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Annex A

(Informative)
Digital Storage Medium Command and Control [DSM CC]

A.0 Introduction

The DSM CC protocol is a specific application protocol intended to provide the basic control functions and operations specific to managing an ITU T Rec. H.222.0†|†ISO/IEC 13818-1 bitstream on digital storage media. This DSM CC is a low-level protocol above network/OS layers and below application layers.

The DSM CC shall be transparent in the following sense:

it is independent of the DSM used,
it is independent of whether the DSM is located at a local or remote site,
it is independent of the network protocol with which the DSM CC is interfaced,
it is independent of the various operating systems on which the DSM is operated.

A.0.1 Purpose

Many applications of ITU T Rec. H.222.0†|†ISO/IEC 13818-1 DSM Control Commands require access to an ITU T Rec. H.222.0†|†ISO/IEC 13818-1 bitstream stored on a variety of digital storage media at a local or remote site. Different DSM have their own specific control commands and thus a user would need to know different sets of specific DSM control commands in order to access ITU T Rec. H.222.0†|†ISO/IEC 13818 1 bitstreams from different DSM. This brings many difficulties to the interface design of an ITU T Rec. H.222.0†|†ISO/IEC 13818-1 or ISO 11172-1 application system. To overcome this difficulty, a set of common DSM control commands, which is independent of the specific DSM used, is suggested in this annex. This annex is informative only. ISO/IEC 13818-6 defines DSM-CC extension with a broader scope.

A.0.2 Future applications

Beyond the immediate applications supported by the current DSM control commands, future applications based on extensions of DSM command control could include the following:

Video on demand
Video programs are provided as requested by a customer through various communication channels. The customer could select a video program from a list of programs available from a video server. Such applications could be used by hotels, cable TV, educational institutions, hospitals, etc.
Interactive video services
In these applications, the user provides frequent feedback controlling the manipulation of stored video and audio. These services can include video based games, user controlled video tours, electronic shopping, etc.
Video networks
Various applications may wish to exchange stored audio and video data through some type of computer network. Users could route AV information through the video network to their terminals. Electronic publishing and multimedia applications are examples of this kind of application.

A.0.3 Benefits

Specifying the DSM control commands independ of the DSM, end-users can perform ITU T Rec. H.222.0†|†ISO/IEC 13818-1 decoding without having to fully understand the detailed operation of the specific DSM used.

The DSM control commands are codes to give end users the assurance that the ISO/IEC 13818 1 bitstreams can be played and stored with the same semantics, independent of the DSM and user interface. They are fundamental commands for the control of DSM operation.

A.0.4 Basic functions

A.0.4.1 Stream selection

The DSM CC provides the means to select an ITU T Rec. H.222.0†|†ISO/IEC 13818-1 bitstream upon which to perform the succeeding operations. Such operations include creation of a new bitstream. Parameters of this function include:

index of the ITU T Rec. H.222.0†|†ISO/IEC 13818-1 bitstream (the mapping between this index and a name meaningful to an application is outside the scope of the current DSM CC)
mode (retrieval/storage)

A.0.4.2 Retrieval

The DSM CC provides the means to:

play an identified ITU T Rec. H.222.0†|†ISO/IEC 13818-1 bitstream,
play from a given presentation time,
set the playback speed (normal or fast),
set the playback duration (until a specified presentation time, the end of the bitstream in forward play or the beginning in reverse play or the issuance of a stop command),
set the direction (forward or reverse),
pause,
resume,
change the access point in the bitstream,
stop.

A.0.4.3 Storage

The DSM CC provides the means to:

cause storage of a valid bitstream for a specified duration,
cause storage to stop.

DSM CC provides a useful but limited subset of functionality that may be required in DSM based ITU T Rec. H.222.0†|†ISO/IEC 13818-1 applications. It is fully expected that significant additional capabilities will be added through subsequent extensions.

A.1 General elements

A.1.1 Scope

The scope of this work consists of the development of an international standard to specify a useful set of commands for control of digital storage media on which an ITU T Rec. H.222.0†|†ISO/IEC 13818-1 bitstream is stored. The commands can perform remote control of a digital storage media in a general way independently of the specific DSM and apply to any ITU T Rec. H.222.0†|†ISO/IEC 13818-1 bitstream stored on a DSM.

A.1.2 Overview of the DSM CC application

The current DSM CC syntax and semantics cover the single user to DSM application. The user's system is capable of retrieving an ITU T Rec. H.222.0†|†ISO/IEC 13818-1 bitstream and is also [optionally] capable of generating an ITU T Rec. H.222.0†|†ISO/IEC 13818-1 bitstream. The control channel over which the DSM commands and acknowledgments are sent is shown in Figure A-1 as an out of band channel. This can also be accomplished by inserting the DSM CC commands and acknowledgments into the ITU T Rec. H.222.0†|†ISO/IEC 13818-1 bitstreams if an out of band channel is not available.

Figure A-1 -- Configuration of DSM CC application

A.1.3 The transmission of DSM CC commands and acknowledgments

The DSM CC is encoded into a DSM CC bitstream according to the syntax and semantics defined in A.2.2 through A.2.9. The DSM CC bitstream can be transmitted both as a stand alone bitstream and in an ITU T Rec. H.222.0†|†ISO/IEC 13818-1 Systems bitstream.

When the DSM CC bitstream is transmitted in stand alone mode, its relationship to the Systems bitstream and the decoding process is illustrated in Figure A-2 on page 89. In this case, the DSM CC bitstream is not embedded in the Systems bitstream. This transmission mode can be used in the applications when the DSM is connected directly with the ITU T Rec. H.222.0†|†ISO/IEC 13818-1 decoder. It can also be used in the applications where the DSM CC bitstream could be controlled and transmitted by other types of network multiplexors.

Figure A-2 -- DSM CC bitstream decoded as a standalone bitstream
For some applications, it is desirable to transmit the DSM CC in an ITU T Rec. H.222.0†|†ISO/IEC 13818 1 systems bitstream so that some features of the ITU T Rec. H.222.0†|†ISO/IEC 13818 1 systems bitstream could be applied to the DSM CC bitstream as well. In this case, the DSM CC bitstream is embedded in the systems bitstream by the systems multiplexor.
The DSM CC bitstream is encoded by the systems encoder in the following process. First, the DSM CC bitstream is packetized into an packetized elementary stream (PES) according to the syntax described in 2.4.3.6 of this Specification. The PES packet is then multiplexed into either a Program Stream (PS) or a Transport Stream (TS) according to the requirement of the transmission media. The decoding procedures are the inverse of the encoding procedures and are illustrated in the block diagram of the Systems decoder depicted in Figure A-3.

Figure A-3 -- DSM CC bitstream decoded as part of the system bitstream
In Figure A-3, the output of the Systems decoder is a video bitstream, audio bitstream and/or DSM CC bitstream. The DSM CC bitstream is identified by the stream_id, value '1111 0010' as defined by the stream_id table 2-18 on page 36. Once the DSM CC bitstream is identified, it follows the rules as specified by T STD or P STD.

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