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RFC 2204

 
 
 

ODETTE File Transfer Protocol

Part 3 of 3, p. 50 to 74
Prev RFC Part

 


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8. Protocol State Machine

8.1  ODETTE-FTP State Machine

   The operation of an ODETTE-FTP entity is formally defined by the
   State Machine presented below.  There are five State and Transition
   tables and for each table additional information is given in the
   associated Predicate and Action lists.

   The response of an ODETTE-FTP entity to the receipt of an event is
   defined by a Transition table entry indexed by the Event/State
   intersection within the appropriate State table.

   Each Transition table entry defines the actions taken, events
   generated and new state entered.  Predicates may be used within a
   table entry to select the correct response on the basis of local
   information held by the entity.

   A transition table contains the following fields:

   Index(I)    State transition index.

   Predicate   A list of predicates used to select between different
               possible transitions.  The predicates are defined in the
               Predicate and Action list.

   Actions     A list of actions taken by the entity.  The actions are
               defined in the Predicate and Action list.

   Events      Output events generated by the entity

   Next State  The new state of the entity.

8.2  Error Handling

   The receipt of an event in a given state may be invalid for three
   reasons.

   1.  The case is impossible by construction of the state automata,
       denoted 'X' in the State tables.  For example a timer which has
       not been set cannot run out.

   2.  The event is the result of an error in the Network Service
       implementation, also denoted 'X' in the state tables.  The
       Network Service implementation is considered to be correct.

   3.  For all other cases the event is considered to be a User Error,
       denoted "U" in the state tables.

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   The State tables define the conditions under which a User event is
   valid, thus preventing the generation of a protocol error by the
   ODETTE-FTP entity as a result of a User Monitor error.  The reaction
   of the entity to such errors is undefined and regarded as a local
   implementation issue.

   The State tables also allow protocol errors due to the receipt of
   invalid Exchange Buffers, to be detected.  In such cases the reaction
   of the entity to the error is defined.

8.3  States

   The Command Mode is strictly a Half Duplex Flip-Flop Mode.

   A_NC_ONLY   Responder, Network Connection opened

               The Responder has sent it's Ready Message (SSRM) and is
               waiting for Start Session (SSID) from the Initiator.

   A_WF_CONRS  Responder Waiting for F_CONNECT_RS

               The Responder has received the Initiator's Start Session
               (SSID) and is waiting for a response (F_CONNECT_RS) from
               it's User Monitor.

   CDSTWFCD    CD_RQ stored in WF_CD state

               Since the User Monitor doesn't see the WF_CD state it may
               send a Change Direction request (F_CD_RQ) before the
               ODETTE-FTP receives a Change Direction (CD) command.

   CLIP        Close Input Pending

               The Listener has received an End File (EFID) command and
               is waiting for the Close File response (F_CLOSE_FILE_RS)
               from it's User Monitor.

   CLOP        Close Out Pending

               The Speaker has sent an End File (EFID) command and is
               waiting for an End File Answer (EFPA or EFNA).

   ERSTWFCD    End to End Response stored in WF_CD state

               Since the User Monitor doesn't see the WF_CD state it may
               send F_EERP_RQ, before the ODETTE-FTP receives a Change
               Direction (CD) command.

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   IDLE        Connection IDLE

   IDLELI      Idle Listener

   IDLELICD    Idle Listener, F_CD_RQ Received

               The ODETTE-FTP entity has become the Listener after
               receiving a Change Direction request (F_CD_RQ) from the
               User Monitor.  The receipt of an End Session (ESID) is
               valid in this state.

   IDLESP      Idle Speaker

   IDLESPCD    Idle Speaker, F_CD_IND Sent

               The ODETTE-FTP entity has sent a Change Direction
               indication (F_CD_IND) to the User Monitor.  A Change
               Direction request (F_CD_RQ) is invalid in this state.

   I_WF_NC     Initiator Waiting for Network Connection

               The Initiator has requested a new network connection and
               is waiting for a Connection confirmation (N_CON_CF) from
               the Network Service.

   I_WF_RM     Initiator Waiting for Ready Message

               Before sending Start Session (SSID), the Initiator must
               wait for a Ready Message (SSRM) from the Responder.

   I_WF_SSID   Initiator Waiting for SSID

               The Initiator has sent a Start Session (SSID) command and
               is waiting for Start Session from the Responder.

   OPI         Open Input (Data Transfer Phase)

               The Listener is waiting for the Speaker to send a Data
               Exchange buffer.

   OPIP        Open Input Pending

               The Listener has received a Start File (SFID) command and
               is waiting for the Start File response (F_START_FILE_RS)
               from it's User Monitor.

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   OPO         Open Out (Data Transfer Phase)

               The Speaker has received a Start File Positive Answer
               (SFPA) and is waiting for a Data (F_DATA_RQ) or Close
               File (F_CLOSE_FILE) request from it's User Monitor.

   OPOP        Open Out Pending

               The Speaker has sent a Start File (SFID) command and is
               waiting for a Start File Answer (SFPA or SFNA).

   OPOWFC      Open Out Wait for Credit

               The Speaker is waiting for a Set Credit (CDT) command
               before sending further Data Exchange buffers.

   SFSTWFCD    Start File Request stored in WF_CD state.

               Since the User Monitor doesn't see the WF_CD state it may
               send a Start File request (F_START_FILE_RQ) before the
               ODETTE-FTP receives a Change Direction (CD) command.

   WF_CD       Wait for Change Direction

               The Listener wishes to become the Speaker and is waiting
               for a Change Direction (CD) command after sending an End
               File Positive Answer (EFPA) requesting change direction.

