Network Working Group I. Friend
Request for Comments: 5024 ODETTE
Obsoletes: 2204 November 2007
Category: Informational
 ODETTE File Transfer Protocol 2
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.
IESG Note
 This RFC is not a candidate for any level of Internet Standard. The
 IETF disclaims any knowledge of the fitness of this RFC for any
 purpose and in particular notes that the decision to publish is not
 based on IETF review for such things as security, congestion control,
 or inappropriate interaction with deployed protocols. The RFC Editor
 has chosen to publish this document at its discretion. Readers of
 this document should exercise caution in evaluating its value for
 implementation and deployment. See RFC 3932 for more information.
Abstract
 This memo updates the ODETTE File Transfer Protocol, an established
 file transfer protocol facilitating electronic data interchange of
 business data between trading partners, to version 2.
 The protocol now supports secure and authenticated communication over
 the Internet using Transport Layer Security, provides file
 encryption, signing, and compression using Cryptographic Message
 Syntax, and provides signed receipts for the acknowledgement of
 received files.
 The protocol supports both direct peer-to-peer communication and
 indirect communication via a Value Added Network and may be used with
 TCP/IP, X.25, and ISDN-based networks.
Table of Contents
 1. Introduction ....................................................4
 1.1. Background .................................................4
 1.2. Summary of Features ........................................5
 1.3. General Principles .........................................5
 1.4. Structure ..................................................6
 1.5. Virtual Files ..............................................6
 1.6. Service Description ........................................9
 1.7. Security ...................................................9
 2. Network Service ................................................11
 2.1. Introduction ..............................................11
 2.2. Service Primitives ........................................11
 2.3. Secure ODETTE-FTP Session .................................12
 2.4. Port Assignment ...........................................12
 3. File Transfer Service ..........................................13
 3.1. Model .....................................................13
 3.2. Session Setup .............................................14
 3.3. File Transfer .............................................16
 3.4. Session Take Down .........................................20
 3.5. Service State Automata ....................................23
 4. Protocol Specification .........................................28
 4.1. Overview ..................................................28
 4.2. Start Session Phase .......................................28
 4.3. Start File Phase ..........................................30
 4.4. Data Transfer Phase .......................................34
 4.5. End File Phase ............................................35
 4.6. End Session Phase .........................................36
 4.7. Problem Handling ..........................................36
 5. Commands and Formats ...........................................37
 5.1. Conventions ...............................................37
 5.2. Commands ..................................................37
 5.3. Command Formats ...........................................37
 5.4. Identification Code .......................................68
 6. File Services ..................................................69
 6.1. Overview ..................................................69
 6.2. File Signing ..............................................69
 6.3. File Encryption ...........................................70
 6.4. File Compression ..........................................70
 6.5. V Format Files - Record Lengths ...........................70
 7. ODETTE-FTP Data Exchange Buffer ................................71
 7.1. Overview ..................................................71
 7.2. Data Exchange Buffer Format ...............................71
 7.3. Buffer Filling Rules ......................................72
 8. Stream Transmission Buffer .....................................73
 8.1. Introduction ..............................................73
 8.2. Stream Transmission Header Format .........................73
 9. Protocol State Machine .........................................74
 9.1. ODETTE-FTP State Machine ..................................74
 9.2. Error Handling ............................................75
 9.3. States ....................................................76
 9.4. Input Events ..............................................79
 9.5. Output Events .............................................79
 9.6. Local Variables ...........................................80
 9.7. Local Constants ...........................................81
 9.8. Session Connection State Table ............................82
 9.9. Error and Abort State Table ...............................85
 9.10. Speaker State Table 1 ....................................86
 9.11. Speaker State Table 2 ....................................91
 9.12. Listener State Table .....................................93
 9.13. Example ..................................................96
 10. Miscellaneous .................................................97
 10.1. Algorithm Choice .........................................97
 10.2. Cryptographic Algorithms .................................97
 10.3. Protocol Extensions ......................................97
 10.4. Certificate Services .....................................98
 11. Security Considerations .......................................98
 Appendix A. Virtual File Mapping Example .........................100
 Appendix B. ISO 646 Character Subset .............................103
 Appendix C. X.25 Specific Information ............................104
 C.1. X.25 Addressing Restrictions .............................104
 C.2. Special Logic ............................................105
 C.3. PAD Parameter Profile ....................................116
 Appendix D. OFTP X.25 Over ISDN Recommendation ...................118
 D.1. ODETTE ISDN Recommendation ...............................119
 D.2. Introduction to ISDN .....................................120
 D.3. Equipment Types ..........................................123
 D.4. Implementation ...........................................124
 Acknowledgements .................................................132
 Normative References .............................................132
 Informative References ...........................................133
 ODETTE Address ...................................................134
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.
 ODETTE-FTP allows business applications to exchange files on a peer-
 to-peer basis in a standardised, purely automatic manner and provides
 a defined acknowledgement process on successful receipt of a file.
 ODETTE-FTP is not to be confused as a variant of, or similar to, the
 Internet FTP [FTP], which provides an interactive means for
 individuals to share files and which does not have any sort of
 acknowledgement process. By virtue of its interactive nature, lack
 of file acknowledgements, and client/server design, FTP does not
 easily lend itself to mission-critical environments for the exchange
 of business data.
 Over the last ten years, ODETTE-FTP has been widely deployed on
 systems of all sizes from personal computers to large mainframes
 while the Internet has emerged as the dominant international network,
 providing high-speed communication at low cost. To match the demand
 for EDI over the Internet, ODETTE has decided to extend the scope of
 its file transfer protocol to incorporate security functions and
 advanced compression techniques to ensure that it remains at the
 forefront of information exchange technology.
 The protocol now supports secure and authenticated communication over
 the Internet using Transport Layer Security, provides file
 encryption, signing, and compression using Cryptographic Message
 Syntax, and provides signed receipts for the acknowledgement of
 received files.
 The protocol supports both direct peer-to-peer communication and
 indirect communication via a Value Added Network and may be used with
 TCP/IP, X.25 and ISDN based networks.
 ODETTE-FTP has been defined by the ODETTE Security Working Group
 which consists of a number of ODETTE member organisations. All
 members have significant operational experience working with and
 developing OFTP and EDI solutions.
1.2. Summary of Features
 This memo is a development of version 1.4 of ODETTE-FTP [OFTP] with
 these changes/additions:
 Session level encryption
 File level encryption
 Secure authentication
 File compression
 Signed End to End Response (EERP)
 Signed Negative End Response (NERP)
 Maximum permitted file size increased to 9 PB (petabytes)
 Virtual file description added
 Extended error codes
 Version 1.4 of ODETTE-FTP included these changes and additions to
 version 1.3:
 Negative End Response (NERP)
 Extended Date and Time stamp
 New reason code 14 (File direction refused)
1.3. General Principles
 The aim of 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 of file
 storage and 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 the model.
 The description of 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.
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
 detailed in Sections 1.5.1 to 1.5.4.
1.5.1. Organisation
 Sequential
 Logical records are presented one after another. ODETTE-FTP must
 be aware of the record boundaries.
1.5.2. Identification
 Dataset Name
 Dataset name of the Virtual File being transferred, assigned by
 bilateral agreement.
 Time stamp (HHMMSScccc)
 A file qualifier indicating the time the Virtual File was made
 available for transmission. The counter (cccc=0001-9999) gives
 higher resolution.
 Date stamp (CCYYMMDD)
 A file qualifier indicating the date the Virtual File was made
 available for transmission.
 The Dataset Name, Date, and Time attributes are assigned by the
 Virtual File's originator and are used to uniquely identify a file.
 They are all mandatory and must not be changed by intermediate
 locations.
 The User Monitor may use the Virtual File Date and Time attributes in
 local processes involving date comparisons and calculations. Any
 such use falls outside the scope of this protocol.
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 that delimit
 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 start of
 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.
1.7. Security
 ODETTE-FTP provides a number of security services to protect a
 Virtual File transmission across a hostile network.
 These security services are as follows:
 Confidentiality
 Integrity
 Non-repudiation of receipt
 Non-repudiation of origin
 Secure authentication
 Security services in this specification are implemented as follows:
 Session level encryption
 File level encryption
 Signed files
 Signed receipts
 Session level authentication
 ODETTE-FTP Authentication
 Session level encryption provides data confidentiality by encryption
 of all the protocol commands and data exchanged between two parties,
 preventing a third party from extracting any useful information from
 the transmission.
 This session level encryption is achieved by layering ODETTE-FTP over
 Transport Layer Security [TLS], distinguishing between secure and
 unsecure TCP/IP traffic using different port numbers.
 File encryption provides complementary data confidentiality by
 encryption of the files in their entirety. Generally, this
 encryption occurs prior to transmission, but it is also possible to
 encrypt and send files while in session. File encryption has the
 additional benefit of allowing a file to remain encrypted outside of
 the communications session in which it was sent. The file can be
 received and forwarded by multiple intermediaries, yet only the final
 destination will be able to decrypt the file. File encryption does
 not encrypt the actual protocol commands, so trading partner EDI
 codes and Virtual File names are still viewable.
 Secure authentication is implemented through the session level
 authentication features available in [TLS] and proves the identity of
 the parties wishing to communicate.
 ODETTE-FTP Authentication also provides an authentication mechanism,
 but one that is integral to ODETTE-FTP and is available on all
 network infrastructures over which ODETTE-FTP is operated (this is in
 contrast to [TLS] which is generally only available over TCP/IP-based
 networks). Both parties are required to possess certificates when
 ODETTE-FTP Authentication is used.
 The security features in ODETTE-FTP 2 are centred around the use of
 [X.509] certificates. To take advantage of the complete range of
 security services offered in both directions, each party is required
 to possess an [X.509] certificate. If the confidentiality of data
 between two parties is the only concern, then [TLS] alone can be
 used, which allows the party accepting an incoming connection (the
 Responder) to be the only partner required to possess a certificate.
 For businesses, this means that session level encryption between a
 hub and its trading partners can be achieved without requiring all
 the trading partners to obtain a certificate, assuming that trading
 partners always connect to the hub.
 With the exception of [TLS], all the security services work with X.25
 and ISDN as transport media. Although nothing technically precludes
 [TLS] from working with X.25 or ISDN, implementations are rare.
2. Network Service
2.1. Introduction
 ODETTE-FTP peer entities communicate with each other via the OSI
 Network Service or the Transmission Control Protocol Transport
 Service [RFC793]. 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 its OPEN request upon receipt of
 N_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. Its 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. Secure ODETTE-FTP Session
 [TLS] provides a mechanism for securing an ODETTE-FTP session over
 the Internet or a TCP network. ODETTE-FTP is layered over [TLS],
 distinguishing between secure and unsecure traffic by using different
 server ports.
 The implementation is very simple. Layer ODETTE-FTP over [TLS] in
 the same way as layering ODETTE-FTP over TCP/IP. [TLS] provides both
 session encryption and authentication, both of which may be used by
 the connecting parties. A party acts as a [TLS] server when
 receiving calls and acts as a [TLS] client when making calls. When
 the [TLS] handshake has completed, the responding ODETTE-FTP may
 start the ODETTE-FTP session by sending the Ready Message.
2.4. Port Assignment
 An 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 responding ODETTE-FTP will listen for secure TLS connections on
 Registered Port 6619; the service name is 'odette-ftps'.
3. File Transfer Service
 The File Transfer Service describes the services offered by an
 ODETTE-FTP entity to its User Monitor (generally an application).
 NOTE: The implementation of the service primitives is an application
 issue.
3.1. Model
 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
3.2. Session Setup
3.2.1. Session Connection Service
 These diagrams represent the interactions between two communicating
 ODETTE-FTP entities and their respective User Agents.
 The vertical lines represent the ODETTE-FTP entities. The User
 Agents are not shown.
 | |
 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
 authentication1-> same -----------> authentication2-> 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:
 Y The entity can restart file transfers.
 N The entity cannot restart file transfers.
 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
 ---------------------------------------------------------------------
 Authentication
 Specifies the authentication requirement of the User Monitor.
 Value:
 Y Authentication required.
 N Authentication not required.
 Negotiation: Not negotiable.
 Request Indication Response Confirm
 ---------------------------------------------------------------------
 auth = Y ----> auth = Y ----> auth = Y ----> auth = Y
 auth = N ----> auth = N ----> auth = N ----> auth = 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(-)
 ------------------------------------------------------------------
 filename-------> same ---- ---- ---- ----
 date-time------> same ---- ---- ---- ----
 destination----> same ---- ---- ---- ----
 originator-----> same ---- ---- ---- ----
 rec-format-----> same ---- ---- ---- ----
 rec-size ------> same ---- ---- ---- ----
 file-size------> same ---- ---- ---- ----
 org-file-size--> same ---- ---- ---- ----
 signed-eerp----> same ---- ---- ---- ----
 cipher---------> same ---- ---- ---- ----
 sec-services---> same ---- ---- ---- ----
 compression----> same ---- ---- ---- ----
 envelope-format> same ---- ---- ---- ----
 description----> 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
 | |
 F_DATA_CF <----|(---CDT----)|
 | |
 Note: Unlike other commands, where the F_XXX_CF signal is a result of
 a corresponding F_XXX_RS command, in this case, the local entity
 layer issues this signal when it is ready for the next data
 request. This decision is based on the current credit count and
 the reception of CDT (Set Credit) from the receiver.
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
 Listener may either:
 1. Set Speaker to "Yes" and become the Speaker or
 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 the Speaker, the Speaker receives F_CLOSE_FILE_CF
 (Speaker = NO) and becomes the Listener.
 - If the Listener answers F_CLOSE_FILE_RS(Speaker = NO), it
 remains as the Listener, and the Speaker receives
 F_CLOSE_FILE_CF (Speaker = YES) and remains as the 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, the Speaker may not send
 an F_CD_RQ after receiving an unsolicited F_CD_IND. If the
 Listener receives a solicited F_CD_IND as a result of sending
 EFPA(Speaker=Yes), it is acceptable to immediately relinquish the
 right to speak by sending an F_CD_RQ.
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
 | |
 F_RTR_CF <----|------------|<---- F_RTR_RS
 | |
 Parameters
 Request Indication
 ------------------------------------
 filename -----------> same
 date ---------------> same
 time ---------------> same
 destination --------> same
 originator ---------> same
 hash ---------------> same
 signature ----------> 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 an 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).
 Notes:
 1. The F_EERP_RQ (and also F_NERP_RQ) is confirmed with an F_RTR_CF
 signal. The F_RTR_CF signal is common to both F_EERP_RQ and
 F_NERP_RQ. There should be no ambiguity, since there can only be
 one such request pending at any one time.
 2. The signature is optional and is requested when sending the
 F_START_FILE_RQ.
 3. If it is not possible to sign the EERP, then an unsigned EERP
 should still be sent.
 4. It is an application implementation issue to validate the contents
 of the EERP and its signature and to decide what action to take on
 receipt of an EERP that fails validation or is not signed when a
 signed EERP was requested.
3.3.6. Negative End Response
 This service is initiated by the current speaker (if there is no file
 transfer in progress) to send a Negative End Response when a file
 could not be transmitted to the next destination. It is sent only if
 the problem is of a non-temporary kind.
 This service may also be initiated by the final destination instead
 of sending an End to End Response when a file could not be processed,
 after having successfully received the file.
 | |
 F_NERP_RQ ---->|------------|----> F_NERP_IND
 | |
 F_RTR_CF <----|------------|----- F_RTR_RS
 | |
 Parameters
 Request Indication
 ---------------------------------------------------
 filename ----------------------> same
 date --------------------------> same
 time --------------------------> same
 destination -------------------> same
 originator --------------------> same
 creator of negative response --> same
 reason ------------------------> same
 reason text -------------------> same
 hash --------------------------> same
 signature ---------------------> same
 ---------------------------------------------------
 Relationship with Turn:
 The same as for the End-To-End response (see Section 3.3.5).
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. Data 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)
 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
 These state automata define 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
 F_CD_RQ F_RELEASE_RQ
 | |
 o================o decision o----------o decision o---------------o
 | |---------->| WAIT FOR |<----------| |
 | | F_EERP_RQ | | F_EERP_RQ | |
 | IDLE | | EERP/ | | IDLE |
 | SPEAKER | decision | NERP | decision | SPEAKER |
 | (1) |---------->| CONFIRM. |<----------| (4) |
 | | F_NERP_RQ | | F_NERP_RQ | |
 | | | | | |
 | | | | | CD_IND |
 | | f_rtr_cf | | | just received |
 | |<----------| | | |
 | | o----------o | |
 | | | |
 | | | |
 o================o o---------------o
 A A | |
 | | | decision and P2 decision and P2 |
 | | +-----------------+ +---------------------+
 | | F_START_FILE_RQ | | F_START_FILE_RQ
 | | V V
 | | o---------------o
 | | f_file_start_cf(-) | |
 | +----------------------| OPENING |
 | | |
 | o---------------o
 | |
 f_file_close_cf(-) or f_start_file_cf(+)
 f_file_close_cf(+) and not P1 |
 | V
 o---------------o o---------------o record to send o---------o
 | | | |------------------>| |
 | CLOSING | | DATA TRANSFER | F_DATA_RQ | NEXT |
 | | | | | RECORD |
 | | | | f_data_cf | |
 | | | |<------------------| |
 o---------------o o---------------o o---------o
 | A |
 | | end of file |
 | +-------------------+
 | F_CLOSE_FILE_RQ
 | o-----------------o
 | f_file_close_cf(+) and P1 | IDLE LISTENER |
 +--------------------------------------------->| see (2), Listen |
 | State Diagram |
 Predicates: o-----------------o
 P1: Positive confirmation and Speaker = YES
 P2: Mode = Both or (Mode = Sender-only)
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
 | | F_RTR_RS | |
 o=================o | o-----------------o
 | |<-----------+ | |
 | | | |
 | | f_nerp_ind | |
 | |------------+ | |
 | | F_RTR_RS | | |
 | | | | |
 | |<-----------+ | |
 | IDLE LISTENER | f_eerp_ind | IDLE LISTENER |
 | (2) |<-----------------------------| (3) |
 | | F_RTR_RS | CD_RQ |
 | | | just sent |
 | | f_nerp_ind | |
 | |<-----------------------------| |
 | | F_RTR_RS | |
 | | | |
 | | f_start_file_ind | |
 | | and not P1 | |
 | |---------------------+ | |
 o=================o F_START_FILE_RS(-) | o-----------------o
 A A | A A | | |
 | | | | +-----------------------+ | |
 | | | | | |
 | | | | f_start_file_ind and not P1 | |
 | | | +--------------------------------------+ |
 | | | F_START_FILE_RS(-) |
 | | | |
 | | | f_start_file_ind f_start_file_ind |
 | | | and P1 and P1 |
 | | +----------------------------+ +------------------+
 | | F_START_FILE_RS(+) | | F_START_FILE_RS(+)
 | | V V
 | | o---------------o
 | |f_close_file_ind and not P3 | |
 | +----------------------------| |
 | F_CLOSE_FILE_RS(+,N) | |
 | | DATA |
 | | TRANSFER |
 | f_close_file_ind and not P2 | |-------------+
 +------------------------------| | |
 F_CLOSE_FILE_RS(-) | |<------------+
 o---------------o F_DATA_IND
 o---------------o |
 | IDLESPEAKER | f_close_file_ind and P3 |
 | see (1), Spkr |<--------------------------+
 | State Diagram | F_CLOSE_FILE_RS(+,Y)
 o---------------o
 Predicates:
 P1: Decision to send F_START_FILE_RS(+)
 P2: Decision to send F_CLOSE_FILE_RS(+)
 P3: Decision to become Speaker
4. Protocol Specification
4.1. Overview
 ODETTE-FTP 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
 SECD Security Change Direction
 AUCH Authentication Challenge
 AURP Authentication Response
 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
 NERP Negative 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. Its 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
4.2.3. Secure Authentication
 Having exchanged SSIDs, the Initiator may optionally begin an
 authentication phase, in which each party proves its identity to the
 other.
4.2.4. Protocol Sequence
 The first authentication message must be sent by the Initiator.
 1. Initiator -- SECD ------------> Responder Change Direction
 <------------ AUCH -- Challenge
 -- AURP ------------> Response
 <------------ SECD -- Change Direction
 -- AUCH ------------> Challenge
 <------------ AURP -- Response
 The Initiator sends a Security Change Direction (SECD) to which the
 Responder replies with an Authentication Challenge (AUCH).
 The Responder looks up the public certificate that is linked to the
 purported identity of the Initiator (located in the SSID). If the
 Responder is unable to locate a suitable certificate then
 authentication fails. The Responder uses the public key contained in
 the certificate to encrypt a random challenge, unique for each
 session, for the Initiator. This encrypted challenge is sent as a
 [CMS] envelope to the Initiator as part of the AUCH.
 The Initiator decrypts the challenge using their private key and
 sends the decrypted challenge back to the Responder in the
 Authentication Response (AURP).
 The Responder checks that the data received in the AURP matches the
 random challenge that was sent to the Initiator.
 If the data matches, then the Initiator has authenticated
 successfully and the Responder replies with a Security Change
 Direction (SECD) beginning the complementary process of verifying the
 Responder to the Initiator. If the data does not match, then the
 Initiator fails authentication.
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
 <------------ NERP -- Negative 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 the Virtual File has been successfully delivered to
 its final destination. This allows the originator to perform house
 keeping tasks such as deleting copies of the delivered data.
 If the originator of the Virtual File requested a signed EERP in the
 SFID, the EERP must be signed. Signing allows the originator of the
 file to prove that the EERP was generated by the final destination.
 If the final destination is unable to sign the EERP, it may send back
 an unsigned EERP. It is an implementation issue to allow the
 acceptance of an unsigned EERP if a signed EERP is requested.
