it will do so, using a
   property of the collection of all Trigger Status Resources.  It is
   RECOMMENDED that Trigger Status Resources are not automatically
   deleted by the dCDN for at least 24 hours after they become
   "complete", "processed", "failed" or "cancelled".

   To ensure it is able to get the status of its Trigger Status
   Resources for completed and failed CI/T Commands, it is RECOMMENDED
   that the uCDN polling interval is less than the time after which
   records for completed activity will be deleted.

4.6.  Loop Detection and Prevention

   Given three CDNs, A, B and C, if CDNs B and C delegate delivery of
   CDN A's content to each other, CDN A's CI/T Commands could be passed
   between CDNs B and C in a loop.  More complex networks of CDNs could
   contain similar loops involving more hops.

   In order to prevent and detect such CI/T loops, each CDN uses a CDN
   Provider ID to uniquely identify itself.  In every CI/T Command it
   originates or cascades, each CDN MUST append an array element
   containing its CDN Provider ID to a JSON array under an entry named
   "cdn-path".  When receiving CI/T Commands a dCDN MUST check the cdn-
   path and reject any CI/T Command which already contains its own CDN
   Provider ID in the cdn-path.  Transit CDNs MUST check the cdn-path
   and not cascade the CI/T Command to dCDNs that are already listed in
   cdn-path.

   The CDN Provider Id consists of the two characters "AS" followed by
   the CDN Provider's Autonomous System number [RFC1930], then a colon
   (':') and an additional qualifier that is used to guarantee
   uniqueness in case a particular AS has multiple independent CDNs
   deployed.  For example "AS64496:0".





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   If the CDN provider has multiple Autonomous Systems, the same AS
   number SHOULD be used in all messages from that CDN provider, unless
   there are multiple distinct CDNs.

   If the RI interface described in [I-D.ietf-cdni-redirection] is
   implemented by the dCDN, the CI/T and RI interfaces SHOULD use the
   same CDN Provider Id.

4.7.  Error Handling

   A dCDN can signal rejection of a CI/T Command using HTTP status
   codes.  For example, 400 if the request is malformed, or 403 or 404
   if the uCDN does not have permission to issue CI/T Commands or it is
   trying to act on another CDN's data.

   If any part of the CI/T Trigger Command fails, the trigger SHOULD be
   reported as "failed" once its activity is complete or if no further
   errors will be reported.  The "errors" property in the Trigger Status
   Resource will be used to enumerate which actions failed and the
   reasons for failure, and can be present while the Trigger Status
   Resource is still "pending" or "active", if the CI/T Trigger Command
   is still running for some URLs or Patterns in the Trigger
   Specification.

   Once a request has been accepted, processing errors are reported in
   the Trigger Status Resource using a list of Error Descriptions.  Each
   Error Description is used to report errors against one or more of the
   URLs or Patterns in the Trigger Specification.

   If a surrogate affected by a CI/T Trigger Command is offline in the
   dCDN, or the dCDN is unable to pass a CI/T Command on to any of its
   cascaded dCDNs:

   o  If the CI/T Command is abandoned by the dCDN, the dCDN SHOULD
      report an error.

   o  A CI/T "invalidate" command may be reported as "complete" when
      surrogates that may have the data are offline.  In this case,
      surrogates MUST NOT use the affected data without first
      revalidating it when they are back online.

   o  CI/T "preposition" and "purge" commands can be reported as
      "processed" if affected caches are offline and the activity will
      complete when they return to service.

   o  Otherwise, the dCDN SHOULD keep the Trigger Status Resource in
      state "pending" or "active" until the CI/T Command is acted upon,
      or the uCDN chooses to cancel it.



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4.8.  Content URLs

   If content URLs are transformed by an intermediate CDN in a cascade,
   that intermediate CDN MUST similarly transform URLs in CI/T Commands
   it passes to its dCDN.

   When processing Trigger Specifications, CDNs MUST ignore the URL
   scheme (http or https) in comparing URLs.  For example, for a CI/T
   invalidate or purge command, content MUST be invalidated or purged
   regardless of the protocol clients use to request it.

5.  CI/T Object Properties and Encoding

   The CI/T Commands, Trigger Status Resources and Trigger Collections
   and their properties are encoded using JSON, as defined in sections
   Section 5.1.1, Section 5.2.1, and Section 5.1.2.  They MUST use the
   MIME Media Type 'application/cdni', with parameter 'ptype' values as
   defined below and in Section 7.1.

   Names in JSON are case sensitive.  The names and literal values
   specified in the present document MUST always use lower-case.

   JSON types, including 'object', 'array', 'number' and 'string' are
   defined in [RFC7159].

   Unrecognised name/value pairs in JSON objects SHOULD NOT be treated
   as an error by either the uCDN or dCDN.  They SHOULD be ignored in
   the processing, and passed on by dCDN to any further dCDNs in a
   cascade.

5.1.  CI/T Objects

   The top-level objects defined by the CI/T interface are described in
   this section.

   The encoding of values used by these objects is described in
   Section 5.2.

5.1.1.  CI/T Commands

   CI/T Commands MUST use a MIME Media Type of 'application/cdni;
   ptype=ci-trigger-command'.

   A CI/T Command is encoded as a JSON object containing the following
   name/value pairs.

      Name: trigger




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         Description: A specification of the trigger type, and a set of
         data to act upon.

         Value: A Trigger Specification, as defined in Section 5.2.1.

