Network Working Group A. Adolf

Network Working Group A. Adolf
Request for Comments: 5328 Micronas GmbH
Category: Informational P. MacAvock
DVB Project
September 2008

A Uniform Resource Name (URN) Namespace for
the Digital Video Broadcasting Project (DVB)

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.

Abstract

This document describes a Uniform Resource Name (URN) namespace for
the Digital Video Broadcasting Project (DVB) for naming persistent
resources defined within DVB standards. Example resources include
technical documents and specifications, eXtensible Markup Language
(XML) Schemas, classification schemes, XML Document Type Definitions
(DTDs), namespaces, style sheets, media assets, and other types of
resources produced or managed by DVB.

Table of Contents

1. Introduction ....................................................2
2. Specification Template ..........................................2
3. Examples ........................................................4
4. Namespace Considerations ........................................4
5. Community Considerations ........................................7
6. Security Considerations .........................................9
7. IANA Considerations .............................................9
8. References .....................................................10
8.1. Normative References ......................................10
8.2. Informative References ....................................11

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1. Introduction

The Digital Video Broadcasting Project (DVB) is an industry-led
consortium of over 270 broadcasters, manufacturers, network
operators, software developers, regulatory bodies and others in over
35 countries committed to designing global standards for the global
delivery of digital television and data services. Services using DVB
standards are available on every continent with a total of more than
100 million DVB receivers already deployed.

DVB would like to assign unique, permanent, location-independent
names based on URNs for some resources it produces or manages. These
URNs will be constructed according to the URN syntax defined in
[RFC2141].

This namespace specification is for a formal namespace to be
registered according to the procedures set forth in [RFC3406].

2. Specification Template

This section provides the information required to register a formal
namespace according to the registration procedure defined in
[RFC3406]. The URNs conform to the syntax defined in [RFC2141].

Namespace ID:

"dvb"

Registration Information:

Version: 1
Date: 2007-02-28

Declared registrant of the namespace:

Name: Peter MacAvock
Title: Executive Director, DVB Project Office
Affiliation: DVB Digital Video Broadcasting
Address: Ancienne Route 17a
CH-1218 Geneva
SWITZERLAND
Phone: +41 22 717 2719
Email: [email protected]

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Declaration of structure:

URNs assigned by DVB will have the following hierarchical
structure based on the organizational structure of the DVB
standards:

urn:dvb:<NSS>

where the syntax of "<NSS>" is specified in Section 2.2 of the URN
Syntax requirements ([RFC2141]).

The individual URNs will be assigned by DVB through the process of
development of DVB standards.

Relevant ancillary documentation:

None

Identifier uniqueness considerations:

DVB will establish unique identifiers as appropriate.

Uniqueness is guaranteed as DVB ensures through its
standardization process that an assigned string is never
reassigned.

Identifier persistence considerations:

DVB is committed to maintaining the accessibility and persistence
of all resources that are officially assigned URNs by the
organization.

Process of identifier assignment:

Assignment is limited to DVB and those authorities that are
specifically designated by DVB. DVB may designate portions of its
namespace for assignment by other parties under its regime.

Process of identifier resolution:

DVB will develop and maintain "URN catalogues" that map all
assigned URNs to Uniform Resource Locators (URLs) specifically to
enable Web-based resolution of named resources. In the future, an
interactive online resolution system may be developed to automate
this process. The latest information about DVB-defined metadata
can always be found on the DVB website at:

http://www.dvb.org/metadata

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DVB will authorize additional resolution services as appropriate
and in-line with the DVB standardization process.

Rules for Lexical Equivalence:

The "<NSS>" is case insensitive.

Conformance with URN Syntax:

No special considerations.

Validation mechanism:

None specified. DVB will develop and maintain URN catalogues.
The presence of a URN in a catalogue indicates that it is valid.

Scope:

Global

3. Examples

The following examples are not guaranteed to be real. They are
presented for pedagogical reasons only.

urn:dvb:ipdc:esg:2005
urn:dvb:cs:ZappingTypeCS:2001

4. Namespace Considerations

The urn:dvb namespace is used to identify metadata that is defined by
DVB and describes DVB multimedia and interactive services. The
registration of urn:dvb as a formal namespace enables the use and
referencing of DVB XML fragments in other standards worldwide and
enables those standards to leverage and build upon publicly available
DVB metadata schemas and fragments.

These URNs are used to refer to, in conjunction with, and as part of
commercial or public multimedia broadcast services. In most markets,
these are under the control of a national regulator. So if a
particular market chooses to use DVB services, in general, the
regulator imposes compliance with the relevant DVB specifications to
ensure interoperability and open competition in the marketplace.

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URN assignment procedures:

The individual URNs shall be assigned through the process of
development of DVB standards by the Digital Video Broadcasting
Project (DVB). The latest information about DVB defined metadata
can always be found at the owner's website at:

http://www.dvb.org/metadata

URN resolution/delegation:

The resolution and delegation shall be determined through the
process of development of DVB standards by the Digital Video
Broadcasting Project (DVB).

Since the implementations envisaged cover a wide range of devices
with quite different access methods and capabilities, no single
resolution or delegation mechanism can be referenced in this
document.

Currently, 2 client system classes are covered by DVB
specifications:

o A broadcast set-top box that only has a unidirectional,
receive-only connection. Hence, all DVB URNs need to be
resolvable from the service discovery information received in
the broadcast stream.

o A "home network end device" (HNED) that could be an IPTV set-
top box, networked TV, or personal digital recorder with an
Ethernet or Wireless Local Area Network (WLAN) connection to a
home gateway device.

Further device classes will be addressed as DVB standardization
progresses. The urn:dvb URNs must however remain valid. DVB will
define appropriate resolution/delegation mechanisms to ensure that
DVB URNs remain valid for those new device classes as well.

For the two above example device classes, 3 ways of conveying such
resolution information are currently defined by DVB:

o Repeated, cyclic transmission of Resolution Authority Records
(RAR) and Resolution Records (RR) as auxiliary data in digital
TV broadcast streams over satellite, cable, or terrestrial
transmissions according to [EN300468], [EN301192], and
[TS102323].

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o Repeated, cyclic multicast transmission of Resolution Records
(RR) via the DVBSTP protocol according to [TS102034].

o Unicast delivery of Resolution Records (RR) in response to HTTP
"GET /dvb/sdns" requests according to [TS102034].

Type of resources to be identified:

Types of resources to be identified include XML schema definition
files, classification schemes, and identification systems defined
and openly published by DVB. These resources being identified
constitute a metadata system to describe digital multimedia
broadcast services or content conveyed as part of such services.
The latest DVB defined metadata can always be found at:

http://www.dvb.org/metadata

These metadata definitions are not entirely usable without
knowledge of the DVB specifications listed in the Normative
References section. To make them generally useful for client
platforms typically found in computer network environments today,
XSLT transformations to HTML, or other common formats would be
needed to enable rendering in a standard web browser. On the
other hand, it is expected that with the increasing overlap
between the computer and multimedia worlds - e.g., with the
forthcoming DVB file format definition - DVB metadata formats will
get adopted in player implementations on PC platforms as well.

Type of services to be supported:

Types of services supported include controlled term lookup in
classification schemes and resolution of ids in identification
systems.

Concrete examples of these services include digital television
services, (near) video on-demand services, and digital radio sound
services. Another example is interactive multimedia applications
which are tied to audiovisual content.

This might, e.g., be a quiz show where viewers can compete against
the contestants on the show by picking multiple-choice answers
with their remote control. These end-user services are enabled by
the metadata defined under the urn:dvb namespace.

Another example is the web-portal site for the video-on-demand
offering of an ISP. The portal pages are likely to describe the
content in terms of title, genre, parental guidance, cast, etc.
The ISP might either publish the DVB format description on their

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web-portal site directly, or develop an XSLT transformation to
obtain an HTML incarnation of the data. In either case, a client
device (in this example the home gateway or the ISP's web portal)
will need to be able to resolve references to the urn:dvb
namespace. Describing multimedia content in DVB format is a
likely choice since it provides rich information specially
tailored to multimedia applications like television, movies,
music, etc. Furthermore, the DVB content descriptions for
consumer terminals are, of course, compatible with the DVB
Portable Content Format (PCF, defined in ETSI TS 102 523), which
is used in content production environments so that propagation of
content descriptions along the entire production chain is easily
achieved.