 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 its 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.
 The requesting of a signed EERP is incompatible with the use of
 broadcast facilities because an EERP can be signed by only one
 destination. If this scenario occurs, the intermediate broadcast
 location may continue and ignore the request for a signed EERP or
 send back a NERP.
 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 its 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. Negative End Response (NERP)
 In addition to the EERP, which allows control over successful
 transmission of a file, a Negative End Response signals that a file
 could not be delivered to the final destination or that the final
 destination could not process the received file.
 It may be created by an intermediate node that could not transmit the
 file any further because the next node refuses to accept the file.
 The cause of the refusal has to be non-temporary, otherwise the
 intermediate node has to try the transmission again.
 It may also be created by the final node that is unable to process
 the file because of non-recoverable syntax or semantic errors in the
 file, or because of the failure of any other processing performed on
 the file.
 The NERP will be sent back to the originator of the file.
 The parameters are equal to the ones of the EERP, but with additional
 information about the creator of the NERP and the abort reason.
 Where the NERP is created due to a failure to transmit, the abort
 reason is taken from the refusal reason that was sent by the node
 refusing the file. Because of the NERP, it is possible for the
 intermediate node to stop trying to send the non-deliverable file and
 to delete the file.
 The NERP allows the originator of the file to react to the
 unsuccessful transmission or processing, depending on the reason code
 and the creator of the NERP.
 If the originator of the Virtual File requested a signed EERP in the
 SFID, the NERP must be signed. Signing allows the originator of the
 file to prove by whom the NERP was generated. If the location
 generating the NERP is unable to sign the NERP, it may send back an
 unsigned NERP. It is an implementation issue to allow the acceptance
 of an unsigned EERP if a signed NERP is requested.
4.3.8. Ready To Receive Command (RTR)
 In order to avoid congestion between two adjacent nodes caused by a
 continuous flow of EERPs and NERPs, a Ready To Receive (RTR) command
 is provided. The RTR acts as an EERP/NERP 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
 -- NERP ------------> Negative End Response
 <------------- RTR -- Ready to Receive
 -- SFID ------------> Start File
 or
 -- CD --------------> Exchange the turn
 After sending an EERP or NERP, the Speaker must wait for an RTR
 before sending any other commands. The only acceptable commands to
 follow are:
 EERP
 NERP
 SFID or CD (if there are no more EERPs or NERPs to be sent)
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 Set 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
 Listener <------------ NERP -- Speaker Negative 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. The Speaker may only do this if the Listener has just
 relinquished its role as speaker.
 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 its own error
 handling.
 ODETTE-FTP can detect protocol errors by virtue of its 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 9, "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 7.
5.1. Conventions
5.1.1. Representation Unit
 The basic unit of information is an octet, containing 8 bits.
5.1.2. Values and Characters
 The ISO 646 IRV 7-bit coded character set [ISO-646], according to
 Appendix B, is used to encode constants and strings within Command
 Exchange Buffers except where [UTF-8] is explicitly indicated against
 a field.
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. Commands cannot be compressed. Variable-length
 parameters may be omitted entirely if not required and the associated
 length indicator field set to zero.
 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 fields within a Command Exchange
 Buffer. Where variable-length fields are used, they are preceded
 with a header field indicating the length. All values are
 required except where explicitly indicated.
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 SFIDLRECL field may contain any integer value
 between 00000 and 99999.
 X(n) - An alphanumeric field of length n octets.
 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.
 9(n) - A numeric field of length n octets.
 U(n) - A binary field of length n octets.
 Numbers encoded as binary are always unsigned and in
 network byte order.
 T(n) - An field of length n octets, encoded using [UTF-8].
 String and alphanumeric fields are always left justified and right
 padded with spaces where needed.
 Numeric fields are always right justified and left padded with
 zeros where needed.
 Reserved fields should be padded with spaces.
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 | Data Exchange Buffer Size | V 9(5) |
 | 40 | SSIDSR | Send / Receive Capabilities (S/R/B) | F X(1) |
 | 41 | SSIDCMPR | Buffer Compression Indicator (Y/N) | F X(1) |
 | 42 | SSIDREST | Restart Indicator (Y/N) | F X(1) |
 | 43 | SSIDSPEC | Special Logic Indicator (Y/N) | F X(1) |
 | 44 | SSIDCRED | Credit | V 9(3) |
 | 47 | SSIDAUTH | Secure Authentication (Y/N) | F X(1) |
 | 48 | SSIDRSV1 | Reserved | F X(4) |
 | 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)
 Used to specify the level of the ODETTE-FTP protocol
 Value: '1' for Revision 1.2
 '2' for Revision 1.3
 '4' for Revision 1.4
 '5' for Revision 2.0
 Future release levels will have higher numbers. The
 protocol release level is negotiable, with the lowest level
 being selected.
 Note: ODETTE File Transfer Protocol 1.3 (RFC 2204)
 specifies '1' for the release level, despite adhering
 to revision 1.3.
 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.
 It is an application implementation issue to link the
 expected [X.509] certificate to the SSIDCODE provided.
 SSIDPSWD Initiator's Password String(8)
 Key to authenticate the sender. Assigned by bilateral
 agreement.
 SSIDSDEB Data Exchange Buffer Size Numeric(5)
 Minimum: 128
 Maximum: 99999
 The length, in octets, of the largest Data 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 transmissions will not take place in
 the same session.
 An error occurs if adjacent locations both specify the send
 or receive capability.
 SSIDCMPR Buffer Compression Indicator Character
 Value: 'Y' The location can handle OFTP data buffer compression
 'N' The location cannot handle OFTP buffer compression
 Compression is only used if supported by both locations.
 The compression mechanism referred to here applies to each
 individual OFTP data buffer. This is different from the
 file compression mechanism in OFTP, which involves the
 compression of whole files.
 SSIDREST Restart Indicator Character
 Value: 'Y' The location can handle the restart of a partially
 transmitted file.
 'N' The location cannot restart a file.
 SSIDSPEC Special Logic Indicator Character
 Value: 'Y' Location can handle Special Logic
 'N' Location cannot handle Special Logic
 Special Logic is only used if supported by both locations.
 The Special Logic extensions are only useful to access an
 X.25 network via an asynchronous entry and are not
 supported for TCP/IP connections.
 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 than or
 equal to m)
 Note: negotiated value will be "n".
 SSIDAUTH Secure Authentication Character
 Value: 'Y' The location requires secure authentication. 'N' The
 location does not require secure authentication.
 Secure authentication is only used if agreed by both
 locations.
 If the answer of the Responder does not match with the
 authentication requirements of the Initiator, then the
 Initiator must abort the session.
 No negotiation of authentication is allowed.
 authentication p -- SSID ------------>
 <------------ SSID -- authentication q
 p == q -> continue.
 p != q -> abort.
 SSIDRSV1 Reserved String(4)
 This field is reserved for future use.
 SSIDUSER User Data String(8)
 May be used by 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(3) |
 | 30 | SFIDDATE | Virtual File Date stamp, (CCYYMMDD) | V 9(8) |
 | 38 | SFIDTIME | Virtual File Time stamp, (HHMMSScccc) | V 9(10) |
 | 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(13) |
 | 125 | SFIDOSIZ | Original File Size, 1K blocks | V 9(13) |
 | 138 | SFIDREST | Restart Position | V 9(17) |
 | 155 | SFIDSEC | Security Level | F 9(2) |
 | 157 | SFIDCIPH | Cipher suite selection | F 9(2) |
 | 159 | SFIDCOMP | File compression algorithm | F 9(1) |
 | 160 | SFIDENV | File enveloping format | F 9(1) |
 | 161 | SFIDSIGN | Signed EERP request | F X(1) |
 | 162 | SFIDDESCL | Virtual File Description length | V 9(3) |
 | 165 | SFIDDESC | Virtual File Description | V T(n) |
 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(3)
 This field is reserved for future use.
 SFIDDATE Virtual File Date stamp Numeric(8)
 Format: 'CCYYMMDD' 8 decimal digits representing the century,
 year, month, and day.
 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 Numeric(10)
 Format: 'HHMMSScccc' 10 decimal digits representing hours,
 minutes, seconds, and a counter (0001-9999), which gives
 higher resolution.
 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 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 1.5.4).
 Once a file has been signed, compressed, and/or encrypted,
 in file format terms it becomes unstructured, format U.
 The record boundaries are no longer discernable until the
 file is decrypted, decompressed, and/or verified. SFID
 File Format Field in this scenario indicates the format of
 the original file, and the transmitted file must be treated
 as U format.
 SFIDLRECL Maximum Record Size Numeric(5)
 Maximum: 99999
 Length in octets of the longest logical record that 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'.
 If SFIDFMT is 'V' and the file is compressed, encrypted, or
 signed, then the maximum value of SFIDRECL is '65536'.
 SFIDFSIZ Transmitted File Size Numeric(13)
 Maximum: 9999999999999
 Space in 1K (1024 octet) blocks required at the Originator
 location to store the actual Virtual File that is to be
 transmitted.
 For example, if a file is compressed before sending, then
 this is the space required to store the compressed file.
 This parameter is intended to provide only a good estimate
 of the Virtual File size.
 Using 13 digits allows for a maximum file size of
 approximately 9.3 PB (petabytes) to be transmitted.
 SFIDOSIZ Original File Size Numeric(13)
 Maximum: 9999999999999
 Space in 1K (1024 octet) blocks required at the Originator
 location to store the original before it was signed,
 compressed, and/or encrypted.
 If no security or compression services have been used,
 SFIDOSIZ should contain the same value as SFIDFSIZ.
 If the original file size is not known, the value zero
 should be used.
 This parameter is intended to provide only a good estimate
 of the original file size.
 The sequence of events in file exchange are:
 (a) raw data file ready to be sent
 SFIDOSIZ = Original File Size
 (b) signing/compression/encryption
 (c) transmission
 SFIDFSIZ = Transmitted File Size
 (d) decryption/decompression/verification
 (e) received raw data file for in-house applications
 SFIDOSIZ = Original File Size
 The Transmitted File Size at (c) indicates to the receiver
 how much storage space is needed to receive the file.
 The Original File Size at (e) indicates to the in-house
 application how much storage space is needed to process the
 file.
 SFIDREST Restart Position Numeric(17)
 Maximum: 99999999999999999
 Virtual File restart position.
 The count represents the:
 - Record Number if SSIDFMT is 'F' or 'V'.
 - File offset in 1K (1024 octet) blocks if SFIDFMT is
 'U' or 'T'.
 The count will express the transmitted user data (i.e.,
 before ODETTE-FTP buffer compression, header not included).
 After negotiation between adjacent locations,
 retransmission will start at the lowest value.
 Once a file has been signed, compressed, and/or encrypted,
 in file format terms, it has become unstructured, like
 format U. The file should be treated as format U for the
 purposes of restart, regardless of the actual value in
 SFIDFMT.
 SFIDSEC Security Level Numeric(2)
 Value: '00' No security services
 '01' Encrypted
 '02' Signed
 '03' Encrypted and signed
 Indicates whether the file has been signed and/or encrypted
 before transmission. (See Section 6.2.)
