Request for Comments: 2204 ODETTE
Category: Informational September 1997
ODETTE File Transfer Protocol
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Abstract
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.
Table of Contents
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
2. Network Service (TCP Transport Service) 7
2.1 - Introduction 7
2.2 - Service Primitives 7
2.3 - Port Assignment 9
3. File Transfer Service 9
3.1 - Model 10
3.2 - Session Setup 11
3.3 - File Transfer 13
3.4 - Session Take Down 16
3.5 - Service State Automata 19
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
5. Commands and Formats 28
5.1 - Conventions 28
5.2 - Commands 29
5.3 - Command Formats 29
5.4 - Identification Code 45
6. ODETTE-FTP Data Exchange Buffer 46
6.1 - Overview 46
6.2 - Data Exchange Buffer Format 46
6.3 - Buffer Filling Rules 47
7. Stream Transmission Buffer (TCP only) 47
7.1 - Introduction 47
7.2 - Stream Transmission Header Format 49
8. Protocol State Machine 50
8.1 - ODETTE-FTP State Machine 50
8.2 - Error Handling 50
8.3 - States 51
8.4 - Input Events 53
8.5 - Output Events 54
8.6 - Local Variables 55
8.7 - Local Constants 55
8.8 - Session Connection State Table 56
8.9 - Error and Abort State Table 58
8.10 - Speaker State Table 1 59
8.11 - Speaker State Table 2 63
8.12 - Listener State Table 65
8.13 - Example 68
9. Security Considerations 68
Appendix A Virtual File Mapping Example 69
Appendix B ISO 646 Character Subset 72
Acknowledgements 73
References 73
ODETTE Address 74
Author's Address 74
1. Introduction
1.1 Background
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.
1.2 Relationship to the original ODETTE Standard
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
1.3 General Principles
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.
1. The possible differences of size and sophistication (file storage,
small and large systems).
2. The necessity to work with existing systems (reduce changes to
existing products and allow easy implementation).
3. Systems of different ages.
4. Systems of different manufactures.
5. The potential for growth in sophistication (limit impact and avoid
changes at other locations).
1.4 Structure
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:
1. A File Service provided to a user monitor.
2. A protocol for the exchange of information between peer
ODETTE-FTP entities.
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.
1.5 Virtual Files
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:
1.5.1 Organisation:
Sequential
Logical records are presented one after another. The ODETTE-FTP
must be aware of the record boundaries.
1.5.2 Identification
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.
1.5.3 Record Format
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.
1.5.4 Restart
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.
1.6 Service Description
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.
2. Network Service (TCP Transport Service)
2.1 Introduction
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.
2.2 Service Primitives
All Network primitives can be directly mapped to the respective
Transport primitives when using TCP.
2.2.1 Network Connection
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
2.2.2 Network Data
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
2.2.3 Network Disconnection
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.
2.2.4 Network Reset
------> 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.
2.3 Port Assignment
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'.
3. File Transfer Service
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.
3.1 Model
o-------------------o o-------------------o
| | | |
| USER MONITOR | | USER MONITOR |
| | | |
o-------------------o o-------------------o
| A | A
...............|...|... FILE TRANSFER SERVICE ...|...|...............
| | | |
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
| | | |
...............|...|...... NETWORK SERVICE ......|...|...............
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
3.2 Session Setup
3.2.1 Session Connection Service
| |
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
---------------------------------------------------------------------
3.3 File Transfer
3.3.1 File Opening
| |
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:
1. Retry-later has values "Y" or "N". 2. Cause is the reason for
refusing the transfer (1,..,13,99). 3. Restart-pos1 not equal 0 is
only valid if restart has been agreed
during initial negotiation.
4. Restart-pos2 is less than or equal to restart-pos1.
3.3.2 Data Regime
| |
F_DATA_RQ ---->|------------|----> F_DATA_IND
| |
Notes:
1. The data format within a F_DATA primitive is locally defined.
2. The File Transfer service may have to provide a flow control
mechanism to regulate the flow of F_DATA primitives.
3.3.3 File Closing
| |
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:
1. Set Speaker to "Yes" and become the Speaker. 2. Set Speaker
to "No" and remain the Listener.
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.
3.3.4 Exchanging the Turn
3.3.4.1 Initial Turn (First Speaker)
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).
3.3.4.2 Following Turns
Rules:
1. At each unsuccessful End of File the turn is not exchanged.
2. At each successful End of File the turn is exchanged if requested
by the Listener:
- 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.
3. The Speaker can issue a Change Direction request (F_CD_RQ) to
become the Listener. The Listener receives a Change Direction
indication (F_CD_IND) and becomes the Speaker.
4. In order to prevent loops of F_CD_RQ/IND, it is an error to send
F_CD_RQ immediately after having received a F_CD_IND.
3.3.5 End to End Response
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).
3.4 Session Take Down
3.4.1 Normal Close
| |
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.
