International organisation for standardisation organisation internationale de normalisation

Annex A

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.

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  it is independent of the DSM used,
  
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  it is independent of whether the DSM is located at a local or remote site,
  
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  it is independent of the network protocol with which the DSM CC is interfaced,
  
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  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:

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.

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:

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  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)
  
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  mode (retrieval/storage)
  

A.0.4.2 Retrieval

The DSM CC provides the means to:

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

A.0.4.3 Storage

The DSM CC provides the means to:

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

Figure A-2 -- DSM CC bitstream decoded as a standalone bitstream

Figure A-3 -- DSM CC bitstream decoded as part of the system bitstream