Network Working Group D. Nash Request for Comments: 2204 ODETTE Category: Informational September 1997
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
This memo describes a file transfer protocol to facilitate electronic data interchange between trading partners.
The protocol, denoted the ODETTE File Transfer Protocol, supports both direct communication between installations and indirect communication via a third party clearing centre. It was developed by the Organisation for Data Exchange by Tele Transmission in Europe to facilitate communication within the European motor industry and is presented here to allow for wider use within the Internet community.
1. Introduction 3
1.1 - Background 3
1.2 - Relationship to the original ODETTE Standard 3
1.3 - General Principles 3
1.4 - Structure 4
1.5 - Virtual Files 4
1.6 - Service Description 7
4. Protocol Specification 22
4.1 - Overview 22
4.2 - Start Session Phase 22
4.3 - Start File Phase 23
4.4 - Data Transfer Phase 26
4.5 - End File Phase 27
4.6 - End Session Phase 27
4.7 - Problem Handling 28
The ODETTE File Transfer Protocol (ODETTE-FTP) was defined in 1986 by working group four of the Organisation for Data Exchange by Tele Transmission in Europe (ODETTE) to address the electronic data interchange (EDI) requirements of the European automotive industry. It was designed in the spirit of the Open System Interconnection (OSI) model utilising the Network Service provided by the CCITT X25 recommendation.
Over the last ten years ODETTE-FTP has been widely deployed on systems of all sizes from personal computers to large mainframes. As a result of the wide scale deployment of internet technology and the trend towards global business practices, ODETTE has decided to extend the scope of it's file transfer protocol to allow the use of TCP/IP and to make the protocol available to the Internet community.
This memo describes the ODETTE-FTP protocol using the Transmission Control Protocol for it's network service.
This memo is an interpretation of version 1.3 of the ODETTE File Transfer Protocol [OFTP]. In the event of any ambiguity between this document and the original ODETTE-FTP, the original shall take precedence.
For ODETTE-FTP on TCP/IP the following sections have been added with respect to the original document.
Section 2 - Network Service
Section 7 - Stream Transmission Buffer
Appendix A - Virtual File mapping example
The aim of the ODETTE-FTP is to facilitate the transmission of a file between one or more locations in a way that is independent of the data communication network, system hardware and software environment.
In designing and specifying the protocol, the following factors were considered.
ODETTE-FTP is modelled on the OSI reference model. It is designed to use the Network Service provided by level 3 of the model and provide a File Service to the users. Thus the protocol spans levels 4 to 7 of model.
The description of the ODETTE-FTP contained in this memo is closely related to the original 'X.25' specification of the protocol and in the spirit of the OSI model describes:
A major consideration in adapting the protocol to use the Transmission Control Protocol (TCP) was the desire to make no changes to the existing protocol by adding the functionality required to allow implementors to support internet communication with only minor changes to existing ODETTE-FTP engines. To this end an additional header has been added to the start of each exchange buffer to allow the TCP byte stream to be broken up into the discrete exchange buffers expected by the ODETTE-FTP protocol.
Information is always exchanged between ODETTE-FTP entities in a standard representation called a Virtual File. This allows data transfer without regard for the nature of the communicating systems.
The mapping of a file between a local and virtual representation will vary from system to system and is not defined here.
o---------o
Site | Local |
A | File A |
o---------o
|
o----------------------- Mapping A ------------------------o
| | |
| o---------o |
| | Virtual | |
| | File | |
| o---------o |
| o------------------------------------------------o |
| | | |
| | ODETTE-FTP | |
| | | |
| o------------------------------------------------o |
| o---------o o---------o |
| | Virtual | | Virtual | |
| | File | | File | |
| o---------o o----+----o |
| | | |
o------ Mapping B ------------------------ Mapping C ------o
| |
o---------o o----+----o
| Local | Site Site | Local |
| File B | B C | File C |
o---------o o---------o
A Virtual File is described by a set of attributes identifying and defining the data to be transferred. The main attributes are:
Sequential
Logical records are presented one after another. The ODETTE-FTP must be aware of the record boundaries.
Dataset Name
Dataset name of the Virtual File being transfered, assigned by bilateral agreement.
Time stamp (HHMMSS)
A file qualifier indicating the time the Virtual File was made available for transmission.
Date stamp (YYMMDD)
A file qualifier indicating the date the Virtual File was made available for transmission.
The Dataset Name, Date and Time attributes are assigned by a Virtual File's Originator and are used to uniquely identify the file. They must not be changed by intermediate locations.
The Date attribute represents the decade and year in a two digit field. Since the ODETTE-FTP only uses this information to identify a particular Virtual File it will continue to operate correctly in the year 2000 and beyond.
The User Monitor may use the Virtual File Date attribute in local processes involving date comparisons and calculations. Any such use falls outside the scope of this protocol and year 2000 handling is a local implementation issue.
Four record formats are defined.
Fixed (F)
Each record in the file has the same length.
Variable (V)
The records in the file can have different lengths.
Unstructured (U)
The file contains a stream of data. No structure is defined.
Text File (T)
A Text File is defined as a sequence of ASCII characters, containing no control characters except CR/LF which delimits lines. A line will not have more than 2048 characters.
ODETTE-FTP can negotiate the restart of an interrupted Virtual File transmission. Fixed and Variable format files are restarted on record boundaries. For Unstructured and Text files the restart position is expressed as a file offset in 1K (1024 octet) blocks. The restart position is always calculated relative to the Virtual File.
ODETTE-FTP provides a file transfer service to a user monitor and in turn uses the Internet transport layer stream service to communicate between peers.
These services are specified in this memo using service primitives grouped into four classes as follows:
Request (RQ) An entity asks the service to do some work.
Indication (IND) A service informs an entity of an event.
Response (RS) An entity responds to an event.
Confirm (CF) A service informs an entity of the response.
Services may be confirmed, using the request, indication, response and confirm primitives, or unconfirmed using just the request and indication primitives.
ODETTE-FTP peer entities communicate with each other via the OSI Network Service or the Transmission Control Protocol Transport Service [TCP]. This is described by service primitives representing request, indication, response and confirmation actions.
