










                     SYSTEM USE SHARING

                          PROTOCOL

                          VERSION 1



             A MECHANISM FOR EXTENSIBLE SHARING

             OF ISO 9660:1988 SYSTEM USE AREAS



                   ROCK RIDGE TECHNICAL

                       WORKING GROUP



                       Revision 1.09



                   cdtec@dgdo.Eng.Sun.COM



                          PROPOSAL


























                          CONTENTS

1.  PREFACE.............................................   1
    1.1  Purpose and Scope..............................   1
    1.2  Summary of Sections............................   1
2.  OVERVIEW............................................   2
3.  TERMINOLOGY AND NOTATION............................   3
    3.1  Decimal and Hexadecimal Notation...............   3
    3.2  System Use Areas...............................   3
4.  SYSTEM USE SHARING PROTOCOL.........................   4
    4.1  System Use Field Format........................   5
5.  SYSTEM USE FIELDS PROVIDED BY THIS
    SPECIFICATION.......................................   6
    5.1  Description of the CE System Use Field.........   6
    5.2  Description of the PD System Use Field.........   7
    5.3  Description of the SP System Use Field.........   8
    5.4  Description of the ST System Use Field.........  10
    5.5  Description of the ER System Use Field.........  10
6.  REQUIREMENTS FOR SYSTEMS............................  14
    6.1  Requirements for an Originating System. .......  14
    6.2  Requirements for a Receiving System............  14
    6.3  Requirements for an Application Programming
         Interface......................................  15
    6.4  Coexistence with other Extensions and SUSP
         Registry.......................................  15
    6.5  Implementation Suggestions.....................  16
7.  BIBLIOGRAPHY........................................  17
























                           - i -









                       LIST OF TABLES

TABLE  2.  System Use Field Description - Version 1.....   5
TABLE  4.  CE System Use Field - Version 1..............   7
TABLE  6.  PD System Use Field - Version 1..............   8
TABLE  8.  SP System Use Field - Version 1..............   9
TABLE 10.  ST System Use Field - Version 1..............  10
TABLE 12.  ER System Use Field - Version 1..............  13











































                           - ii -





Rock Ridge Group                 System Use Sharing Protocol


1.  PREFACE

1.1  Purpose and Scope

     The ISO 9660:1988 CD-ROM  format  provides  System  Use
Areas  within  the  Directory  Records to support convenient
extensibility  of  the  specification.   Unfortunately,   no
mechanism  for  coordinating  shared  use of these areas was
provided.   This  has  led  to  very  restricted  and   non-
standardized use of these areas.  It is desirable to develop
the following proposed standard for  shared  utilization  of
the System Use Areas provided by ISO 9660.

1.2  Summary of Sections

Section 1   Contains this preface.
Section 2   Contains an overview of the System Use Sharing Protocol.
Section 3   Contains an overview of the notation used in this document.
Section 4   Contains the System Use Sharing Protocol proposal.
Section 5   Contains the System Use Fields provided by the SUSP.
Section 6   Contains the SUSP Application Programming Interface.
Section 7   Contains the bibliography.
































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System Use Sharing Protocol                 Rock Ridge Group


2.  OVERVIEW

     The System Use Sharing  Protocol  (SUSP)  specifies  an
extension  to  the  ISO 9660 format for CD-ROM which enables
the shared utilization of the System Use Areas  provided  by
ISO  9660:1988  for  recording system-specific extensions to
ISO 9660 defined by multiple independent parties.

The SUSP specifies the definition of a generic field  format
and  a  set  of  generally  applicable System Use Fields for
recording:

                  + Continuation Areas
                  + Padding Areas
                  + Identifier that the System  Use  Sharing
                    Protocol is used
                  + System Use Sharing Protocol Terminator
                  + Identifier of system-specific extensions
                    that are used



































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3.  TERMINOLOGY AND NOTATION

     It is assumed that the SUSP is being utilized within an
ISO  9660:1988  compliant  volume. Unless defined herein, or
otherwise specified,  terms  shall  be  as  defined  in  ISO
9660:1988.

