Internet DRAFT - draft-mcroberts-uri-dvb
draft-mcroberts-uri-dvb
Network Working Group M. McRoberts, Ed.
Internet-Draft British Broadcasting Corportation
Intended status: Informational A. Adolf
Expires: September 27, 2013 Condition-ALPHA
March 26, 2013
Uniform Resource Identifier (URI) Scheme for Digital Video Broadcasting
(DVB) Programme Resources
draft-mcroberts-uri-dvb-10
Abstract
Uniform Resource Identifier (URI) schemes for broadcasting programme
resources transmitted over MPEG-2 Transport Streams [MPEG-Systems]
have been devised in their process of creating standards by the
Digital Video Broadcasting Project (DVB), the Association of Radio
Industries and Businesses in Japan (ARIB) and the OpenCable
Application Platform (OCAP) to acquire current and future scheduled
publications of broadcast media content from multimedia applications
such as HTTP, MHP [DVB-MHP], OCAP [OCAP1.0] or other XML based
metadata.
These URI are used to locate the actual digital TV, Radio or other
multimedia broadcast programme services (i.e., channels or events)
and also the audio-visual components related to that programme, for
example an HTTP-based programme guide on the Web or other XML-based
electronic programme guides in digital broadcast receivers.
This document defines the "dvb" URI scheme for the benefit of the
Internet community, given its definition as part of the Digital Video
Broadcasting (DVB) suite of ETSI standards.
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."
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This Internet-Draft will expire on September 27, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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.
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1. Introduction
Standards governing televisions, set-top boxes and other consumer
electronics devices have for some time been developed with the
Internet in mind. The use of Universal Resource Identifiers (URIs)
[RFC3986] is now commonplace, including for the purpose of
identifying resources delivered by way of terrestrial, satellite and
cable broadcasts.
For this purpose, a URI scheme was developed as part of the Digital
Video Broadcasting [DVB] suite of standards specifically for the
purpose of identifying broadcasts delivered by way of DVB-compliant
broadcasting systems.
With the advent of digital broadcasting, digital multimedia broadcast
services to the home, based on MPEG-2 Transport Streams
[MPEG-Systems], have been widely available in recent years. Each
broadcast programme and component (i.e. audio-visual and generic data
components) are identifiable within the MPEG-2 Transport Stream.
Beyond digital broadcast, television and radio programmes can be
delivered to receivers over an IP-based network within MPEG-2
Transport Stream packets.
The Electronic Programme Guide (EPG) service for television and radio
programmes which allows people to find and select programmes must be
able to identify a given programme in a canonical form. As programme
guides are increasingly being made available on the Web, and on-
device programme guides are taking advantage of Internet
connectivity, and as receiving devices are increasingly able to
present programmes delivered both via digital broadcast and a variety
of IP-based protocols, the the use of URIs to identify programmes is
an obvious pragmatic choice.
This document defines the Uniform Resource Identifier (URI) schemes
for broadcast programme resources over MPEG-2 Transport Stream
[MPEG-Systems] for DVB services, conforming to the generic URI syntax
[RFC3986] to aid in interoperability with existing IP-based services.
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
500 million DVB receivers already deployed. More information on DVB
can be found on their website at http://www.dvb.org
This URI specification is for a permanent assignment.
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1.1. Transmission Scheme
The audio, visual or private data components constituting a TV/radio
programme ("service") are defined as elementary stream (ES)
components. Several of these TV/radio programmes are bundled in a
transport stream (TS) multiplex for delivering over a broadcast
transmission network (e.g. satellite, cable or terrestrial). The
distinguished unique number for each TS multiplexed packet,
elementary stream component, transport stream and transmission
network is assigned and transmitted over the satellite, cable or
terrestrial broadcasting media, or over an IP network, together with
an information table which describesthese assigned numbers, as
described by the MPEG-2 standard [MPEG-Systems].