For the internet environment, the service primitives mentioned below for the Network Service have to be mapped to the respective Transport Service primitives. This section describes the network service primitives used by ODETTE-FTP and their relationship to the TCP interface. In practice the local transport service application programming interface will be used to access the TCP service.
All Network primitives can be directly mapped to the respective Transport primitives when using TCP.
N_CON_RQ ------> N_CON_IND
N_CON_CF <------ N_CON_RS
This describes the setup of a connection. The requesting ODETTE-FTP peer uses the N_CON_RQ primitive to request an active OPEN of a connection to a peer ODETTE-FTP, the Responder, which has previously requested a passive OPEN. The Responder is notified of the incoming connection via N_CON_IND and accepts it with N_CON_RS. The requester is notified of the completion of it's OPEN request upon receipt of _CON_CF.
Parameters
Request Indication Response Confirmation --------------------------------------------------------------------- Dest addr ------> same same same
N_DATA_RQ ------> N_DATA_IND
Data exchange is an unconfirmed service. The Requester passes data for transmission to the network service via the N_DATA_RQ primitive. The Responder is notified of the availability of data via N_DATA_IND. In practice the notification and receipt of data may be combined, such as by the return from a blocking read from the network socket.
Parameters
Request Indication --------------------------------------------------------------------- Data ------------------> same
N_DISC_RQ ------> N_DISC_IND
An ODETTE-FTP requests the termination of a connection with the N_DISC_RQ service primitive. It's peer is notified of the CLOSE by a N_DISC_IND event. It is recognised that each peer must issue a N_DISC_RQ primitive to complete the TCP symmetric close procedure.
------> N_RST_IND
An ODETTE-FTP entity is notified of a network error by a N_RST_IND event. It should be noted that N_RST_IND would also be generated by a peer RESETTING the connection, but this is ignored here as N_RST_RQ is never sent to the Network Service by ODETTE-FTP.
A ODETTE-FTP requester will select a suitable local port.
The responding ODETTE-FTP will listen for connections on Registered Port 3305, the service name is 'odette-ftp'.
The File Transfer Service describes the services offered by an ODETTE-FTP Entity to it's User Monitor. The implementation of the service primitives is a local matter.
o-------------------o o-------------------o
| | | |
| USER MONITOR | | USER MONITOR |
| | | |
o-------------------o o-------------------o
| A | A
| | | |
F_XXX_RQ/RS | | F_XXX_IND/CF F_XXX_RQ/RS | | F_XXX_IND/CF
V | V |
o-------------------o o-------------------o
| |- - - - - - >| |
| ODETTE-FTP Entity | E-Buffer | ODETTE-FTP Entity |
| |< - - - - - -| |
o-------------------o o-------------------o
| A | A
N_XXX_RQ/RS | | N_XXX_IND/CF N_XXX_RQ/RS | | N_XXX_IND/CF
| | | |
V | V |
o---------------------------------------------------------o
| |
| N E T W O R K |
| |
o---------------------------------------------------------o
Key: E-Buffer - Exchange Buffer
F_ - File Transfer Service Primitive
N_ - Network Service Primitive
| |
F_CONNECT_RQ ---->|------------|----> F_CONNECT_IND
| |
F_CONNECT_CF <----|------------|<---- F_CONNECT_RS
| |
Parameters
Request Indication Response Confirm --------------------------------------------------------------------- called-address -> same --- ---- calling-address-> same --- ---- ID1 ------------> same ID2 ------------> same PSW1------------> same PSW2 -----------> same mode1 ----------> mode2 ----------> mode3 ----------> same restart1 -------> same -----------> restart2 -------> same ---------------------------------------------------------------------
Mode
Specifies the file transfer capabilities of the entity sending or receiving a F_CONNECT primitive for the duration of the session.
Value:
Sender-Only The entity can only send files.
Receiver-Only The entity can only receive files.
Both The entity can both send and receive files.
Negotiation:
Sender-Only Not negotiable.
Receiver-Only Not negotiable.
Both Can be negotiated down to Sender-Only or
Receiver-Only by the User Monitor or the
ODETTE-FTP entity.
Request Indication Response Confirm --------------------------------------------------------------------- Sender-only ----> Receiver-only --> Receiver-only --> Sender-only
Receiver-only --> Sender-only ----> Sender-only ----> Receiver-only
Both -----+-----> Both ----+------> Both -----------> Both
| or +------> Receiver-only --> Sender-only
| or +------> Sender-only ----> Receiver-only
|
or +-----> Receiver-only --> Receiver-only --> Sender-only
or +-----> Sender-only ----> Sender-only ----> Receiver-only
---------------------------------------------------------------------
Restart
Specifies the file transfer restart capabilities of the User Monitor.
Value:
Negotiation:
Request Indication Response Confirm
---------------------------------------------------------------------
restart = Y ----> restart = Y --+-> restart = Y ----> restart = Y
or +-> restart = N ----> restart = N
restart = N ----> restart = N ----> restart = N ----> restart = N
---------------------------------------------------------------------
| |
F_START_FILE_RQ ---->|------------|----> F_START_FILE_IND
| |
F_START_FILE_CF(+|-) <----|------------|<---- F_START_FILE_RS(+|-)
| |
Parameters:
Request Ind. RS(+) CF(+) RS(-) CF(-) -------------------------------------------------------------------- file-name ----> same ---- ---- ---- ---- date-time ----> same ---- ---- ---- ---- destination---> same ---- ---- ---- ---- originator----> same ---- ---- ---- ---- rec-format----> same ---- ---- ---- ---- rec-size -----> same ---- ---- ---- ---- file-size-----> same ---- ---- ---- ---- restart-pos1--> same-> restart-pos2-> same ---- ---- ---- ---- ---- ---- cause ------> same ---- ---- ---- ---- retry-later-> same --------------------------------------------------------------------
Notes:
| |
F_DATA_RQ ---->|------------|----> F_DATA_IND
| |
Notes:
| |
F_CLOSE_FILE_RQ --->|------------|----> F_CLOSE_FILE_IND
| |
F_CLOSE_FILE_CF(+|-) <---|------------|<---- F_CLOSE_FILE_RS(+|-)
| |
Parameters
Request Ind RS(+) CF(+) RS(-) CF(-)
---------------------------------------------------------------------
rec-count ---> same ---- ---- ---- ----
unit-count --> same ---- ---- ---- ----
---- ---- Speaker=Y ---> Speaker=N ---- ----
---- ---- Speaker=N ---> Speaker=Y ---- ----
---- ---- ---- ---- cause ---> same
---------------------------------------------------------------------
In a positive Close File response (F_CLOSE_FILE_RS(+)) the current Speaker may either:
The File Transfer service will ensure that the setting of the speaker parameter is consistent with the capabilities of the peer user.