The following notation is used in this document.

3.1  Decimal and Hexadecimal Notation

     Numbers in decimal notation are represented by  decimal
digits, namely 0 to 9.

Numbers  in  hexadecimal   notation   are   represented   by
hexadecimal  digits,  namely  0  to  9  and A to F, shown in
parentheses. E.g. the hexadecimal number 7F will be  written
as (7F).

3.2  System Use Areas

     ISO  9660:1988  provides  System   Use   Areas   within
Directory  Records.  While a similar mechanism could be used
in many other ways  within  the  ISO  9660  structure,  this
System  Use  Sharing  Protocol addresses only the System Use
Areas within the Directory Records.

In the descriptions in this document, the phrase "System Use
Area"  shall refer equally to the System Use Areas specified
as  well  as  any  Continuation  of  the  System  Use  Areas
designated  through the use of "CE" System Use Fields (CE is
described in the section titled "SYSTEM USE FIELDS  PROVIDED
BY THIS SPECIFICATION").





















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System Use Sharing Protocol                 Rock Ridge Group


4.  SYSTEM USE SHARING PROTOCOL

     The System Use Sharing Protocol divides any System  Use
Area  into  a number of variable length fields called System
Use Fields.  There may be zero or more System Use Fields  in
each  System  Use Area.  Each System Use Field is identified
by a System Use Field Signature Word (described below).

More than one System Use Field with the same signature  word
is  allowed, unless otherwise specified in the definition of
a specific System Use Field.  If allowed,  the  significance
of  the  order,  if any, of the recording of multiple System
Use Fields with the same signature word shall  be  specified
in  the  definition  of  the  particular  System  Use  Field
involved.  In all other situations, the order in  which  the
System Use Fields appear is not significant.

Unless otherwise specified in the definition of  a  specific
System  Use  Field,  each  System  Use Field recorded in the
System Use Area of the last extent of  a  multi-extent  file
shall  apply  to  all extents of the file and shall override
any System Use Field with the same  signature  recorded  for
any  other  extent  of  the file.  Thus, unless an alternate
mechanism is provided in the definition of a specific System
Use  Field, failure to record a valid instance of the System
Use Field for the final extent of a multi-extent file  shall
be  treated  the same as if this field had not been recorded
for any extent of the file.

With the exception of the "SP" field, which is  recorded  as
specified  in  section  5.3,  the  first  System  Use  Field
recorded in a System Use Area of any Directory Record  shall
begin  in byte LEN_SKP+1 of the System Use Area (see section
5.3 [5]).  The  first  System  Use  Field  recorded  in  any
Continuation  of  a System Use Area shall begin in the first
byte of the Continuation.  If more than one System Use Field
is   to   be  recorded  in  the  same  System  Use  Area  or
Continuation, they shall be recorded contiguously.

If the remaining allocated space following the last recorded
System  Use  Field  in  a  System Use Area is less than four
bytes long, it cannot be a System Use  Field  and  shall  be
ignored.  Otherwise  the  use  of  the  System  Use  Sharing
Protocol should be terminated by the "ST"  field  or  filled
with the "PD" field, which are described in Chapter 5.









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Rock Ridge Group                 System Use Sharing Protocol


4.1  System Use Field Format

     The System Use Field format is as follows:

     [1]  "BP 1 to BP 2 - Signature Word" shall  specify  an
          identification  of a System Use Field.  This field
          shall contain two bytes.  Each  byte  is  recorded
          according  to  the  ISO  9660:1988  Format Section
          7.1.1.

     [2]  "BP 3 - Length (LEN_SUF)" shall specify as  an  8-
          bit  number  the length in bytes of the System Use
          Field,  including  the  Signature  Word,   Length,
          Version  and System Use content.  This field shall
          be recorded  according  to  the  ISO  9660  Format
          section 7.1.1.