         Mandatory: No, but exactly one of "trigger" or "cancel" MUST be
         present in a CI/T Command.

      Name: cancel

         Description: The URLs of Trigger Status Resources for CI/T
         Trigger Commands that the uCDN wants to cancel.

         Value: A non-empty JSON array of URLs represented as JSON
         strings.

         Mandatory: No, but exactly one of "trigger" or "cancel" MUST be
         present in a CI/T Command.

      Name: cdn-path

         Description: The CDN Provider Identifiers of CDNs that have
         already issued the CI/T Command to their dCDNs.

         Value: A non-empty JSON array of JSON strings, where each
         string is a CDN Provider Identifier as defined in Section 4.6.

         Mandatory: Yes.

5.1.2.  Trigger Status Resource

   Trigger Status Resources MUST use a MIME Media Type of 'application/
   cdni; ptype=ci-trigger-status'.

   A Trigger Status Resource is encoded as a JSON object containing the
   following name/value pairs.

      Name: trigger

         Description: The Trigger Specification posted in the body of
         the CI/T Command.  Note that this need not be a byte-for-byte
         copy.  For example, in the JSON representation the dCDN may re-
         serialise the information differently.

         Value: A Trigger Specification, as defined in Section 5.2.1.

         Mandatory: Yes




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      Name: ctime

         Description: Time at which the CI/T Command was received by the
         dCDN.  Time is determined by the dCDN, there is no requirement
         to synchronise clocks between interconnected CDNs.

         Value: Absolute Time, as defined in Section 5.2.5.

         Mandatory: Yes

      Name: mtime

         Description: Time at which the Trigger Status Resource was last
         modified.  Time is determined by the dCDN, there is no
         requirement to synchronise clocks between interconnected CDNs.

         Value: Absolute Time, as defined in Section 5.2.5.

         Mandatory: Yes

      Name: etime

         Description: Estimate of the time at which the dCDN expects to
         complete the activity.  Time is determined by the dCDN, there
         is no requirement to synchronise clocks between interconnected
         CDNs.

         Value: Absolute Time, as defined in Section 5.2.5.

         Mandatory: No

      Name: status

         Description: Current status of the triggered activity.

         Value: Trigger Status, as defined in Section 5.2.3.

         Mandatory: Yes

      Name: errors

         Description: Descriptions of errors that have occurred while
         processing a Trigger Command.

         Value: An array of Error Description, as defined in
         Section 5.2.6.  An empty array is allowed, and equivalent to
         omitting "errors" from the object.




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         Mandatory: No.

5.1.3.  Trigger Collection

   Trigger Collections MUST use a MIME Media Type of 'application/cdni;
   ptype=ci-trigger-collection'.

   A Trigger Collection is encoded as a JSON object containing the
   following name/value pairs.

      Name: triggers

         Description: Links to Trigger Status Resources in the
         collection.

         Value: A JSON array of zero or more URLs, represented as JSON
         strings.

         Mandatory: Yes

      Name: staleresourcetime

         Description: The length of time for which the dCDN guarantees
         to keep a completed Trigger Status Resource.  After this time,
         the dCDN SHOULD delete the Trigger Status Resource and all
         references to it from collections.

         Value: A JSON number, which must be a positive integer,
         representing time in seconds.

         Mandatory: Yes, in the collection of all Trigger Status
         Resources if the dCDN deletes stale entries.  If the property
         is present in the filtered collections, it MUST have the same
         value as in the collection of all Trigger Status Resources.

      Names: coll-all, coll-pending, coll-active, coll-complete, coll-
      failed

         Description: Link to a Trigger Collection.

         Value: A URL represented as a JSON string.

         Mandatory: Links to all of the filtered collections are
         mandatory in the collection of all Trigger Status Resources, if
         the dCDN implements the filtered collections.  Otherwise,
         optional.

      Name: cdn-id



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         Description: The CDN Provider Identifier of the dCDN.

         Value: A JSON string, the dCDN's CDN Provider Identifier, as
         defined in Section 4.6.

         Mandatory: Only in the collection of all Trigger Status
         Resources, if the dCDN implements the filtered collections.
         Optional in the filtered collections (the uCDN can always find
         the dCDN's cdn-id in the collection of all Trigger Status
         Resources, but the dCDN can choose to repeat that information
         in its implementation of filtered collections).

5.2.  Properties of CI/T Objects

   This section defines the values that can appear in the top level
   objects described in Section 5.1, and their encodings.

5.2.1.  Trigger Specification

   A Trigger Collection is encoded as a JSON object containing the
   following name/value pairs.

   An unrecognised name/value pair in the Trigger Specification object
   contained in a CI/T Command SHOULD be preserved in the Trigger
   Specification of any Trigger Status Resource it creates.

      Name: type

         Description: This property defines the type of the CI/T Trigger
         Command.

         Value: Trigger Type, as defined in Section 5.2.2.

         Mandatory: Yes

      Name: metadata.urls

         Description: The uCDN URLs of the metadata the CI/T Trigger
         Command applies to.

         Value: A JSON array of URLs represented as JSON strings.

         Mandatory: No, but at least one of 'metadata.*' or 'content.*'
         MUST be present and non-empty.

      Name: content.urls





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         Description: URLs of content the CI/T Trigger Command applies
         to, see Section 4.8.

         Value: A JSON array of URLs represented as JSON strings.

         Mandatory: No, but at least one of 'metadata.*' or 'content.*'
         MUST be present and non-empty.