   WF_RTR      Wait for Ready To Receive

               The Initiator has sent an End to End Response (EERP)
               command and must wait for Ready To Receive (RTR) from the
               Responder.

   WF_NDISC    Wait for N_DISC_IND

               ODETTE-FTP has sent an End Session (ESID) command and is
               waiting for a Disconnection indication (N_DISC_IND) from
               the Network Service.

8.4  Input Events

   User Monitor Input Events (Section 3)

     F_DATA_RQ   F_CONNECT_RQ   F_START_FILE_RQ      F_CLOSE_FILE_RQ
     F_EERP_RQ   F_CONNECT_RS   F_START_FILE_RS(+)   F_CLOSE_FILE_RS(+)
     F_CD_RQ     F_ABORT_RQ     F_START_FILE_RS(-)   F_CLOSE_FILE_RS(-)
                 F_RELEASE_RQ

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   Network Input Events (Section 2.2)

      N_CON_IND   N_CON_CF   N_DATA_IND   N_DISC_IND   N_RST_IND

   Peer ODETTE-FTP Input Events (Section 4)

      SSID   SFID   SFPA   SFNA   EFID   EFPA   EFNA
      DATA   ESID   EERP   RTR    CD     CDT    SSRM

   Internal Input Events

      TIME-OUT - Internal ODETTE-FTP timer expires.

   Input event parameters are denoted I.Event-name.Parameter-name within
   the state table action and predicate lists.  Their value can be
   examined but not changed by the ODETTE-FTP entity.

8.5  Output Events

   User Monitor Output Events (Section 3)

     F_DATA_IND  F_CONNECT_IND  F_START_FILE_IND     F_CLOSE_FILE_IND
     F_EERP_IND  F_CONNECT_CF   F_START_FILE_CF(+)   F_CLOSE_FILE_CF(+)
     F_CD_IND    F_ABORT_IND    F_START_FILE_CF(-)   F_CLOSE_FILE_CF(-)
                 F_RELEASE_IND

   Network Output Events (Section 2.2)

      N_CON_RQ   N_CON_RS   N_DATA_RQ   N_DISC_RQ

   Peer ODETTE-FTP Output Events (Section 4)

      SSID   SFID   SFPA   SFNA   EFID   EFPA   EFNA
      DATA   ESID   EERP   RTR    CD     CDT    SSRM

   Output event parameters are denoted O.Event-name.Parameter-name
   within the state table action and predicate lists.  Their values can
   be examined and changed by the ODETTE-FTP entity.

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8.6  Local Variables

   The following variables are maintained by the ODETTE-FTP entity to
   assist the operation of the protocol.  They are denoted V.Variable-
   name within the state table action and predicate lists.  Their value
   can be examined and changed by the ODETTE-FTP entity.  The initial
   value of each variable is undefined.

   Variable     Type       Comments
   ---------------------------------------------------------------------
   Buf-size     Integer    Negotiated Exchange Buffer size.
   Called-addr  Address    Used to build O.F_CONNECT_IND.Called-addr
   Calling-addr Address    To build O.F_CONNECT_IND.Calling-addr
   Compression  Yes/No     Compression in used as agreed.
   Credit_L     Integer    Listeners credit counter.
   Credit_S     Integer    Speaker's credit counter.
   Id           String     Used to build O.SSID.Id
   Mode                    Sender-only, Receiver-only, Both.
   Pswd         String     Password, used to build O.SSID.Pswd
   Req-buf      Primitive  Input event (F_XXX_RQ) stored in WF_CD state.
   Restart      Yes/No     Restart in used as agreed.
   Restart-pos  Integer    Used only during file opening.
   Window       Integer    The Credit value negotiated for the session.
   ---------------------------------------------------------------------

8.7  Local Constants

   The following constants define the capabilities of a given ODETTE-FTP
   entity.  They are denoted C.Constant-name within the state table
   action and predicate lists.  Their value can be examined but not
   changed by the ODETTE-FTP entity.

   Constant         Value               Comments
   ---------------------------------------------------------------------
   Cap-compression  Yes/No              Compression supported?
   Cap-init         Initiator           Must be Initiator.
                    Responder           Must be Responder.
                    Both                Can be Initiator or Responder.
   Cap-mode         Sender-only         Must be sender.
                    Receiver-only       Must be receiver.
                    Both                Can be sender or receiver.
   Max-buf-size     127 < Int < 100000  Maximum buffer size supported.
   Max-window       Int < 1000          Local maximum credit value.
   ---------------------------------------------------------------------

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8.8  Session Connection State Table

8.8.1  State Table

   o----------------------------------------------o
   |   | Other States                             |
   |   |--------------------------------------o   |
   | S | A_WF_CONRS                           |   |
   |   |----------------------------------o   |   |
   | T | A_NC_ONLY                        |   |   |
   |   |------------------------------o   |   |   |
   | A | I_WF_SSID                    |   |   |   |
   |   |--------------------------o   |   |   |   |
   | T | I_WF_RM                  |   |   |   |   |
   |   |----------------------o   |   |   |   |   |
   | E | I_WF_NC              |   |   |   |   |   |
   |   |------------------o   |   |   |   |   |   |
   |   | IDLE             |   |   |   |   |   |   |
   |==================o---+---+---+---+---+---+---|
   |   | F_CONNECT_RQ | A | X | X | X | X | X | X |
   |   |--------------+---+---+---+---+---+---+---|
   | E | N_CON_CF     | X | C | X | X | X | X | X |
   |   |--------------+---+---+---+---+---+---+---|
   | V | SSRM         | X | X | H | X | X | X | X |
   |   |--------------+---+---+---+---+---+---+---|
   | E | SSID         | X | X | X | D | E | F | F |
   |   |--------------+---+---+---+---+---+---+---|
   | N | N_CON_IND    | B | X | X | X | X | X | X |
   |   |--------------+---+---+---+---+---+---+---|
   | T | F_CONNECT_RS | X | U | U | U | U | G | U |
   |   |--------------+---+---+---+---+---+---+---|
   |   | ESID(R=10)   | X | X | X | F | X | X | X |
   o----------------------------------------------o

