Network Working Group Nigel Earnshaw
Internet-Draft BBC Research and Development
Expires: April 19, 2004 Alex Ashley
Philips Research
Wataru Kameyama
GITS, Waseda University
October 20, 2003
The TV-Anytime Content Reference Identifier (CRID)
Uniform Resource Locator
draft-earnshaw-tv-anytime-crid-01.txt
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
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
including the Internet.
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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).
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 to the home may
give rise to new information and entertainment services providing
audio visual programme material sourced directly to the home over the
Internet.
Alongside this expansion there is also an increased growth in
complexity of the device available to the home user that will allow
the home 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
the programme material through off air recording or downloading by
the 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. This location data is platform specific and outside the
scope of this document. In the case of the television distribution
model these locators provide programme broadcast timing and tuning
information such that the user appliance can record the programme
when broadcast in real time. For the case of internet delivery the
locators need to be of the form associated with streaming protocols
or file exchange protocols with the time (or time window) of
availability indicated.
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Since 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 such aggregation decisions is
part of the CRID authoring process and is not standardised.
The CRID resolution process ultimately enabling the user agent to
acquire the 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
<first>/<second>
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://<authority>/<data>
where <authority> is of the form <DNS name><name_extension>
<DNS name> is a registered Internet domain name. The <DNS name> is
case insensitive and must be a fully qualified name according to the
rules given in RFC 1591 [DNS].
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<name_extension> is an optional string (beginning with a ';'
character) to enable multiple authorities to use the same DNS name.
All <name_extension> elements which share the same <DNS name> must be
unique. The <name_extension> section is case insensitive.
<data> is a free format string that is Uniform Resource Identifier
(URI) compliant, and is meaningful to the authority given by the
authority field. The <data> portion of the field is case
insensitive.
In its entirety, the CRID is URI compliant as specified in RFC 2396
[URI]. As per RFC 2396 the CRID:// part of the syntax is case
insensitive.
5 Examples of CRID syntax
CRID://company.com/foobar
CRID created by 'company.com' authority, with data part of foobar
CRID://broadcaster.co.jp;comedy/wibble
CRID created by 'broadcaster.co.jp;comedy' authority, with a data
part of 'wibble'
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 DNS namespace
It is important to note that the use of the registered Internet
Domain does not mean 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
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services that are not Internet based.
For the case of business scenarios that do 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-Meta] 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 other data
supporting the publication and usage of programme material.
7 IANA Considerations
7.1 General
The 'CRID:' URI scheme should be 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
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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 such resolution
target resource designation issues 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 through national governmental bodies.
7.2 Registration Template in accordance with RFC 2717 [URL]
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
Intended Use: see Section 6
Application and protocols which use this scheme: See Section 6
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-Meta], [TVA-Sys], [TVA-
Prot]
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.
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When conveyed as part of a larger data set which may have commercial
value or critical binding between a CRID and the accompanying data,
then 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-Prot], though it
is not mandated that users adopt this. In any case there may be
other wider system security functions in place or the absence of
perceived need for such precautions.
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.
References
[TVA-CR] ETSI TS 102 822-4 v1.1.1 (2003-10) Broadcast and On-line
Services: Search, select and rightful use of content on
personal storage systems ("TV-Anytime Phase 1"). Part 4:
Content Referencing
[TVA-Meta] ETSI TS 102 822-3-1 V1.1.1 (2003-10) 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
[TVA-Prot] ETSI TS 102 822-7 V1.1.1 (2003-10) 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
[TVA-Sys] ETSI TS 102 822-2 V1.1.1 (2003-10) Broadcast and On-line
Services: Search, select and rightful use of content on
personal storage systems ("TV-Anytime Phase 1"). Part 2
System Description (Informative with Normative Annex B)
[DNS] Domain Name System Structure and Delegation. RFC 1591
J. Postel.
[URI] Uniform Resource Identifiers (URI): Generic Syntax. RFC 2396
T. Berners-Lee, R. Fielding, U.C. Irvine, L. Masinter
[URL] Registration Procedures for URL Scheme Names. RFC 2717
R. Petke, I. King
Acknowledgements
The authors would like to acknowledge the support of the members of
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the TV-Anytime forum and their work in the development of the
TV-Anytime CRID.
Authors Address
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
Alex Ashley
Philips Research Labs
Cross Oak Lane
Redhill
Surrey
United Kingdom
Phone: +44 1293 815487
Email: alex.ashley@philips.com
Wataru KAMEYAMA, Vice Chairman and Secretary of the TV-Anytime Forum
1-3-10 Nishi-Waseda, Shinjuku-ku
Tokyo, 169-0051, JAPAN
Phone: +81 3 5286 9852
Email: wataru@waseda.jp
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