5. Community Considerations

With the digitization of the audiovisual broadcasting technologies,
television receiver platforms have become quite similar to personal
computer equipment in terms of performance, resources, and
interfaces. Hence, cross-use of content from the respective other
platform (i.e., TV and PC) becomes interesting to consumers and
service providers alike. Web pages can for instance today be viewed
on a general purpose computer, a set-top box, and a mobile phone just
the same. Audio/video broadcasting services are arriving on mobile
phones today ("mobile TV"), and efforts are clearly visible to bring
such services to personal computer platforms as well ("IPTV").

Hence, cross-linking between these two domains, the Internet/personal
computer domain and the TV/broadcast domain is called for. Linking
from broadcast domain metadata to Internet-based services is already
enabled through the various URN and URI schemes established in the
relevant DVB standards ([EN300468], [TS102323], and [TS102034]).
Linking from Internet/web resources to DVB multimedia services is not
yet possible in a well-defined way. Thus, a URN scheme is proposed
for DVB defined metadata describing DVB services. As DVB issues its
publications as international standards and has a well-defined
compliance regime, this request is for a formal namespace.

Open assignment and use of identifiers within the namespace:

With on-going development of DVB standards, DVB will establish
requirements for assignment and use of identifiers within the DVB
namespace. Current identifier assignments can be inferred from
the relevant DVB standards and from http://www.dvb.org/metadata.

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Considerations for resolution server software:

With on-going development of DVB standards, DVB will establish
requirements and seek candidates for operating resolution servers
as appropriate.

Sources for resolution information can either be stand-alone
resolution services, which are announced as part of the Service
Discovery and Selection (SD&S), or data conveyed as part of the
SD&S information itself. To boot-strap the resolution process, a
DVB client hence needs to discover an entry point (or set of) from
which to obtain an initial Service Discovery and Selection XML
record.

By default, the actual service discovery information is provided
on the IANA registered well-known port dvbservdsc (port number
3937) via tcp and udp (see http://www.iana.org/assignments/port-
numbers) on the IANA registered well-known multicast addresses
224.0.23.14 (DvbServDisc on IPv4) and FF0X:0:0:0:0:0:0:12D
(DvbServDisc on IPv6).

As set forth in [TS102034], a list of non-default Service
Discovery and Selection (SD&S) entry points addresses may also be
provided via DNS based on the service location resource record
(SRV RR) [RFC2782]. The service name for DVB services is
"_dvbservdsc", the protocol may be tcp or udp, while the rest of
the name is the domain name maintained by DVB for service
discovery. This domain name is set to "services.dvb.org". The
DVB organization will maintain the services.dvb.org domain name
for service discovery, and new service providers should register
with DVB to add them to the DNS SRV list.

Considerations for resolution client software:

With on-going development of DVB standards, DVB members will
develop software implementations of its standards for various
platforms. Today, these platforms typically include Open Source-
based platforms such as Linux.

To resolve a urn:dvb name, a client needs to retrieve Service
Discovery and Selection (SD&S) data since this either directly
contains resolution data, or lists stand-alone resolution services
from which Resolution Authority Records (RAR) can be retrieved.

To obtain the initial Service Discovery and Selection (SD&S) XML
record, a client must by default first join the IANA registered
well-known multicast addresses 224.0.23.14 (DvbServDisc on IPv4)
and/or FF0X:0:0:0:0:0:0:12D (DvbServDisc on IPv6) and try to

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obtain a boot-strap record from the IANA registered well-known
port dvbservdsc (port number 3937) via tcp and udp (see
http://www.iana.org/assignments/port-numbers).

To discover non-default entry points addresses, [TS102034] defines
that a list of Service Discovery and Selection (SD&S) entry points
addresses may be acquired via DNS according to the service
location resource record (SRV RR) [RFC2782]. The service name is
"_dvbservdsc"; the protocol may be tcp or udp, while the rest of
the name is the domain name maintained by DVB for service
discovery. This domain name is set to "services.dvb.org". So the
lookup shall be either "_dvbservdsc._tcp.services.dvb.org" or
"_dvbservdsc._udp.services.dvb.org". This requires that the
terminal support an SRV cognizant DNS client and in a way
according to the specification in [RFC2782]. The DVB organization
will maintain the services.dvb.org domain name for service
discovery. HTTP servers will be found via the tcp protocol method
whilst the multicast addresses will be found via the udp protocol
method.

6. Security Considerations

There are no additional security considerations other than those
normally associated with the use and resolution of URNs in general,
which are described in [RFC1737], [RFC2141], and [RFC3406].

This document registers a namespace for URNs. DVB may assign special
meaning to certain of the characters of the Namespace Specific String
in its specifications. Any security consideration resulting from
such assignment is outside the scope of this document.

When URNs are resolved, i.e., translated from names to locations, the
way the locations are used or accessed may require the resources to
be authenticated. The information about the authentication of either
the name or the resource to which it refers should be carried by
separate information passed along with the URN rather than in the URN
itself. The design of such resolution mechanisms by DVB for DVB URNs
is guided by [RFC2276] and such mechanisms will be published as DVB
specifications.

7. IANA Considerations

This document defines a URN NID registration of "dvb". IANA has
registered "dvb" in the URN Namespaces registry.

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8. References

Note: The ETSI specifications listed below - as all ETSI standards -
are available to the general public free of charge. They are
accessible by going to http://www.etsi.org and visiting the
standards download page. Select "Standards" from the
navigation bar at the top, then choose "Download ETSI
Standards" in the contents box on the left. A "Publications
Download Area" link occurs at the top of the body text). The
direct link to the downloads page is
http://pda.etsi.org/pda/queryform.asp. When clicking on the
download link on the search results page, an email address is
requested for the PDF download. As being free-of-charge is
funded by the European Commission, the email addresses are
collected for statistical purposes only to demonstrate benefit
to the general public.

The ETSI specifications are normative references since the URNs
are used to refer to, in conjunction with, and as part of
commercial or public multimedia broadcast services. In most
markets, these are under the control of a national regulator.
So if a particular market chooses to use DVB services, in
general, the regulator imposes compliance with the relevant DVB
specifications to ensure interoperability and open competition
in the marketplace. Some of the specifications also have "EN"
status, which means that the European Commission has overridden
any national regulations by mandating that if any commercial
service is rolled out in Europe in the respective area, it must
comply with the relevant DVB EN specification(s). Apart from
those legal implications, DVB has become a brand to which
consumers link certain expectations with regard to the level of
service and interoperability. Of course, DVB wants to help
manufacturers meeting those expectations by fostering
interoperability.

8.1. Normative References

[RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997.

[RFC3406] Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
"Uniform Resource Names (URN) Namespace Definition
Mechanisms", BCP 66, RFC 3406, October 2002.

[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.

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[EN300468] European Telecommunications Standards Institute (ETSI),
"Digital Video Broadcasting (DVB); Specification for
Service Information (SI) in DVB systems", October 2007.

[EN301192] European Telecommunications Standards Institute (ETSI),
"Digital Video Broadcasting (DVB); DVB specification for
data broadcasting", November 2004.

[TS102323] European Telecommunications Standards Institute (ETSI),
"Digital Video Broadcasting (DVB); Carriage and signalling
of TV-Anytime information in DVB transport streams",
November 2005.

[TS102034] European Telecommunications Standards Institute (ETSI),
"Digital Video Broadcasting (DVB); Transport of MPEG-2 TS
Based DVB Services over IP Based Networks", October 2007.

8.2. Informative References

[RFC1737] Sollins, K. and L. Masinter, "Functional Requirements for
Uniform Resource Names", RFC 1737, December 1994.

[RFC2276] Sollins, K., "Architectural Principles of Uniform Resource
Name Resolution", RFC 2276, January 1998.

Authors' Addresses

Alexander Adolf
Micronas GmbH
Frankenthalerstrasse 2
D-81539 Munich
GERMANY
Tel: +49 89 54845 7203
Fax: +49 89 54845 7900
EMail: [email protected]

Peter MacAvock
DVB Digital Video Broadcasting
Ancienne Route 17a
CH-1218 Geneva
SWITZERLAND
Tel: +41 22 717 2717
EMail: [email protected]

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