rfc905.txt

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     Network Working Group                                         ISO
     Request for Comments:  905                             April 1984



                   ISO Transport Protocol Specification
                                ISO DP 8073


   Status of this Memo:       

     This document is distributed as an RFC for information only.   It
     does not specify a standard for the ARPA-Internet.

   Notes:

     1)  RFC 892 is an older version of  the  ISO  Transport  Protocol
         Specification.   Therefore  this  RFC  should  be  assumed to
         supercede RFC 892.

     2)  This document has been  prepared  by  retyping  the  text  of
         ISO/TC97/SC16/N1576  and  then  applying  proposed  editorial
         corrections  contained  in  ISO/TC97/SC16/N1695.   These  two
         documents,  taken  together, are undergoing voting within ISO
         as a Draft International Standard (DIS).

     3)  Although this RFC has been  reviewed  after  typing,  and  is
         believed  to  be  substantially  correct, it is possible that
         typographic errors not present in the ISO documents have been
         overlooked.

         Alex McKenzie
         BBN



























                             Table of Contents




     1   SCOPE AND FIELD OF APPLICATION........................ 3
     1.1   This International Standard specifies:.............. 3
     1.2   The procedures are defined in terms of:............. 4
     1.3   .................................................... 4
     1.4   .................................................... 5
     2   REFERENCES............................................ 5
     3   DEFINITIONS........................................... 6
     3.1   .................................................... 6
     3.2   .................................................... 6
     3.2.1   equipment:........................................ 7
     3.2.2   transport service user:........................... 7
     3.2.3   network service provider:......................... 7
     3.2.4   local matter:..................................... 7
     3.2.5   initiator:........................................ 7
     3.2.6   responder:........................................ 8
     3.2.7   sending transport entity:......................... 8
     3.2.8   receiving transport entity:....................... 8
     3.2.9   preferred class:.................................. 8
     3.2.10   alternative class:............................... 8
     3.2.11   proposed class:.................................. 9
     3.2.12   selected class:.................................. 9
     3.2.13   proposed parameter:.............................. 9
     3.2.14   selected parameter:.............................. 9
     3.2.15   error indication:................................ 9
     3.2.16   invalid TPDU:................................... 10
     3.2.17   protocol error:................................. 10
     3.2.18   sequence number:................................ 10
     3.2.19   transmit window:................................ 10
     3.2.20   lower window edge:.............................. 11
     3.2.21   upper window edge:.............................. 11
     3.2.22   upper window edge allocated to  the  peer
       entity:
          .................................................... 11
     3.2.23   closed window:.................................. 11
     3.2.24   window information:............................. 11
     3.2.25   frozen reference:............................... 12
     3.2.26   unassigned reference:........................... 12
     3.2.27   transparent (data):............................. 12



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     3.2.28   owner (of a network connection):................ 12
     3.2.29   retained TPDU:.................................. 12
     4   SYMBOLS AND ABBREVIATIONS............................ 13
     4.1   Data units......................................... 13
     4.2   Types of transport protocol data units............. 13
     4.3   TPDU fields........................................ 13
     4.4   Times and associated variables..................... 14
     4.5   Miscellaneous...................................... 14
     5   OVERVIEW OF THE TRANSPORT PROTOCOL................... 15
     5.1   Service provided by the transport layer............ 15
     5.2   Service assumed from the network layer............. 16
     5.3   Functions of the Transport Layer................... 18
     5.3.1   Overview of functions............................ 18
     5.3.1.1   Functions used at all times.................... 19
     5.3.1.2   Connection Establishment....................... 19
     5.3.1.3   Data Transfer.................................. 20
     5.3.1.4   Release........................................ 21
     5.4   Classes and options................................ 21
     5.4.1   General.......................................... 21
     5.4.2   Negotiation...................................... 22
     5.4.3   Choice of network connection..................... 22
     5.4.4   Characteristics of Class 0....................... 23
     5.4.5   Characteristics of Class 1....................... 23
     5.4.6   Characteristics of Class 2....................... 24
     5.4.6.1   General........................................ 24
     5.4.6.2   Use of explicit flow control................... 24
     5.4.6.3   Non-use of explicit flow control............... 24
     5.4.7   Characteristics of Class 3....................... 24
     5.4.8   Characteristics of Class 4....................... 25
     5.5   Model of the transport layer....................... 25
     6   ELEMENTS OF PROCEDURE................................ 27
     6.1   Assignment to network connection................... 27
     6.1.1   Purpose.......................................... 27
     6.1.2   Network service primitives....................... 27
     6.1.3   Procedure........................................ 28
     6.2   Transport protocol data unit (TPDU) transfer....... 29
     6.2.1   Purpose.......................................... 29
     6.2.2   Network Service Primitives....................... 30
     6.2.3   Procedure........................................ 30
     6.3   Segmenting and reassembling........................ 30
     6.3.1   Purpose.......................................... 30
     6.3.2   TPDUs and parameter used......................... 31
     6.3.3   Procedure........................................ 31



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     6.4   Concatenation and separation....................... 31
     6.4.1   Purpose.......................................... 31
     6.4.2   Procedure........................................ 32
     6.5   Connection establishment........................... 32
     6.5.1   Purpose.......................................... 32
     6.5.2   Network service primitives....................... 33
     6.5.3   TPDUs and parameters used........................ 33
     6.5.4   Procedure........................................ 34
     6.6   Connection refusal................................. 40
     6.6.1   Purpose.......................................... 40
     6.6.2   TPDUs and parameters used........................ 40
     6.6.3   Procedure........................................ 41
     6.7   Normal release..................................... 41
     6.7.1   Purpose.......................................... 41
     6.7.2   Network service primitives....................... 42
     6.7.3   TPDUs and parameters used........................ 42
     6.7.4   Procedure for implicit variant................... 43
     6.7.5   Procedure for explicit variant................... 43
     6.8   Error Release...................................... 44
     6.8.1   Purpose.......................................... 45
     6.8.2   Network service primitives....................... 45
     6.8.3   Procedure........................................ 45
     6.9    Association   of   TPDUs   with   transport
       connections
          .................................................... 45
     6.9.1   Purpose.......................................... 45
     6.9.2   Network service primitives....................... 46
     6.9.3   TPDUs and parameters uses........................ 46
     6.9.4   Procedures....................................... 46
     6.9.4.1   Identification of TPDUs........................ 46
     6.9.4.2   Association of individual TPDUs................ 47
     6.10   Data TPDU numbering............................... 49
     6.10.1   Purpose......................................... 49
     6.10.2   TPDUs and parameters used....................... 49
     6.10.3   Procedure....................................... 50
     6.11   Expedited data transfer........................... 50
     6.11.1   Purpose......................................... 50
     6.11.2   Network service primitives...................... 50
     6.11.3   TPDUs and parameter used........................ 51
     6.11.4   Procedures...................................... 51
     6.12   Reassignment after failure........................ 52
     6.12.1   Purpose......................................... 52
     6.12.2   Network service primitives...................... 52



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     6.12.3   Procedure....................................... 52
     6.12.4   Timers.......................................... 54
     6.13   Retention until acknowledgement of TPDUs.......... 56
     6.13.1   Purpose......................................... 56
     6.13.2   Network service primitives...................... 56
     6.13.3   TPDUs and parameters used....................... 56
     6.13.4   Procedures...................................... 57
     6.14   Resynchronization................................. 60
     6.14.1   Purpose......................................... 60
     6.14.2   Network service primitives...................... 60
     6.14.3   TPDUs and parameters used....................... 60
     6.14.4   Procedure....................................... 61
     6.14.4.1   Active resynchronization procedures........... 61
     6.14.4.2   Passive resynchronization procedures.......... 62
     6.14.4.3   Data Resynchronization Procedures............. 63
     6.15   Multiplexing and demultiplexing................... 64
     6.15.1   Purpose......................................... 64
     6.15.2   TPDUs and parameters used....................... 64
     6.15.3   Procedure....................................... 65
     6.16   Explicit Flow Control............................. 65
     6.16.1   Purpose......................................... 65
     6.16.2   TPDUs and parameters used....................... 65
     6.16.3   Procedure....................................... 66
     6.17   Checksum.......................................... 66
     6.17.1   Purpose......................................... 66
     6.17.2   TPDUs and parameters used....................... 66
     6.17.3   Procedure....................................... 67
     6.18   Frozen references................................. 68
     6.18.1   Purpose......................................... 68
     6.18.2   Procedure....................................... 68
     6.18.2.1   Procedure for classes 0 and 2................. 68
     6.18.2.2   Procedure for classes 1 and 3................. 69
     6.18.2.3   Procedure for classes 4....................... 70
     6.19   Retransmission on time-out........................ 70
     6.19.1   Purpose......................................... 70
     6.19.2   TPDUs used...................................... 70
     6.19.3   Procedure....................................... 70
     6.20   Resequencing...................................... 70
     6.20.1   Purpose......................................... 71
     6.20.2   TPDUs and parameters used....................... 71
     6.20.3   Procedure....................................... 71
     6.21   Inactivity control................................ 71
     6.21.1   Purpose......................................... 71



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     6.21.2   Procedure....................................... 72
     6.22   Treatment of protocol errors...................... 72
     6.22.1   Purpose......................................... 72
     6.22.2   TPDUs and parameters used....................... 72
     6.22.3   Procedure....................................... 72
     6.23   Splitting and recombining......................... 74
     6.23.1   Purpose......................................... 74
     6.23.2   Procedure....................................... 74
     7   Protocol Classes..................................... 76
     8   SPECIFICATION FOR CLASS 0. SIMPLE CLASS.............. 79
     8.1   Functions of class 0............................... 79
     8.2   Procedures for class 0............................. 79
     8.2.1   Procedures applicable at all times............... 79
     8.2.2   Connection establishment......................... 79
     8.2.3   Data transfer.................................... 80
     8.2.4   Release.......................................... 80
     9    SPECIFICATION  FOR  CLASS  1:   BASIC   ERROR
       RECOVERY CLASS
          .................................................... 81
     9.1   Functions of Class 1............................... 81
     9.2   Procedures for Class 1............................. 81
     9.2.1   Procedures applicable at all times............... 81
     9.2.2   Connection establishment......................... 82
     9.2.3   Data Transfer.................................... 82
     9.2.3.1   General........................................ 82
     9.2.3.2   Expedited Data................................. 83
     9.2.4   Release.......................................... 84
     10   SPECIFICATION  FOR  CLASS  2  -  MULTIPLEXING
       CLASS
          .................................................... 85
     10.1   Functions of class 2.............................. 85
     10.2   Procedures for class 2............................ 85
     10.2.1   Procedures applicable at all times.............. 85
     10.2.2   Connection establishment........................ 86
     10.2.3   Data transfer when non  use  of  explicit
       flow control
          .................................................... 86
     10.2.4   Data transfer when use of  explicit  flow
       control
          .................................................... 86
     10.2.4.1   General....................................... 86
     10.2.4.2   Flow control.................................. 87
     10.2.4.3   Expedited data................................ 88



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     10.2.5   Release......................................... 89
     11   SPECIFICATION FOR CLASS 3: ERROR RECOVERY AND
       MULTIPLEXING CLASS
          .................................................... 90
     11.1   Functions of Class 3.............................. 90
     11.2   Procedures for Class 3............................ 90
     11.2.1   Procedures applicable at all times.............. 90
     11.2.2   Connection Establishment........................ 91
     11.2.3   Data Transfer................................... 91
     11.2.3.1   General....................................... 91
     11.2.3.2   Use of RJ TPDU................................ 92
     11.2.3.3   Flow Control.................................. 93
     11.2.3.4   Expedited data................................ 93
     11.2.4   Release......................................... 94
     12   SPECIFICATION FOR CLASS  4:  ERROR  DETECTION
       AND RECOVERY CLASS
          .................................................... 95
     12.1   Functions of Class 4.............................. 95
     12.2   Procedures for Class 4............................ 95
     12.2.1   Procedures available at all times............... 95
     12.2.1.1   Timers used at all times...................... 95
     12.2.1.1.1   NSDU lifetime (MLR, MRL).................... 98
     12.2.1.1.2   Expected maximum transit delay  (ELR,
       ERL)
          .................................................... 98
     12.2.1.1.3   Acknowledge Time (AR, AL)................... 99
     12.2.1.1.4   Local retransmission time (T1).............. 99
     12.2.1.1.5   Persistence Time (R)........................ 99
     12.2.1.1.6    Bound  on  References  and  Sequence
       Numbers (L)
          ................................................... 100
     12.2.1.2   General Procedures........................... 100
     12.2.2   Procedures for Connection Establishment........ 102
     12.2.2.1   Timers used in Connection Establishment...... 102
     12.2.2.2   General Procedures........................... 103
     12.2.3   Procedures for Data Transfer................... 104
     12.2.3.1   Timers used in Data Transfer................. 104
     12.2.3.2   General Procedures for data transfer......... 104
     12.2.3.3   Inactivity Control........................... 105
     12.2.3.4   Expedited Data............................... 105
     12.2.3.5   Resequencing................................. 106
     12.2.3.6   Explicit Flow Control........................ 107
     12.2.3.7   Sequencing of received AK TPDUs.............. 108



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     12.2.3.8   Procedure for transmission of AK TPDUs....... 109
     12.2.3.8.1   Retransmission of AK TPDUs for window
       synchronization
          ................................................... 109
     12.2.3.8.2   Sequence control for transmission  of
       AK TPDUs
          ................................................... 109
     12.2.3.8.3   Retransmission of AK TPDUs after  CDT
       set to zero
          ................................................... 110
     12.2.3.8.4   Retransmission  procedures  following
       reduction of the
          ................................................... 111
     12.2.3.9    Use  of  Flow   Control   Confirmation
       parameter
          ................................................... 112
     12.2.4   Procedures for Release......................... 113
     12.2.4.1   Timers used for Release...................... 113
     12.2.4.2   General Procedures for Release............... 113
     13   STRUCTURE AND ENCODING OF TPDUs.................... 114
     13.1   Validity......................................... 114
     13.2   Structure........................................ 116
     13.2.1   Length indicator field......................... 117
     13.2.2   Fixed part..................................... 117
     13.2.2.1   General...................................... 117
     13.2.2.2   TPDU code.................................... 117
     13.2.3   Variable part.................................. 118
     13.2.3.1   Checksum Parameter (Class 4 only)............ 120
     13.2.4   Data Field..................................... 120
     13.3   Connection Request (CR) TPDU..................... 120
     13.3.1   Structure...................................... 120
     13.3.2   LI............................................. 121
     13.3.3   Fixed Part (Octets 2 to 7)..................... 121