 SFIDCIPH Cipher suite selection Numeric(2)
 Value: '00' No security services
 '01' See Section 10.2
 Indicates the cipher suite used to sign and/or encrypt the
 file and also to indicate the cipher suite that should be
 used when a signed EERP or NERP is requested.
 SFIDCOMP File compression algorithm Numeric(1)
 Value: '0' No compression
 '1' Compressed with [ZLIB] algorithm
 Indicates the algorithm used to compress the file.
 (See Section 6.4.)
 SFIDENV File enveloping format Numeric(1)
 Value: '0' No envelope
 '1' File is enveloped using [CMS]
 Indicates the enveloping format used in the file.
 If the file is encrypted/signed/compressed or is an
 enveloped file for the exchange and revocation of
 certificates, this field must be set accordingly.
 SFIDSIGN Signed EERP request Character
 Value: 'Y' The EERP returned in acknowledgement of the file
 must be signed
 'N' The EERP must not be signed
 Requests whether the EERP returned for the file must be
 signed.
 SFIDDESCL Virtual File Description length Numeric(3)
 Length in octets of the field SFIDDESC.
 A value of 0 indicates that no description is present.
 SFIDDESC Virtual File Description [UTF-8](n)
 May be used by ODETTE-FTP in any way. If not used,
 SFIDDESCL should be set to zero.
 No general structure is defined for this attribute, but it
 is expected that a bilateral agreement exists as to the
 meaning of the data.
 It is encoded using [UTF-8] to support a range of national
 languages.
 Maximum length of the encoded value is 999 octets.
5.3.4. SFPA - Start File Positive Answer
 o-------------------------------------------------------------------o
 | 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(17) |
 o-------------------------------------------------------------------o
 SFPACMD Command Code Character
 Value: '2' SFPA Command identifier.
 SFPAACNT Answer Count Numeric(17)
 The Listener must enter a count lower than 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.
5.3.5. SFNA - Start File Negative Answer
 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) |
 | 4 | SFNAREASL | Answer Reason Text Length | V 9(3) |
 | 7 | SFNAREAST | Answer Reason Text | V T(n) |
 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.
 '14' File direction refused.
 '15' Cipher suite not supported.
 '16' Encrypted file not allowed.
 '17' Unencrypted file not allowed.
 '18' Compression not allowed.
 '19' Signed file not allowed.
 '20' Unsigned file not allowed.
 '99' Unspecified reason.
 Reason why transmission cannot proceed.
 SFNARRTR Retry Indicator Character
 Value: 'N' Transmission should not be retried.
 'Y' The transmission may be retried later.
 This parameter is used to advise the Speaker if it should
 retry at a later 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 is therefore recommended that when an SFNA with Retry =
 Y is received the User Monitor attempts to retransmit the
 relevant file in a subsequent session.
 SFNAREASL Answer Reason Text Length Numeric(3)
 Length in octets of the field SFNAREAST.
 0 indicates that no SFNAREAST field follows.
 SFNAREAST Answer Reason Text [UTF-8](n)
 Reason why transmission cannot proceed in plain text.
 It is encoded using [UTF-8].
 Maximum length of the encoded reason is 999 octets.
 No general structure is defined for this attribute.
5.3.6. DATA - Data Exchange Buffer
 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 U(n) |
 o-------------------------------------------------------------------o
 DATACMD Command Code Character
 Value: 'D' DATA Command identifier.
 DATABUF Data Exchange Buffer payload Binary(n)
 Variable-length buffer containing the data payload. The
 Data Exchange Buffer is described in Section 7.
5.3.7. CDT - Set Credit
 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.
5.3.8. EFID - End File
 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(17) |
 | 18 | EFIDUCNT | Unit Count | V 9(17) |
 o-------------------------------------------------------------------o
 EFIDCMD Command Code Character
 Value: 'T' EFID Command identifier.
 EFIDRCNT Record Count Numeric(17)
 Maximum: 99999999999999999
 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
 buffer compression, header not included). The total count
 is always used, even during restart processing.
 EFIDUCNT Unit Count Numeric(17)
 Maximum: 99999999999999999
 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.
5.3.9. EFPA - End File Positive Answer
 o-------------------------------------------------------------------o
 | 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.
5.3.10. EFNA - End File Negative Answer
 o-------------------------------------------------------------------o
 | 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) |
 | 3 | EFNAREASL | Answer Reason Text Length | V 9(3) |
 | 6 | EFNAREAST | Answer Reason Text | V T(n) |
 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.
 '14' File direction refused.
 '15' Cipher suite not supported.
 '16' Encrypted file not allowed.
 '17' Unencrypted file not allowed.
 '18' Compression not allowed.
 '19' Signed file not allowed.
 '20' Unsigned file not allowed.
 '21' Invalid file signature.
 '22' File decryption failure.
 '23' File decompression failure.
 '99' Unspecified reason.
 Reason why transmission failed.
 EFNAREASL Answer Reason Text Length Numeric(3)
 Length in octets of the field EFNAREAST.
 0 indicates that no EFNAREAST field follows.
 EFNAREAST Answer Reason Text [UTF-8](n)
 Reason why transmission failed in plain text.
 It is encoded using [UTF-8].
 Maximum length of the encoded reason is 999 octets.
 No general structure is defined for this attribute.
5.3.11. ESID - End Session
 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 | ESIDREASL | Reason Text Length | V 9(3) |
 | 6 | ESIDREAST | Reason Text | V T(n) |
 | | 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 differs from 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
 '11' Invalid challenge response
 '12' Secure authentication requirements incompatible
 '99' Unspecified Abort code
 An error was detected for which no specific code is
 defined.
 ESIDREASL Reason Text Length Numeric(3)
 Length in octets of the field ESIDREAST.
 0 indicates that no ESIDREAST field is present.
 ESIDREAST Reason Text [UTF-8](n)
 Reason why session ended in plain text.
 It is encoded using [UTF-8].
 Maximum length of the encoded reason is 999 octets.
 No general structure is defined for this attribute.
 ESIDCR Carriage Return Character
 Value: Character with hex value '0D' or '8D'.
5.3.12. CD - Change Direction
 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.
5.3.13. EERP - End to End Response
 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(3) |
 | 30 | EERPDATE | Virtual File Date stamp, (CCYYMMDD) | V 9(8) |
 | 38 | EERPTIME | Virtual File Time stamp, (HHMMSScccc) | V 9(10) |
 | 48 | EERPUSER | User Data | V X(8) |
 | 56 | EERPDEST | Destination | V X(25) |
 | 81 | EERPORIG | Originator | V X(25) |
 | 106 | EERPHSHL | Virtual File hash length | V U(2) |
 | 108 | EERPHSH | Virtual File hash | V U(n) |
 | | EERPSIGL | EERP signature length | V U(2) |
 | | EERPSIG | EERP signature | V U(n) |
 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(3)
 This field is reserved for future use.
 EERPDATE Virtual File Date stamp Numeric(8)
 Format: 'CCYYMMDD' 8 decimal digits representing the century,
 year, month, and day, respectively.
 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 Numeric(10)
 Format: 'HHMMSScccc' 10 decimal digits representing hours,
 minutes, seconds, and a counter (0001-9999), which gives
 higher resolution.
 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 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 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 process it accordingly. It is also the
 location that creates the EERP for the received file.
 EERPHSHL Virtual File hash length Binary(2)
 Length in octets of the field EERPHSH.
 A binary value of 0 indicates that no hash is present.
 This is always the case if the EERP is not signed.
 EERPHSH Virtual File hash Binary(n)
 Hash of the transmitted Virtual File, i.e., not the hash of
 the original file.
 The algorithm used is determined by the bilaterally agreed
 cipher suite specified in the SFIDCIPH.
 It is an application implementation issue to validate the
 EERPHSH to ensure that the EERP is acknowledging the exact
 same file as was originally transmitted.
 EERPSIGL EERP signature length Binary(2)
 0 indicates that this EERP has not been signed.
 Any other value indicates the length of EERPSIG in octets
 and indicates that this EERP has been signed.
 EERPSIG EERP signature Binary(n)
 Contains the [CMS] enveloped signature of the EERP.
 Signature = Sign{EERPDSN
 EERPDATE
 EERPTIME
 EERPDEST
 EERPORIG
 EERPHSH}
 Each field is taken in its entirety, including any padding.
 The envelope must contain the original data, not just the
 signature.
 The [CMS] content type used is SignedData.
 The encapsulated content type used is id-data.
 It is an application issue to validate the signature with
 the contents of the EERP.
5.3.14. NERP - Negative End Response
 o-------------------------------------------------------------------o
 | NERP Negative End Response |
 | |
 | Start File Phase Speaker ----> Listener |
 | End File Phase Speaker ----> Listener |
 |-------------------------------------------------------------------|
 | Pos | Field | Description | Format |
 |-----+-----------+---------------------------------------+---------|
 | 0 | NERPCMD | NERP Command, 'N' | F X(1) |
 | 1 | NERPDSN | Virtual File Dataset Name | V X(26) |
 | 27 | NERPRSV1 | Reserved | F X(6) |
 | 33 | NERPDATE | Virtual File Date stamp, (CCYYMMDD) | V 9(8) |
 | 41 | NERPTIME | Virtual File Time stamp, (HHMMSScccc) | V 9(10) |
 | 51 | NERPDEST | Destination | V X(25) |
 | 76 | NERPORIG | Originator | V X(25) |
 | 101 | NERPCREA | Creator of NERP | V X(25) |
 | 126 | NERPREAS | Reason code | F 9(2) |
 | 128 | NERPREASL | Reason text length | V 9(3) |
 | 131 | NERPREAST | Reason text | V T(n) |
 | | NERPHSHL | Virtual File hash length | V U(2) |
 | | NERPHSH | Virtual File hash | V U(n) |
 | | NERPSIGL | NERP signature length | V U(2) |
 | | NERPSIG | NERP signature | V U(n) |
 o-------------------------------------------------------------------o
 NERPCMD Command Code Character
 Value: 'N' NERP Command identifier.
 NERPDSN 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)
 NERPRSV1 Reserved String(6)
 This field is reserved for future use.
 NERPDATE Virtual File Date stamp Numeric(8)
 Format: 'CCYYMMDD' 8 decimal digits representing the century,
 year, month, and day, respectively.
 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)
 NERPTIME Virtual File Time stamp Numeric(10)
 Format: 'HHMMSScccc' 10 decimal digits representing hours,
 minutes, seconds, and a counter (0001-9999), which gives
 higher resolution.
 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)
 NERPDEST Destination String(25)
 Format: See Identification Code (Section 5.4)
 Originator of the Virtual File.
 This is the location that created the data for
 transmission.
 NERPORIG Originator 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.
 NERPCREA Creator of the NERP String(25)
 Format: See Identification Code (Section 5.4)
 It is the location that created the NERP.
 NERPREAS Reason code Numeric(2)
 This attribute will specify why transmission cannot proceed
 or why processing of the file failed.
