rfc905.txt

RFC 相关的技术文档

     13.5.2   LI............................................. 129
     13.5.3   Fixed Part (Octets 2 to 7...................... 130
     13.5.4   Variable Part (Octets 8 to p).................. 131
     13.5.5   User Data (Octets p+1 to the end).............. 131
     13.6   Disconnect Confirm (DC) TPDU..................... 132
     13.6.1   Structure...................................... 132
     13.6.2   LI............................................. 132
     13.6.3   Fixed Part (Octets 2 to 6)..................... 132
     13.6.4   Variable Part.................................. 133
     13.7   Data (DT) TPDU................................... 133
     13.7.1   Structure...................................... 133
     13.7.2   LI............................................. 134
     13.7.3   Fixed Part..................................... 134
     13.7.4   Variable Part.................................. 135
     13.7.5   User Data Field................................ 135
     13.8   Expedited Data (ED) TPDU......................... 135
     13.8.1   Structure...................................... 135
     13.8.2   LI............................................. 136
     13.8.3   Fixed Part..................................... 136
     13.8.4   Variable Part.................................. 137
     13.8.5   User Data Field................................ 137
     13.9   Data Acknowledgement (AK) TPDU................... 137
     13.9.1   Structure...................................... 137
     13.9.2   LI............................................. 138
     13.9.3   Fixed Part..................................... 138
     13.9.4   Variable Part.................................. 139
     13.10   Expedited Data Acknowledgement (EA) TPDU........ 140
     13.10.1   Structure..................................... 140
     13.10.2   LI............................................ 141
     13.10.3   Fixed Part.................................... 141
     13.10.4   Variable Part................................. 141
     13.11   Reject (RJ) TPDU................................ 141
     13.11.1   Structure..................................... 142
     13.11.2   LI............................................ 142
     13.11.3   Fixed Part.................................... 142
     13.11.4   Variable Part................................. 143
     13.12   TPDU Error (ER) TPDU............................ 143
     13.12.1   Structure..................................... 143
     13.12.2   LI............................................ 143
     13.12.3   Fixed Part.................................... 144
     13.12.4   Variable Part................................. 144
     14   CONFORMANCE........................................ 145
     14.1   ................................................. 145



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     14.2   ................................................. 145
     14.3   ................................................. 145
     14.4   ................................................. 145
     14.5   ................................................. 146
     14.6   Claims of Conformance Shall State................ 146









































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     INTRODUCTION

     The Transport Protocol Standard is one of a set of  International
     Standards  produced to facilitate the interconnection of computer
     systems.  The set of standards covers the services and  protocols
     required to achieve such interconnection.

     The Transport Protocol Standard is  positioned  with  respect  to
     other  related  standards  by the layers defined in the Reference
     Model for Open Systems Interconnection (ISO 7498).   It  is  most
     closely  related  to, and lies within the field of application of
     the Transport Service Standard (DP 8072).  It also uses and makes
     reference  to  the  Network  Service  Standard  (DP  8348), whose
     provisions it  assumes  in  order  to  accomplish  the  transport
     protocol's  aims.   The  interelationship  of  these standards is
     depicted in figure 1.





     -------------------------TRANSPORT SERVICE DEFINITION------------
     Transport     | --- Reference to aims --------------
     Protocol      |
     Specification | --- Reference to assumptions -------
     -------------------------NETWORK SERVICE DEFINITION--------------

      Relationaship between Transport Protocol and adjacent services
                                Figure 1 .



     The International Standard specifies  a  common  encoding  and  a
     number  of  classes  of  transport protocol procedures to be used
     with different network qualities of service.

     It is intended that the Transport Protocol should be  simple  but
     general  enough  to  cater for the total range of Network Service
     qualities possible, without restricting future extensions.

     The protocol is structured to give rise to  classes  of  protocol
     which  are  designed  to  minimize possible incompatibilities and
     implementation costs.



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     The classes are selectable with  respect  to  the  Transport  and
     Network Services in providing the required quality of service for
     the interconnection of two session entities (note that each class
     provides  a different set of functions for enhancement of service
     qualities).

     This protocol standard defines mechanisms that  can  be  used  to
     optimize  network  tariffs and enhance the following qualities of
     service:

        a)  different throughput rates;

        b)  different error rates;

        c)  integrity of data requirements;

        d)  reliability requirements.

     It does not  require  an  implementation  to  use  all  of  these
     mechanisms,  nor  does  it  define methods for measuring achieved
     quality of service or  criteria  for  deciding  when  to  release
     transport connections following quality of service degradation.