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8.8.2  Transition Table

    I | Predicate    Actions     Output Events               Next State
   ===o=================================================================
    A | P1:                      F_ABORT_IND                 IDLE
      | not P1:      1           N_CON_RQ                    I_WF_NC
   ---+-----------------------------------------------------------------
    B | P3:                      N_DISC_RQ                   IDLE
      | not P3:                  N_CON_RS
      |                          SSRM                        A_NC_ONLY
   ---+-----------------------------------------------------------------
    C |              2                                       I_WF_RM
   ---+-----------------------------------------------------------------
    D | P2:          4,2,5       F_CONNECT_CF                IDLESP
      | not P2:      4,2         ESID(R=10)
      |                          F_ABORT_IND(R,AO=L)         WF_NDISC
   ---+-----------------------------------------------------------------
    E | P4:          4           N_DISC_RQ                   IDLE
      | not P4:                  F_CONNECT_IND               A_WF_CONRS
   ---+-----------------------------------------------------------------
    F |                          F_ABORT_IND
      |                          N_DISC_RQ                   IDLE
   ---+-----------------------------------------------------------------
    G | P2:          4,2,5       SSID                        IDLELI
      | not P2:      4,2         ESID(R=10)
      |                          F_ABORT_IND(R,AO=L)         WF_NDISC
   ---+-----------------------------------------------------------------
    H |              4,2,3       SSID                        I_WF_SSID
   ---------------------------------------------------------------------

8.8.3  Predicates and Actions.

   Predicate P1:  (No resources available) OR
                  (C.Cap-init = Responder) OR
                  (C.Cap-mode = Sender-only AND
                     I.F_CONNECT_RQ.Mode = Receiver-only) OR
                  (C.Cap-mode = Receiver-only AND
                     I.F_CONNECT_RQ.Mode = Sender-only)

   Predicate P2:  Negotiation of (Buf-size, Restart, Compression,
                                  Mode, Credit) is OK.

   Predicate P3:  C.Cap-init = Initiator

   Predicate P4:  Mode in SSID incompatible with C.Cap-mode

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       Action 1:  Set V.Mode from (C.Cap-mode, I.F_CONNECT_RQ.Mode)
                  Set V.Pswd, V.Id, V.Restart from I.F_CONNECT_RQ
                  Set V.Buf-size = C.Max-buf-size
                  Set V.Compression = C.Cap-compression
                  Build O.N_CON_RQ

       Action 2:  Start inactivity timer

       Action 3:  Set parameters in O.SSID = from local variables

       Action 4:  Stop timer

       Action 5:  Set V.Mode, V.Restart, V.Compression, V.Buf-size,
                      V.Window = from SSID

8.9  Error and Abort State Table

8.9.1  State Table

   o--------------------------------------o
   |   | Other States                     |
   | S |------------------------------o   |
   | T | WF_NDISC                     |   |
   | A |--------------------------o   |   |
   | T | I_WF_NC                  |   |   |
   | E |----------------------o   |   |   |
   |   | IDLE                 |   |   |   |
   |======================o---+---+---+---|
   |   | TIME-OUT         | X | X | A | B |
   |   |------------------+---+---+---+---|
   | E | F_ABORT_RQ       | X | A | X | C |
   | V |------------------+---+---+---+---|
   | E | N_RST_IND        | X | X | A | D |
   | N |------------------+---+---+---+---|
   | T | N_DISC_IND       | X | E | F | G |
   |   |------------------+---+---+---+---|
   |   | Invalid Buffer   | X | X | H | I |
   o--------------------------------------o

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8.9.2  Transition Table

    I | Predicate    Actions     Output Events              Next State
   ===o=================================================================
    A |                          N_DISC_RQ                 IDLE
   ---+-----------------------------------------------------------------
    B |                          F_ABORT_IND
      |                          N_DISC_RQ                 IDLE
   ---+-----------------------------------------------------------------
    C |              1           N_DISC_RQ                 IDLE
   ---+-----------------------------------------------------------------
    D |              1           N_DISC_RQ
      |                          F_ABORT_IND               IDLE
   ---+-----------------------------------------------------------------
    E |                          F_ABORT_IND               IDLE
   ---+-----------------------------------------------------------------
    F |              1                                     IDLE
   ---+-----------------------------------------------------------------
    G |              1           F_ABORT_IND               IDLE
   ---+-----------------------------------------------------------------
    H |                                                    WF_NDISC
   ---+-----------------------------------------------------------------
    I |              1,2         ESID(R=01)
      |                          F_ABORT_IND(R,AO=L)       WF_NDISC
   ---------------------------------------------------------------------

8.9.3  Predicates and Actions.

       Action 1:  Stop inactivity timer

       Action 2:  Start inactivity timer

8.10  Speaker State Table 1

8.10.1  State Table

   The following abbreviations are used in the Speaker State table.

      F_REL_RQ(Ok)   -  F_RELEASE_RQ Reason = Normal
      F_REL_RQ(Err)  -  F_RELEASE_RQ Reason = Error

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   o------------------------------------------------------------------o
   |   | Other State                                                  |
   |   |----------------------------------------------------------o   |
   |   | WF_NDISC                                                 |   |
   |   |------------------------------------------------------o   |   |
   |   | OPOWFC                                               |   |   |
   |   |--------------------------------------------------o   |   |   |
   |   | OPO                                              |   |   |   |
   | S |----------------------------------------------o   |   |   |   |
   |   | OPOP                                         |   |   |   |   |
   | T |------------------------------------------o   |   |   |   |   |
   |   | CDSTWFCD                                 |   |   |   |   |   |
   | A |--------------------------------------o   |   |   |   |   |   |
   |   | SFSTWFCD                             |   |   |   |   |   |   |
   | T |----------------------------------o   |   |   |   |   |   |   |
   |   | ERSTWFCD                         |   |   |   |   |   |   |   |
   | E |------------------------------o   |   |   |   |   |   |   |   |
   |   | WF_CD                        |   |   |   |   |   |   |   |   |
   |   |--------------------------o   |   |   |   |   |   |   |   |   |
   |   | WF_RTR                   |   |   |   |   |   |   |   |   |   |
   |   |----------------------o   |   |   |   |   |   |   |   |   |   |
   |   | IDLESPCD             |   |   |   |   |   |   |   |   |   |   |
   |   |------------------o   |   |   |   |   |   |   |   |   |   |   |
   |   | IDLESP           |   |   |   |   |   |   |   |   |   |   |   |
   |===+==============o---+---+---+---+---+---+---+---+---+---+---+---|
   |   | F_EERP_RQ    | A | A | W | F | W | U | U | U | U | U | U | U |
   |   |--------------+---+---+---+---+---+---+---+---+---+---+---+---|
   |   | F_START_     | B | B | W | G | W | U | U | U | U | U | X | U |
   |   |   FILE_RQ    |   |   |   |   |   |   |   |   |   |   |   |   |
   |   |--------------+---+---+---+---+---+---+---+---+---+---+---+---|
   |   | SFPA         | C | C | C | C | C | C | C | K | C | C | S | C |
   |   |--------------+---+---+---+---+---+---+---+---+---+---+---+---|
   | E | SFNA         | C | C | C | C | C | C | C | L | C | C | S | C |
   |   |--------------+---+---+---+---+---+---+---+---+---+---+---+---|
   | V | CD           | C | C | C | H | R | I | J | C | C | C | S | C |
   |   |--------------+---+---+---+---+---+---+---+---+---+---+---+---|
   | E | F_DATA_RQ    | U | U | U | U | U | U | U | U | M | V | S | U |
   |   |--------------+---+---+---+---+---+---+---+---+---+---+---+---|
   | N | CDT          | C | C | C | C | C | C | C | C | P | O | S | C |
   |   |--------------+---+---+---+---+---+---+---+---+---+---+---+---|
   | T | F_CD_RQ      | D | U | W | T | W | U | U | U | U | U | X | U |
   |   |--------------+---+---+---+---+---+---+---+---+---+---+---+---|
   |   | F_REL_RQ(Ok) | U | E | U | U | U | U | U | U | U | U | X | U |
   |   |--------------+---+---+---+---+---+---+---+---+---+---+---+---|
   |   | F_REL_RQ(Err)| Q | Q | Q | Q | Q | Q | Q | Q | Q | Q | S | Q |
   |   |--------------+---+---+---+---+---+---+---+---+---+---+---+---|
   |   | RTR          | C | C | N | C | C | C | C | C | C | C | S | C |
   o------------------------------------------------------------------o

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8.10.2  Transition Table

    I | Predicate    Actions     Output Events              Next State
   ===o=================================================================
    A |              1,2,3       EERP                       WF_RTR
   ---+-----------------------------------------------------------------
    B | P1:                                                 UE
      | not P1:      1,2,5       SFID                       OPOP
   ---+-----------------------------------------------------------------
    C |              1,2         ESID(R=02)
      |                          F_ABORT_IND(R,AO=L)        WF_NDISC
   ---+-----------------------------------------------------------------
    D |              1,2         CD                         IDLELICD
   ---+-----------------------------------------------------------------
    E |              1,2         ESID(R=00)                 WF_NDISC
   ---+-----------------------------------------------------------------
    F |              4                                      ERSTWFCD
   ---+-----------------------------------------------------------------
    G | P1:                                                 UE
      | not P1:      6                                      SFSTWFCD
   ---+-----------------------------------------------------------------
    H |              1,2                                    IDLESP
   ---+-----------------------------------------------------------------
    I |              1,2,10      SFID                       OPOP
   ---+-----------------------------------------------------------------
    J |              1,2         CD                         IDLELICD
   ---+-----------------------------------------------------------------
    K | P2:          1,2         ESID(R=02)
      |                          F_ABORT_IND(R,AO=L)        WF_NDISC
      | not P2:      1,2,7,12    F_START_FILE_CF(+)         OPO
   ---+-----------------------------------------------------------------
    L |              1,2,8       F_START_FILE_CF(-)         IDLESP
   ---+-----------------------------------------------------------------
    M | P3:          1,2,11,13   DATA                       OPOWFC
      | not P3:      1,2,11,13   DATA                       OPO
   ---+-----------------------------------------------------------------
    N |                          Note 3                     IDLESP
   ---+-----------------------------------------------------------------
    O |              12                                     OPO
      |                                                     See Note 1
   ---+-----------------------------------------------------------------
    P | Protocol     1,2         ESID(R=02)
      | Error                    F_ABORT_IND(R,AO=L)        WF_NDISC
   ---+-----------------------------------------------------------------
    Q |              1,2         ESID(R)                    WF_NDISC
   ---+-----------------------------------------------------------------
                                                            Continued -->

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    I | Predicate    Actions     Output Events              Next State
   ===o=================================================================
    R |              1,2,9       EERP                       WF_RTR
   ---+-----------------------------------------------------------------
    S |                                                     WF_NDISC
   ---+-----------------------------------------------------------------
    T |                                                     CDSTWFCD
   ---+-----------------------------------------------------------------
    U |                          User Error                 UE
   ---+-----------------------------------------------------------------
    V |                          User Error - Note 1        UE
   ---+-----------------------------------------------------------------
    W |                          User Error - Note 2        UE
   ---+-----------------------------------------------------------------
    X |                          Error
   ---------------------------------------------------------------------

8.10.3  Predicates and Actions.

   Predicate P1:  (I.F_START_FILE_RQ.Restart-pos > 0) AND
                  ((V.Restart = No) OR (V.Mode = Receiver-only))

           Note:  Restart requested and not supported for this session.

   Predicate P2:  (I.SFPA.Restart-pos > V.Restart-pos)

           Note:  Protocol error due to the restart position in the
                  SFPA acknowledgement being greater than the position
                  requested in the SFID request.

   Predicate P3:  V.Credit_S - 1 = 0

           Note:  Speaker's Credit is exhausted.

       Action 1:  Stop inactivity timer

       Action 2:  Start inactivity timer

       Action 3:  Build an EERP from F_EERP_RQ

       Action 4:  Store F_EERP_RQ in V.Req-buf

       Action 5:  Build SFID from F_START_FILE_RQ
                  V.Restart-pos = I.F_START_FILE_RQ.Restart-pos

       Action 6:  Store F_START_FILE_RQ in V.Req-buf

       Action 7:  Build F_START_FILE_CF(+) from I.SFPA

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       Action 8:  Build F_START_FILE_CF(-) from I.SFNA

       Action 9:  Build EERP from F_EERP_RQ stored in V.Req-buf

       Action 10: Build SFID from F_START_FILE_RQ stored in V.Req-buf
                  Set V.Restart-pos

       Action 11: Build Exchange Buffer

       Action 12: V.Credit_S = V.Window

       Action 13: V.Credit_S = V.Credit_S - 1

          Note 1: The OPOWFC state prevents the Speaker from sending
                  data buffers because it is waiting for credit.  The
                  ODETTE-FTP entity may need to control the flow of Data
                  requests (F_DATA_RQ) from it's User Monitor to protect
                  it's own buffers.  Any such mechanism and the
                  behaviour of the entity should a User Error occur are
                  regarded as local implementation issues.

          Note 2: The choice to accept this "Request/Event" while in
                  this state is a matter of local implementation.  The
                  ODETTE state tables are based on the assumption that
                  this event cannot occur in this state and is
                  considered to be a user error (UE).

          Note 3: It is a local matter to make the User Monitor aware
                  that since the RTR is received, the protocol machine
                  is now ready to accept the next request.

8.11  Speaker State Table 2

8.11.1  State Table

   o---------------------------------o
   | S | CLOP                        |
   | T |-------------------------o   |
   | A | OPOWFC                  |   |
   | T |---------------------o   |   |
   | E | OPO                 |   |   |
   |=====================o---+---+---|
   | E | F_CLOSE_FILE_RQ | A | E | U |
   | V |-----------------+---+---+---|
   | E | EFPA            | B | B | C |
   | N |-----------------+---+---+---|
   | T | EFNA            | B | B | D |
   o---------------------------------o

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8.11.2  Transition Table

    I | Predicate    Actions     Output Events              Next State
   ===o=================================================================
    A |              1,2,5,7     EFID                       CLOP
   ---+-----------------------------------------------------------------
    B |              1,2         ESID(R=02)
      |                          F_ABORT_IND(R,AO=L)        WF_NDISC
   ---+-----------------------------------------------------------------
    C | P1:          1,2,3       F_CLOSE_FILE_CF(+,SP=No)
      |                          CD                         IDLELI
      | not P1:      1,2,4       F_CLOSE_FILE_CF(+,SP=Yes)  IDLESP
   ---+-----------------------------------------------------------------
    D |              1,2,6       F_CLOSE_FILE_CF(-)         IDLESP
   ---+-----------------------------------------------------------------
    E |                          See Note 1
   ---+-----------------------------------------------------------------
    U |                          User Error                 UE
   ---------------------------------------------------------------------

8.11.3  Predicates and Actions.

   Predicate P1: (I.EFPA.CD-Request = Yes)  AND (V.Mode = Both)

       Action 1:  Stop inactivity timer

       Action 2:  Start inactivity timer

       Action 3:  O.F_CLOSE_FILE_CF(+).Speaker = No

       Action 4:  O.F_CLOSE_FILE_CF(+).Speaker = Yes

       Action 5:  Build EFID from F_CLOSE_FILE_RQ

       Action 6:  Build F_CLOSE_FILE_CF(-) from EFNA

       Action 7:  Set V.Credit_S = 0

         Note 1:  In order to respect the "half duplex" property of
                  ODETTE-FTP it is forbidden to send EFID while in the
                  OPOWFC state. EFID can be sent only in the OPO state.

                  The ODETTE-FTP implementation must avoid sending EFID
                  (or receiving F_CLOSE_FILE_RQ) while in the OPOWFC
                  state.