      Name: content.ccid

         Description: The Content Collection Identifier of content the
         trigger applies to.  The 'ccid' is a grouping of content, as
         defined by [I-D.ietf-cdni-metadata].

         Value: A JSON array of strings, where each string is a Content
         Collection Identifier.

         Mandatory: No, but at least one of 'metadata.*' or 'content.*'
         MUST be present and non-empty.

      Name: metadata.patterns

         Description: The metadata the trigger applies to.

         Value: A JSON array of Pattern Match, as defined in
         Section 5.2.4.

         Mandatory: No, but at least one of 'metadata.*' or 'content.*'
         MUST be present and non-empty, and metadata.patterns MUST NOT
         be present if the TriggerType is Preposition.

      Name: content.patterns

         Description: The content data the trigger applies to.

         Value: A JSON array of Pattern Match, as defined in
         Section 5.2.4.

         Mandatory: No, but at least one of 'metadata.*' or 'content.*'
         MUST be present and non-empty, and content.patterns MUST NOT be
         present if the TriggerType is Preposition.

5.2.2.  Trigger Type

   Trigger Type is used in a Trigger Specification to describe trigger
   action.





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   All trigger types MUST be registered in the IANA CI/T Trigger Types
   registry (see Section 7.2).

   A dCDN receiving a request containing a trigger type it does not
   recognise or does not support MUST reject the request by creating a
   Trigger Status Resource with status to "failed" and the "errors"
   array containing an Error Description with error "eunsupported".

   The following trigger types are defined by this document:

   +-------------+-----------------------------------------------------+
   | JSON String | Description                                         |
   +-------------+-----------------------------------------------------+
   | preposition | A request for the dCDN to acquire metadata or       |
   |             | content.                                            |
   | invalidate  | A request for the dCDN to invalidate metadata or    |
   |             | content. After servicing this request the dCDN will |
   |             | not use the specified data without first re-        |
   |             | validating it using, for example, an "If-None-      |
   |             | Match" HTTP request. The dCDN need not erase the    |
   |             | associated data.                                    |
   | purge       | A request for the dCDN to erase metadata or         |
   |             | content. After servicing the request, the specified |
   |             | data MUST NOT be held on the dCDN (the dCDN should  |
   |             | re-acquire the metadata or content from uCDN if it  |
   |             | needs it).                                          |
   +-------------+-----------------------------------------------------+

5.2.3.  Trigger Status

   This describes the current status of a Trigger.  It MUST be one of
   the JSON strings in the following table:



















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   +------------+------------------------------------------------------+
   | JSON       | Description                                          |
   | String     |                                                      |
   +------------+------------------------------------------------------+
   | pending    | The CI/T Trigger Command has not yet been acted      |
   |            | upon.                                                |
   | active     | The CI/T Trigger Command is currently being acted    |
   |            | upon.                                                |
   | complete   | The CI/T Trigger Command completed successfully.     |
   | processed  | The CI/T Trigger Command has been accepted and no    |
   |            | further status update will be made (can be used in   |
   |            | cases where completion cannot be confirmed).         |
   | failed     | The CI/T Trigger Command could not be completed.     |
   | cancelling | Processing of the CI/T Trigger Command is still in   |
   |            | progress, but the CI/T Trigger Command has been      |
   |            | cancelled by the uCDN.                               |
   | cancelled  | The CI/T Trigger Command was cancelled by the uCDN.  |
   +------------+------------------------------------------------------+

5.2.4.  PatternMatch

   A Pattern Match consists of a string pattern to match against a URI,
   and flags describing the type of match.

   It is encoded as a JSON object with the following name/value pairs:

      Name: pattern

         Description: A pattern for URI matching.

         Value: A JSON string representing the pattern.  The pattern may
         contain the wildcards * and ?, where * matches any sequence of
         characters (including the empty string) and ? matches exactly
         one character.  The three literals "\" , "*" and "?"  MUST be
         escaped as "\\", "\*" and "\?".

         Mandatory: Yes.

      Name: case-sensitive

         Description: Flag indicating whether or not case-sensitive
         matching should be used.

         Value: One of the JSON values 'true' (the matching is case-
         sensitive) or 'false' (the matching is case-insensitive).

         Mandatory: No, default is case-insensitive match.




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      Name: match-query-string

         Description: Flag indicating whether or not the query part of
         the URI should be included in the pattern match.

         Value: One of the JSON values 'true' (the full URI including
         the query part should be compared against the given pattern),
         or 'false' (the query part of the URI should be dropped before
         comparison with the given pattern).

         Mandatory: No, default is 'false', the query part of the URI
         should be dropped before comparison with the given pattern.

   Example of case-sensitive prefix match against
   "https://www.example.com/trailers/":

   {
       "pattern": "https://www.example.com/trailers/*",
       "case-sensitive": true
   }

5.2.5.  Absolute Time

   A JSON number, seconds since the UNIX epoch, 00:00:00 UTC on 1
   January 1970.

5.2.6.  Error Description

   An Error Description is used to report failure of a CI/T Command, or
   in the activity it triggered.  It is encoded as a JSON object with
   the following name/value pairs:

      Name: error

         Value: Error Code, as defined in Section 5.2.7.

         Mandatory: Yes.

      Names: metadata.urls, content.urls, metadata.patterns,
      content.patterns

         Description: Metadata and content references copied from the
         Trigger Specification.  Only those URLs and patterns to which
         the error applies are included in each property, but those URLs
         and patterns MUST be exactly as they appear in the request, the
         dCDN MUST NOT generalise the URLs.  (For example, if the uCDN
         requests prepositioning of URLs "https://content.example.com/a"
         and "https://content.example.com/b", the dCDN must not



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         generalise its error report to Pattern
         "https://content.example.com/*".)

         Value: A JSON array of JSON strings, where each string is
         copied from a 'content.*' or 'metadata.*' value in the
         corresponding Trigger Specification.

         Mandatory: At least one of these name/value pairs is mandatory
         in each Error Description object.

      Name: description

         Description: A human-readable description of the error.

         Value: A JSON string, the human-readable description.

         Mandatory: No.

5.2.7.  Error Code

   This type is used by the dCDN to report failures in trigger
   processing.  All error codes MUST be registered in the IANA CI/T
   Error Codes registry (see Section 7.3).  Unknown error codes MUST be
   treated as fatal errors, and the request MUST NOT be automatically
   retried without modification.

   The following error codes are defined by this document, and MUST be
   supported by an implementation of the CI/T interface.























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   +--------------+----------------------------------------------------+
   | Error Code   | Description                                        |
   +--------------+----------------------------------------------------+
   | emeta        | The dCDN was unable to acquire metadata required   |
   |              | to fulfil the request.                             |
   | econtent     | The dCDN was unable to acquire content (CT/T       |
   |              | preposition commands only).                        |
   | eperm        | The uCDN does not have permission to issue the     |
   |              | CI/T Command (for example, the data is owned by    |
   |              | another CDN).                                      |
   | ereject      | The dCDN is not willing to fulfil the CI/T Command |
   |              | (for example, a preposition request for content at |
   |              | a time when the dCDN would not accept Request      |
   |              | Routing requests from the uCDN).                   |
   | ecdn         | An internal error in the dCDN or one of its        |
   |              | downstream CDNs.                                   |
   | ecancelled   | The uCDN cancelled the request.                    |
   | eunsupported | The Trigger Specification contained a "type" that  |
   |              | is not supported by the dCDN. No action was taken  |
   |              | bythe dCDN other than to create a Trigger Status   |
   |              | Resource in state "failed".                        |
   +--------------+----------------------------------------------------+

6.  Examples

   The following sections provide examples of different CI/T objects
   encoded as JSON.

   Discovery of the triggers interface is out of scope of this document.
   In an implementation, all CI/T URLs are under the control of the
   dCDN.  The uCDN MUST NOT attempt to ascribe any meaning to individual
   elements of the path.

   In examples in this section, the URL 'https://dcdn.example.com/
   triggers' is used as the location of the collection of all Trigger
   Status Resources, and the CDN Provider Id of uCDN is "AS64496:1".

6.1.  Creating Triggers

   Examples of the uCDN triggering activity in the dCDN:

6.1.1.  Preposition

   An example of a CI/T preposition command, a POST to the collection of
   all Trigger Status Resources.

   Note that "metadata.patterns" and "content.patterns" are not allowed
   in a preposition Trigger Specification.



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   REQUEST:

     POST /triggers HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*
     Content-Type: application/cdni; ptype=ci-trigger-command
     Content-Length: 352

     {
       "trigger" : {
         "type": "preposition",

         "metadata.urls" : [ "https://metadata.example.com/a/b/c" ],
         "content.urls" : [
             "https://www.example.com/a/b/c/1",
             "https://www.example.com/a/b/c/2",
             "https://www.example.com/a/b/c/3",
             "https://www.example.com/a/b/c/4"
           ]
       },
       "cdn-path" : [ "AS64496:1" ]
     }

   RESPONSE:

     HTTP/1.1 201 Created
     Date: Wed, 04 May 2016 08:48:10 GMT
     Content-Length: 467
     Content-Type: application/cdni; ptype=ci-trigger-status
     Location: https://dcdn.example.com/triggers/0
     Server: example-server/0.1

     {
         "ctime": 1462351690,
         "etime": 1462351698,
         "mtime": 1462351690,
         "status": "pending",
         "trigger": {
             "content.urls": [
                 "https://www.example.com/a/b/c/1",
                 "https://www.example.com/a/b/c/2",
                 "https://www.example.com/a/b/c/3",
                 "https://www.example.com/a/b/c/4"
             ],
             "metadata.urls": [
                 "https://metadata.example.com/a/b/c"
             ],



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             "type": "preposition"
         }
     }

6.1.2.  Invalidate

   An example of a CI/T invalidate command, another POST to the
   collection of all Trigger Status Resources.  This instructs the dCDN
   to re-validate the content at "https://www.example.com/a/index.html",
   as well as any metadata and content whose URLs are prefixed by
   "https://metadata.example.com/a/b/" using case-insensitive matching,
   and "https://www.example.com/a/b/" respectively, using case-sensitive
   matching.