     The primary aim of this International Standard is  to  provide  a
     set  of  rules  for  communication  expressed  in  terms  of  the
     procedures to be carried out by peer  entities  at  the  time  of
     communication.   These  rules  for  communication are intended to
     provide a sound basis for development in order to serve a variety
     of purposes:

        a)  as a guide for implementors and designers;

        b)  for use in the testing and procurement of equipment;

        c)  as part of an agreement for the admittance of systems into
            the open systems environment;

        d)  as a refinement of the understanding of OSI.

     It is expected  that  the  initial  users  of  the  International
     Standard  will be designers and implementors of equipment and the
     International Standard contains, in notes or in annexes, guidance
     on the implementation of the procedures defined in the standard.



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     It should  be  noted  that,  as  the  number  of  valid  protocol
     sequences  is  very  large,  it  is  not  possible  with  current
     technology to verify that  an  implementation  will  operate  the
     protocol  defined  in this International Standard correctly under
     all circumstances.   It  is  possible  by  means  of  testing  to
     establish  confidence  that  an implementation correctly operates
     the protocol in a representative sample of circumstances.  It is,
     however, intended that this International Standard can be used in
     circumstances where two implementations fail  to  communicate  in
     order to determine whether one or both have failed to operate the
     protocol correctly.

     This International Standard contains a section on conformance  of
     equipment   claiming   to   implement   the  procedures  in  this
     International Standard.  Attention is drawn to the fact that  the
     standard   does   not  contain  any  tests  to  demonstrate  this
     conformance.

     The variations and options available  within  this  International
     Standard  are  essential  to  enable  a  Transport  Service to be
     provided for a wide variety of applications  over  a  variety  of
     network  qualities.   Thus, a minimally conforming implementation
     will not be suitable for use in all possible  circumstances.   It
     is  important,  therefore,  to  qualify  all  references  to this
     International Standard with statements of the options provided or
     required  or with statements of the intended purpose of provision
     or use.




     1  SCOPE AND FIELD OF APPLICATION

     1.1  This International Standard specifies:

        a)  five classes of procedures:

            1) Class 0.  Simple class;
            2) Class 1.  Basic error recovery class;
            3) Class 2.  Multiplexing class;
            4) Class 3.  Error recovery and multiplexing class;
            5) Class 4.  Error detection and recovery class,




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            for the connection oriented transfer of data  and  control
            information  from one transport entity to a peer transport
            entity;

        b)  the means of negotiating the class  of  procedures  to  be
            used by the transport entities;

        c)  the structure and encoding of the transport protocol  data
            units   used   for   the  transfer  of  data  and  control
            information;




     1.2  The procedures are defined in terms of:

        a)  the interactions between peer transport  entities  through
            the exchange of transport protocol data units;

        b)  the  interactions  between  a  transport  entity  and  the
            transport  service  user  in  the  same system through the
            exchange of transport service primitives;

        c)  the  interactions  between  a  transport  entity  and  the
            network  service  provider through the exchange of network
            service primitives.

     These procedures are defined in the main  text  of  the  standard
     supplemented by state tables in annex A.




     1.3

     These procedures are applicable  to  instances  of  communication
     between  systems  which  support  the  Transport Layer of the OSI
     Reference Model and which wish to interconnect in an open systems
     environment.







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     1.4

     This   International   Standard   also   specifies    conformance
     requirements  for systems implementing these procedures.  It does
     not  contain  tests  which  can  be  used  to  demonstrate   this
     conformance.




     2  REFERENCES

     ISO 7498  Information   processing   systems   -   Open   systems
               interconnection - Basic Reference Model

     DP 8072   Information   processing   systems   -   Open   systems
               interconnection - Transport service definition

     DP 8348   Information   processing   systems   -   Open   systems
               interconnection  -  Connection-oriented network service
               definition.

























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     SECTION ONE.  GENERAL




     3  DEFINITIONS

     NOTE - The definitions contained  in  this  clause  make  use  of
     abbreviations defined in clause 4.




     3.1

     This International Standard is based on the concepts developed in
     the  Reference  Model for Open Systems Interconnection (DIS 7498)
     and makes use of the following terms defined in that standard:

        a)  concatenation and separation;

        b)  segmenting and reassembling;

        c)  multiplexing and demultiplexing;

        d)  splitting and recombining;

        e)  flow control.




     3.2

     For the purpose of this  International  Standard,  the  following
     definitions apply:










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     3.2.1  equipment:

     Hardware or software or a combination of both;  it  need  not  be
     physically distinct within a computer system.




     3.2.2  transport service user: