RFC4078 - The TV-Anytime Content Reference Identifier (CRID)

Network Working Group                                        N. Earnshaw
Request for Comments: 4078                  BBC Research and Development
Category: Informational                                          S. Aoki
                                                    TokyoFM Broadcasting
                                                               A. Ashley
                                                             NDS Limited
                                                             W. Kameyama
                                                 GITS, Waseda University
                                                                May 2005


           The TV-Anytime Content Reference Identifier (CRID)

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   The Uniform Resource Locator (URL) scheme "CRID:" has been devised to
   allow references to current or future scheduled publications of
   broadcast media content over television distribution platforms and
   the Internet.

   The initial intended application is as an embedded link within
   scheduled programme description metadata that can be used by the home
   user or agent to associate a programme selection with the
   corresponding programme location information for subsequent automatic
   acquisition.

   This document reproduces the TV-Anytime CRID definition found in the
   TV-Anytime content referencing specification, and is published as an
   RFC for ease of access and registration with the Internet Assigned
   Numbers Authority (IANA).

Table of Contents

   1. Introduction ....................................................2
   2. Ancestry ........................................................3
   3. Notation Used in This Document ..................................3
   4. The CRID URL Scheme .............................................3
   5. Examples of CRID Syntax .........................................4
   6. Usage ...........................................................4
      6.1. Normative Specification ....................................4
      6.2. Role of Domain Name System (DNS) Namespace .................5
      6.3. CRID Resolving .............................................5
      6.4. CRID Related Metadata ......................................5
   7. IANA Considerations .............................................6
      7.1. General ....................................................6
      7.2. Registration Template in Accordance with RFC 2717 ..........6
   8. Security Considerations .........................................7
   9. Acknowledgements ................................................7
   10. References .....................................................8
       10.1. Normative References .....................................8
       10.2. Informative References ...................................8

1.  Introduction

   In recent years there has been an expansion in the number of
   broadcast television and radio services available to the home.  In
   addition to the broadcast services delivered over traditional
   distribution channels such as Digital Terrestrial, Satellite and
   Cable, the advent of high-speed Internet connection will give rise to
   even more information and entertainment services, providing audio-
   visual programme material sourced directly to the home over the
   Internet.

   Alongside this expansion there has also been increased growth in
   complexity of devices available to the home user, which will allow
   the user to operate in a 'search-select-acquire' paradigm.  In this
   model, the user or user agent uses descriptive information about
   audio visual programmes as a basis for selecting the programme for
   subsequent acquisition and viewing.  Increasingly, home appliances
   are being furnished with local storage, enabling the automatic
   capture of programme material through off-air recording or
   downloading by a home appliance.

   The 'CRID:' Uniform Resource Locator is designed to be the bridge
   between programme-related descriptive metadata and corresponding
   programme location data that may be published over a different
   distribution network or at a different time.

   Programme location data provides the home user agent with the
   information required to acquire the programme at the time of
   publication.  In the case of the television distribution model, these
   locators provide programme broadcast timing and tuning information so
   that the user appliance can record the programme when it is broadcast
   in real time.  In the case of Internet delivery, the locators have to
   be of the form associated with streaming protocols or file exchange
   protocols with the time (or time window) of availability indicated.

   Because a content publisher may release audio-video material in the
   same form on a number of platforms or repeatedly over some time
   interval, the CRID can be used to aggregate these different
   publications and associate them with a single description.
   Furthermore, there may be other meaningful semantic associations
   between otherwise unrelated programme publications with assigned CRID
   that can be further aggregated under a higher-level CRID.  This
   higher-level CRID can be described through its own descriptive
   metadata.  The subjective nature of these aggregation decisions is
   part of the CRID authoring process and is not standardised.

   The CRID resolution process ultimately enabling the user agent to
   acquire audio-visual programme material may be a timely process, with
   resolution updates delivered dynamically from the service provider.
   This is to reflect common business practice of adjusting the time of
   content availability close to the original published time to
   accommodate a live, managed, reactive broadcast service.

2.  Ancestry

   The Uniform Resource Locator scheme 'CRID:' is taken from the
   TV-Anytime forum Content Reference Identifier and is a result of the
   consensus reached by members of this forum between March 2000 and
   June 2002.  The TV-Anytime CRID and associated supporting data is
   specified in the TV-Anytime Phase 1 Content Referencing Specification
   [TVA-CR].

3.  Notation Used in This Document

   The notation used in this document takes the form

               /

   in which the component names are in angle brackets and any characters
   outside angle brackets are literal separators.

4.  The CRID URL Scheme

   The CRID URL takes the form

               crid:///

   in which  is a registered Internet domain name that takes
   the form of domain name described in Section 3 of [RFC1034] and
   Section 2.1 of [RFC1123].

    is a free format string that is URI [RFC3986] compliant, and
   that is meaningful to the authority given by the authority field.
   The portion of the field is case insensitive.  It is recommended that
   all characters not within the range of characters allowed in a URI
   must be encoded into UTF-8 and included in the URI as a sequence of
   escaped octets.  An escaped octet is encoded as a character triplet,
   consisting of the percent character, "%", followed by the two
   hexadecimal digits representing the octet code.