3.4.2 Abnormal close
| |
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:
1. The service provider will initiate an abnormal release in the
following cases:
1. Protocol error, 2. Failure of the Start Session (SSID)
negotiation, 3. Command not recognised, 4. Exchange buffer size
error, 5. Resources not available, 6. Other unspecified abort code
(with "REASON" = unspecified).
2. The User Monitor will initiate an abnormal release in the
following cases:
1. Local site emergency close down, 2. Resources not available, 3.
Other unspecified abort code (with "REASON" = unspecified).
Other error types may be handled by an abort of the connection.
3.4.3 Abort
| |
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.
3.4.4 Explanation of Session Take Down Services
User | OFTP | Network | OFTP | User
---------------|------|----------------------|------|---------------
| | | |
1. Normal Release
F_RELEASE_RQ | | ESID(R=normal) | | F_RELEASE_IND
*--------------|-> ==|======================|=> --|-------------->
(R=normal) | | | |
2. User Initiated Abnormal Release
F_RELEASE_RQ | | ESID(R=error) | | F_ABORT_IND
*--------------|-> ==|======================|=> -|-------------->
(R=error value)| | | | (R=error,AO=D)
User | OFTP | Network | OFTP | User
---------------|------|----------------------|------|---------------
| | | |
3. Provider Initiated Abnormal Release
F_ABORT_IND | | ESID(R=error) | | F_ABORT_IND
<--------------|-* *=|======================|=> --|-------------->
| | | |
4. User Initiated Connection Abort
F_ABORT_RQ | | N_DISC_RQ | | F_ABORT_IND
*--------------|-> --|--------->..----------|-> --|-------------->
| | N_DISC_IND | | (R=unsp.,AO=D)
5. Provider Initiated Connection Abort
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
3.5 Service State Automata
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.
3.5.1 Idle State Diagram
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
3.5.2 Speaker State Diagram
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)
3.5.3 Listener State Diagram
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(+))
4. Protocol Specification
4.1 Overview
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.
4.2 Start Session Phase
The Start Session phase is entered immediately after the network
connection has been established.
4.2.1 Entity Definition
The ODETTE-FTP entity that took the initiative to establish the
network connection becomes the Initiator. It's peer becomes the
Responder.
4.2.2 Protocol Sequence
The first message must be sent by the Responder.
1. Initiator <-------------SSRM -- Responder Ready Message
-- SSID ------------> Identification
<------------ SSID -- Identification
4.3 Start File Phase
4.3.1 Entity Definition
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.
4.3.2 Protocol Sequence
1. Speaker -- SFID ------------> Listener Start File
<------------ SFPA -- Answer YES
2. Speaker -- SFID ------------> Listener Start File
<------------ SFNA -- Answer NO
Go To 1
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
4.3.3 Restart Facilities
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.
4.3.4 Broadcast Facilities
The destination in a Start File command can be specified as follows.
1. An explicitly defined destination.
2. A group destination that allows an intermediate location to
broadcast the Virtual File to multiple destinations.
The Listener will send a negative answer to the Speaker when the
destination is not known.
4.3.5 Priority
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.
4.3.6 End To End Response (EERP)
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
4.3.7 Ready To Receive Command (RTR)
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.
4.4 Data Transfer Phase
Virtual File data flows from the Speaker to the Listener during the
Data Transfer phase which is entered after the Start File phase.
4.4.1 Protocol Sequence
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
2. If the Credit Value is set to 2
Speaker -- Data ------------> Listener Start File
-- Data ------------>
<------------- CDT -- Set Credit
-- Data ------------>
-- EFID ------------> End File
4.5 End File Phase
4.5.1 Protocol Sequence
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
2. Speaker -- EFID ------------> Listener End File
<------------ EFPA -- Answer YES + CD
-- CD --------------> Change Direction
Listener <------------ EERP -- Speaker End to End Response
-------------- RTR -> Ready to Receive
Go to Start File Phase
3. Speaker -- EFID ------------> Listener End File
<------------ EFNA -- Answer NO
4.6 End Session Phase
4.6.1 Protocol Sequence
The Speaker terminates the session by sending an End Session (ESID)
command.
1. Speaker -- EFID ------------> Listener End File
<------------ EFPA -- Answer YES
-- CD --------------> Change Direction
Listener <------------ ESID -- Speaker End Session
4.7 Problem Handling
Error detection and handling should be done as close as possible to
the problem. This aids problem determination and correction. Each
layer of the reference model is responsible for it's own error
handling.
ODETTE-FTP can detect protocol errors through the construction of
it's state machine, and uses activity timers to detect session hang
conditions. These mechanisms are separate from the End to End
controls.
4.7.1 Protocol Errors
If a protocol error occurs the session will be terminated and
application activity aborted. Both locations enter the IDLE state.
4.7.2 Timers
To protect against application and network hang conditions ODETTE-FTP
uses activity timers for all situations where a response is required.