 "SFNA(RETRY=N)" below should be interpreted as "EFNA or
 SFNA(RETRY=N)" where appropriate.
 Value '03' ESID received with reason code '03'
 (user code not known)
 '04' ESID received with reason code '04'
 (invalid password)
 '09' ESID received with reason code '99'
 (unspecified reason)
 '11' SFNA(RETRY=N) received with reason code '01'
 (invalid file name)
 '12' SFNA(RETRY=N) received with reason code '02'
 (invalid destination)
 '13' SFNA(RETRY=N) received with reason code '03'
 (invalid origin)
 '14' SFNA(RETRY=N) received with reason code '04'
 (invalid storage record format)
 '15' SFNA(RETRY=N) received with reason code '05'
 (maximum record length not supported)
 '16' SFNA(RETRY=N) received with reason code '06'
 (file size too big)
 '20' SFNA(RETRY=N) received with reason code '10'
 (invalid record count)
 '21' SFNA(RETRY=N) received with reason code '11'
 (invalid byte count)
 '22' SFNA(RETRY=N) received with reason code '12'
 (access method failure)
 '23' SFNA(RETRY=N) received with reason code '13'
 (duplicate file)
 '24' SFNA(RETRY=N) received with reason code '14'
 (file direction refused)
 '25' SFNA(RETRY=N) received with reason code '15'
 (cipher suite not supported)
 '26' SFNA(RETRY=N) received with reason code '16'
 (encrypted file not allowed)
 '27' SFNA(RETRY=N) received with reason code '17'
 (unencrypted file not allowed)
 '28' SFNA(RETRY=N) received with reason code '18'
 (compression not allowed)
 '29' SFNA(RETRY=N) received with reason code '19'
 (signed file not allowed)
 '30' SFNA(RETRY=N) received with reason code '20'
 (unsigned file not allowed)
 '31' File signature not valid.
 '32' File decompression failed.
 '33' File decryption failed.
 '34' File processing failed.
 '35' Not delivered to recipient.
 '36' Not acknowledged by recipient.
 '50' Transmission stopped by the operator.
 '90' File size incompatible with recipient's
 protocol version.
 '99' Unspecified reason.
 NERPREASL Reason Text Length Numeric(3)
 Length in octets of the field NERPREAST.
 0 indicates that no NERPREAST field follows.
 NERPREAST Reason Text [UTF-8](n)
 Reason why transmission cannot proceed in plain text.
 It is encoded using [UTF-8].
 Maximum length of the encoded reason is 999 octets.
 No general structure is defined for this attribute.
 NERPHSHL Virtual File hash length Binary(2)
 Length in octets of the field NERPHSH.
 A binary value of 0 indicates that no hash is present.
 This is always the case if the NERP is not signed.
 NERPHSH Virtual File hash Binary(n)
 Hash of the Virtual File being transmitted.
 The algorithm used is determined by the bilaterally agreed
 cipher suite specified in the SFIDCIPH.
 NERPSIGL NERP Signature length Binary(2)
 0 indicates that this NERP has not been signed.
 Any other value indicates the length of NERPSIG in octets
 and indicates that this NERP has been signed.
 NERPSIG NERP Signature Binary(n)
 Contains the [CMS] enveloped signature of the NERP.
 Signature = Sign{NERPDSN
 NERPDATE
 NERPTIME
 NERPDEST
 NERPORIG
 NERPCREA
 NERPHSH}
 Each field is taken in its entirety, including any padding.
 The envelope must contain the original data, not just the
 signature.
 The [CMS] content type used is SignedData.
 The encapsulated content type used is id-data.
 It is an application issue to validate the signature with
 the contents of the NERP.
5.3.15. RTR - Ready To Receive
 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.
5.3.16. SECD - Security Change Direction
 o-------------------------------------------------------------------o
 | SECD Security Change Direction |
 | |
 | Start Session Phase Initiator <---> Responder |
 |-------------------------------------------------------------------|
 | Pos | Field | Description | Format |
 |-----+-----------+---------------------------------------+---------|
 | 0 | SECDCMD | SECD Command, 'J' | F X(1) |
 o-------------------------------------------------------------------o
 SECDCMD Command Code Character
 Value: 'J' SECD Command identifier.
5.3.17. AUCH - Authentication Challenge
 o-------------------------------------------------------------------o
 | AUCH Authentication Challenge |
 | |
 | Start Session Phase Initiator <---> Responder |
 |-------------------------------------------------------------------|
 | Pos | Field | Description | Format |
 |-----+-----------+---------------------------------------+---------|
 | 0 | AUCHCMD | AUCH Command, 'A' | F X(1) |
 | 1 | AUCHCHLL | Challenge Length | V U(2) |
 | 3 | AUCHCHAL | Challenge | V U(n) |
 o-------------------------------------------------------------------o
 AUCHCMD Command Code Character
 Value: 'A' AUCH Command identifier.
 AUCHCHLL Challenge length Binary(2)
 Indicates the length of AUCHCHAL in octets.
 The length is expressed as an unsigned binary number using
 network byte order.
 AUCHCHAL Challenge Binary(n)
 A [CMS] encrypted 20-byte random number uniquely generated
 each time an AUCH is sent.
 NOTE:
 Any encryption algorithm that is available through a defined cipher
 suite (Section 10.2) may be used. See Section 10.1 regarding the
 choice of a cipher suite.
5.3.18. AURP - Authentication Response
 o-------------------------------------------------------------------o
 | AURP Authentication Response |
 | |
 | Start Session Phase Initiator <---> Responder |
 |-------------------------------------------------------------------|
 | Pos | Field | Description | Format |
 |-----+-----------+---------------------------------------+---------|
 | 0 | AURPCMD | AURP Command, 'S' | F X(1) |
 | 1 | AURPRSP | Response | V U(20) |
 o-------------------------------------------------------------------o
 AURPCMD Command Code Character
 Value: 'S' AURP Command identifier.
 AURPRSP Response Binary(20)
 Contains the decrypted challenge (AUCHCHAL).
 IMPORTANT:
 It is an application implementation issue to validate a received AURP
 to ensure that the response matches the challenge. This validation
 is extremely important to ensure that a party is correctly
 authenticated.
5.4. Identification Code
 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 Subaddress | 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,
 and space and hyphen characters.
 SIOCSA Computer Subaddress String(6)
 A locally assigned address that uniquely identifies a
 system within an organisation (defined by an Organisation
 Identifier).
6. File Services
6.1. Overview
 ODETTE-FTP provides services for compressing, encrypting, and signing
 files. These services should generally be performed off line,
 outside of the ODETTE-FTP communications session for performance
 reasons, although this is not a strict requirement.
 ODETTE-FTP requires that the following steps must be performed in
 this exact sequence, although any of steps 2, 3, or 4 may be omitted.
 Step 1 is required only if any of steps 2, 3, or 4 are performed:
 1. Insert record length indicators (V format files only; see Section
 6.5)
 2. Sign
 3. Compress
 4. Encrypt
 The cipher suite for the encryption and signing algorithms is
 assigned by bilateral agreement.
 Secured and/or compressed files must be enveloped. The envelope
 contains additional information about the service used that is
 necessary for a receiving party to fully process the file.
 The [CMS] content types used are:
 EnvelopedData - Indicates encrypted data
 CompressedData - Indicates compressed data
 SignedData - Indicates signed content
 Data - Indicates unstructured data
 For signed or encrypted data, the encapsulated content type
 (eContentType field) is id-data.
6.2. File Signing
 Files that are to be signed are enveloped according to the file
 enveloping format (SFIDENV). Generally, this will be as a [CMS]
 package.
 A file may be signed more than once to ease the changeover between
 old and new certificates.
 It is recommended that the envelope does not contain the public
 certificate of the signer. Where files are sent to the same
 recipient continuously, it would serve no benefit to repeatedly send
 the same certificate. Both the original file data and signature are
 stored within the [CMS] package.
6.3. File Encryption
 Files that are to be encrypted are enveloped according to the file
 enveloping format (SFIDENV). Generally, this will be as a [CMS]
 package.
 It is recommended that encryption should be performed before the
 ODETTE-FTP session starts because a large file takes a long time to
 encrypt and could cause session time outs, even on high-performance
 machines.
 Likewise, decryption of the file should occur outside of the session.
 However, an application may choose to allow in-session encryption and
 decryption for very small files.
6.4. File Compression
 Files that are to be compressed are enveloped according to the file
 enveloping format (SFIDENV). Generally, this will be as a [CMS]
 package using the [CMS-Compression] data type, which uses the [ZLIB]
 compression algorithm by default.
 Unlike the buffer compression method, this method operates on a whole
 file. Because of the increased levels of compression, file level
 compression essentially deprecates the older buffer compression
 inside ODETTE-FTP. The buffer compression is kept for backwards
 compatibility.
6.5. V Format Files - Record Lengths
 A file that has been signed, compressed, and/or encrypted will have
 lost its record structure, so ODETTE-FTP will not be able to insert
 the End of Record Flag in subrecord headers in Data Exchange Buffers.
 To preserve the record structure, V format files must have record
 headers inserted into them prior to signing, compression, or
 encryption. These 2-byte binary numbers, in network byte order,
 indicate the length of each record, allowing the receiving system,
 where appropriate, to recreate the files complete with the original
 variable-length records. Note that the header bytes hold the number
 of data bytes in the record and don't include themselves.
 This is only applicable to V format files, which themselves are
 typically only of concern for mainframes.
7. ODETTE-FTP Data Exchange Buffer
7.1. Overview
 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.
 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.
7.2. Data Exchange Buffer Format
 For transmission of Virtual File records, data is divided into
 subrecords, each of which is preceded by a 1-octet Subrecord Header.
 The Data Exchange Buffer is made up of the initial Command Character
 followed by pairs of Subrecord Headers and subrecords, as follows.
 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 1-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 6 bits are available, the next subrecord may represent
 between 0 and 63 octets of the Virtual File.
7.3. Buffer Filling Rules
 A Data Exchange Buffer may be any length up to the value negotiated
 in the Start Session exchange.
 Virtual File records may be concatenated within one Data 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:
 1. Truncate the Exchange Buffer, and put the complete subrecord
 (preceded by its header octet) in a new Exchange Buffer.
 2. Split the subrecord into two, filling the remainder of the
 Exchange Buffer with the first new subrecord and starting a new
 Exchange Buffer with the second.
 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.
8. Stream Transmission Buffer
8.1. Introduction
 To utilise the TCP stream, 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.
 Note: The Stream Transmission Buffer is not used when using ODETTE-
 FTP over an X.25 network.
 This is because ODETTE-FTP can rely 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. TCP
 offers a stream-based connection that does not provide these
 functions.
 The Stream Transmission Buffer is composed of an STH and an OEB.
 o-----+-----------------+-----+--------------------+-----+------
 | STH | OEB | STH | OEB | STH | OEB/
 o-----+-----------------+-----+--------------------+-----+----
 STH - Stream Transmission Header
 OEB - ODETTE-FTP Exchange Buffer
8.2. Stream Transmission Header Format
 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 an STB length of 100003.