     [3]  "BP 4 - System Use Field Version" shall specify as
          an  8-bit  number an identification of the version
          of the System  Use  Field.  This  field  shall  be
          recorded  according  to  ISO  9660  Format section
          7.1.1.

     [4]  "BP 5 to LEN_SUF - Data" shall contain the content
          of the System Use Field.  The format of this field
          depends on the Signature Word and Version  of  the
          System Use Field.  The Data field is optional.


     TABLE 2.  System Use Field Description - Version 1

   ______________________________________________________

    SIG1    SIG2    LENGTH   VERSION         DATA
    (BP1)   (BP2)   (BP3)     (BP4)    (BP5 to LEN_SUF)

   ______________________________________________________

















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System Use Sharing Protocol                 Rock Ridge Group


5.  SYSTEM USE FIELDS PROVIDED BY THIS SPECIFICATION

     The System Use Sharing Protocol defines  the  following
fundamental System Use Fields:


       "CE"   Continuation Area
       "PD"   Padding Field
       "SP"   System Use Sharing Protocol Indicator
       "ST"   System Use Sharing Protocol Terminator
       "ER"   Extensions Reference


5.1  Description of the CE System Use Field

     The purpose of the "CE" System Use Field is  to  extend
the  System  Use Area to store additional System Use Fields.
The "CE" System Use Field is optional.  There is at most one
"CE" System Use Field in a System Use or Continuation Area.

The entire single  Logical  Sector  which  begins  with  the
Logical  Block  referred to by a "CE" System Use Field shall
be used as an additional System Use Area.  The recording  in
any  Continuation  of  the  System Use Area shall follow the
Format of the System Use Area as described in  the  previous
section of this document.  All Continuation Areas identified
by "CE" fields must reside on the same Volume  as  the  "CE"
field.   If  additional space is needed, the Continuation of
the System Use Area identified by a "CE"  System  Use  Field
may  contain  another  "CE"  System  Use  Field  designating
another Continuation of  the  System  Use  Area.   The  "CE"
System  Use  Field indicates a Continuation Area that should
be  processed  after  the  current  System   Use   Area   or
Continuation Area is processed.

Note: For maximum compatibility with  pre-existing  systems,
system  use fields which predate this document should not be
recorded within Continuation Areas.

The format of the "CE" System Use Field is as follows:

     [1]  "BP 1 to BP 2 -  Signature  Word"  shall  indicate
          that  the  System  Use Field is a "CE" type System
          Use Field.  The  bytes  in  this  field  shall  be
          (43)(45) ("CE").

     [2]  "BP 3 - Length (LEN_SUF)" shall specify as  an  8-
          bit  number the length in bytes of the "CE" System
          Use Field.  The number in this field shall  be  28
          for  this  version.   This field shall be recorded
          according to  the  ISO  9660:1988  Format  section
          7.1.1.


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     [3]  "BP 4 - System Use Field Version" shall specify as
          an  8-bit  number an identification of the version
          of the "CE" System Use Field.  The number in  this
          field  shall  be  1  for this version.  This field
          shall be recorded according to the  ISO  9660:1988
          Format section 7.1.1.

     [4]  "BP 5 to BP  12  -  Location  of  Continuation  of
          System  Use Area" shall specify as a 32-bit number
          the Logical Block  Number  of  the  first  Logical
          Block  of  the  Logical  Sector  that contains the
          start of this Continuation of the Sytem Use  Area.
          This  field shall be recorded according to the ISO
          9660:1988 Format section 7.3.3.

     [5]  "BP 13 to BP 20 - Offset to Start of Continuation"
          shall  specify  as  a 32-bit number the offset, in
          bytes, from the start of the  block  specified  in
          [4]  above  to the start of the area that is to be
          used for this Continuation of the System Use Area.
          This  field shall be recorded according to the ISO
          9660:1988 Format section 7.3.3.

     [6]  "BP 21 to BP 28  -  Length  of  the  Continuation"
          shall  specify  as  a  32-bit number the number of
          bytes that are to be used for this Continuation of
          the System Use Area.  This field shall be recorded
          according to  the  ISO  9660:1988  Format  section
          7.3.3.


