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.
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.
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.
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
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.
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.
---------------------------------------------------------------------
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
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
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
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
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
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
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.
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
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.
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.
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!.... .......... .........! .!........ ..........
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.
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.
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
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