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8.12  Listener State Table

8.12.1  State Table

   o-----------------------------------------o
   |   | CLIP                                |
   |   |---------------------------------o   |
   |   | OPI                             |   |
   | S |-----------------------------o   |   |
   | T | OPIP                        |   |   |
   | A |-------------------------o   |   |   |
   | T | IDLELICD                |   |   |   |
   | E |---------------------o   |   |   |   |
   |   | IDLELI              |   |   |   |   |
   |=====================o---+---+---+---+---|
   |   | SFID            | A | A | B | B | B |
   |   |-----------------+---+---+---+---+---|
   | E | DATA            | B | B | B | I | B |
   | V |-----------------+---+---+---+---+---|
   | E | EFID            | B | B | B | J | B |
   | N |-----------------+---+---+---+---+---|
   | T | F_START_FILE_RS | U | U | H | U | U |
   |   |-----------------+---+---+---+---+---|
   |   | F_CLOSE_FILE_RS | U | U | U | U | K |
   |   |-----------------+---+---+---+---+---|
   |   | CD              | C | B | B | B | B |
   |   |-----------------+---+---+---+---+---|
   |   | ESID R=Normal   | D | F | D | D | D |
   |   |-----------------+---+---+---+---+---|
   |   | ESID R=Error    | D | D | D | D | D |
   |   |-----------------+---+---+---+---+---|
   |   | EERP            | E | G | B | B | B |
   o-----------------------------------------o

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8.12.2  Transition Table

    I | Predicate    Actions       Output Events             Next State
   ===o=================================================================
    A | P1:          1,2           ESID(R=02)
      |                            F_ABORT_IND(R,AO=L)       WF_NDISC
      | not P1:      1,2,3         F_START_FILE_IND          OPIP
   ---+-----------------------------------------------------------------
    B |              1,2           ESID(R=02)
      |                            F_ABORT_IND(R,AO=L)       WF_NDISC
   ---+-----------------------------------------------------------------
    C |              1,2           F_CD_IND                  IDLESPCD
   ---+-----------------------------------------------------------------
    D |              1             F_ABORT_IND(Received
      |                               ESID Reason,AO=D)
      |                            N_DISC_RQ                 IDLE
   ---+-----------------------------------------------------------------
    E |              4             F_EERP_IND
      |              8             See Note 2
      |                            RTR                       IDLELI
   ---+-----------------------------------------------------------------
    F |              1             F_RELEASE_IND
      |                            N_DISC_RQ                 IDLE
   ---+-----------------------------------------------------------------
    G |                            F_EERP_IND
      |              8             See Note 2
      |                            RTR                       IDLELI
   ---+-----------------------------------------------------------------
    H | P4:                        User Error                UE
      | P2,not P4:   1,2           SFPA                      OPI
      | not(P2,P4):  1,2           SFNA                      IDLELI
   ---+-----------------------------------------------------------------
    I | P5:          1,2           ESID(R=02)
      |                            F_ABORT_IND(R,A0=L)       WF_NDISC
      | not(P5,P6):  1,2,5         F_DATA_IND                OPI
      | not P5,P6:   1,2           F_DATA_IND
      |              6,7           See Note 1
      |                            CDT                       OPI
   ---+-----------------------------------------------------------------
    J |              1,2           F_CLOSE_FILE_IND          CLIP
   ---+-----------------------------------------------------------------
    K | P2,P3:       1,2           EFPA(CD-Req)              WF_CD
      | P2,not P3:   1,2           EFPA(no CD)               IDLELI
      | not P2:      1,2           EFNA                      IDLELI
   ---+-----------------------------------------------------------------
    U |                            User Error                UE
   ---------------------------------------------------------------------

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8.12.3  Predicates and Actions.

   Predicate P1:  (I.SFID.Restart-pos > 0) AND (V.Restart = No)

           Note:  Invalid Start File command

   Predicate P2:  Positive Response

   Predicate P3:  I.F_CLOSE_FILE_RS(+).Speaker = Yes

   Predicate P4:  I.F_START_FILE_RS(+).Restart-pos > V.Restart

   Predicate P5:  V.Credit_L - 1 < 0

           Note:  Protocol Error because the Speaker has exceeded it's
                  available transmission credit.

   Predicate P6:  V.Credit_L - 1 = 0

           Note:  The Speaker's credit must be reset before it can send
                  further Data Exchange buffers.

       Action 1:  Stop inactivity timer.

       Action 2:  Start inactivity timer

       Action 3:  Build F_START_FILE_IND from I.SFID
                  V.Restart-pos = I.SFID.Restart-pos

       Action 4:  Build F_EERP_IND from I.EERP

       Action 5:  V.Credit_L = V.Credit_L - 1

       Action 6:  Wait for sufficient resources to receive up to
                  V.Window Data Exchange Buffers.

       Action 7:  V.Credit_L = V.Window

       Action 8:  Wait for resources required to process a new EERP.

         Note 1:  Flow control in case of reception.

                  The ODETTE-FTP Listener must periodically send new
                  credit to the Speaker.  The timing of this operation
                  will depend on:

                  1. The User Monitor's capacity the receive data.
                  2. The number of buffers available to ODETTE-FTP.

Top      Up      ToC       Page 68 
                  3. The Speaker's available credit, which must be
                     equal to zero.

         Note 2:  Generally, the ODETTE-FTP Listener will send RTR
                  immediately after receiving EERP.  If required, it can
                  delay the RTR until the resources required to process
                  a new EERP are available.

