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).
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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.
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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.
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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/%E3%82%A8%E3%82%A4%E3%82%AC
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
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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.
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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 "%C3%80",
and the character KATAKANA LETTER A would be represented as
"%E3%82%A2".
Intended Use: See Section 6
Application and protocols which use this scheme: See Section 6
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Interoperability considerations: None (Section 4 contains the first
version of the CRID URL definition)
Security considerations: See Section 8
Relevant publications: See [TVA-CR], [TVA-Met], [TVA-Sys], [TVA-Prt]
Contact: Wataru KAMEYAMA, Vice Chairman and Secretary of the TV-
Anytime Forum, wataru@waseda.jp
Author/Change controller: IESG
8. Security Considerations
The CRID URL described here provides a referencing mechanism. The
values of the URL contain the authoring 'Authority' name as a DNS
namespace identifier and a data portion to distinguish it from other
CRIDs from the same authority. There should be no reason to prevent
disclosure of the values within the CRID and no commercial
sensitivity associated with these values.
When the binding conveyed as part of a larger data set which may have
commercial value or critical binding between a CRID and the
accompanying data, the security and integrity of the binding is a
matter for the wider system implementers to judge and protect
accordingly. One such method for protecting metadata can be found in
[TVA-Prt], though it is not mandated that users adopt this. In any
case, there may be other, wider system security functions in place or
such precautions may not be seen as necessary.
Tampering with values of CRIDs during transmission or distribution
over public or open networks has only nuisance or denial-of-service
effects unless it causes alternative location resolution data or
programme metadata to be referenced. Again, this can be dealt with
as a system delivery of data integrity issue not specific to the
CRID.
Impersonating a CRID authority by authoring CRID with an authority
portion for which the bogus author does not have permission from the
registered DNS name holder would be a misuse of the DNS name holder's
identity and should be dealt with through normal business practice.
9. Acknowledgements
The authors would like to acknowledge the support of the members of
the TV-Anytime forum and their work in the development of the TV-
Anytime CRID.
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10. References
10.1. Normative References
[TVA-CR] European Telecommunications Standards Institute, "ETSI TS
102 822-4 v1.1.2 ; Broadcast and On-line Services: Search,
select and rightful use of content on personal storage
systems ("TV-Anytime Phase 1"); Part 4: Content
referencing", October 2004.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
RFC 1034, November 1987.
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", RFC 1123, October 1989.
[RFC2717] Petke, R. and I. King, "Registration Procedures for URL
Scheme Names", RFC 2717, November 1999.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005.
10.2. Informative References
[TVA-Sys] European Telecommunications Standards Institute, "ETSI TS
102 822-2 v1.2.1 ; Broadcast and On-line Services: Search,
select and rightful use of content on personal storage
systems ("TV-Anytime Phase 1"). Part 2 System
Description", September 2004.
[TVA-Met] European Telecommunications Standards Institute, "ETSI TS
102 822-3-1 v1.2.1 ; Broadcast and On-line Services:
Search, select and rightful use of content on personal
storage systems ("TV-Anytime Phase 1"). Part 3 Metadata.
Sub-part 1: Metadata Schemas", September 2004.
[TVA-Prt] European Telecommunications Standards Institute, "ETSI TS
102 822-7 v1.1.1 ; Broadcast and On-line Services: Search,
select and rightful use of content on personal storage
systems ("TV-Anytime Phase 1"). Part 7 Bi-directional
Metadata Delivery Protection", October 2003.
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Authors' Addresses
Nigel Earnshaw
BBC Research and Development
Kingswood Warren
Tadworth, Surrey KT20 6NP
United Kingdom
Phone: +44 1737 839618
EMail: nigel.earnshaw@rd.bbc.co.uk
Shigeru Aoki
TokyoFM Broadcasting
1-7 Kojimachi
Chiyoda-ku, TOKYO 102-8080
JAPAN
Phone: +81 3 3221 0244
EMail: shig@center.jfn.co.jp
Alex Ashley
NDS Limited
One London Road
Staines, Middlesex TW18 4EX
United Kingdom
Phone: +44 208 4768270
EMail: aashley@ndsuk.com
Wataru Kameyama
GITS, Waseda University
1011 Okuboyama, Nishi-tomida
Honjo-shi, SAITAMA 367-0035
JAPAN
Phone: +81 495 24 6052
EMail: wataru@waseda.jp
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