   REQUEST:

     POST /triggers HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*
     Content-Type: application/cdni; ptype=ci-trigger-command
     Content-Length: 387

     {
       "trigger" : {
         "type": "invalidate",

         "metadata.patterns" : [
             { "pattern" : "https://metadata.example.com/a/b/*" }
           ],

         "content.urls" : [ "https://www.example.com/a/index.html" ],
         "content.patterns" : [
             { "pattern" : "https://www.example.com/a/b/*",
               "case-sensitive" : true
             }
           ]
       },
       "cdn-path" : [ "AS64496:1" ]
     }

   RESPONSE:

     HTTP/1.1 201 Created
     Date: Wed, 04 May 2016 08:48:11 GMT
     Content-Length: 545
     Content-Type: application/cdni; ptype=ci-trigger-status
     Location: https://dcdn.example.com/triggers/1



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     Server: example-server/0.1

     {
         "ctime": 1462351691,
         "etime": 1462351699,
         "mtime": 1462351691,
         "status": "pending",
         "trigger": {
             "content.patterns": [
                 {
                     "case-sensitive": true,
                     "pattern": "https://www.example.com/a/b/*"
                 }
             ],
             "content.urls": [
                 "https://www.example.com/a/index.html"
             ],
             "metadata.patterns": [
                 {
                     "pattern": "https://metadata.example.com/a/b/*"
                 }
             ],
             "type": "invalidate"
         }
     }

6.2.  Examining Trigger Status

   Once Trigger Status Resources have been created, the uCDN can check
   their status as shown in these examples.

6.2.1.  Collection of All Triggers

   The uCDN can fetch the collection of all Trigger Status Resources it
   has created that have not yet been deleted or removed as expired.
   After creation of the "preposition" and "invalidate" triggers shown
   above, this collection might look as follows:














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   REQUEST:

     GET /triggers HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*


   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 341
     Expires: Wed, 04 May 2016 08:49:11 GMT
     Server: example-server/0.1
     ETag: "-936094426920308378"
     Cache-Control: max-age=60
     Date: Wed, 04 May 2016 08:48:11 GMT
     Content-Type: application/cdni; ptype=ci-trigger-collection

     {
         "cdn-id": "AS64496:0",
         "coll-active": "/triggers/active",
         "coll-complete": "/triggers/complete",
         "coll-failed": "/triggers/failed",
         "coll-pending": "/triggers/pending",
         "staleresourcetime": 86400,
         "triggers": [
             "https://dcdn.example.com/triggers/0",
             "https://dcdn.example.com/triggers/1"
         ]
     }

6.2.2.  Filtered Collections of Trigger Status Resources

   The filtered collections are also available to the uCDN.  Before the
   dCDN starts processing the two CI/T Trigger Commands shown above,
   both will appear in the collection of Pending Triggers, for example:














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   REQUEST:

     GET /triggers/pending HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*


   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 152
     Expires: Wed, 04 May 2016 08:49:11 GMT
     Server: example-server/0.1
     ETag: "4331492443626270781"
     Cache-Control: max-age=60
     Date: Wed, 04 May 2016 08:48:11 GMT
     Content-Type: application/cdni; ptype=ci-trigger-collection

     {
         "staleresourcetime": 86400,
         "triggers": [
             "https://dcdn.example.com/triggers/0",
             "https://dcdn.example.com/triggers/1"
         ]
     }

   At this point, if no other Trigger Status Resources had been created,
   the other filtered views would be empty.  For example:






















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   REQUEST:

     GET /triggers/complete HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*


   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 54
     Expires: Wed, 04 May 2016 08:49:11 GMT
     Server: example-server/0.1
     ETag: "7958041393922269003"
     Cache-Control: max-age=60
     Date: Wed, 04 May 2016 08:48:11 GMT
     Content-Type: application/cdni; ptype=ci-trigger-collection

     {
         "staleresourcetime": 86400,
         "triggers": []
     }

6.2.3.  Individual Trigger Status Resources

   The Trigger Status Resources can also be examined for detail about
   individual CI/T Trigger Commands.  For example, for the CI/T
   "preposition" and "invalidate" commands from previous examples:






















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   REQUEST:

     GET /triggers/0 HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*


   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 467
     Expires: Wed, 04 May 2016 08:49:10 GMT
     Server: example-server/0.1
     ETag: "6990548174277557683"
     Cache-Control: max-age=60
     Date: Wed, 04 May 2016 08:48:10 GMT
     Content-Type: application/cdni; ptype=ci-trigger-status

     {
         "ctime": 1462351690,
         "etime": 1462351698,
         "mtime": 1462351690,
         "status": "pending",
         "trigger": {
             "content.urls": [
                 "https://www.example.com/a/b/c/1",
                 "https://www.example.com/a/b/c/2",
                 "https://www.example.com/a/b/c/3",
                 "https://www.example.com/a/b/c/4"
             ],
             "metadata.urls": [
                 "https://metadata.example.com/a/b/c"
             ],
             "type": "preposition"
         }
     }














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   REQUEST:

     GET /triggers/1 HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*


   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 545
     Expires: Wed, 04 May 2016 08:49:11 GMT
     Server: example-server/0.1
     ETag: "-554385204989405469"
     Cache-Control: max-age=60
     Date: Wed, 04 May 2016 08:48:11 GMT
     Content-Type: application/cdni; ptype=ci-trigger-status

     {
         "ctime": 1462351691,
         "etime": 1462351699,
         "mtime": 1462351691,
         "status": "pending",
         "trigger": {
             "content.patterns": [
                 {
                     "case-sensitive": true,
                     "pattern": "https://www.example.com/a/b/*"
                 }
             ],
             "content.urls": [
                 "https://www.example.com/a/index.html"
             ],
             "metadata.patterns": [
                 {
                     "pattern": "https://metadata.example.com/a/b/*"
                 }
             ],
             "type": "invalidate"
         }
     }

6.2.4.  Polling for Change

   The uCDN SHOULD use the Entity Tags of collections or Trigger Status
   Resources when polling for change in status, as shown in the
   following examples:



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   REQUEST:

     GET /triggers/pending HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*
     If-None-Match: "4331492443626270781"


   RESPONSE:

     HTTP/1.1 304 Not Modified
     Content-Length: 0
     Expires: Wed, 04 May 2016 08:49:11 GMT
     Server: example-server/0.1
     ETag: "4331492443626270781"
     Cache-Control: max-age=60
     Date: Wed, 04 May 2016 08:48:11 GMT
     Content-Type: application/cdni; ptype=ci-trigger-collection

   REQUEST:

     GET /triggers/0 HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*
     If-None-Match: "6990548174277557683"


   RESPONSE:

     HTTP/1.1 304 Not Modified
     Content-Length: 0
     Expires: Wed, 04 May 2016 08:49:10 GMT
     Server: example-server/0.1
     ETag: "6990548174277557683"
     Cache-Control: max-age=60
     Date: Wed, 04 May 2016 08:48:10 GMT
     Content-Type: application/cdni; ptype=ci-trigger-status

   When the CI/T Trigger Command is complete, the contents of the
   filtered collections will be updated along with their Entity Tags.
   For example, when the two example CI/T Trigger Commands are complete,
   the collections of pending and complete Trigger Status Resources
   might look like:






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   REQUEST:

     GET /triggers/pending HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*


   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 54
     Expires: Wed, 04 May 2016 08:49:15 GMT
     Server: example-server/0.1
     ETag: "1337503181677633762"
     Cache-Control: max-age=60
     Date: Wed, 04 May 2016 08:48:15 GMT
     Content-Type: application/cdni; ptype=ci-trigger-collection

     {
         "staleresourcetime": 86400,
         "triggers": []
     }




























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   REQUEST:

     GET /triggers/complete HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*


   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 152
     Expires: Wed, 04 May 2016 08:49:22 GMT
     Server: example-server/0.1
     ETag: "4481489539378529796"
     Cache-Control: max-age=60
     Date: Wed, 04 May 2016 08:48:22 GMT
     Content-Type: application/cdni; ptype=ci-trigger-collection

     {
         "staleresourcetime": 86400,
         "triggers": [
             "https://dcdn.example.com/triggers/0",
             "https://dcdn.example.com/triggers/1"
         ]
     }

6.2.5.  Deleting Trigger Status Resources

   The uCDN can delete completed and failed Trigger Status Resources to
   reduce the size of the collections, as described in Section 4.4.  For
   example, to delete the "preposition" request from earlier examples:

   REQUEST:

     DELETE /triggers/0 HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*


   RESPONSE:

     HTTP/1.1 204 No Content
     Date: Wed, 04 May 2016 08:48:22 GMT
     Content-Length: 0
     Content-Type: text/html; charset=UTF-8
     Server: example-server/0.1



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   This would, for example, cause the collection of completed Trigger
   Status Resources shown in the example above to be updated to:

   REQUEST:

     GET /triggers/complete HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*


   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 105
     Expires: Wed, 04 May 2016 08:49:22 GMT
     Server: example-server/0.1
     ETag: "-6938620031669085677"
     Cache-Control: max-age=60
     Date: Wed, 04 May 2016 08:48:22 GMT
     Content-Type: application/cdni; ptype=ci-trigger-collection

     {
         "staleresourcetime": 86400,
         "triggers": [
             "https://dcdn.example.com/triggers/1"
         ]
     }

6.2.6.  Error Reporting

   In this example the uCDN has requested prepositioning of
   "https://newsite.example.com/index.html", but the dCDN was unable to
   locate metadata for that site:

















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   REQUEST:

     GET /triggers/2 HTTP/1.1
     User-Agent: example-user-agent/0.1
     Host: dcdn.example.com
     Accept: */*


   RESPONSE:

     HTTP/1.1 200 OK
     Content-Length: 486
     Expires: Wed, 04 May 2016 08:49:26 GMT
     Server: example-server/0.1
     ETag: "5182824839919043757"
     Cache-Control: max-age=60
     Date: Wed, 04 May 2016 08:48:26 GMT
     Content-Type: application/cdni; ptype=ci-trigger-status

     {
         "ctime": 1462351702,
         "errors": [
             {
                 "content.urls": [
                     "https://newsite.example.com/index.html"
                 ],
                 "description": "newsite.example.com not in HostIndex",
                 "error": "emeta"
             }
         ],
         "etime": 1462351710,
         "mtime": 1462351706,
         "status": "active",
         "trigger": {
             "content.urls": [
                 "https://newsite.example.com/index.html"
             ],
             "type": "preposition"
         }
     }

7.  IANA Considerations

   [RFC Editor Note: Please replace references to [RFCthis] in this
   section with this document's RFC number before publication.]






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7.1.  CDNI Payload Type Parameter Registrations

   The IANA is requested to register the following new Payload Types in
   the CDNI Payload Type Parameter registry defined by [RFC7736], for
   use with the 'application/cdni' MIME media type.

                 +-----------------------+---------------+
                 | Payload Type          | Specification |
                 +-----------------------+---------------+
                 | ci-trigger-command    | [RFCthis]     |
                 | ci-trigger-status     | [RFCthis]     |
                 | ci-trigger-collection | [RFCthis]     |
                 +-----------------------+---------------+

7.2.  CDNI CI/T Trigger Types Registry

   The IANA is requested to create a new "CDNI CI/T Trigger Types"
   subregistry under the "Content Delivery Networks Interconnection
   (CDNI) Parameters" registry.

   Additions to the CDNI CI/T Error Code Registry will be made via "RFC
   Required" as defined in [RFC5226].

   The initial contents of the CDNI CI/T Trigger Types Registry comprise
   the names and descriptions listed in section Section 5.2.2 of this
   document, with this document acting as the specification.

7.3.  CDNI CI/T Error Codes Registry

   The IANA is requested to create a new "CDNI CI/T Error Codes"
   subregistry under the "Content Delivery Networks Interconnection
   (CDNI) Parameters" registry.

   Additions to the CDNI CI/T Error Codes Registry will be made via
   "Specification Required" as defined in [RFC5226].  The Designated
   Expert will verify that new error code registrations do not duplicate
   existing error code definitions (in name or functionality), prevent
   gratuitous additions to the namespace, and prevent any additions to
   the namespace that would impair the interoperability of CDNI
   implementations.

   The initial contents of the CDNI CI/T Error Codes Registry comprise
   the names and descriptions of the Error Codes listed in Section 5.2.7
   of this document, with this document acting as the specification.







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8.  Security Considerations

   The CI/T interface provides a mechanism to allow a uCDN to generate
   requests into the dCDN and to inspect its own CI/T requests and their
   current state.  The CI/T interface does not allow access to or
   modification of the uCDN or dCDN metadata relating to content
   delivery, or to the content itself.  It can only control the presence
   of that metadata in the dCDN, and the processing work and network
   utilisation involved in ensuring that presence.

   By examining pre-positioning requests to a dCDN, and correctly
   interpreting content and metadata URLs, an attacker could learn the
   uCDN or content owner's predictions for future content popularity.
   By examining invalidate or purge requests, an attacker could learn
   about changes in the content owner's catalogue.

   By injecting CI/T commands an attacker, or a misbehaving uCDN, would
   generate work in the dCDN and uCDN as they process those requests.
   And so would a man in the middle attacker modifying valid CI/T
   commands generated by the uCDN.  In both cases, that would decrease
   the dCDN caching efficiency by causing it to unnecessarily acquire or
   re-acquire content metadata and/or content.

   A dCDN implementation of CI/T MUST restrict the actions of a uCDN to
   the data corresponding to that uCDN.  Failure to do so would allow
   uCDNs to detrimentally affect each other's efficiency by generating
   unnecessary acquisition or re-acquisition load.

   An origin that chooses to delegate its delivery to a CDN is trusting
   that CDN to deliver content on its behalf, CDN-interconnection is an
   extension of that trust to downstream CDNs.  That trust relationship
   is a commercial arrangement, outside the scope of the CDNi protocols.
   So, while a malicious CDN could deliberately generate load on a dCDN
   using the CI/T, the protocol does not otherwise attempt to address
   malicious behaviour between interconnected CDNs.

8.1.  Authentication, Authorization, Confidentiality, Integrity
      Protection

   A CI/T implementation MUST support TLS transport for HTTP (https) as
   per [RFC2818] and [RFC7230].

   TLS MUST be used by the server-side (dCDN) and the client-side (uCDN)
   of the CI/T interface, including authentication of the remote end,
   unless alternate methods are used for ensuring the security of the
   information in the CI/T interface requests and responses (such as
   setting up an IPsec tunnel between the two CDNs or using a physically




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   secured internal network between two CDNs that are owned by the same
   corporate entity).

   The use of TLS for transport of the CI/T interface allows:

   o  The dCDN and the uCDN to authenticate each other using TLS client
      auth and TLS server auth.

   And, once they have mutually authenticated each other, it allows:

   o  The dCDN and the uCDN to authorize each other (to ensure they are
      receiving CI/T Commands from, or reporting status to, an
      authorized CDN).

   o  CDNI commands and responses to be transmitted with
      confidentiality.

   o  Protection of the integrity of CDNI commands and responses.

   When TLS is used, the general TLS usage guidance in [RFC7525] MUST be
   followed.

   The mechanisms for access control are dCDN-specific, not standardised
   as part of this CI/T specification.

   HTTP requests that attempt to access or operate on CI/T data
   belonging to another CDN MUST be rejected using, for example, HTTP
   "403 Forbidden" or "404 Not Found".  This is intended to prevent
   unauthorised users from generating unnecessary load in dCDN or uCDN
   due to revalidation, reacquisition, or unnecessary acquisition.

   When deploying a network of interconnected CDNs, the possible
   inefficiencies related to the "diamond" configuration discussed in
   Section 2.2.1 should be considered.

8.2.  Denial of Service

   This document does not define a specific mechanism to protect against
   Denial of Service (DoS) attacks on the CI/T.  However, CI/T endpoints
   can be protected against DoS attacks through the use of TLS transport
   and/or via mechanisms outside the scope of the CI/T interface, such
   as firewalling or use of Virtual Private Networks (VPNs).

   Depending on the implementation, triggered activity may consume
   significant processing and bandwidth in the dCDN.  A malicious or
   faulty uCDN could use this to generate unnecessary load in the dCDN.
   The dCDN should consider mechanisms to avoid overload, for example by




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   rate-limiting acceptance or processing of CI/T Commands, or batching
   up its processing.

8.3.  Privacy

   The CI/T protocol does not carry any information about individual End
   Users of a CDN, there are no privacy concerns for End Users.