+---------------------------------------------------+
| BROADCASTING NETWORK |
| (e.g. Satellite, Cable, Terrestrial) |
| +---------------------------------------+ |
| | TRANSPORT STREAM MULTIPLEX |-* |
| | (e.g. channel) | | |
| | +-----------------------------+ | | |
| | | SERVICE |-* | | |
| | | +---------------------+ | | | | |
| | | | Audio/Visual and |-* | | | | |
| | | | Private Data | | | | | | |
| | | | Components | | | | | | |
| | | +---------------------+ | | | | | |
| | | *---------------------* | | | | |
| | | | | | | |
| | +-----------------------------+ | | | |
| | *-----------------------------* | | |
| | | | |
| +---------------------------------------+ | |
| *---------------------------------------* |
| |
+---------------------------------------------------+
Programme Delivery Scheme in MPEG-2 Transport Stream
These elements are unambiguously identified in DVB systems through
numerical identifiers:
o A *network_id* identifies a broadcast transmission network. On
satellite and IP broadband, typically one network_id corresponds
to an operator. On cable and terrestrial, where different radio
frequencies might be used in different regions, operators
typically use one network_id per such region.
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o An *original_network_id* is used where TV/radio programmes are
taken from one network and are re-transmitted on another one
(noting that a "network" in this context may simply be a different
broadcast region for the same operator). The original_network_id
is therefore used by receivers as a means of determining
equivalence across different networks.
o A *transport_stream_id* is used to refer to a time-domain
multiplex of several programmes carried in TS packets. One or
more multiplexes can be transmitted on any given radio frequency
in a DVB network.
o A *service_id* identifies a TV, radio or data programme within a
TS multiplex. The number of programmes is limited by the capacity
of the underlying physical channel.
o A *component_tag* identifies an elementary stream (ES) of video,
audio, teletext, subtitles, or other data within a service.
+---------+
| |-------+
| | >+++++ Service 1 +++++
| > TS 1 |
| | >***** Service 2 *****
| NET 1 |-------+
| |-------+
| | >===== Service 3 =====
| > TS 2 >xxxxx Service 4 xxxxx
| | >##### Service 5 #####
| |-------+
+---------+
Relationship of Network, Transport Stream, and Service
The original_network_id is an attribute of a transport stream (TS).
In the simplest case, all services originate from the network on
which they are transmitted. In this case, the original_network_id of
all the TS will be equal to the network_id, and this typically occurs
on networks operated by public broadcasters. If one of the public
broadcaster's transport streams is, for example, re-transmitted by a
cable operator, the information about this stream would containe the
cable operator's network_id, and the original_network_id of the
public broadcaster.
Thus, all assigned network_id values must correlate with actual
broadcast infrastructure, whereas this is not required for
original_network_id values which have a more logical basis. A
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globally active content provider may for example choose to register
an original_network_id, and distribute pre-multiplexed transport
stream to broadcasters, without operating any broadcast network of
its own.
The assignment of values for both original_network_id and the
network_id are coordinated by the DVB Project. The DVB Project in
turn has delegated the management of DVB identifiers to DVB Services
Sarl [DVB-SVCS]. DVB Services maintains a public register of all
assignments, and accepts requests for new assignments on their
website.
Due to the way broadcast transmission networks are operated (and, to
an extent, the design of MPEG-2), some relationships exist between
these identifiers:
o Each TS is part of exactly one orginial_network_id (see above).
o Hence, each TS is unambiguously identified by the tuple
{original_network_id, transport_stream_id}.
o According to [DVB-SI-SPEC], each service_id is unique within a TS.
Hence a service is unambiguously identified by the tuple
{original_network_id, transport_stream_id, service_id}.
o [DVB-SI-GDL] additionally requires that each service_id be unique
within an original_network_id. Hence, in areas where [DVB-SI-GDL]
has been made part of the broadcast profile, the tuple
{original_network_id, service_id} unambiguously identifies a
service.
During the process of performing a "service scan", a receiver will
capture the identifying information contained within the transport
streams and store their transport_stream_id, original_network_id and
network_id, as well as the service_id values of all of the services
carried within that transport stream. As each radio frequency
channel is scanned, the receiver constructs a table correlating each
of these tuples with the radio frequency channels and other
modulation parameters, such that when it is required to switch to
specific service within a transport stream, it can tune the radio
receiver appropriately. Within the context of [DVB-IPTV], of course,
there are no radio frequencies, however the same model of
broadcasters, networks and services is maintained and the same
identifiers are used with the same semantics.