8.13  Example

   Consider an ODETTE-FTP entity that has sent a Start File (SFID)
   command and entered the Open Out Pending (OPOP) state.  It's response
   on receiving a Positive Answer (SFPA) is documented in Speaker State
   Table 1 which shows that transition 'K' should be applied and is
   interpreted as follows:

      if (I.SFPA.Restart-pos > V.Restart-pos) then
      begin                                       // invalid restart
         Actions:   Stop inactivity timer,        // reset timer
                    Start inactivity timer;
         Output:    ESID(R=02),                   // to peer ODETTE-FTP
                    F_ABORT_IND(R,AO=L);          // to user monitor
         New State: WF_NDISC;
      end
      else begin
         Actions:   Stop inactivity timer,        // reset timer
                    Start inactivity timer;
                    Build F_START_FILE_CF(+) from I.SFPA
                    V.Credit_S = V.Window         // initialise credit
         Output:    F_START_FILE_CF(+);           // to user monitor
         New State: OPO;
      end

   The ODETTE-FTP checks the restart position in the received Start File
   Positive Answer (SFPA) command.  If it is invalid it aborts the
   session by sending an End Session (ESID) command to it's peer and an
   Abort indication (F_ABORT_IND) to it's User Monitor.  If the restart
   position is valid a Start File confirmation (F_START_FILE_CF) is
   built and sent to the User Monitor, the credit window is initialised
   and the Open Out (OPO) state is entered.

9.  Security Considerations

   ODETTE-FTP exchanges user identity and password information in clear
   text.  It is therefore recommended that a lower layer (session,
   network or linkage) security protocol is used to protect the session
   from casual identity collection.

Top      Up      ToC       Page 69 
Appendix A.  Virtual File Mapping Example

   This example demonstrates the mapping of a Virtual File into a
   sequence of ODETTE-FTP Data Exchange Buffers and shows how each
   Stream Transmission Buffer is built from an ODETTE-FTP Data Exchange
   Buffer prefixed by a Stream Transmission Header.

   Each line in this extract from 'The Hunting of the Snark' by Lewis
   Carroll [SNARK] is considered to be a separate record in a file
   containing variable length records.  Note that it does not represent
   a text file and CR/LF record separators are not used.  The blank line
   is represented by a zero length record.

      "It's a Snark!" was the sound that first came to their ears,
           And seemed almost too good to be true.
      Then followed a torrent of laughter and cheers:
           Then the ominous words "It's a Boo-"

      Then, silence.  Some fancied they heard in the air
           A weary and wandering sigh
      Then sounded like "-jum!" but the others declare
           It was only a breeze that went by.

   Assuming that the minimum exchange buffer length of 128 octets has
   been negotiated the result of mapping the text into Stream
   Transmission Buffers may be as follows.

   Stream Transmission Buffer 1

      Text  :  ....D."It' s a Snark! " was the  sound that  first cam
      Hex-H :  10084B2472 7262566762 2276727662 7676627667 2667772666
      Hex-L :  00044C2947 30103E12B1 2071304850 3F5E404814 069234031D
      Key   :  ----D!.... .......... .......... .......... ..........

      Text  :  e to their  ears,. .A nd seemed  almost too  good to b
      Hex-H :  6276276667 26677242A4 6627666662 6666772766 2666627626
      Hex-L :  504F048592 05123C5061 E40355D540 1CDF3404FF 07FF404F02
      Key   :  .......... ......!.!. .......... .......... ..........

      Text  :  e true..Th en followe d a torren t
      Hex-H :  6277762156 6626666676 6262767766 72
      Hex-L :  504255E848 5E06FCCF75 40104F225E 40
      Key   :  .......!.. .......... .......... ..

      Text  :  ....D.of l aughter an d cheers:.  .Then the  ominous w
      Hex-H :  1007496626 6766767266 6266667734 2A56662766 2666667727
      Hex-L :  000847F60C 157845201E 40385523A5 04485E0485 0FD9EF5307
      Key   :  ----D!.... .......... .........! .!........ ..........

Top      Up      ToC       Page 70 
      Text  :  ords "It's  a Boo-".. Then, sile nce.  Some  fancied t
      Hex-H :  6767224727 262466228B 5666227666 6662225666 2666666627
      Hex-L :  F243029473 0102FFD202 485EC039C5 E35E003FD5 061E395404
      Key   :  .......... ........!! .......... .......... ..........

      Text  :  hey heard  in the air
      Hex-H :  6672666762 6627662667
      Hex-L :  8590851240 9E04850192
      Key   :  .......... ..........

   Stream Transmission Buffer 3

      Text  :  ....D. .A  weary and  wandering  sigh.Then  sounded li
      Hex-H :  1007442942 7667726662 7666676662 7666B56662 7676666266
      Hex-L :  0008450A10 7512901E40 71E4529E70 39780485E0 3F5E4540C9
      Key   :  ----D!.!.. .......... .......... ....!..... ..........

      Text  :  ke "-jum!"  but the o thers decl are. .It w as only a
      Hex-H :  6622267622 2677276626 7667726666 67642A4727 6726667262
      Hex-L :  B502DA5D12 025404850F 485230453C 1255029407 130FEC9010
      Key   :  .......... .......... .......... ...!.!.... ..........

      Text  :  breeze tha t went by.
      Hex-H :  6766762766 7276672672
      Hex-L :  2255A50481 4075E4029E
      Key   :  .......... ..........

   Notes:
      Hex-H       High order bits of octet
      Hex-L       Low order bits of octet
      Key:  ----  Stream Transmission Header
            D     Data Exchange Buffer command code 'D'
            !     Subrecord header octet
            .     Place holder
      All headers are represented with a period in the Text line.