 The length is expressed as a binary number in network byte order.
 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.
9. Protocol State Machine
9.1. ODETTE-FTP State Machine
 The operation of an ODETTE-FTP entity is formally defined by the
 State Machine presented below. There are five State and Transition
 tables, and for each table additional information is given in the
 associated Predicate and Action lists.
 The response of an ODETTE-FTP entity to the receipt of an event is
 defined by a Transition table entry indexed by the Event/State
 intersection within the appropriate state table.
 Each Transition table entry defines the actions taken, events
 generated, and new state entered. Predicates may be used within a
 table entry to select the correct response on the basis of local
 information held by the entity.
 A Transition table contains the following fields:
 Index (I) State transition index.
 Predicate A list of predicates used to select between different
 possible transitions. The predicates are defined in
 the Predicate and Action lists.
 Actions A list of actions taken by the entity. The actions are
 defined in the Predicate and Action lists.
 Events Output events generated by the entity.
 Next State The new state of the entity.
9.2. Error Handling
 The receipt of an event in a given state may be invalid for three
 reasons.
 1. The case is impossible by design of the state automata, denoted
 'X' in the state tables. For example, a timer that has not been
 set cannot run out.
 2. The event is the result of an error in the Network Service
 implementation, also denoted 'X' in the state tables. The
 Network Service implementation is considered to be correct.
 3. For all other cases, the event is considered to be a User Error,
 denoted "U" in the state tables.
 The state tables define the conditions under which a User event is
 valid, thus preventing the generation of a protocol error by the
 ODETTE-FTP entity as a result of a User Monitor error. The reaction
 of the entity to such errors is undefined and regarded as a local
 implementation issue.
 The state tables also allow protocol errors due to the receipt of
 invalid Exchange Buffers, to be detected. In such cases, the
 reaction of the entity to the error is defined.
9.3. States
 The Command Mode is strictly a half-duplex flip-flop mode.
 A_NC_ONLY Responder, Network Connection opened
 The Responder has sent its 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
 its 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 its 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 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.
 NRSTWFCD Negative End Response stored in WF_CD state
 Since the User Monitor doesn't see the WF_CD state, it
 may send F_NERP_RQ, before ODETTE-FTP receives a Change
 Direction (CD) command.
 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 its 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 its 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.
 RTRP Ready to Receive (RTR) Pending
 The Listener has received an EERP or a NERP and is
 waiting for the Ready to Receive response (F_RTR_RS) from
 its User Monitor.
 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 Speaker has sent an End to End Response (EERP) or a
 Negative End Response (NERP) command and must wait for
 Ready To Receive (RTR) from the Listener.
 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.
 WF_SECD Wait for Security Change Direction
 The Speaker is expecting a Security Change Direction
 (SECD) from the Listener.
 WF_AUCH Wait for Authentication Challenge
 The Speaker has sent a Security Change Direction (SECD)
 command and must wait for Authentication Challenge (AUCH)
 from the Listener.
 WF_AURP Wait for Authentication Response
 The Speaker has sent an Authentication Challenge (AUCH)
 command and must wait for Authentication Response (AURP)
 from the Listener.
9.4. Input Events
 User Monitor Input Events (Section 3)
 F_DATA_RQ F_CONNECT_RQ F_START_FILE_RQ F_CLOSE_FILE_RQ
 F_EERP_RQ F_CONNECT_RS F_START_FILE_RS(+) F_CLOSE_FILE_RS(+)
 F_NERP_RQ F_ABORT_RQ F_START_FILE_RS(-) F_CLOSE_FILE_RS(-)
 F_CD_RQ F_RELEASE_RQ F_RTR_RS
 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
 NERP SECD AUCH AURP
 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.
9.5. Output Events
 User Monitor Output Events (Section 3)
 F_DATA_IND F_CONNECT_IND F_START_FILE_IND F_CLOSE_FILE_IND
 F_EERP_IND F_CONNECT_CF F_START_FILE_CF(+) F_CLOSE_FILE_CF(+)
 F_CD_IND F_ABORT_IND F_START_FILE_CF(-) F_CLOSE_FILE_CF(-)
 F_NERP_IND F_RELEASE_IND F_DATA_CF F_RTR_CF
 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
 NERP SECD AUCH AURP
 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.
9.6. Local Variables
 The following variables are maintained by the ODETTE-FTP entity to
 assist the operation of the protocol. They are denoted V.Variable-
 name within the state table action and predicate lists. Their value
 can be examined and changed by the ODETTE-FTP entity. The initial
 value of each variable is undefined.
 Variable Type Comments
 ---------------------------------------------------------------------
 Buf-size Integer Negotiated Data 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 use as agreed.
 Credit_L Integer Listener's 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.
 Caller Yes/No This entity initiated the ODETTE-FTP
 session.
 Authentication Yes/No Secure authentication in use as agreed
 Challenge Binary Random challenge
 ---------------------------------------------------------------------
9.7. Local Constants
 The following constants define the capabilities of a given ODETTE-FTP
 entity. They are denoted C.Constant-name within the state table
 action and predicate lists. Their value can be examined but not
 changed by the ODETTE-FTP entity.
 Constant Value Comments
 ---------------------------------------------------------------------
 Cap-compression Yes/No Compression supported?
 Cap-init Initiator Must be Initiator.
 Responder Must be Responder.
 Both Can be Initiator or Responder.
 Cap-mode Sender-only Must be sender.
 Receiver-only Must be receiver.
 Both Can be sender or receiver.
 Max-buf-size 127 < Int < 100000 Maximum Data Exchange Buffer
 size supported.
 Max-window 0 < Int < 1000 Local maximum credit value.
 Cap-restart Yes/No Restart supported?
 Cap-logic 0, 1, 2 0 = does not support special
 logic
 1 = supports special logic
 2 = needs special logic
 ---------------------------------------------------------------------
9.8. Session Connection State Table
9.8.1. State Table
 o----------------------------------------------------------o
 | | Other States |
 | |--------------------------------------------------o |
 | | WF_SECD | |
 | |----------------------------------------------o | |
 | | WF_AURP | | |
 | |------------------------------------------o | | |
 | | WF_AUCH | | | |
 | |--------------------------------------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 | X | X | X |
 | |--------------+---+---+---+---+---+---+---+---+---+---|
 | E | N_CON_CF | X | C | X | X | X | X | X | X | X | X |
 | |--------------+---+---+---+---+---+---+---+---+---+---|
 | V | SSRM | X | X | H | X | X | X | L | L | L | X |
 | |--------------+---+---+---+---+---+---+---+---+---+---|
 | E | SSID | X | X | X | D | E | F | L | L | L | F |
 | |--------------+---+---+---+---+---+---+---+---+---+---|
 | N | N_CON_IND | B | X | X | X | X | X | X | X | X | X |
 | |--------------+---+---+---+---+---+---+---+---+---+---|
 | T | F_CONNECT_RS | X | U | U | U | U | G | X | X | X | U |
 | |--------------+---+---+---+---+---+---+---+---+---+---|
 | | ESID | X | X | X | F | X | X | F | F | F | X |
 | |--------------+---+---+---+---+---+---+---+---+---+---|
 | | AUCH | X | X | U | U | X | X | I | L | L | U |
 | |--------------+---+---+---+---+---+---+---+---+---+---|
 | | AURP | X | X | U | U | X | X | L | K | L | U |
 | |--------------+---+---+---+---+---+---+---+---+---+---|
 | | SECD | X | X | U | U | X | X | L | L | J | U |
 o----------------------------------------------------------o
9.8.2. Transition Table
 I | Predicate Actions Output Events Next State
 ===o=============================================================
 A | P1: F_ABORT_IND IDLE
 | !P1: 1,2 N_CON_RQ I_WF_NC
 ---+-------------------------------------------------------------
 B | P3: N_DISC_RQ IDLE
 | !P3: 2 N_CON_RS
 | SSRM A_NC_ONLY
 ---+-------------------------------------------------------------
 C | 4,2 I_WF_RM
 ---+-------------------------------------------------------------
 D | P2 & P8 & P11: 4,2,5 SECD WF_AUCH
 | P2 & P8 & !P11: 4,2,5 F_CONNECT_CF IDLESP
 | P2 & !P8: 4,2 ESID(R=12)
 | F_ABORT_IND(R,AO=L) WF_NDISC
 | else: 4,2 ESID(R=10)
 | F_ABORT_IND(R,AO=L) WF_NDISC
 ---+-------------------------------------------------------------
 E | P4: 4 N_DISC_RQ IDLE
 | !P4: 4,2 F_CONNECT_IND A_WF_CONRS
 ---+-------------------------------------------------------------
 F | 4 F_ABORT_IND
 | N_DISC_RQ IDLE
 ---+-------------------------------------------------------------
 G | P2 & P9 & P10: 4,2,5 SSID WF_SECD
 | P2 & !P9 & P10: 4,2,5 SSID IDLELI
 | !P10: 4,2 ESID(R=12)
 | F_ABORT_IND(R,AO=L) WF_NDISC
 | else: 4,2 ESID(R=10)
 | F_ABORT_IND(R,AO=L) WF_NDISC
 ---+-------------------------------------------------------------
 H | 4,2,3 SSID I_WF_SSID
 ---+-------------------------------------------------------------
 I | P5: 4,2 AURP WF_SECD
 | !P5: 4,2 AURP IDLELI
 ---+-------------------------------------------------------------
 J | 4,2 AUCH WF_AURP
 ---+-------------------------------------------------------------
 K | P6: 4,2 F_CONNECT_CF IDLESP
 | P7: 4,2 SECD WF_AUCH
 | else: 4,2 ESID(R=11)
 | F_ABORT_IND(R,AO=L) WF_NDISC
 ---+-------------------------------------------------------------
 L | 4,2 ESID(R=02)
 | F_ABORT_IND(R,AO=L) WF_NDISC
 ---+-------------------------------------------------------------
9.8.3. Predicates and Actions
 Predicate P1: (No resources available) OR
 (C.Cap-init = Responder) OR
 (C.Cap-mode = Sender-only AND
 I.F_CONNECT_RQ.Mode = Receiver-only) OR
 (C.Cap-mode = Receiver-only AND
 I.F_CONNECT_RQ.Mode = Sender-only)
 Predicate P2: SSID negotiation is successful
 (for these, Buf-size, Restart, Compression, Mode,
 Special logic, and Window, compare the inbound SSID
 with the local constants to set the local variables.
 Any incompatibilities result in failure of the
 negotiation.)