A DVB service is composed of one or more components. These are
identified within the context of a service by their component_tag. A
component can be either an elementary stream (ES) carrying video,
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audio, teletext, subtitles, or other synchronised data or generic
data (see also [DVB-DATA], [DVB-TVA] and [DVB-MHP]). Each of these
components is sliced into fragments and packetised in TS packets
[MPEG-Systems]. All packets for a given component are labeled with
the same TS Packet Identifier (PID), effectively providing a virtual
channel within the TS for that component. The packets are time-
division multiplexed according to each component's data rate
requirements for broadcast.
...|v|v|v|a|t|v|v|v|v|v|a|s|v|v|a|v|v|t|a|v|v|...
|1|1|1|1|1|2|2|2|2|2|2|2|1|1|1|2|2|1|2|1|2|
---------------------------------------------------->
time
|x| : a TS packet
|x|
v1, a1, t1: SD video, audio and teletext of service 1
v2, a2, s2: HD video, audio and subtitles of service 2
Example TS time domain multiplex
In the above figure, all TS packets for "v1" would share the same PID
value. Similarly, all TS packets for "a2" would also share a
different PID value, and so on. The metadata describing the network,
transport streams, services, and their components is transmitted
within a TS using well-known PID values according to [MPEG-Systems]
and [DVB-SI-SPEC]. These metadata TS packets are not shown in the
above figure for clarity.
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2. Digital Video Broadcasting URI Scheme
The DVB URI is defined by [DVB-URI], and that shall be considered the
authoritative source of the definition of the scheme-specific-part of
the DVB URI.
URIs employing the dvb scheme are URLs. DVB URLs may refer to any of
the following kinds of resource:
o A DVB service
o Components within a DVB service (such as an audio or video stream)
o An event (for example, a programme)
o A transport stream
o A file contained within a DSM-CC object carousel
o Interactive applications
2.1. Syntax
This section details the components of the syntax. The syntax also
makes use of components defined in [RFC3986] and [RFC5234]. These
are not reproduced here for brevity. Future revisions of [DVB-URI]
and related specifications may add additional syntax elements or
otherwise extend the dvb URI scheme to support emerging DVB-based
applications.
This URI scheme is in conformance with the generic URI syntax
[RFC3986] and uses the registry-based naming authority version of
that. It takes the form:
DVB-URI = dvb-scheme ":" dvb-path
dvb-scheme = "dvb"
dvb-path = ( "//" ( dvb-net-entity [ path-absolute ] ))
/ ( "//" dvb-app-entity )
/ path-absolute
When the dvb-path part only consists of a path-absolute, the URI
refers to a file in the default object carousel within the current
DVB service. The "current" service is dependent on the usage
context.
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2.1.1. dvb-scheme
The dvb-scheme name represents the transmission system using the
MPEG-2 standard in the digital broadcasting service in accordance
with Section 3.1 of [RFC3986].
In this definition "dvb" represents the DVB system which is based on
[BT.1306], [BO.1516], [J.83], and [DVB-IPTV].
2.1.2. dvb-net-entity
A dvb-net-entity uniquely identifies an originator, transport stream,
service, event or component within the DVB system, either by way of
numeric identifiers or through the use of textual service identifiers
(some of which are pre-defined, while others may be advertised within
the system). The dvb-net-entity may also refer to a specific DVB
carousel, or include a timed event constraint.
