rfc2204.txt

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               Go to Start File Phase


   3. Speaker  -- EFID ------------> Listener   End File
               <------------ EFNA --            Answer NO

4.6  End Session Phase

4.6.1  Protocol Sequence

   The Speaker terminates the session by sending an End Session (ESID)
   command.

   1. Speaker  -- EFID ------------> Listener   End File
               <------------ EFPA --            Answer YES
               -- CD -------------->            Change Direction
      Listener <------------ ESID -- Speaker    End Session








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4.7  Problem Handling

   Error detection and handling should be done as close as possible to
   the problem.  This aids problem determination and correction.  Each
   layer of the reference model is responsible for it's own error
   handling.

   ODETTE-FTP can detect protocol errors through the construction of
   it's state machine, and uses activity timers to detect session hang
   conditions.  These mechanisms are separate from the End to End
   controls.

4.7.1  Protocol Errors

   If a protocol error occurs the session will be terminated and
   application activity aborted.  Both locations enter the IDLE state.

4.7.2  Timers

   To protect against application and network hang conditions ODETTE-FTP
   uses activity timers for all situations where a response is required.
   The timers and actions to be taken if they expire are described in
   section 8, the Protocol State Machine.

4.7.3  Clearing Centres

   The use of clearing centres introduces the possibility of errors
   occurring as a result of data processing activities within the
   centre.  Such errors are not directly related to ODETTE-FTP or the
   communication network and are therefore outside the scope of this
   specification.

5. Commands and Formats

   ODETTE-FTP entities communicate via Exchange Buffers.  The Command
   Exchange Buffers are described below.  Virtual File data is carried
   in Data Exchange Buffers which are described in Section 6.

5.1  Conventions

5.1.1  Representation unit:

   The basic unit of information is an octet, containing eight bits.

5.1.2  Values and Characters:

   The ISO 646 IRV 7-bit coded character set [ISO-646] is used to encode
   constants and strings within command exchange buffers.



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5.2  Commands

   A Command Exchange Buffer contains a single command starting at the
   beginning of the buffer.  Commands and data are never mixed within an
   Exchange Buffer.  Each command has a fixed length and can not be
   compressed.

   Components:

   1. Command identifier:

      The first octet of an Exchange Buffer is the Command Identifier
      and defines the format of the buffer.

   2. Parameter(s):

      Command parameters are stored in fixed fields within a Command
      Exchange Buffer.  All values are required.

5.3  Command Formats

   The ODETTE-FTP commands are described below using the following
   definitions.

   Position (Pos.)

      Field offset within the command exchange buffer, relative to a
      zero origin.

      Field

      The name of the field.

   Description

      A description of the field.

   Format

      F    - A field containing fixed values.  All allowable values for
             the field are enumerated in the command definition.

      V    - A field with variable values within a defined range.  For
             example the SFIDFSIZ field may contain any integer value
             between 0000000 and 9999999.

      X(n) - An alphanumeric field of length n octets.




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      9(n) - A numeric field of length n octets.

      All attributes are in character format.

      A String contains alphanumeric characters from the following set:

         The numerals:               0 to 9
         The upper case letters:     A to Z
         The following special set:  / - . & ( ) space.

      Space is not allowed as an embedded character.

      Numeric fields are always right justified and left padding with
      zeros must be done when needed.

5.3.1  SSRM - Start Session Ready Message

   o-------------------------------------------------------------------o
   |       SSRM        Start Session Ready Message                     |
   |                                                                   |
   |       Start Session Phase     Initiator <---- Responder           |
   |-------------------------------------------------------------------|
   | Pos | Field     | Description                           | Format  |
   |-----+-----------+---------------------------------------+---------|
   |   0 | SSRMCMD   | SSRM Command, 'I'                     | F X(1)  |
   |   1 | SSRMMSG   | Ready Message, 'ODETTE FTP READY '    | F X(17) |
   |  18 | SSRMCR    | Carriage Return                       | F X(1)  |
   o-------------------------------------------------------------------o

   SSRMCMD   Command Code                                      Character

      Value: 'I'  SSRM Command identifier.

   SSRMMSG   Ready Message                                    String(17)

      Value: 'ODETTE FTP READY '

   SSRMCR    Carriage Return                                   Character

      Value: Character with hex value '0D' or '8D'.