 Predicate P3: C.Cap-init = Initiator
 Predicate P4: Mode in SSID incompatible with C.Cap-mode
 Predicate P5: V.Caller = Yes
 Predicate P6: (V.Caller = Yes) AND (AURP.Signature verifies with
 V.Challenge)
 Predicate P7: (V.Caller = No) AND (AURP.Signature verifies with
 V.Challenge)
 Predicate P8: V.Authentication = I.SSID.Authentication
 Predicate P9: I.F_CONNECT_RS.Authentication = Yes
 Predicate P10: O.F_CONNECT_IND.Authentication =
 I.F_CONNECT_RS.Authentication
 Predicate P11: V.Authentication = Yes
 Action 1: Set V.Mode from (C.Cap-mode, I.F_CONNECT_RQ.Mode)
 Set V.Pswd, V.Id, V.Restart, and
 V.Authentication from I.F_CONNECT_RQ
 Set V.Buf-size = C.Max-buf-size
 Set V.Compression = C.Cap-compression
 Set V.Caller = Yes
 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, V.Authentication = from SSID
 Action 6: Set V.Challenge = A random number unique to the
 session
9.9. Error and Abort State Table
9.9.1. State Table
 o--------------------------------------o
 | | Other States |
 | S |------------------------------o |
 | T | WF_NDISC | |
 | A |--------------------------o | |
 | T | I_WF_NC | | |
 | E |----------------------o | | |
 | | IDLE | | | |
 |======================o---+---+---+---|
 | | TIME-OUT | X | X | A | B |
 | |------------------+---+---+---+---|
 | E | F_ABORT_RQ | X | A | X | C |
 | V |------------------+---+---+---+---|
 | E | N_RST_IND | X | X | A | D |
 | N |------------------+---+---+---+---|
 | T | N_DISC_IND | X | E | F | G |
 | |------------------+---+---+---+---|
 | | Invalid Buffer | X | X | H | I |
 o--------------------------------------o
9.9.2. Transition Table
 I | Predicate Actions Output Events Next State
 ===o=================================================================
 A | N_DISC_RQ IDLE
 ---+-----------------------------------------------------------------
 B | F_ABORT_IND
 | N_DISC_RQ IDLE
 ---+-----------------------------------------------------------------
 C | 1 N_DISC_RQ IDLE
 ---+-----------------------------------------------------------------
 D | 1 N_DISC_RQ
 | F_ABORT_IND IDLE
 ---+-----------------------------------------------------------------
 E | F_ABORT_IND IDLE
 ---+-----------------------------------------------------------------
 F | 1 IDLE
 ---+-----------------------------------------------------------------
 G | 1 F_ABORT_IND IDLE
 ---+-----------------------------------------------------------------
 H | WF_NDISC
 ---+-----------------------------------------------------------------
 I | 1,2 ESID(R=01)
 | F_ABORT_IND(R,AO=L) WF_NDISC
 ---------------------------------------------------------------------
9.9.3. Predicates and Actions
 Action 1: Stop inactivity timer
 Action 2: Start inactivity timer
9.10. Speaker State Table 1
9.10.1. State Table
 The following abbreviations are used in the Speaker state table.
 F_REL_RQ(Ok) - F_RELEASE_RQ Reason = Normal
 F_REL_RQ(Err) - F_RELEASE_RQ Reason = Error
 o--------------------------------------------------------------------o
 | | Other States |
 | |--------------------------------------------------------------o |
 | | WF_NDISC | |
 | |----------------------------------------------------------o | |
 | | OPOWFC | | |
 | |------------------------------------------------------o | | |
 | | OPO | | | |
 |S|--------------------------------------------------o | | | |
 | | OPOP | | | | |
 |T|----------------------------------------------o | | | | |
 | | CDSTWFCD | | | | | |
 |A|------------------------------------------o | | | | | |
 | | SFSTWFCD | | | | | | |
 |T|--------------------------------------o | | | | | | |
 | | NRSTWFCD | | | | | | | |
 |E|----------------------------------o | | | | | | | |
 | | ERSTWFCD | | | | | | | | |
 | |------------------------------o | | | | | | | | |
 | | WF_CD | | | | | | | | | |
 | |--------------------------o | | | | | | | | | |
 | | WF_RTR | | | | | | | | | | |
 | |----------------------o | | | | | | | | | | |
 | | IDLESPCD | | | | | | | | | | | |
 | |------------------o | | | | | | | | | | | |
 | | IDLESP | | | | | | | | | | | | |
 |=+==============o---+---+---+---+---+---+---+---+---+---+---+---+---|
 | | F_EERP_RQ | A | A | W | F | W | W | U | U | U | U | U | U | U |
 | |--------------+---+---+---+---+---+---+---+---+---+---+---+---+---|
 | | F_NERP_RQ | Y | Y | W | Z | W | W | U | U | U | U | U | U | U |
 | |--------------+---+---+---+---+---+---+---+---+---+---+---+---+---|
 | | F_START_ | B | B | W | G | W | W | U | U | U | U | U | X | U |
 | | FILE_RQ | | | | | | | | | | | | | |
 | |--------------+---+---+---+---+---+---+---+---+---+---+---+---+---|
 | | SFPA | C | C | C | C | C | C | C | C | K | C | C | S | C |
 | |--------------+---+---+---+---+---+---+---+---+---+---+---+---+---|
 |E| SFNA | C | C | C | C | C | C | C | C | L | C | C | S | C |
 | |--------------+---+---+---+---+---+---+---+---+---+---+---+---+---|
 |V| CD | C | C | C | H | R | Z1| I | J | C | C | C | S | C |
 | |--------------+---+---+---+---+---+---+---+---+---+---+---+---+---|
 |E| F_DATA_RQ | U | U | U | U | U | U | U | U | U | M | U | S | U |
 | |--------------+---+---+---+---+---+---+---+---+---+---+---+---+---|
 |N| CDT | C | C | C | C | C | C | C | C | C | P | O | S | C |
 | |--------------+---+---+---+---+---+---+---+---+---+---+---+---+---|
 |T| F_CD_RQ | D | U | W | T | W | W | U | U | U | U | U | X | U |
 | |--------------+---+---+---+---+---+---+---+---+---+---+---+---+---|
 | | F_REL_RQ(Ok) | U | E | U | U | U | U | U | U | U | U | U | X | U |
 | |--------------+---+---+---+---+---+---+---+---+---+---+---+---+---|
 | | F_REL_RQ(Err)| Q | Q | Q | Q | Q | Q | Q | Q | Q | Q | Q | S | Q |
 | |--------------+---+---+---+---+---+---+---+---+---+---+---+---+---|
 | | RTR | C | C | N | C | C | C | C | C | C | C | C | S | C |
 o--------------------------------------------------------------------o
9.10.2. Transition Table
 I | Predicate Actions Output Events Next State
 ===o=================================================================
 A | P5: 1,2,3,18 EERP WF_RTR
 | !P5: 1,2,3 EERP WF_RTR
 ---+-----------------------------------------------------------------
 B | P1: UE
 | !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
 | !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
 | !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
 | !P3: 1,2,11,13 DATA
 | F_DATA_CF OPO
 ---+-----------------------------------------------------------------
 N | F_RTR_CF IDLESP
 ---+-----------------------------------------------------------------
 O | 12 F_DATA_CF OPO
 ---+-----------------------------------------------------------------
 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
 ---+-----------------------------------------------------------------
 W | User Error - Note 1 UE
 ---+-----------------------------------------------------------------
 X | Error
 ---+-----------------------------------------------------------------
 Y | P4 & P5: 1,2,15,18 NERP WF_RTR
 | !P4 & !P5: 1,2,15,14 NERP WF_RTR
 | P4 & !P5: 1,2,15 NERP WF_RTR
 | !P4 & P5: 1,2,15,14,18 NERP WF_RTR
 ---+-----------------------------------------------------------------
 Z | 16 NRSTWFCD
 ---------------------------------------------------------------------
 Z1| P4: 1,2,17 NERP WF_RTR
 | !P4: 1,2,17,14 NERP WF_RTR
 ---------------------------------------------------------------------
9.10.3. Predicates and Actions
 Predicate P1: (I.F_START_FILE_RQ.Restart-pos > 0 AND V.Restart = No)
 OR (V.Mode = Receiver-only)
 Note: Restart requested and not supported for this session.
 Predicate P2: I.SFPA.Restart-pos > V.Restart-pos
 Note: Protocol error due to the restart position in the SFPA
 acknowledgement being greater than the position
 requested in the SFID request.
 Predicate P3: V.Credit_S - 1 = 0
 Note: Speaker's Credit is exhausted.
 Predicate P4: No special logic is in use
 Predicate P5: Signed EERP/NERP requested
 Action 1: Stop inactivity timer
 Action 2: Start inactivity timer
 Action 3: Build an EERP from F_EERP_RQ
 Action 4: Store F_EERP_RQ in V.Req-buf
 Action 5: Build SFID from F_START_FILE_RQ
 V.Restart-pos = I.F_START_FILE_RQ.Restart-pos
 Action 6: Store F_START_FILE_RQ in V.Req-buf
 Action 7: Build F_START_FILE_CF(+) from I.SFPA
 Action 8: Build F_START_FILE_CF(-) from I.SFNA
 Action 9: Build EERP from F_EERP_RQ stored in V.Req-buf
 Action 10: Build SFID from F_START_FILE_RQ stored in V.Req-buf
 Set V.Restart-pos
 Action 11: Build Exchange Buffer
 Action 12: V.Credit_S = V.Window
 Action 13: V.Credit_S = V.Credit_S - 1
 Action 14: Activate CRC-calculus function. Wrap Exchange buffer
 in special logic
 Action 15: Build a NERP from F_NERP_RQ
 Action 16: Store F_NERP_RQ in V.Req-buf
 Action 17: Build NERP from F_NERP_RQ stored in V.Req-buf
 Action 18: Sign the contents of NERP/EERP
 Note 1: Whether 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).
9.11. Speaker State Table 2
9.11.1. State Table
 o---------------------------------o
 | S | CLOP |
 | T |-------------------------o |
 | A | OPOWFC | |
 | T |---------------------o | |
 | E | OPO | | |
 |=====================o---+---+---|
 | E | F_CLOSE_FILE_RQ | A | E | U |
 | V |-----------------+---+---+---|
 | E | EFPA | B | B | C |
 | N |-----------------+---+---+---|
 | T | EFNA | B | B | D |
 o---------------------------------o
9.11.2. Transition Table
 I | Predicate Actions Output Events Next State
 ===o=================================================================
 A | 1,2,5,7 EFID CLOP
 ---+-----------------------------------------------------------------
 B | 1,2 ESID(R=02)
 | F_ABORT_IND(R,AO=L) WF_NDISC
 ---+-----------------------------------------------------------------
 C | P1: 1,2,3 F_CLOSE_FILE_CF(+,SP=No)
 | CD IDLELI
 | !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
 ---------------------------------------------------------------------
9.11.3. Predicates and Actions
 Predicate P1: (I.EFPA.CD-Request = Yes)
 Predicate P2: No special logic is in use
 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
 Action 8: Wrap Exchange buffer in special logic
 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.