The general syntax of the dvb-net-entity is:
dvb-net-entity = transport-stream / service-entity
transport-stream = original-network-id "." transport-stream-id
service-entity = dvb-service [ "." component-set [ "$" carousel-id ]]
[ event-constraint ]
dvb-service = ( original-network-id "." [ transport-stream-id ] "." service-id )
/ ( "'" textual-service-identifier "'" )
original-network-id = hex-string
transport-stream-id = hex-string
service-id = hex-string
textual-service-identifier = reg-name
carousel-id = hex-string
hex-string = 1*HEXDIG
The dvb-net-entity, if present, may identify one the following:
o A transport stream (through combination of original_network_id and
transport_stream_id)
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o A service, either through hexadecimal numeric identifiers or
through in textual form
o An audio, visual, or data component within a service
o A carousel contained within a component of a service
o An event which occurs within a service
2.1.2.1. component-set
The component-set referenced in the syntax above is used to identify
one or more components of a service and takes the form:
component-set = component-tag-set
/ qualified-component-set
/ fully-qualified-component-set
component-tag-set = component-tag *( "&" component-tag )
component-tag = hex-string
qualified-component-set = qualified-component *( "&" qualified-component )
qualified-component = component-type "=" component-id
component-type = "video" / "audio" / "data" / "subtitle"
/ "teletext" / "dvbst"
component-id = component-tag / iso639-language-code
/ "default" / "current"
/ "hearing_impaired" / "visually_impaired"
/ "none"
fully-qualified-component-set = fully-qualified-component
*( "&" fully-qualified-component )
fully-qualified-component = "fqc=" stream-content-and-component-type
"," component-tag
[ "," iso639-language-code ]
stream-content-and-component-type = hex-string
iso639-language-code = 3ALPHA
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2.1.2.2. event-constraint
An event-constraint identifies an event occurring within a service:
event-constraint = ( event-ref [time-constraint] )
/ time-constraint
event-ref = ";" [ event-id ] [ ";" tva-id ]
event-id = hex-string
tva-id = hex-string
time-constraint = "~" time-duration
time-duration = start-time "--" duration
start-time = date "T" time "Z"
duration = "PT" hours "H" minutes "M" [ seconds "S" ]
date = year month day
time = hours minutes [ seconds ]
year = DIGIT DIGIT DIGIT DIGIT
month = DIGIT DIGIT
day = DIGIT DIGIT
hours = DIGIT DIGIT
minutes = DIGIT DIGIT
seconds = DIGIT DIGIT
An event may be identified by its event-id, a TV-Anytime tva-id, a
start-time and duration according to UTC, or a combination of some or
all of the three.
2.1.3. dvb-app-entity
A dvb-app-entity is a specific form of DVB entity identifier which is
used in interactive applications, and takes the form:
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dvb-app-entity = ( "current" [ ( ".audio" / ".video" / ".av" ) ] )
/ "original"
/ ( ( "current" / dvb-service ) ".ait/" ait-abs-path )
ait-abs-path = "app-root" / ait-application
ait-application = org-id-part "." app-id-part [ "?" ait-params ]
ait-params = "arg_" 1*DIGIT "=" *uric [ "&" ait-params ]
org-id-part = lowposhex-string
app-id-part = lowposhex-string
lowposhex-string = lowposhex *lowhex
lowhex = DIGIT / "a" / "b" / "c" / "d" / "e" / "f"
posdigit = "1" / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9"
lowposhex = posdigit / "a" / "b" / "c" / "d" / "e" / "f"
DVB interactive applications are Java Xlets that are carried in the
broadcast signal. Terminals extract and then execute these Xlets.
They are advertised inside the broadcast signal in the Application
Information Table (AIT). The dvb-app-entity can thus refer to such
application advertisements in its ".ait/" form. In its other forms,
the dvb-app-entity refers to a DVB service or components thereof
which are used in conjunction with the currently running application.
For further information, please see [DVB-MHP].
2.2. Encoding
Section 5 of [DVB-URI] specifies 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."
2.3. Community Considerations
2.3.1. Context of Use
The "dvb" URIs are used as references to resources in digitial
multimedia programmes, most often within the context of DVB itself:
interactive television applications use them in order to locate
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resources and to reference services and programmes. These are
typically broadcast via satellite, cable and terrestrial systems, but
may also be retrieved on-demand from a server via the Internet.
Providers of such broadcast services may e.g. reference programmes in
the broadcast from an Electronic Programme Guide (EPG) which is
published on their web- site. On another example, the metadata which
is part of the multimedia broadcasts can also contain such URIs to
establish hyperlinks between broadcast services. This might for
instance include multi-angle video services (e.g. for sports events).
Users of suitably-equipped clients -- i.e. with a suitable tuner card
and software installed (Open Source tools including
<http://www.linuxtv.org/> and <http://www.mythtv.org/>) -- are able
to exchange such URIs (e.g. via an instant messaging service or
email) to provide each other clickable hyperlinks to multimedia
content they deem of interest.
DVB has published specifications for the distribution of multimedia
services via IP unicast and multicast mechanisms. In this context,
such URIs are usable in any player client software (no tuner card
required) that implements the respective protocols and has the
relevant audio and video codecs installed.
o For example, a receiver connected to a local area network might
allow other devices to query it for information regarding the
current programme or service: in this context, a dvb URI would
typically be the most authoritative single identifier which could
be used to to refer to that programme.
o Similarly, a web service can be implemented by a platform operator
or a broadcaster (or some party working on their behalf) which
allows resolution of dvb URIs - this would allow a device to
retrieve web pages or other content which relate to the current
programme (or some other entry in the device's Electronic
Programme Guide).
Implementing such a system naturally requires some mechanism for
devices to discover an appropriate resolution service. DVB has
developed has developed a service discovery and selection (SD&S)
solution as part of [DVB-IPTV].
2.3.2. Resolution Considerations
The resolution process is determined through the 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
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document.
Currently 2 client system classes are covered by DVB specifications:
o A broadcast set-top box or other receiver which only has a
unidirectional, receive-only connection -- for example by way of a
UHF radio receiver. Hence, all DVB URIs need to be resolvable
from the service discovery information received within the
broadcast stream.
o A "home network end device" (HNED) which could be an IPTV set-top
box, networked TV or personal digital recorder with an Ethernet or
WLAN connection to a home gateway device.
Further device classes will be addressed as DVB standardisation
progresses. The dvb URIs must however remain valid. DVB will define
appropriate resolution mechanisms to ensure that DVB URIs remain
valid for those new device classes as well.
For the two above example device classes, three mechanisms of
conveying such resolution information are currently defined by DVB:
o Repeated, cyclic transmission of service discovery information as
auxiliary data in digital TV broadcast streams over satellite,
cable or terrestrial transmissions according to [DVB-SI-SPEC],
[DVB-DATA] and [DVB-TVA]. Typically, this information is collated
and stored during a "service scan". It can then be looked up at
point of resolution, and the receiver may tune to the associated
frequency and if demultiplex the appropriate transport stream.
o Repeated, cyclic multicast transmission of SD&S Records via the
DVBSTP protocol according to [DVB-IPTV].
o Unicast delivery of SD&S Records in response to HTTP "GET /dvb/
sdns" requests according to [DVB-IPTV].
2.3.2.1. Identifier Management
For some of the identifiers used in the DVB URI syntax, DVB provides
a public registry which is operated by DVB Services Sarl [DVB-SVCS]
and is available on the Web at http://www.dvbservices.com/. [1] On
that site, the registry tables can be viewed, downloaded, and
applications for new identifiers can be submitted. Most of the
identifiers not listed in the registry are under the scope of one of
the registered identifiers (for example the service_id is under
control of the holder of a network_id or original_network_id). A
select few identifiers are not open for registration to the public,
and are managed by DVB itself. For details on the nature of each
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identifier, please refer ot the corresponding DVB standard.
2.3.3. Implementation Considerations
2.3.3.1. 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.
To boot-strap the resolution process, a DVB client needs to discover
an entry point (or set of) from which to obtain an initial Service
Discovery and Selection XML record:
o By default, the 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).
o As set forth in [DVB-IPTV], 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.
2.3.3.2. Considerations for resolution client software
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 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, [DVB-IPTV] 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, whilst the suffix is
implementation-defined. A client MAY attempt resolution using
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multiple suffixes if required, and MAY employ [RFC6762] in order to
perform resolution.
HTTP servers are advertised through this mechanism using the "tcp"
protocol, while multicast addresses are advertised using the "udp"
protocol.