         TABLE 4.  CE System Use Field - Version 1

___________________________________________________________________

 'C'   'E'   28     1     LOCATION        OFFSET     LEN of CONTINUATION
(BP1) (BP2) (BP3) (BP4) (BP5 to BP12) (BP13 to BP20)   (BP21 to BP28)

___________________________________________________________________


5.2  Description of the PD System Use Field

     The purpose of the "PD" System Use Field is to  provide
flexibility.   The "PD" System Use Field is optional.  There
may be more than one "PD" System Use Field in a  System  Use
Area.   The  "PD" System Use Field(s) may appear anywhere in
the System Use Area.






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System Use Sharing Protocol                 Rock Ridge Group


The format of the "PD" System Use Field is as follows:

     [1]  "BP 1 to BP 2 -  Signature  Word"  shall  indicate
          that  the  System  Use Field is a "PD" type System
          Use Field.  The  bytes  in  this  field  shall  be
          (50)(44) ("PD").

     [2]  "BP 3 - Length (LEN_PAD)" shall specify as  an  8-
          bit  number the length in bytes of the "PD" System
          Use Field.  This field shall be recorded according
          to the ISO 9660:1988 Format Section 7.1.1.

     [3]  "BP 4 - System Use Field Version" shall specify as
          an  8-bit  number an identification of the version
          of the "PD" System Use Field.  The number in  this
          field  shall  be  1  for this version.  This field
          shall be recorded according to the  ISO  9660:1988
          Format section 7.1.1.

     [4]  "BP 5 to LEN_PAD - Padding Area" shall be  ignored
          in  interchange.   The contents are not restricted
          by this specification.


         TABLE 6.  PD System Use Field - Version 1

    ___________________________________________________

      'P'     'D'    LENGTH     1       PADDING AREA
     (BP1)   (BP2)   (BP3)    (BP4)   (BP5 to LEN_PAD)

    ___________________________________________________


5.3  Description of the SP System Use Field

     The purpose of the "SP" System Use Field is to  provide
an  identifier that the System Use Sharing Protocol is being
used within the given volume.  Additionally the "SP"  System
Use  Field  specifies the number of bytes skipped within the
System Use Area  of  a  Directory  Record  before  recording
System  Use  Fields  (except  the  "."  entry  of  the  root
directory).

The "SP" System Use Field is mandatory.  The "SP" System Use
Field  must be recorded starting in byte position one (BP 1)
in the System Use Area of the first Directory Record of  the
root  directory  of  each  directory  structure in which the
System Use Sharing Protocol  is  utilized.   Only  one  "SP"
System   Use  Field  should  be  recorded  within  a  single
directory structure.



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The format of the "SP" System Use Field is as follows:

     [1]  "BP 1 to BP 2 - Signature" shall indicate that the
          System  Use Field is a "SP" type System Use Field.
          The bytes in this field shall be (53)(50) ("SP").

     [2]  "BP 3 - Length" shall specify as an  8-bit  number
          the  length in bytes of the "SP" System Use Field.
          The number in this  field  shall  be  7  for  this
          version.  It  shall  be  recorded according to ISO
          9660 Format section 7.1.1.

     [3]  "BP 4 - System Use Field Version" shall specify as
          an  8-bit  number an identification of the version
          of the "SP" System Use Field. The number  in  this
          field  shall  be  1  for  this version. This field
          shall be recorded according  to  ISO  9660  Format
          section 7.1.1.

     [4]  "BP 5 to BP 6 - Check  Bytes"  shall  contain  two
          check  bytes.  The  value of the bytes recorded in
          this field shall be verified in  interchange.  The
          bytes in this field shall be (BE)(EF).

     [5]  "BP 7 - Bytes Skipped (LEN_SKP)" shall specify  as
          an  8-bit number the number of bytes to be skipped
          within the  System  Use  Area  of  each  Directory
          Record   (except   the   "."  entry  of  the  root
          directory)  before  recording  System  Use  Fields
          other  than  the  "SP"  field.  The number in this
          field shall be  recorded  according  to  ISO  9660
          Format section 7.1.1.


         TABLE 8.  SP System Use Field - Version 1

 _________________________________________________________

   'S'     'P'      7       1     (BE)    (EF)    LEN_SKP
  (BP1)   (BP2)   (BP3)   (BP4)   (BP5)   (BP6)    (BP7)

 _________________________________________________________


Note:  To allow compatibility with other uses of the  System
Use  Area, the contents of BP 1 to LEN_SKP of the System Use
Area of each Directory Record are  not  restricted  by  this
specification.






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System Use Sharing Protocol                 Rock Ridge Group


5.4  Description of the ST System Use Field

     The purpose of the "ST" System Use Field is to  provide
a  terminator for the use of the System Use Sharing Protocol
for a particular System Use Area or Continuation Area.   The
"ST"  System  Use  Field  indicates  the  completion  of any
information that conforms to the System Use Sharing Protocol
within  the particular System Use or Continuation Area.  The
"ST" System Use Field is optional.

The format of the "ST" System Use Field is as follows:

     [1]  "BP 1 to BP 2 - Signature" shall indicate that the
          System  Use Field is a "ST" type System Use Field.
          The bytes in this field shall be (53)(54) ("ST").

     [2]  "BP 3 - Length" shall specify as an  8-bit  number
          the  length in bytes of the "ST" System Use Field.
          The number in this  field  shall  be  4  for  this
          version.  It  shall  be  recorded according to ISO
          9660 Format section 7.1.1.

     [3]  "BP 4 - System Use Field Version" shall specify as
          an  8-bit  number an identification of the version
          of the "ST" System Use Field. The number  in  this
          field  shall  be  1  for  this version. This field
          shall be recorded according  to  ISO  9660  Format
          section 7.1.1.


         TABLE 10.  ST System Use Field - Version 1

              _______________________________

                'S'     'T'      4       1
               (BP1)   (BP2)   (BP3)   (BP4)

              _______________________________


Note:  The Data field of the System Use Field  is  optional,
thus it is not used in the "ST" System Use Field.


5.5  Description of the ER System Use Field

     The purpose of the "ER"  (Extension  Reference)  System
Use   Field   is   to  store  information  which  (uniquely)
identifies a  specification  of  system-specific  extensions
utilized on a specific volume.




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Whether this System Use Field is mandatory or optional shall
be  specified  by  each  complying system-specific extension
specification.  Multiple copies of this System Use Field may
occur  specifying  the  encoding  of multiple collections of
system-specific extensions used within  a  single  directory
structure.

This System Use Field,  if  recorded,  must  appear  in  the
System  Use  Area  of  the  first  ("dot" or (00)) Directory
Record of the root directory of the directory  structure  in
which  the  system-specific  extensions  to  which this "ER"
System Use Field refers are used.

It is the  responsibility  of  the  Publisher  to  avoid  or
resolve    conflicts   between   different   system-specific
extensions utilized on their publications.

Note that the instance of the  root  Directory  Record  that
appears  in  the  Primary Volume Descriptor cannot contain a
System Use Area, thus the root Directory Record as  recorded
in  the  "dot"  entry  of the root directory must be used to
record and retrieve this information.

The format of the "ER" System Use Field is as follows:

     [1]  "BP 1 to BP 2 -  Signature  Word"  shall  indicate
          that  the  System  Use Field is a "ER" type System
          Use Field.  The  bytes  in  this  field  shall  be
          (45)(52) ("ER").

     [2]  "BP 3 - Length (LEN_ER)" shall specify as an 8-bit
          number  the length in bytes of the "ER" System Use
          Field.  The number in this  field  shall  be  8  +
          LEN_ID + LEN_DES + LEN_SRC for this version.  This
          field shall  be  recorded  according  to  the  ISO
          9660:1988 Format Section 7.1.1.

     [3]  "BP 4 - System Use Field Version" shall specify as
          an  8-bit  number an identification of the version
          of the "ER" System Use Field.  The number in  this
          field  shall  be  1  for this version.  This field
          shall be recorded according to the  ISO  9660:1988
          Format section 7.1.1.

     [4]  "BP 5 - Identifier Length (LEN_ID)" shall  specify
          as  an  8-bit  number  the  length in bytes of the
          Extension Identifier recorded in this "ER"  System
          Use Field.  This field shall be recorded according
          to the ISO 9660:1988 Format Section 7.1.1.





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     [5]  "BP 6 - Descriptor Length (LEN_DES)" shall specify
          as  an  8-bit  number  the  length in bytes of the
          Extension Descriptor recorded in this "ER"  System
          Use Field.  This field shall be recorded according
          to the ISO 9660:1988 Format Section 7.1.1.

     [6]  "BP 7 - Source Length (LEN_SRC)" shall specify  as
          an  8-bit  number  the  length  in  bytes  of  the
          Extension Specification Source  recorded  in  this
          "ER"  System  Use  Field..   This  field  shall be
          recorded according to  the  ISO  9660:1988  Format
          Section 7.1.1.

     [7]  "BP 8 - Extension Version (EXT_VER)" Shall specify
          as  an  8-bit  number  an  identification  of  the
          version of the system-specific extensions to which
          this  "ER" System Use Field refers.  The number in
          this field shall be specified by the  organization
          which  defined  the  extensions to which this "ER"
          System Use Field  refers.   This  field  shall  be
          recorded  according  to  the  ISO 9660:1988 Format
          Section 7.1.1.

     [8]  "BP  9  to  8  +  LEN_ID  -  Extension  Identifier
          (EXT_ID)"   shall   contain  the  content  of  the
          Extension  Identifier.   The  recording  of   this
          identifier shall use d-characters or d1-characters
          as defined by ISO  9660:1988  section  7.4.   This
          field  is  mandatory.   The  exact content of this
          field  is  specified  by  the  organization  which
          defined  the  extensions to which this "ER" System
          Use Field refers.

     [9]  "BP 9 + LEN_ID to 8 + LEN_ID + LEN_DES - Extension
          Descriptor (EXT_DES)" shall contain the content of
          the Extension Descriptor.  The recording  of  this
          descriptor shall use a-characters or a1-characters
          as defined by ISO  9660:1988  section  7.4.   This
          field  is  optional.   The minimal content of this
          field may  be  specified  or  recommended  by  the
          organization which defined the extensions to which
          this "ER" System Use Field refers.   Recording  of
          information   in  addition  to  any  such  minimal
          information specified shall follow  the  recording
          of said information.









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    [10] "BP 9 + LEN_ID + LEN_DES to 8 + LEN_ID + LEN_DES +
          LEN_SRC   -   Extension  Source  (EXT_SRC)"  shall
          contain the content of the Extension Source.   The
          recording of this Source shall use a-characters or
          a1-characters as defined by ISO 9660:1988  section
          7.4.    This  field  is  mandatory.   The  minimal
          content  of  this  field  may  be   specified   or
          recommended  by the organization which defined the
          extensions to which this  "ER"  System  Use  Field
          refers.   Recording  of information in addition to
          any  such  minimal  information  specified   shall
          follow the recording of said information.


             TABLE 12.  ER System Use Field - Version 1

_______________________________________________________________________

 'E'     'R'    LENGTH     1     LEN_ID   LEN_DES   LEN_SRC   EXT_VER
(BP1)   (BP2)   (BP3)    (BP4)   (BP5)     (BP6)     (BP7)     (BP8)

_______________________________________________________________________



       ______________________________________________________

             EXT_ID                     EXT_DES
        (BP9 to 8+LEN_ID)   (BP9+LEN_ID to 8+LEN_ID+LEN_DES)

       ______________________________________________________



         __________________________________________________

                              EXT_SRC
          (BP9+LEN_ID+LEN_DES to 8+LEN_ID+LEN_DES+LEN_SRC)

         __________________________________________________














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6.  REQUIREMENTS FOR SYSTEMS

     The System Use Sharing Protocol specifies that  certain
information  shall  be  communicated  between  a user and an
implementation.