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5.3.2  SSID - Start Session

   o-------------------------------------------------------------------o
   |       SSID        Start Session                                   |
   |                                                                   |
   |       Start Session Phase     Initiator <---> Responder           |
   |-------------------------------------------------------------------|
   | Pos | Field     | Description                           | Format  |
   |-----+-----------+---------------------------------------+---------|
   |   0 | SSIDCMD   | SSID Command 'X'                      | F X(1)  |
   |   1 | SSIDLEV   | Protocol Release Level                | F 9(1)  |
   |   2 | SSIDCODE  | Initiator's Identification Code       | V X(25) |
   |  27 | SSIDPSWD  | Initiator's Password                  | V X(8)  |
   |  35 | SSIDSDEB  | Exchange Buffer Size                  | V 9(5)  |
   |  40 | SSIDSR    | Send / Receive Capabilities (S/R/B)   | F X(1)  |
   |  41 | SSIDCMPR  | Compression Indicator (Y/N)           | F X(1)  |
   |  42 | SSIDREST  | Restart Indicator (Y/N)               | F X(1)  |
   |  43 | SSIDSPEC  | Special Logic Indicator (N)           | F X(1)  |
   |  44 | SSIDCRED  | Credit                                | V 9(3)  |
   |  47 | SSIDRSV1  | Reserved                              | F X(5)  |
   |  52 | SSIDUSER  | User Data                             | V X(8)  |
   |  60 | SSIDCR    | Carriage Return                       | F X(1)  |
   o-------------------------------------------------------------------o

   SSIDCMD   Command Code                                      Character

      Value: 'X'  SSID Command identifier.

   SSIDLEV   Protocol Release Level                           Numeric(1)

      Value: '1' ODETTE-FTP protocol release level 1.

             Future release levels will have higher numbers.  The
             protocol release level is negotiable, with the lowest level
             being selected.

   SSIDCODE  Initiator's Identification Code                  String(25)

    Format:  See Identification Code (Section 5.4)

             Uniquely identifies the Initiator (sender) participating
             in the ODETTE-FTP session.

   SSIDPSWD  Password                                          String(8)

             Key to authenticate the sender.  Assigned by bilateral
             agreement.




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   SSIDSDEB  Exchange Buffer Size                             Numeric(5)

    Minimum: 128
    Maximum: 99999

             The length, in octets, of the largest Exchange Buffer that
             can be accepted by the location.  The length includes the
             command octet but does not include the Stream Transmission
             Header.

             After negotiation the smallest size will be selected.

   SSIDSR    Send / Receive Capabilities                       Character

      Value: 'S'  Location can only send files.
             'R'  Location can only receive files.
             'B'  Location can both send and receive files.

             Sending and receiving will be serialised during the
             session, so parallel sessions will not take place.

             An error occurs if adjacent locations both specify the send
             or receive capability.

   SSIDCMPR  Compression Indication                            Character

      Value: 'Y'  The location can handle compressed data.
             'N'  The location can not handle compressed data.

             Compression is only used if supported by both locations.
             The compression mechanism is described in Section 6.2

   SSIDREST  Restart Indication                                Character

      Value: 'Y'  The location can handle the restart of a partially
                  transmitted file.
             'N'  The location can not restart a file.

   SSIDSPEC  Special Logic Indication                          Character

      Value: 'N'  Only valid value for TCP.

             The Special Logic extensions are only useful in an X.25
             environment and are not supported for TCP/IP.







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   SSIDCRED  Credit                                           Numeric(3)

    Maximum: 999

             The number of consecutive Data Exchange Buffers sent by the
             Speaker before it must wait for a Credit (CDT) command from
             the Listener.

             The credit value is only applied to Data flow in the Data
             Transfer phase.

             The Speaker's available credit is initialised to SSIDCRED
             when it receives a Start File Positive Answer (SFPA)
             command from the Listener.  It is zeroed by the End File
             (EFID) command.

             After negotiation, the smallest size must be selected in
             the answer of the Responder, otherwise a protocol error
             will abort the session.

             Negotiation of the "credit-window-size" parameter.

             Window Size m  -- SSID ------------>
                            <------------ SSID --  Window Size n
                                                   (n less or equal m)
             Note: negotiated value will be "n".

   SSIDRSV1  Reserved                                          String(5)

             This field is reserved for future use.

   SSIDUSER  User Data                                         String(8)

             May be used by the ODETTE-FTP in any way.  If unused it
             should be initialised to spaces.  It is expected that a
             bilateral agreement exists as to the meaning of the data.

   SSIDCR    Carriage Return                                   Character

      Value: Character with hex value '0D' or '8D'.











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5.3.3  SFID - Start File
   o-------------------------------------------------------------------o
   |       SFID        Start File                                      |
   |