SRV RRs will be published for the forseeable future with the suffix
"services.dvb.org" (resulting in the fully-qualified domain names
"_dvbservdsc._tcp.services.dvb.org" and
"_dvbservdsc._udp.services.dvb.org"). This suffix MAY be used for
resolution as a fall-back in the event that resolution using any
configuration- or implementation-defined suffixes fails.
2.4. Rights to Use Trademarks
Conforming to section 7.4 of [RFC3978], the DVB Project who is the
holder of various trademark and logo rights amongst others but not
limited to the term "dvb", hereby grants IETF a perpetual license to
use any such trademarks or service marks solely in exercising its
rights to reproduce, publish and modify this IETF contribution. This
license does not authorize any IETF participant to use any trademark
or service mark in connection with any product or service offering,
but only in the context of IETF Documents and discussions.
2.5. Examples
These examples make heavy use of the identifiers defined by DVB to
identify entities. Please see Section 1 for an explanation of the
concepts.
2.5.1. Referring to transport streams and services
In the below examples, a receiver uses the identifiers in the URI to
search its internal database of radio frequencies and modulation
parameters, which it built during a service scan run. It uses the
identifiers as keys to look up in the various tables.
dvb://233a.1041
The DVB transport stream multiplex with id 0x1041 and with
original network id 0x233a. This might be used by a broadcaster
to provide an entry point to its service offering, without picking
out any of his services in particular.
dvb://233a.1041.10bf
The DVB service with id 0x10bf in the DVB transport stream with id
0x1041 and with original network id 0x233a. This could be used as
the link behind a "watch this now" button.
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dvb://233a..10bf
The DVB service with id 0x10bf and with original network id
0x233a. This could be used as the link behind a "watch this now"
button. Note that compared to the previous example the transport
stream id is omitted. This is possible in areas where
[DVB-SI-GDL] is applicable.
dvb://'MetroTV'
The DVB service named "MetroTV". Note that as opposed to the
previous example, the reference to the service's name is not
necessarily unambiguous and requires more contextual information
to be resolved. For "speaking" or "promotional" URIs, [DVB-TVA]
might be a more general alternative.
2.5.2. Referring to service components
In addition to referring to a TV/radio programme as a whole, it might
be desirable to be able to pick out specific variations of audio and
video provided by a programme. One could for instance always be
interested in the video with open signing, or in the audio for the
visually impaired.
dvb://233a.1041.10bf.audio=fra
The default video stream and the French language audio stream in
the indicated DVB service.
dvb://233a.1041.10bf.audio=qaa&subtitles=eng
The default video stream, the original language audio stream, and
the English language subtitle stream in the indicated DVB service.
dvb://233a.1041.10bf.video=default&audio=visually_impaired The
default video stream and the audio stream for the visually
impaired in the indicated DVB service.
dvb://233a.1041.10bf.fqc=50B,3&fqc=640,5,fra The HD video stream
(stream_content 0x5 and component_type 0x0B) with component_tag 3,
and the French language ("fra") HE.AAC audio for the visually
impaired (stream_content 0x6 and component_type 0x40) with
component_tag 5.
2.5.3. References for triggering
Applications might want to trigger on the start and/or end of TV/
radio programmes. The user might e.g. have set a flag on the
programme, so that the receiver will remind him when it begins, or
might even automatically switch to the respective service when the
programme begins, and back to the previous service whe it is over.
Or a user might have selected a programme for recording. These
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scenarios require that an application has some notion of the start
and end times of TV/radio programmes.
Creating accurate recordings of broadcast content is a non-trivial
task. For a wider discussion of this, please see [DVB-TVA].
Although individual service components can be selected for recording,
all components of the service should generally be recorded where
appropriate. This would for instance enable to use the original
language audio instead of the dubbed version on special playback
occasions.
dvb://233a.1004.1044;8fff
Event with id 0x8fff within the indicated DVB service. A receiver
would look up the EPG information for the given service, and for
the indicated event within that service. The EPG information will
contain the wall-clock start time and duration of the programme as
published e.g. also in print. Since the actual times of
transmission may be different, triggers should only be fired with
appropriate lead-in and lead-out times relative to the published
EPG times. Receivers can also use additional information in the
EPG, in particular the running_status. Not all broadcasters do
however manage the running_status reliably or in real-time.
dvb://233a.1004.1044.audio=fra;8fff French audio version of the
event with id 0x8fff within the indicated DVB service. The video
would also be implied if it is a TV service. See also previous
example.
dvb://233a.1004.1044;8fff~20100706T000315Z--PT00H31M17S
Event with id 0x8fff within the indicated DVB service, starting at
00 hours, 03 minutes and 15 seconds UTC on July, 6th, 2010,
lasting for 00 hours, 31 minutes and 17 seconds. This form of the
URI can be used to convey more accurate transmission times for the
content. The programme may be advertised as starting at 00:00 and
ending at 00:30 in the EPG. This extended information in the
locator can be used to get a much more accurate trigger for the
programme. The lead-in and lead-out times can be reduced to the
minimum needed to account for the skews of the local and
broadcaster clocks.
2.5.4. Referring to data objects
[DVB-DATA] defines - among other things - an object carousel which
can be mounted as a file system. The data for this object carousel
is transmitted repeatedly.
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dvb://233a.1041.10bf/doc/form.pdf
File in a subdirectory of an object carousel, for which the root
object is carried in the default object carousel of the referenced
DVB service.
dvb:/image.png
File in root directory of an object carousel, for which the root
object is carried in the default object carousel of the current
service.
dvb://233a..10bf.3$10a1240f/doc/form.pdf
File in a subdirectory of an object carousel, for which the root
object has the transaction id 10a1240f and is carried in the ES
with component_tag 3 of the referenced DVB service. Note that
compared to the first example the transport stream id is omitted.
This is possible in areas where [DVB-SI-GDL] is applicable.
2.5.5. References used with interactive applications
[DVB-MHP] defines - among other things - how interactive applications
can make use of audiovisual or other multimedia services and service
components.
dvb://233a.1041.10bf.ait/1a2f.23b0?arg_1=Everest&arg_2=Kilimanjaro
Reference to the application with id 23b0, published by the
organisation with id 1a2f, as advertised in the AIT which is
transmitetd as part of the service identified by 233a.1041.10bf.
In case the application were to be launched, it should be passed
two arguments; the first argument is "Everest", and the second
argument is "Kilimanjaro".
dvb://current
The service currently selected by the Java Xlet via the
javax.tv.service.selection package.
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3. IANA Considerations
This specification requests the IANA permanently register the "dvb"
URI scheme as specified in this document and summarized in the
following template, per [BCP115]:
3.1. DVB Registration Template
URI scheme name: dvb
Status: Permanent
URI scheme syntax: See Section 2.
URI scheme semantics: See Section 2.
Encoding considerations: Conformance with RFC3986, no special
considerations.
Applications/protocols that use this URI scheme name: dvb URIs are
used throughout DVB-compliant broadcasting systems, for example
within Freeview and Freesat in the United Kingdom. They are also
used in TV-Anytime [TV-Anytime] metadata where it relates to
services transmitted by DVB systems.
Interoperability considerations: None.
Security considerations: See Section 3.2.
Contact:
Name: Mr. Alexander Adolf
Title: Chair - DVB TM-GBS working group
Affiliation: Condition-ALPHA Digital Broadcast Technology
Address: Gabelsbergerstrasse 60b, 80333 Muenchen, GERMANY
Phone: +4915112722124
Email: alexander.adolf@me.com
Author/Change controller:
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Name: Mr. Peter Siebert
Title: Executive Director
Affiliation: DVB Project
Address: 17a Ancienne Route, 1218 Grand-Sacconnex, SWITZERLAND
Phone: +41227172717
Email: siebert@dvb.org
3.2. Security Considerations
Section 7 of [RFC3986] describes general security considerations for
URI schemes. The sections relating to reliability and consistency,
malicious construction, back-end transcoding, rare IP address formats
and semantic attacks all apply to dvb URIs. The section relating to
sensitive information does not apply, given that dvb URIs do not
contain authentication information.
The security considerations of the Digital Video Broadcasting suite
of standards in general are not covered in this document.
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4. References
4.1. Normative References
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", RFC 3986,
January 2005.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 5234, January 2008.
[RFC3978] Bradner, S., "IETF Rights in Contributions", RFC 3978,
March 2005.
[DVB-URI] DVB Project, "Digital Video Broadcasting (DVB); Uniform
Resource Identifiers (URI) for DVB Systems", ETSI TS 102
851, <http://www.etsi.org/deliver/etsi_ts/102800_102899/
102851/01.01.01_60/ts_102851v010101p.pdf>.
4.2. Informative References
[BT.1306] International Telecommunication Union, "Error-correction,
data framing, modulation and emission methods for digital
terrestrial television broadcasting", ITU-R BT.1306,
October 2000.
[BO.1516] International Telecommunication Union, "Digital
multiprogramme television systems for use by satellites
operating in the 11/12 GHz frequency range", ITU-
R BO.1516, April 2001.
[J.83] International Telecommunication Union, "Digital multi-
programme systems for television, sound and data services
for cable distribution", ITU-T J.83, April 1997.
[MPEG-Systems]
Society of Motion Picture and Television Engineers,
"Information technology -- Generic coding of moving
pictures and associated audio information: Systems", ISO/
IEC 13818-1, December 2000.
[DVB] "DVB Project", <http://www.dvb.org/>.
[DVB-SVCS]
"DVB Services Sarl", <http://www.dvbservices.com/>.
[TV-Anytime]
"TV-Anytime Forum", <http://www.tv-anytime.org/>.
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[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
February 2013.
[DVB-IPTV]
DVB Project, "Digital Video Broadcasting (DVB); Transport
of MPEG-2 TS Based DVB Services over IP Based Networks",
ETSI TS 102 034, <http://www.etsi.org/deliver/etsi_ts/
102000_102099/102034/01.04.01_60/ts_102034v010401p.pdf>.
[DVB-TVA] DVB Project, "Digital Video Broadcasting (DVB); Carriage
and signalling of TV-Anytime information in DVB transport
streams", ETSI TS 102 323, <http://www.etsi.org/deliver/
etsi_ts/102300_102399/102323/01.04.01_60/
ts_102323v010401p.pdf>.
[DVB-MHP] DVB Project, "Digital Video Broadcasting (DVB); Multimedia
Home Platform (MHP) Specification 1.1.1", ETSI TS 102 812,
<http://www.etsi.org/deliver/etsi_ts/102800_102899/102812/
01.02.02_60/ts_102812v010202p.pdf>.
[DVB-SI-SPEC]
DVB Project, "Digital Video Broadcasting (DVB);
Specification for Service Information (SI) in DVB
systems", ETSI EN 300 468, <http://www.etsi.org/deliver/
etsi_en/300400_300499/300468/01.11.01_60/
en_300468v011101p.pdf>.
[DVB-SI-GDL]
DVB Project, "Digital Video Broadcasting (DVB); Guidelines
on implementation and usage of Service Information (SI)",
ETSI TS 101 211, <http://www.etsi.org/deliver/etsi_tr/
101200_101299/101211/01.09.01_60/tr_101211v010901p.pdf>.
[DVB-DATA]
DVB Project, "Digital Video Broadcasting (DVB); DVB
specification for data broadcasting", ETSI EN 301 192, <ht
tp://www.etsi.org/deliver/etsi_en/301100_301199/301192/
01.04.02_60/en_301192v010402p.pdf>.
[OCAP1.0] CableLabs, "OpenCable Application Platform (OCAP)
specification, I16", OCAP OC-SP-OCAP1.0-I16-050803.
[BCP115] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
Registration Procedures for New URI Schemes", RFC 4395,
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BCP 115, February 2006.
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URIs
[1] <http://www.dvbservices.com/>
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Authors' Addresses
Mo McRoberts (editor)
British Broadcasting Corportation
Email: mo.mcroberts@bbc.co.uk
URI: http://www.bbc.co.uk/
Alexander Adolf
Condition-ALPHA
Gabelsbergerstrasse 60b
Munich 80333
GERMANY
Email: alexander.adolf@me.com
URI: http://www.condition-alpha.com
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