   The CI/T protocol does carry information which could be considered
   commercially sensitive by CDN operators and content owners.  The use
   of mutually authenticated TLS to establish a secure session for the
   transport of CI/T data, as discussed in Section 8.1, provides
   confidentiality while the CI/T data is in transit, and prevents
   parties other than the authorised dCDN from gaining access to that
   data.  The dCDN MUST ensure that it only exposes CI/T data related to
   a uCDN to clients it has authenticated as belonging to that uCDN.

9.  Acknowledgements

   The authors thank Kevin Ma for his input, and Carsten Bormann for his
   review and formalization of the JSON data.

10.  References

10.1.  Normative References

   [I-D.ietf-cdni-metadata]
              Niven-Jenkins, B., Murray, R., Caulfield, M., and K. Ma,
              "CDN Interconnection Metadata", draft-ietf-cdni-
              metadata-16 (work in progress), April 2016.

   [RFC1930]  Hawkinson, J. and T. Bates, "Guidelines for creation,
              selection, and registration of an Autonomous System (AS)",
              BCP 6, RFC 1930, DOI 10.17487/RFC1930, March 1996,
              <http://www.rfc-editor.org/info/rfc1930>.

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

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.






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   [RFC6707]  Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
              Distribution Network Interconnection (CDNI) Problem
              Statement", RFC 6707, September 2012.

   [RFC7159]  Bray, T., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, March 2014.

   [RFC7230]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Message Syntax and Routing", RFC 7230, June
              2014.

   [RFC7231]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Semantics and Content", RFC 7231, June 2014.

   [RFC7232]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Conditional Requests", RFC 7232, June 2014.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, May 2015.

10.2.  Informative References

   [I-D.greevenbosch-appsawg-cbor-cddl]
              Vigano, C. and H. Birkholz, "CBOR data definition language
              (CDDL): a notational convention to express CBOR data
              structures", draft-greevenbosch-appsawg-cbor-cddl-08 (work
              in progress), March 2016.

   [I-D.ietf-cdni-redirection]
              Niven-Jenkins, B. and R. Brandenburg, "Request Routing
              Redirection interface for CDN Interconnection", draft-
              ietf-cdni-redirection-18 (work in progress), April 2016.

   [RFC7336]  Peterson, L., Davie, B., and R. van Brandenburg,
              "Framework for Content Distribution Network
              Interconnection (CDNI)", RFC 7336, August 2014.

   [RFC7337]  Leung, K. and Y. Lee, "Content Distribution Network
              Interconnection (CDNI) Requirements", RFC 7337, August
              2014.

   [RFC7736]  Ma, K., "Content Delivery Network Interconnection (CDNI)
              Media Type Registration", RFC 7736, DOI 10.17487/RFC7736,
              December 2015, <http://www.rfc-editor.org/info/rfc7736>.





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Appendix A.  Formalization of the JSON Data

   This appendix is non-normative.

   The JSON data described in this document has been formalised using
   CDDL [I-D.greevenbosch-appsawg-cbor-cddl] as follows:

 CIT-object = CIT-command / Trigger-Status-Resource / Trigger-Collection

 CIT-command ; use media type application/cdni; ptype=ci-trigger-command
 = {
   ? trigger: Triggerspec
   ? cancel: [* URI]
   cdn-path: [* Cdn-PID]
 }

 Trigger-Status-Resource ; application/cdni; ptype=ci-trigger-status
 = {
   trigger: Triggerspec
   ctime: Absolute-Time
   mtime: Absolute-Time
   ? etime: Absolute-Time
   status: Trigger-Status
   ? errors: [* Error-Description]
 }

 Trigger-Collection ; application/cdni; ptype=ci-trigger-collection
 = {
   triggers: [* URI]
   ? staleresourcetime: int ; time in seconds
   ? coll-all: URI
   ? coll-pending: URI
   ? coll-active: URI
   ? coll-complete: URI
   ? coll-failed: URI
   ? cdn-id: Cdn-PID
 }

 Triggerspec = { ; 5.2.1
   type: Trigger-Type
   ? metadata.urls: [* URI]
   ? content.urls: [* URI]
   ? content.ccid: [* Ccid]
   ? metadata.patterns: [* Pattern-Match]
   ? content.patterns: [* Pattern-Match]
 }

 Trigger-Type = "preposition" / "invalidate" / "purge" ; 5.2.2



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 Trigger-Status = "pending" / "active" / "complete" / "processed"
    / "failed" / "cancelling" / "cancelled" ; 5.2.3

 Pattern-Match = { ; 5.2.4
   pattern: tstr
   ? case-sensitive: bool
   ? match-query-string: bool
 }

 Absolute-Time = number ; seconds since UNIX epoch, 5.2.5

 Error-Description = { ; 5.2.6
   error: Error-Code
   ? metadata.urls: [* URI]
   ? content.urls: [* URI]
   ? metadata.patterns: [* Pattern-Match]
   ? content.patterns: [* Pattern-Match]
   ? description: tstr
 }

 Error-Code = "emeta" / "econtent" / "eperm" / "ereject"
    / "ecdn" / "ecancelled"  ; 5.2.7

 Ccid = tstr ; see I-D.ietf-cdni-metadata

 Cdn-PID = tstr .regexp "AS[0-9]+:[0-9]+"

 URI = tstr

Authors' Addresses

   Rob Murray
   Nokia
   3 Ely Road
   Milton, Cambridge  CB24 6DD
   UK

   Email: rob.murray@nokia.com


   Ben Niven-Jenkins
   Nokia
   3 Ely Road
   Milton, Cambridge  CB24 6DD
   UK

   Email: ben.niven-jenkins@nokia.com




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