The turn is never exchanged in the case of a negative response or confirmation.
Only the Speaker is allowed to issue F_XXX_FILE_RQ primitives.
The Initiator becomes the first Speaker at the end of the Session Setup (F_CONNECT_CF received by Initiator and F_CONNECT_RS sent by Responder).
Rules:
- The current Listener receives F_CLOSE_FILE_IND
(Speaker = choice).
- If the Listener answers F_CLOSE_FILE_RS(Speaker = YES), it
becomes Speaker, the Speaker receives F_CLOSE_FILE_CF (Speaker =
NO) and becomes Listener.
- If the Listener answers F_CLOSE_FILE_RS(Speaker = NO), it
remains Listener, and the Speaker receives F_CLOSE_FILE_CF
(Speaker = YES) and remains Speaker.
This service is initiated by the current Speaker (if there is no file transfer in progress) to send an End-to-End response from the final destination to the originator of a file.
| |
F_EERP_RQ ---->|------------|----> F_EERP_IND
| |
Parameters
Request Indication
------------------------------------
filename -------> same
date -----------> same
time -----------> same
destination ----> same
originator -----> same
------------------------------------
Relationship with Turn:
- Only the Speaker may send an End to End Response request.
- Invoking the EERP service does not change the turn.
- If a F_CD_IND has been received just before F_EERP_RQ is issued,
this results in leaving the special condition created by the
reception of F_CD_IND; i.e. while it was possible to issue
F_RELEASE_RQ and not possible to issue F_CD_RQ just after the
reception of F_CD_IND, after having issued F_EERP_RQ the normal Speaker status is entered again (F_CD_RQ valid, but F_RELEASE_RQ not valid).
| |
F_RELEASE_RQ ---->|------------|----> F_RELEASE_IND
| |
Parameters
Request Indication --------------------------------------------------------------------- reason = normal -------> ---- ---------------------------------------------------------------------
The Release service can only be initiated by the Speaker.
The Speaker can only issue a Release request (F_RELEASE_RQ) just after receiving an unsolicited Change Direction indication (F_CD_IND). This ensures that the other partner doesn't want to send any more files in this session.
Peer ODETTE-FTP entities action a normal session release by specifying Reason = Normal in an End Session (ESID) command.
| |
F_RELEASE_RQ ---->|------------|----> F_ABORT_IND
| |
Parameters
Request Indication
---------------------------------------------------------------------
reason = error value --> same (or equivalent)
AO (Abort Origin) = (L)ocal or (D)istant
---------------------------------------------------------------------
Abnormal session release can be initiated by either the Speaker or the Listener and also by the user or provider.
Abnormal session release can occur at any time within the session.
Peer ODETTE-FTP entities action an abnormal session release by specifying Reason = Error-value in an End Session (ESID) command.
The abnormal session release deals with the following types of error:
Other error types may be handled by an abort of the connection.
| |
F_ABORT_RQ ---->|------------|----> F_ABORT_IND
| |
User Initiated Abort
| |
F_ABORT_IND <----|------------|----> F_ABORT_IND
| |
Provider Initiated Abort
Parameters
Request Indication --------------------------------------------------------------------- -- R (Reason): specified or unspecified -- AO (Abort Origin): (L)ocal or (D)istant ---------------------------------------------------------------------
The Abort service may be invoked by either entity at any time.
The service provider may initiate an abort in case of error detection.
User | OFTP | Network | OFTP | User
---------------|------|----------------------|------|---------------
| | | |
F_RELEASE_RQ | | ESID(R=normal) | | F_RELEASE_IND
*--------------|-> ==|======================|=> --|-------------->
(R=normal) | | | |
F_RELEASE_RQ | | ESID(R=error) | | F_ABORT_IND
*--------------|-> ==|======================|=> -|-------------->
(R=error value)| | | | (R=error,AO=D)
User | OFTP | Network | OFTP | User
---------------|------|----------------------|------|---------------
| | | |
F_ABORT_IND | | ESID(R=error) | | F_ABORT_IND
<--------------|-* *=|======================|=> --|-------------->
| | | |
F_ABORT_RQ | | N_DISC_RQ | | F_ABORT_IND
*--------------|-> --|--------->..----------|-> --|-------------->
| | N_DISC_IND | | (R=unsp.,AO=D)
F_ABORT_IND | | N_DISC_RQ | | F_ABORT_IND
<--------------|-* *-|--------->..----------|-> --|-------------->
(R=error,AO=L) | | N_DISC_IND | | (R=unsp.,AO=D)
Key: * Origin of command flow
F_ ---> File Transfer Service primitive
N_ ---> Network Service primitive
===> ODETTE-FTP (OFTP) protocol message
This state automata defines the service as viewed by the User Monitor. Events causing a state transition are shown in lower case and the resulting action in upper case where appropriate.
o------------o
decision | | f_connect_ind
+-----------------| IDLE |-----------------+
| F_CONNECT_RQ | (0) | F_CONNECT_RS |
| o------------o |
V |
o-----------------o |
| | |
| I_WF_FCONNECTCF | |
| | |
o--------+--------o |
| |
| F_CONNECT_CF |
V V
o-----------------o o-----------------o
| | | |
| IDLE SPEAKER | | IDLE LISTENER |
| (1) | | (2) |
| See Speaker | | See Listener |
| State Diagram | | State Diagram |
| | | |
o-----------------o o-----------------o
o-----------------o o-----------------o
| IDLE LISTENER | | IDLE |
| CD_RQ just sent | | see (0) |
| see (3), Listen | | Idle |
| State Diagram | | State Diagram |
o-----------------o o-----------------o
A A
| |
decision decision decision
F_CD_RQ +----------------+ F_RELEASE_RQ
| | F_EERP_RQ | |
o=================o | o-----------------o
| |<-------------+ | IDLE SPEAKER |
| IDLE SPEAKER | | (4) |
| (1) | decision | CD_IND |
| |<-----------------------------| just received |
o=================o F_EERP_RQ o-----------------o
A A | |
| | | decision and P1 decision and P1 |
| | +-----------------+ +---------------------+
| | F_START_FILE_RQ | | F_START_FILE_RQ
| | V V
| | o---------------o
| | f_file_start_cf(-) | |
| +----------------------| OPENING |
| | |
| o---------------o
| |
f_file_close_cf(-) f_start_file_cf(+)
and not P2 |
| V
o---------------o o---------------o
| | | |------------------+
| CLOSING | | DATA TRANSFER | record to send |
| | | |<-----------------+
o---------------o o---------------o F_DATA_RQ
| A |
| | end of file |
| +-------------------+
| F_CLOSE_FILE_RQ
| o-----------------o
| f_close_file(+) and P2 | IDLE LISTENER |
+--------------------------------------------->| see (2), Listen |
| State Diagram |
Predicates: o-----------------o
P1: Mode = Both or (Mode = Sender-Only)
P2: Negative confirmation or (positive confirmation, Speaker = YES)
o-----------------o o-----------------o
| IDLE SPEAKER | | IDLE |
| CD_IND just | | |
| received see(4) | | see (0) |
| Speaker State | | Idle |
| Diagram | | State Diagram |
o-----------------o o-----------------o
A A
| |
decision f_eerp_ind decision
F_CD_IND +--------------+ F_RELEASE_IND
| | | |
o=================o | o-----------------o
| |<-----------+ f_eerp_ind | |
| |<-----------------------------| IDLE LISTENER |
| IDLE LISTENER | | (3) |
| | f_start_file_ind | CD_RQ |
| (2) | and not p2 | just sent |
| |---------------------+ | |
o=================o F_START_FILE_RS(-) | o-----------------o
A | A A | | |
| | | +-----------------------+ | |
| | | | |
| | | f_start_file_ind and not p2 | |
| | +--------------------------------------+ |
| | F_START_FILE_RS(-) |
| | |
| | f_start_file_ind f_start_file_ind |
| | and p2 and p2 |
| +-------------------------------+ +------------------+
| F_START_FILE_RS(+) | | F_START_FILE_RS(+)
| V V
| o---------------o
| f_close_file_ind and not p1 | DATA |-------------+
+------------------------------| TRANSFER | |
F_CLOSE_FILE_RS(-) | |<------------+
o---------------o F_DATA_IND
o---------------o |
| IDLE SPEAKER | f_close_file_ind and p1 |
| see (1), Spkr |<--------------------------+
| State Diagram | F_CLOSE_FILE_RS(+)
o---------------o
Predicates:
P1: (decision to send F_CLOSE_FILE_RS(+)) and
(decision to set Speaker = yes in F_CLOSE_FILE_RS(+))
P2: (decision to send F_START_FILE_RS(+))
The ODETTE-FTP protocol is divided into five operating phases.
Start Session
Start File
Data Transfer
End File
End Session
After the End File phase an ODETTE-FTP entity may enter a new Start File phase or terminate the session via the End Session phase.
ODETTE-FTP peers communicate by sending and receiving messages in Exchange Buffers via the Network Service. Each Exchange Buffer contains one of the following commands.
SSRM Start Session Ready Message
SSID Start Session
SFID Start File
SFPA Start File Positive Answer
SFNA Start File Negative Answer
DATA Data
CDT Set Credit
EFID End File
EFPA End File Positive Answer
EFNA End File Negative Answer
ESID End Session
CD Change Direction
EERP End to End Response
RTR Ready To Receive
The remainder of this section describes the protocol flows. Section five details the command formats.
The Start Session phase is entered immediately after the network connection has been established.
The ODETTE-FTP entity that took the initiative to establish the network connection becomes the Initiator. It's peer becomes the Responder.
The first message must be sent by the Responder.
1. Initiator <-------------SSRM -- Responder Ready Message
-- SSID ------------> Identification
<------------ SSID -- Identification
The Initiator from the Start Session phase is designated the Speaker while the Responder becomes the Listener. The roles are reversed by the Speaker sending a Change Direction command to the Listener.
1. Speaker -- SFID ------------> Listener Start File
<------------ SFPA -- Answer YES
Note: The User Monitor should take steps to prevent a loop situation occurring.
2. Speaker -- CD --------------> Listener Change Direction
Listener <------------ EERP -- Speaker End to End Response
-- RTR -------------> Ready to Receive
<------------ SFID -- Start File
The Start File command includes a count allowing the restart of an interrupted transmission to be negotiated. If restart facilities are not available the restart count must be set to zero. The sender will start with the lowest record count + 1.
The destination in a Start File command can be specified as follows.
The Listener will send a negative answer to the Speaker when the destination is not known.
The prioritisation of files for transmission is left to the local implementation. To allow some flexibility, a change direction mechanism is available in the End File phase.
The End to End Response (EERP) command notifies the originator of a Virtual File that it has been successfully delivered to it's final destination. This allows the originator to perform house keeping tasks such as deleting copies of the delivered data.
A Response Command must be sent from the location performing the final processing or distribution of the data to the originator. The Response is mandatory and may be sent in the same or in any subsequent session.
When an intermediate location broadcasts or distributes a Virtual File it must receive a Response command from all the locations to which it forwarded the data before sending it's own Response. This ensures that the Response received by the Virtual File's originator accounts for all the destination locations. An intermediate location therefore needs to track the status of files it processes over time.