The timers and actions to be taken if they expire are described in
section 8, the Protocol State Machine.
4.7.3 Clearing Centres
The use of clearing centres introduces the possibility of errors
occurring as a result of data processing activities within the
centre. Such errors are not directly related to ODETTE-FTP or the
communication network and are therefore outside the scope of this
specification.
5. Commands and Formats
ODETTE-FTP entities communicate via Exchange Buffers. The Command
Exchange Buffers are described below. Virtual File data is carried
in Data Exchange Buffers which are described in Section 6.
5.1 Conventions
5.1.1 Representation unit:
The basic unit of information is an octet, containing eight bits.
5.1.2 Values and Characters:
The ISO 646 IRV 7-bit coded character set [ISO-646] is used to encode
constants and strings within command exchange buffers.
5.2 Commands
A Command Exchange Buffer contains a single command starting at the
beginning of the buffer. Commands and data are never mixed within an
Exchange Buffer. Each command has a fixed length and can not be
compressed.
Components:
1. Command identifier:
The first octet of an Exchange Buffer is the Command Identifier
and defines the format of the buffer.
2. Parameter(s):
Command parameters are stored in fixed fields within a Command
Exchange Buffer. All values are required.
5.3 Command Formats
The ODETTE-FTP commands are described below using the following
definitions.
Position (Pos.)
Field offset within the command exchange buffer, relative to a
zero origin.
Field
The name of the field.
Description
A description of the field.
Format
F - A field containing fixed values. All allowable values for
the field are enumerated in the command definition.
V - A field with variable values within a defined range. For
example the SFIDFSIZ field may contain any integer value
between 0000000 and 9999999.
X(n) - An alphanumeric field of length n octets.
9(n) - A numeric field of length n octets.
All attributes are in character format.
A String contains alphanumeric characters from the following set:
The numerals: 0 to 9
The upper case letters: A to Z
The following special set: / - . & ( ) space.
Space is not allowed as an embedded character.
Numeric fields are always right justified and left padding with
zeros must be done when needed.
5.3.1 SSRM - Start Session Ready Message
o-------------------------------------------------------------------o
| SSRM Start Session Ready Message |
| |
| Start Session Phase Initiator <---- Responder |
|-------------------------------------------------------------------|
| Pos | Field | Description | Format |
|-----+-----------+---------------------------------------+---------|
| 0 | SSRMCMD | SSRM Command, 'I' | F X(1) |
| 1 | SSRMMSG | Ready Message, 'ODETTE FTP READY ' | F X(17) |
| 18 | SSRMCR | Carriage Return | F X(1) |
o-------------------------------------------------------------------o
SSRMCMD Command Code Character
Value: 'I' SSRM Command identifier.
SSRMMSG Ready Message String(17)
Value: 'ODETTE FTP READY '
SSRMCR Carriage Return Character
Value: Character with hex value '0D' or '8D'.
5.3.2 SSID - Start Session
o-------------------------------------------------------------------o
| SSID Start Session |
| |
| Start Session Phase Initiator <---> Responder |
|-------------------------------------------------------------------|
| Pos | Field | Description | Format |
|-----+-----------+---------------------------------------+---------|
| 0 | SSIDCMD | SSID Command 'X' | F X(1) |
| 1 | SSIDLEV | Protocol Release Level | F 9(1) |
| 2 | SSIDCODE | Initiator's Identification Code | V X(25) |
| 27 | SSIDPSWD | Initiator's Password | V X(8) |
| 35 | SSIDSDEB | Exchange Buffer Size | V 9(5) |
| 40 | SSIDSR | Send / Receive Capabilities (S/R/B) | F X(1) |
| 41 | SSIDCMPR | Compression Indicator (Y/N) | F X(1) |
| 42 | SSIDREST | Restart Indicator (Y/N) | F X(1) |
| 43 | SSIDSPEC | Special Logic Indicator (N) | F X(1) |
| 44 | SSIDCRED | Credit | V 9(3) |
| 47 | SSIDRSV1 | Reserved | F X(5) |
| 52 | SSIDUSER | User Data | V X(8) |
| 60 | SSIDCR | Carriage Return | F X(1) |
o-------------------------------------------------------------------o
SSIDCMD Command Code Character
Value: 'X' SSID Command identifier.
SSIDLEV Protocol Release Level Numeric(1)
Value: '1' ODETTE-FTP protocol release level 1.
Future release levels will have higher numbers. The
protocol release level is negotiable, with the lowest level
being selected.
SSIDCODE Initiator's Identification Code String(25)
Format: See Identification Code (Section 5.4)
Uniquely identifies the Initiator (sender) participating
in the ODETTE-FTP session.
SSIDPSWD Password String(8)
Key to authenticate the sender. Assigned by bilateral
agreement.
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'.
5.3.3 SFID - Start File
o-------------------------------------------------------------------o
| 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