   Each Data Exchange Buffer is preceded by a Stream Transmission
   Header.

   In the above mapping the first Data Exchange Buffer is 128 octets in
   length.  The last record has been continued in the second buffer.

   The second Data Exchange Buffer has been truncated at 116 octets to
   finish at the end of a record.  The following record being completely
   contained in the third buffer.  This is an alternative to spanning
   the record as shown between the first and second Data Exchange
   Buffers.

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   The blank line has been encoded as a single header octet of '80' hex,
   indicating a zero length subrecord with the end of record flag set.

   The indented lines have been compressed.

Top      Up      ToC       Page 72 
Appendix B.  ISO 646 Character Subset

   o-----------------------------------------------------------------o
   |            |   7| 0   | 0   | 0   | 0   | 1   | 1   | 1   | 1   |
   |            | B -+-----+-----+-----+-----+-----+-----+-----+-----|
   |            | I 6|  0  |  0  |  1  |  1  |  0  |  0  |  1  |  1  |
   |            | T -+-----+-----+-----+-----+-----+-----+-----+-----|
   |            |   5|   0 |   1 |   0 |   1 |   0 |   1 |   0 |   1 |
   |            |----+-----+-----+-----+-----+-----+-----+-----+-----|
   |            |    |     |     |     |     |     |     |     |     |
   |            |    |     |     |     |     |     |     |     |     |
   |------------|    |  0  |  1  |  2  |  3  |  4  |  5  |  6  |  7  |
   |    BIT     |    |     |     |     |     |     |     |     |     |
   | 4  3  2  1 |    |     |     |     |     |     |     |     |     |
   |============o====o=====+=====+=====+=====+=====+=====+=====+=====|
   | 0  0  0  0 |  0 |     |     | SP  |  0  |     |  P  |     |     |
   |------------|----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 0  0  0  1 |  1 |     |     |     |  1  |  A  |  Q  |     |     |
   |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 0  0  1  0 |  2 |     |     |     |  2  |  B  |  R  |     |     |
   |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 0  0  1  1 |  3 |     |     |     |  3  |  C  |  S  |     |     |
   |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 0  1  0  0 |  4 |     |     |     |  4  |  D  |  T  |     |     |
   |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 0  1  0  1 |  5 |     |     |     |  5  |  E  |  U  |     |     |
   |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 0  1  1  0 |  6 |     |     |  &  |  6  |  F  |  V  |     |     |
   |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 0  1  1  1 |  7 |     |     |     |  7  |  G  |  W  |     |     |
   |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 1  0  0  0 |  8 |     |     |  (  |  8  |  H  |  X  |     |     |
   |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 1  0  0  1 |  9 |     |     |  )  |  9  |  I  |  Y  |     |     |
   |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 1  0  1  0 | 10 |     |     |     |     |  J  |  Z  |     |     |
   |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 1  0  1  1 | 11 |     |     |     |     |  K  |     |     |     |
   |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 1  1  0  0 | 12 |     |     |     |     |  L  |     |     |     |
   |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 1  1  0  1 | 13 |     |     |  -  |     |  M  |     |     |     |
   |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 1  1  1  0 | 14 |     |     |  .  |     |  N  |     |     |     |
   |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
   | 1  1  1  1 | 15 |     |     |  /  |     |  O  |     |     |     |
   o-----------------------------------------------------------------o

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Acknowledgements

   This document draws extensively on revision 1.3 of the ODETTE File
   Transfer Specification [OFTP].

   Numerous people have contributed to the development of this protocol
   and their work is hereby acknowledged.  The extensions required to
   utilise the Transmission Control Protocol were formulated and agreed
   by the current members of ODETTE Working Group Four, who also
   provided helpful reviews and comments on this document.

References

   [OFTP]  Organisation for Data Exchange by Tele Transmission in
   Europe, Odette File Transfer Protocol, Revision 1.3:1993

   [RFC-739]  Postel, J., Transmission Control Protocol, STD 7, RFC 739,
   September 1981

   [ISO-646] International Organisation for Standardisation, ISO
   Standard 646:1991, "Information technology -- ISO 7-bit coded
   character set for information interchange", 1991

   [ISO-6523] International Organisation for Standardisation, ISO
   Standard 6523:1984, "Data interchange -- Structures for the
   identification of organisations", 1984

   [ISO-8601] International Organisation for Standardisation, ISO
   Standard 8601:1988 "Data elements and interchange formats --
   Information interchange -- Representation of dates and times", 1988

   [NIFTP] High Level Protocol Group, "A Network Independent File
   Transfer Protocol", 1981

   [SNARK] Carroll, Lewis "The Hunting of the Snark", 1876

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ODETTE Address

   The ODETTE File Transfer Protocol is a product of Working Group Four
   of the Organisation for Data Exchange by Tele Transmission in Europe.
   The working group can be contacted via the ODETTE Secretariat:

   ODETTE Secretariat
   Forbes House
   Halkin Street
   London
   SW1X 7DS
   United Kingdom

   Phone: +44 (0)171 344 9227
   Fax:   +44 (0)171 235 7112
   EMail  odette@odette.org
          keith.oxley@odette.org
          stephanie.bioux@odette.org


Author's Address

   The author can be contacted at

   David Nash
   Ford Motor Company Limited
   Room 1/148, Central Office
   Eagle Way
   Warley
   Brentwood
   Essex
   CM13 3BW
   United Kingdom

   Phone: +44 (0)1277 253043
   EMail: dnash@ford.com