Example: Point to Point
Location A sends file Ba to Location B which will send an EERP to location A after it successfully receives the file.
o----------o o-----------o | Loc. A |----------- S1 ---------->| Loc. B | | | | | | [Ba] |<---------- R2 -----------| [Ba] | +----------o o-----------o
Key:
S - File Transfer R - Response EERP [Ba] - File for B from A
Example: Data distribution
Location A sends a Virtual File containing data for distribution to locations B and C via clearing centres E1 and E2. Clearing centre E1 must wait for a response from E2 (for file Ba) and location C before it sends it's response, R8, to location A. Clearing centre E2 can only send response R7 to E1 when location B acknowledges file Ba with response R6.
o---------o o---------o o---------o o---------o
| Loc. A |-- S1 ->| Loc. E1 |-- S2 ->| Loc. E2 |-- S5 ->| Loc. B |
| | | | | | | |
| [Ba,Ca] |<- R8 --| [Ba,Ca] |<- R7 --| [Ba] |<- R6 --| [Ba] |
o---------o o---------o o---------o o---------o
A |
| | o---------o
| +----- S3 ->| Loc. C |
| | |
+--------- R4 --| [Ca] |
o---------o
Example: Data collection
Locations A and B send files Ca and Cb to clearing centre E1 which forwards both files to location C in a single Virtual File. When it receives response R4 from C, clearing centre E1 sends response R5 to location A and R6 to location B.
o---------o o---------o o---------o
| Loc. A |-- S1 ->| Loc. E1 |-- S3 ->| Loc. C |
| | | | | |
| [Ca] |<- R5 --| [Ca,Cb] |<- R4 --| [Ca,Cb] |
o---------o o---------o o---------o
A |
o---------o | |
| Loc. B |-- S2 -----+ |
| | |
| [Cb] |<- R6 ---------+
o---------o
In order to avoid congestion between two adjacent nodes caused by a continuous flow of EERP's, a Ready To Receive (RTR) command is provided. The RTR acts as an EERP acknowledgement for flow control but has no end-to-end significance.
Speaker -- EERP ------------> Listener End to End Response
<------------- RTR -- Ready to Receive
-- EERP ------------> End to End Response
<------------- RTR -- Ready to Receive
-- SFID ------------> Start File
or
-- CD --------------> Exchange the turn
After sending an EERP, the Speaker must wait for an RTR before sending any other commands.
Virtual File data flows from the Speaker to the Listener during the Data Transfer phase which is entered after the Start File phase.
To avoid congestion at the protocol level a flow control mechanism is provided via the Credit (CDT) command.
A Credit limit is negotiated in the Start Session phase, this represents the number of Data Exchange Buffers that the Speaker may send before it is obliged to wait for a Credit command from the Listener.
The available credit is initially set to the negotiated value by the Start File positive answer, which acts as an implicit Credit command. The Speaker decreases the available credit count by one for each data buffer sent to the Listener.
When the available credit is exhausted, the Speaker must wait for a Credit command from the Listener otherwise a protocol error will occur and the session will be aborted.
The Listener should endeavour to send the Credit command without delay to prevent the Speaker blocking.
1. Speaker -- SFID ------------> Listener Start File
<------------ SFPA -- Answer YES
Speaker -- Data ------------> Listener Start File
-- Data ------------>
<------------- CDT -- Set Credit
-- Data ------------>
-- EFID ------------> End File
The Speaker notifies the Listener that it has finished sending a Virtual File by sending an End File (EFID) command. The Listener replies with a positive or negative End File command and has the option to request a Change Direction command from the Speaker.
1. Speaker -- EFID ------------> Listener End File
<------------ EFPA -- Answer YES
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
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.
If a protocol error occurs the session will be terminated and application activity aborted. Both locations enter the IDLE state.
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.
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.
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.
The basic unit of information is an octet, containing eight bits.
The ISO 646 IRV 7-bit coded character set [ISO-646] is used to encode constants and strings within command exchange buffers.
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:
The first octet of an Exchange Buffer is the Command Identifier and defines the format of the buffer.
Command parameters are stored in fixed fields within a Command Exchange Buffer. All values are required.
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.
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.
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'.
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.
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.
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'.
| SFID Start File | | | | Start File Phase Speaker ----> Listener | |-------------------------------------------------------------------| | Pos | Field | Description | Format | |-----+-----------+---------------------------------------+---------| | 0 | SFIDCMD | SFID Command, 'H' | F X(1) | | 1 | SFIDDSN | Virtual File Dataset Name | V X(26) | | 27 | SFIDRSV1 | Reserved | F X(9) | | 36 | SFIDDATE | Virtual File Date stamp, (YYMMDD) | V X(6) | | 42 | SFIDTIME | Virtual File Time stamp, (HHMMSS) | V X(6) | | 48 | SFIDUSER | User Data | V X(8) | | 56 | SFIDDEST | Destination | V X(25) | | 81 | SFIDORIG | Originator | V X(25) | | 106 | SFIDFMT | File Format, (F/V/U/T) | F X(1) | | 107 | SFIDLRECL | Maximum Record Size | V 9(5) | | 112 | SFIDFSIZ | File Size, 1K blocks | V 9(7) | | 119 | SFIDREST | Restart Position | V 9(9) | o-------------------------------------------------------------------o SFIDCMD Command Code Character
Value: 'H' SFID Command identifier.
SFIDDSN Virtual File Dataset Name String(26)
Dataset name of the Virtual File being transferred, assigned by bilateral agreement.
No general structure is defined for this attribute.
See Virtual Files - Identification (Section 1.5.2)
SFIDRSV1 Reserved String(9)
This field is reserved for future use.
SFIDDATE Virtual File Date stamp String(6)
Format: 'YYMMDD' 6 decimal digits representing the year, month and day respectively [ISO-8601].
Date stamp assigned by the Virtual File's Originator indicating when the file was made available for transmission.
See Virtual Files - Identification (Section 1.5.2)
SFIDTIME Virtual File Time stamp String(6)
Format: 'HHMMSS' 6 decimal digits representing hours, minutes and seconds respectively [ISO-8601].
Time stamp assigned by the Virtual File's Originator indicating when the file was made available for transmission.
See Virtual Files - Identification (Section 1.5.2)
SFIDUSER 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.
SFIDDEST Destination String(25)
Format: See Identification Code (Section 5.4)
The Final Recipient of the Virtual File.
This is the location that will look into the Virtual File content and perform mapping functions. It is also the location that creates the End to End Response (EERP) command for the received file.
SFIDORIG Originator String(25)
Format: See Identification Code (Section 5.4)
Originator of the Virtual File.
It is the location that created (mapped) the data for
transmission.
SFIDFMT File Format Character
Value: 'F' Fixed format binary file.
'V' Variable format binary file.
'U' Unstructured binary file.
'T' Text
Virtual File format. Used to calculate the restart position. (Section 1.5.3)
SFIDLRECL Maximum Record Size Numeric(5)
Maximum: 99999
Length in octets of the longest logical record which may be transferred to a location. Only user data is included.
If SFIDFMT is 'T' or 'U' then this attribute must be set to '00000'.
SFIDFSIZ File Size Numeric(7)
Maximum: 9999999
Space in 1K (1024 octet) blocks required at the Originator location to store the Virtual File.
This parameter is intended to provide only a good estimate of the Virtual File size.
SFIDREST Restart Position Numeric(9)
Maximum: 999999999
Virtual File restart position.
The count represents the:
- Record Number if SSIDFMT is 'F' or 'V'.
- File offset in 1K (1024 octet) blocks if SSIDFMT is
'U' or 'T'.
The count will express the transmitted user data (i.e. before compression, header not included).
After negotiation between adjacent locations,
retransmission will start at the lowest value.
| SFPA Start File Positive Answer | | | | Start File Phase Speaker <---- Listener | |-------------------------------------------------------------------| | Pos | Field | Description | Format | |-----+-----------+---------------------------------------+---------| | 0 | SFPACMD | SFPA Command, '2' | F X(1) | | 1 | SFPAACNT | Answer Count | V 9(9) | o-------------------------------------------------------------------o
SFPACMD Command Code Character
Value: '2' SFPA Command identifier.
SFPAACNT Answer Count Numeric(9)
The Listener must enter a count lower or equal to the restart count specified by the Speaker in the Start File (SFID) command. The count expresses the received user data. If restart facilities are not available, a count of zero must be specified.
o-------------------------------------------------------------------o
| SFNA Start File Negative Answer | | | | Start File Phase Speaker <---- Listener | |-------------------------------------------------------------------| | Pos | Field | Description | Format | |-----+-----------+---------------------------------------+---------| | 0 | SFNACMD | SFNA Command, '3' | F X(1) | | 1 | SFNAREAS | Answer Reason | F 9(2) | | 3 | SFNARRTR | Retry Indicator, (Y/N) | F X(1) | o-------------------------------------------------------------------o SFNACMD Command Code Character
Value: '3' SFNA Command identifier.
SFNAREAS Answer Reason Numeric(2)
Value: '01' Invalid filename.
'02' Invalid destination.
'03' Invalid origin.
'04' Storage record format not supported.
'05' Maximum record length not supported.
'06' File size is too big.
'10' Invalid record count.
'11' Invalid byte count.
'12' Access method failure.
'13' Duplicate file.
'99' Unspecified reason.
Reason why transmission can not proceed.
SFNARRTR Retry Indicator Character
Value: 'N' Transmission should not be retried.
'Y' The transmission may be retried latter.
This parameter is used to advise the Speaker if it should retry at a latter point in time due to a temporary condition at the Listener site, such as a lack of storage space. It should be used in conjunction with the Answer Reason code (SFNAREAS).
An invalid file name error code may be the consequence of a problem in the mapping of the Virtual File on to a real file. Such problems cannot always be resolved immediately. It it therefore recommended that when a SFNA with Retry = Y is received the User Monitor attempts to retransmit the relevant file in a subsequent session.
o-------------------------------------------------------------------o
| DATA Data Exchange Buffer | | | | Data Transfer Phase Speaker ----> Listener | |-------------------------------------------------------------------| | Pos | Field | Description | Format | |-----+-----------+---------------------------------------+---------| | 0 | DATACMD | DATA Command, 'D' | F X(1) | | 1 | DATABUF | Data Exchange Buffer payload | V X(n) | o-------------------------------------------------------------------o DATACMD Command Code Character
Value: 'D' DATA Command identifier.
DATABUF Data Exchange Buffer payload String(n)
Variable length buffer containing the data payload. The Data Exchange Buffer is described in Section 6.
o-------------------------------------------------------------------o
| CDT Set Credit | | | | Data Transfer Phase Speaker <---- Listener | |-------------------------------------------------------------------| | Pos | Field | Description | Format | |-----+-----------+---------------------------------------+---------| | 0 | CDTCMD | CDT Command, 'C' | F X(1) | | 1 | CDTRSV1 | Reserved | F X(2) | o-------------------------------------------------------------------o CDTCMD Command Code Character
Value: 'C' CDT Command identifier.
CDTRSV1 Reserved String(2)
This field is reserved for future use.
o-------------------------------------------------------------------o
| EFID End File | | | | End File Phase Speaker ----> Listener | |-------------------------------------------------------------------| | Pos | Field | Description | Format | |-----+-----------+---------------------------------------+---------| | 0 | EFIDCMD | EFID Command, 'T' | F X(1) | | 1 | EFIDRCNT | Record Count | V 9(9) | | 10 | EFIDUCNT | Unit Count | V 9(12) | o-------------------------------------------------------------------o EFIDCMD Command Code Character
Value: 'T' EFID Command identifier.
EFIDRCNT Record Count Numeric(9)
Maximum: 999999999
For SSIDFMT 'F' or 'V' the exact record count.
For SSIDFMT 'U' or 'T' zeros.
The count will express the real size of the file (before compression, header not included). The total count is always used, even during restart processing.
EFIDUCNT Unit Count Numeric(12)
Maximum: 999999999999
Exact number of units (octets) transmitted.
The count will express the real size of the file. The total count is always used, even during restart processing.
| EFPA End File Positive Answer | | | | End File Phase Speaker <---- Listener | |-------------------------------------------------------------------| | Pos | Field | Description | Format | |-----+-----------+---------------------------------------+---------| | 0 | EFPACMD | EFPA Command, '4' | F X(1) | | 1 | EFPACD | Change Direction Indicator, (Y/N) | F X(1) | o-------------------------------------------------------------------o EFPACMD Command Code Character
Value: '4' EFPA Command identifier.
EFPACD Change Direction Indicator Character
Value: 'N' Change direction not requested.
'Y' Change direction requested.
This parameter allows the Listener to request a Change Direction (CD) command from the Speaker.
| EFNA End File Negative Answer | | | | End File Phase Speaker <---- Listener | |-------------------------------------------------------------------| | Pos | Field | Description | Format | |-----+-----------+---------------------------------------+---------| | 0 | EFNACMD | EFNA Command, '5' | F X(1) | | 1 | EFNAREAS | Answer Reason | F 9(2) | o-------------------------------------------------------------------o
EFNACMD Command Code Character
Value: '5' EFNA Command identifier.
EFNAREAS Answer Reason Numeric(2)
Value: '01' Invalid filename.
'02' Invalid destination.
'03' Invalid origin.
'04' Storage record format not supported.
'05' Maximum record length not supported.
'06' File size is too big.
'10' Invalid record count.
'11' Invalid byte count.
'12' Access method failure.
'13' Duplicate file.
'99' Unspecified reason.
Reason why transmission can not proceed.
o-------------------------------------------------------------------o
| ESID End Session | | | | End Session Phase Speaker ----> Listener | |-------------------------------------------------------------------| | Pos | Field | Description | Format | |-----+-----------+---------------------------------------+---------| | 0 | ESIDCMD | ESID Command, 'F' | F X(1) | | 1 | ESIDREAS | Reason Code | F 9(2) | | 3 | ESIDCR | Carriage Return | F X(1) | o-------------------------------------------------------------------o ESIDCMD Command Code Character
Value: 'F' ESID Command identifier.
ESIDREAS Reason Code Numeric(2)
Value '00' Normal session termination
'01' Command not recognised
An Exchange Buffer contains an invalid command code (1st octet of the buffer).
'02' Protocol violation
An Exchange Buffer contains an invalid command for the current state of the receiver.
'03' User code not known
A Start Session (SSID) command contains an unknown or invalid Identification Code.
'04' Invalid password
A Start Session (SSID) command contained an invalid password.
'05' Local site emergency close down
The local site has entered an emergency close down mode. Communications are being forcibly terminated.
'06' Command contained invalid data
A field within a Command Exchange buffer contains invalid data.
'07' Exchange Buffer size error
The length of the Exchange Buffer as determined by the Stream Transmission Header is different to the length implied by the Command Code.
'08' Resources not available
The request for connection has been denied due to a resource shortage. The connection attempt should be retried later.
'09' Time out
'10' Mode or capabilities incompatible
'99' Unspecified Abort code
An error was detected for which no specific code is defined.
ESIDCR Carriage Return Character
Value: Character with hex value '0D' or '8D'.
o-------------------------------------------------------------------o
| CD Change Direction | | | | Start File Phase Speaker ----> Listener | | End File Phase Speaker ----> Listener | | End Session Phase Initiator <---> Responder | |-------------------------------------------------------------------| | Pos | Field | Description | Format | |-----+-----------+---------------------------------------+---------| | 0 | CDCMD | CD Command, 'R' | F X(1) | o-------------------------------------------------------------------o CDCMD Command Code Character
Value: 'R' CD Command identifier.
o-------------------------------------------------------------------o
| EERP End to End Response | | | | Start File Phase Speaker ----> Listener | | End File Phase Speaker ----> Listener | |-------------------------------------------------------------------| | Pos | Field | Description | Format | |-----+-----------+---------------------------------------+---------| | 0 | EERPCMD | EERP Command, 'E' | F X(1) | | 1 | EERPDSN | Virtual File Dataset Name | V X(26) | | 27 | EERPRSV1 | Reserved | F X(9) | | 36 | EERPDATE | Virtual File Date stamp, (YYMMDD) | V X(6) | | 42 | EERPTIME | Virtual File Time stamp, (HHMMSS) | V X(6) | | 48 | EERPUSER | User Data | V X(8) | | 56 | EERPDEST | Destination | V X(25) | | 81 | EERPORIG | Originator | V X(25) | o-------------------------------------------------------------------o EERPCMD Command Code Character
Value: 'E' EERP Command identifier.
EERPDSN Virtual File Dataset Name String(26)
Dataset name of the Virtual File being transferred, assigned by bilateral agreement.
No general structure is defined for this attribute. See Virtual Files - Identification (Section 1.5.2)
EERPRSV1 Reserved String(9)
This field is reserved for future use.
EERPDATE Virtual File Date stamp String(6)
Format: 'YYMMDD' 6 decimal digits representing the year, month and day respectively [ISO-8601].
Date stamp assigned by the Virtual File's Originator indicating when the file was made available for transmission.
See Virtual Files - Identification (Section 1.5.2)
EERPTIME Virtual File Time stamp String(6)
Format: 'HHMMSS' 6 decimal digits representing hours, minutes and seconds respectively [ISO-8601].
Time stamp assigned by the Virtual File's Originator indicating when the file was made available for transmission.
See Virtual Files - Identification (Section 1.5.2)
EERPUSER 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.
EERPDEST Destination String(25)
Format: See Identification Code (Section 5.4)
Originator of the Virtual File.
This is the location that created (mapped) the data for transmission.
EERPORIG Originator String(25)
Format: See Identification Code (Section 5.4)
Final Recipient of the Virtual File.
This is the location that will look into the Virtual File
content and perform mapping functions. It is also the
location that creates the EERP for the received file.
o-------------------------------------------------------------------o
| RTR Ready To Receive | | | | Start File Phase Initiator <---- Responder | | End File Phase Initiator <---- Responder | |-------------------------------------------------------------------| | Pos | Field | Description | Format | |-----+-----------+---------------------------------------+---------| | 0 | RTRCMD | RTR Command, 'P' | F X(1) | o-------------------------------------------------------------------o RTRCMD Command Code Character
Value: 'P' RTR Command identifier.
The Initiator (sender) and Responder (receiver) participating in an
ODETTE-FTP session are uniquely identified by an Identification Code
based on [ISO 6523], Structure for the Identification of
Organisations (SIO). The locations are considered to be adjacent for
the duration of the transmission.
The SIO has the following format.
o-------------------------------------------------------------------o
| Pos | Field | Description | Format | |-----+-----------+---------------------------------------+---------| | 0 | SIOOID | ODETTE Identifier | F X(1) | | 1 | SIOICD | International Code Designator | V 9(4) | | 5 | SIOORG | Organisation Code | V X(14) | | 19 | SIOCSA | Computer Sub-Address | V X(6) | o-------------------------------------------------------------------o SIOOID ODETTE Identifier Character
Value: 'O' Indicates ODETTE assigned Organisation Identifier. Other values may be used for non-ODETTE codes.
SIOICD International Code Designator String(4)
A code forming part of the Organisation Identifier.
SIOORG Organisation Code String(14)
A code forming part of the Organisation Identifier. This field may contain the letters A to Z, the digits 0 to 9, apace and hyphen characters.
SIOCSA Computer Sub-Address String(6)
A locally assigned address which uniquely identifies a system within an organisation (defined by an Organisation Identifier).
Virtual Files are transmitted by mapping the Virtual File records into Data Exchange Buffers, the maximum length of which was negotiated between the ODETTE-FTP entities via the Start Session (SSID) commands exchanged during the Start Session Phase of the protocol. The format is based on the Network Independent File Transfer Protocol [NIFTP].
Virtual File records may be of arbitrary length. A simple compression scheme is defined for strings of repeated characters.
An example of the use of the Data Exchange Buffer can be found in Appendix A.
For transmission of Virtual File records, data is divided into Subrecords, each of which is preceded by a one octet Subrecord Header.
The Data Exchange Buffer is made up of the initial Command character,
o--------------------------------------------------------
| C | H | | H | | H | | /
| M | D | SUBRECORD | D | SUBRECORD | D | SUBRECORD | /_
| D | R | | R | | R | | /
o-------------------------------------------------------
CMD
The Data Exchange Buffer Command Character, 'D'.
HDR
A one octet Subrecord Header defined as follows:
0 1 2 3 4 5 6 7
o-------------------------------o
| E | C | |
| o | F | C O U N T |
| R | | |
o-------------------------------o
Bits
0 End of Record Flag
Set to indicate that the next subrecord is the last subrecord of the current record.
Unstructured files are transmitted as a single record, in this case the flag acts as an end of file marker.
1 Compression Flag
Set to indicate that the next subrecord is compressed.
2-7 Subrecord Count
The number of octets in the Virtual File represented by the next subrecord expressed as a binary value.
For uncompressed data this is simply the length of the subrecord.
For compressed data this is the number of times that the single octet in the following subrecord must be inserted in the Virtual File.
As six bits are available, the next subrecord may represent between 0 and 63 octets of the Virtual File.
An Exchange Buffer may be any length up to the value negotiated in the Start Session exchange.
Virtual File records may be concatenated within one Exchange Buffer or split across a number of buffers.
A subrecord is never split between two Exchange Buffers. If the remaining space in the current Exchange Buffer is insufficient to contain the next 'complete' subrecord one of the following strategies should be used:
A record of length zero may appear anywhere in the Exchange Buffer.
A subrecord of length zero may appear anywhere in the record and/or the Exchange Buffer.
The ODETTE-FTP was originally designed to utilise the ISO Network Service, specifically the X.25 specification. It relies on the fact that the network service will preserve the sequence and boundaries of data units transmitted through the network and that the network service will pass the length of the data unit to the receiving ODETTE-FTP. The TCP offers a stream based connection which does not provide these functions.
In order to utilise the TCP stream without disruption to the existing ODETTE-FTP a Stream Transmission Buffer (STB) is created by adding a Stream Transmission Header (STH) to the start of all Command and Data Exchange Buffers before they are passed to the TCP transport service. This allows the receiving ODETTE-FTP to recover the original Exchange Buffers.
STH - Stream Transmission Header
OEB - ODETTE-FTP Exchange Buffer
The Stream Transmission Buffer comprises of a STH and OEB.
o-----+-----------------+-----+--------------------+-----+------
| STH | OEB | STH | OEB | STH | OEB/ o-----+-----------------+-----+--------------------+-----+----
The Stream Transmission Header is shown below. The fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Flags | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version
Value: 0001 (binary)
Stream Transmission Header version number.
Flags
Value: 0000 (binary)
Reserved for future use.
Length
Range: 5 - 100003 (decimal)
The length of the Stream Transmission Buffer (STH+OEB).
The smallest STB is 5 octets consisting of a 4 octet header followed by a 1 octet Exchange Buffer such as a Change Direction (CD) command.
The maximum Exchange Buffer length that can be negotiated is 99999 octets (Section 5.3.2) giving a STB length of 100003.
The length is expressed as a binary number with the most significant bit on the left.
It is expected that implementations of this protocol will follow the Internet robustness principle of being conservative in what is sent and liberal in what is accepted.
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.
The receipt of an event in a given state may be invalid for three reasons.
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.
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.
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.
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.
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. ---------------------------------------------------------------------
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.
---------------------------------------------------------------------
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
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
---------------------------------------------------------------------
Predicate P1: (No resources available) OR
(C.Cap-init = Responder) OR
(C.Cap-mode = Sender-only AND
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
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
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
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
---------------------------------------------------------------------
Action 1: Stop inactivity timer
Action 2: Start inactivity timer
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=================================================================
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 -->
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
---------------------------------------------------------------------
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
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.
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
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
---------------------------------------------------------------------
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.
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
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
---------------------------------------------------------------------
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
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:
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.
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.
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.
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.
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
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.
[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
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
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