An information  processing  system  that  conforms  to  this
protocol  shall  be  the  subject  of  a  description  which
identifies the means by  which  the  user  may  supply  such
information,  or may obtain it when it is made available, as
specified in this standard.

6.1  Requirements for an Originating System

     All originating systems which claim  to  implement  the
System  Use  Sharing  Protocol must comply with the protocol
throughout each recorded System Use Area.

The implementation shall be capable of recording  a  set  of
System  Use Fields in System Use Areas that are specified in
this standard, on a Volume Set in accordance with one of the
interchange levels specified in ISO 9660:1988.

The implementation shall allow the data preparer  to  supply
the  information  that  is  to be recorded in the System Use
Area according to the System Use Sharing Protocol and  shall
supply the information for a field if the data preparer does
not supply it.

6.2  Requirements for a Receiving System

     All receiving systems  which  claim  to  implement  the
System  Use  Sharing Protocol must implement the "CE" System
Use Field as defined in this specification.

Any System Use Field which the  receiving  system  does  not
recognize is to be ignored and skipped.

The implementation shall be capable  of  reading  a  set  of
System  Use Fields in System Use Areas that are specified in
this standard from a Volume Set in accordance  with  one  of
the interchange levels specified in ISO 9660:1988.

The  implementation  shall  allow   the   user   to   supply
information  sufficient  to  enable  the  implementation  to
locate the System Use Fields in System Use Areas required by
the  user,  and  to  locate  the  volumes on which these are
recorded.

The implementation shall make  available  to  the  user  the
information  that  is  recorded  in  each  of the System Use
Fields in each System Use Area.


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6.3  Requirements for an Application Programming Interface

     All receiving systems  which  claim  to  implement  the
System  Use  Sharing  Protocol must implement an Application
Programming  Interface  (API)  to  provide  access  to   the
information  recorded  in  the  System  Use  Areas  within a
volume.

The API must provide a mechanism to verify the  use  of  the
SUSP  (by  checking for the existence of a valid "SP" field)
and retrieve data recorded in the System Use Areas within  a
volume.   The  mechanism  must,  at  a  minimum,  be able to
retrieve, for each Directory Record:


   + a complete, individual System Use Field, including  all
     header  information,  selectable  by  Signature,  field
     count or both; and,
   + the contents of the Skip Area, BP 1 to LEN_SKP  of  the
     System Use Area of the Directory Record.


Optionally,  the  API  may  also  provide  a  mechanism   to
retrieve, for each Directory Record:


   + a concatenated collection of all fields with a specific
     Signature in recorded order; or,
   + a concatenated collection of  all  fields  in  recorded
     order.


The  mechanism  to  retrieve  such  data  must  be  able  to
correctly  and transparently interpret pertinent "CE" System
Use Fields to assure the complete retrieval of the requested
data.

6.4  Coexistence with other Extensions and SUSP Registry

     Adherence to the System Use Sharing  Protocol  provides
for  the  mutual  coexistence  of  different system-specific
extensions to ISO 9660:1988 by defining System Use Fields to
be recorded in System Use Areas.

A registry system will be established to monitor and  record
existing   and  new  System  Use  Field  specifications  and
distribute this information to individuals or  organizations
pursuing   the   implementation  of  new  and/or  compatible
system-specific extensions.





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6.5  Implementation Suggestions

     For special cases, receiving systems are encouraged  to
provide  a  mechanism  to  optionally disable the System Use
Sharing Protocol in its entirety.

















































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7.  BIBLIOGRAPHY

   + ISO 9660:1988 - Information  Processing  -  Volume  and
     file structure of CD-ROM for information interchange
   + Wong, T. September 12, 1989. Extensions to the ISO 9660
     CD-ROM  Volume  and  File  Structure  Format to support
     POSIX File System Semantics.















































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