   In its entirety, the CRID is URI compliant as specified in [RFC3986].
   As per [RFC3986], the crid:// part of the syntax is case insensitive.

5.  Examples of CRID Syntax

   The following are examples of a valid CRID:

            crid://example.com/foobar

   The above CRID was created by "example.com" authority, with data part
   of foobar:

            crid://example.co.jp/エイガ

   The above CRID was created by "example.co.jp" authority, with a data
   part of "E", "I", and "GA" (meaning "movie"), represented as KATAKANA
   LETTERS (Japanese characters) in UTF-8 encoding preceded by "%".

6.  Usage

6.1.  Normative Specification

   The Uniform Resource Locator scheme 'CRID:' identifies the URL as the
   TV-Anytime Content Reference Identifier and conforms to the TV-
   Anytime Content Referencing Specification [TVA-CR].  The TV-Anytime
   CRID is a key component in the TV-Anytime forum specification series
   as described in the informative overview Systems Description
   Specification [TVA-Sys].  The normative Content Referencing
   Specification [TVA-CR] also includes the details of the contents and
   format of the associated content referencing tables that resolve the
   TV-Anytime CRID into further CRID instances or transport system-
   dependent locations.

6.2.  Role of Domain Name System (DNS) Namespace

   Note that the use of the registered Internet Domain does not mean
   that the DNS resolving service is to be employed for the resolution
   of CRID URL.  Indeed the resolution information is fully specified in
   [TVA-CR] and does not require the use of the DNS resolution service.
   This is especially important as one key application area is broadcast
   television and radio distribution services that are not Internet
   based.

   In business scenarios that exploit Internet connectivity to the home,
   the DNS portion of the CRID can be used to resolve the Internet
   location of the service provider, who in turn will provide location
   resolution information in a form described in [TVA-CR].

6.3.  CRID Resolving

   As addressed in [TVA-CR], the CRID is ultimately resolved either
   directly by the CRID authority or by another party.  If another party
   is providing resolution, the ability to resolve the CRID requires the
   flow of some information from the authority to the resolution
   provider, in order to tie the CRID to its resolution.  Examples of
   relationships between CRID authors and the suppliers of resolution
   information are given in [TVA-Sys].

   As described in [TVA-CR], there will in all likelihood be more than
   one CRID that can resolve directly or indirectly to a given single
   locator at a given time.

   Also shown in [TVA-CR], CRIDs that resolve directly to the location
   of the scheduled content are likely to resolve to more than one
   location, as television and radio programmes are often published
   repeatedly within broadcast schedules or across different broadcast
   services or distribution platforms over an extended period of time.

6.4.  CRID Related Metadata

   TV-Anytime specification [TVA-Met] specifies the format and contents
   of the programme-related descriptive metadata designed to convey the
   TV-Anytime CRID for the purpose outlined here, as well as that of
   other data supporting the publication and usage of programme
   material.

7.  IANA Considerations

7.1.  General

   The 'crid:' URI scheme is reserved to designate that the URI relates
   to the TV-Anytime CRID and is to be used in accordance with the
   TV-Anytime Content Referencing Specification [TVA-CR].

   The designation of the value of each CRID is the responsibility of
   the CRID author, as identified through the 'authority' field.

   The policy of assignment of CRID values lies with the CRID author
   associated with the authority field.  It is likely that there will be
   a number of diverse (and possibly changing) authoring policies as
   required by various organisations as they address their respective
   audiences.  These individual policies will address resolution target
   resource designation issues such as the subjective equivalence of
   programme material available from different locations, the grouping
   of CRIDs under another CRID for collective description and resolution
   purposes, the cross referencing of CRID between authorities, CRID
   lifetime, and CRID reuse.

   It is likely that some authoring policies may be set through
   collaborative business arrangements, localised operational
   agreements, or national governmental bodies.

7.2.  Registration Template in Accordance with [RFC2717]

   URL scheme name: crid

   URL scheme syntax: See Section 4

   Character encoding considerations: TV-Anytime does not specify the
   character encoding scheme to be adopted by each implementation.
   However, in the case where Internet interoperability is desired, it
   is recommended that all characters not within the range of characters
   allowed in a URI must be encoded into UTF-8 and included in the URI
   as a sequence of escaped octets.  An escaped octet is encoded as a
   character triplet, consisting of the percent character, "%", followed
   by the two hexadecimal digits representing the octet code.  For
   example, the character A would be represented as "A", the character
   LATIN CAPITAL LETTER A WITH GRAVE would be represented as "Ã
            
            

            

              

                  
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