9.12. Listener State Table
9.12.1. State Table
 o---------------------------------------------o
 | | RTRP |
 | |-------------------------------------o |
 | | CLIP | |
 | |---------------------------------o | |
 | | OPI | | |
 | S |-----------------------------o | | |
 | T | OPIP | | | |
 | A |-------------------------o | | | |
 | T | IDLELICD | | | | |
 | E |---------------------o | | | | |
 | | IDLELI | | | | | |
 |=====================o---+---+---+---+---+---+
 | | SFID | A | A | B | B | B | B |
 | |-----------------+---+---+---+---+---+---+
 | E | DATA | B | B | B | I | B | B |
 | V |-----------------+---+---+---+---+---+---+
 | E | EFID | B | B | B | J | B | B |
 | N |-----------------+---+---+---+---+---+---+
 | T | F_START_FILE_RS | U | U | H | U | U | U |
 | |-----------------+---+---+---+---+---+---+
 | | F_CLOSE_FILE_RS | U | U | U | U | K | U |
 | |-----------------+---+---+---+---+---+---+
 | | CD | C | B | B | B | B | B |
 | |-----------------+---+---+---+---+---+---+
 | | ESID R=Normal | D | F | D | D | D | D |
 | |-----------------+---+---+---+---+---+---+
 | | ESID R=Error | D | D | D | D | D | D |
 | |-----------------+---+---+---+---+---+---+
 | | EERP | E | E | B | B | B | B |
 | |-----------------+---+---+---+---+---+---+
 | | NERP | L | L | B | B | B | B |
 | |-----------------+---+---+---+---+---+---+
 | | F_RTR_RS | U | U | U | U | U | M |
 o---------------------------------------------o
9.12.2. Transition Table
 I | Predicate Actions Output Events Next State
 ===o=================================================================
 A | P1: 1,2 ESID(R=02)
 | F_ABORT_IND(R,AO=L) WF_NDISC
 | !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 | 1,2,4 F_EERP_IND RTRP
 ---+-----------------------------------------------------------------
 F | 1 F_RELEASE_IND
 | N_DISC_RQ IDLE
 ---+-----------------------------------------------------------------
 H | P4: User Error UE
 | P2 & !P4 & !P5: 1,2,8 SFPA OPI
 | !P2 & !P4 & !P5: 1,2 SFNA IDLELI
 | P2 & !P4 & P5: 1,2,5,8 SFPA OPI
 | !P2 & !P4 & P5: 1,2,5 SFNA IDLELI
 ---+-----------------------------------------------------------------
 I | P6: 1,2 ESID(R=02)
 | F_ABORT_IND(R,A0=L) WF_NDISC
 | !P5 & !P6 & !P7: 1,2,7 F_DATA_IND (See Note 1) OPI
 | !P5 & !P6 & P7: 1,2,8 F_DATA_IND
 | CDT (See Note 1) OPI
 | P5 & !P6 & P8: 1,2 ESID(R=07)
 | F_ABORT_IND(R,A0=L) WF_NDISC
 | P5 & !P6 & !P7 : 1,2,6,7 F_DATA_IND (See Note 1) OPI
 | & !P8
 | P5 & !P6 & P7 : 1,2,5,6,8 F_DATA_IND OPI
 | & !P8 CDT (See Note 1)
 ---+-----------------------------------------------------------------
 J | 1,2 F_CLOSE_FILE_IND CLIP
 ---+-----------------------------------------------------------------
 K | P2 & P3 & !P5: 1,2 EFPA(CD-Req) WF_CD
 | P2 & !P3 & !P5: 1,2 EFPA(no CD) IDLELI
 | !P2 & !P5: 1,2 EFNA IDLELI
 | P2 & !P3 & P5: 1,2,5 EFPA(no CD) IDLELI
 | !P2 & P5: 1,2,5 EFNA IDLELI
 | P2 & P3 & P5: 1,2,5 EFPA(CD-Req) WF_CD
 ---+-----------------------------------------------------------------
 L | 1,2,10 F_NERP_IND RTRP
 ---+-----------------------------------------------------------------
 M | 1,2 RTR IDLELI
 ---+-----------------------------------------------------------------
 U | User Error UE
 ---------------------------------------------------------------------
9.12.3. Predicates and Actions
 Predicate P1: (I.SFID.Restart-pos > 0 AND V.Restart = No) OR (V.Mode
 = Sender-only)
 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: Special logic is used
 Predicate P6: V.Credit_L - 1 < 0
 Note: Protocol Error because the Speaker has exceeded its
 available transmission credit.
 Predicate P7: V.Credit_L - 1 = 0
 Note: The Speaker's credit must be reset before it can send
 further Data Exchange Buffers.
 Predicate P8: The calculus of the received CRC indicates an error
 Action 1: Stop inactivity timer
 Action 2: Start inactivity timer
 Action 3: Build F_START_FILE_IND from I.SFID
 V.Restart-pos = I.SFID.Restart-pos
 Action 4: Build F_EERP_IND from I.EERP
 Action 5: Add special logic header to the command to be sent to
 the Speaker
 Action 6: Suppress the special logic header from the data buffer
 before giving it to the user
 Action 7: V.Credit_L = V.Credit_L - 1
 Action 8: V.Credit_L = V.Window
 Action 10: Build F_NERP_IND from I.NERP
 Note 1: Flow control in case of reception.
 The ODETTE-FTP Listener must periodically send new
 credit to the Speaker. The timing of this operation
 will depend on:
 1. The User Monitor's capacity to receive data.
 2. The number of buffers available to ODETTE-FTP.
 3. The Speaker's available credit, which must be
 equal to zero.
9.13. Example
 Consider an ODETTE-FTP entity that has sent a Start File (SFID)
 command and entered the Open Out Pending (OPOP) state. Its 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
 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 its peer and an
 Abort indication (F_ABORT_IND) to its 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.
10. Miscellaneous
10.1. Algorithm Choice
 The choice of algorithms to use for security or compression between
 partners is for bilateral agreement outside of ODETTE-FTP.
10.2. Cryptographic Algorithms
 The algorithms for symmetric and asymmetric cryptography and hashing
 are represented by a coded value, the cipher suite:
 Cipher Suite Symmetric Asymmetric Hashing
 ------------ ----------------- ------------ -------
 01 3DES_EDE_CBC_3KEY RSA_PKCS1_15 SHA-1
 02 AES_256_CBC RSA_PKCS1_15 SHA-1
 Support of all cipher suites listed here is mandatory.
 The certificates used must be [X.509] certificates.
 TripleDES is using Cipher Block Chaining (CBC) mode for added
 security and uses the Encryption Decryption Encryption (EDE) process
 with 3 different 64-bit keys.
 RSA padding is as defined in [PKCS#1].
 AES is using a 256-bit key in CBC mode.
 An extended list of optional cipher suites may be used (Section
 10.3), but there is no guarantee that two communicating ODETTE-FTP
 entities would both support these optional cipher suites.
10.3. Protocol Extensions
 The algorithms and file enveloping formats available in ODETTE-FTP
 may be extended outside of this document.
 An up-to-date list of cipher suite values for use in ODETTE-FTP is
 maintained by ODETTE International, and published on their website at
 www.odette.org.
10.4. Certificate Services
 Certificates and certificate revocation lists may be exchanged as
 [CMS] enveloped files. It is therefore valid to exchange a [CMS]
 file that is neither encrypted, compressed, nor signed. It is an
 application implementation issue to determine the correct course of
 action on receipt of such a file.
11. Security Considerations
 ODETTE-FTP security requires the use of [X.509] certificates. If no
 security options are agreed for use, the send and receive passwords
 are sent in plain text. Whilst this is acceptable over X.25 and ISDN
 networks, this is a risky practice over insecure public networks such
 as the Internet.
 All, some, or none of the security options available in ODETTE-FTP
 may be used. No recommendations for the use of these options are
 provided in this specification. Whilst use of the highest-strength
 encryption algorithms may seem admirable, there is often a
 performance tradeoff to be made, and signing all files and
 acknowledgements has potential legal implications that should be
 considered.
 It should be noted that whilst the security measures ensure that an
 ODETTE-FTP partner is authenticated, it does not necessarily mean
 that the partner is authorised. Having proven the identity of a
 partner, it is an application issue to decide whether that partner is
 allowed to connect or exchange files.
 Extracted from [RFC3850]:
 "When processing certificates, there are many situations where the
 processing might fail. Because the processing may be done by a user
 agent, a security gateway, or other program, there is no single way
 to handle such failures. Just because the methods to handle the
 failures have not been listed, however, the reader should not assume
 that they are not important. The opposite is true: if a certificate
 is not provably valid and associated with the message, the processing
 software should take immediate and noticeable steps to inform the end
 user about it.
 Some of the many situations in which signature and certificate
 checking might fail include the following:
 No certificate chain leads to a trusted CA
 No ability to check the Certificate Revocation List (CRL) for a
 certificate
 An invalid CRL was received
 The CRL being checked is expired
 The certificate is expired
 The certificate has been revoked
 There are certainly other instances where a certificate may be
 invalid, and it is the responsibility of the processing software to
 check them all thoroughly, and to decide what to do if the check
 fails. See RFC 3280 for additional information on certificate path
 validation."
 The push / pull nature of ODETTE-FTP means that a party can make an
 outbound connection from behind a firewall to another party and
 exchange files in both directions. There is no need for both
 partners to open ports on their firewalls to allow incoming
 connections; only one party needs to allow incoming connections.
 See Section 1.7 for a discussion of the benefits of session security
 [TLS] versus file security.
Appendix A. Virtual File Mapping Example
 This example demonstrates the mapping of a Virtual File into a
 sequence of ODETTE-FTP Data Exchange Buffers.
 Each line in this extract from 'The Rime of the Ancient Mariner' by
 Coleridge [RIME] is separated by CR-LFs in a file that is being
 transmitted as a T format file.
 It is an ancient Mariner,
 And he stoppeth one of three.
 "By thy long grey beard and glittering eye,
 Now wherefore stopp'st thou me?
 "The Bridegroom's doors are opened wide,
 And I am next of kin;
 The guests are met, the feast is set:
 May'st hear the merry din."
 He holds him with his skinny hand,
 "There was a ship," quoth he.
 "Hold off! unhand me, grey-beard loon!"
 Eftsoons his hand dropt he.
 He holds him with his glittering eye--
 The Wedding-Guest stood still,
 And listens like a three years; child:
 The Mariner hath his will.
 The Wedding-Guest sat on a stone:
 He cannot chuse but hear;
 And thus spake on that ancient man,
 The bright-eyed Mariner.
 The ship was cheered, the harbour cleared,
 Merrily did we drop
 Below the kirk, below the hill,
 Below the light-house top.
 The Exchange Buffers below were built from the above. The top line
 of each represents the ASCII code, while the two lines below give the
 hexadecimal value.
 Note that:
 . The "D" at the beginning of each Exchange Buffer is the command
 code.
 . The "?" preceding each subrecord is the header octet (see the
 hexadecimal value).
 Exchange Buffer 1
 D?It is an ancient Mariner,..And he stoppeth one of three..."By
 4347267266266666672467666720046626627767767626662662767662002472
 4F9409301E01E395E40D129E52CDA1E4085034F005480FE50F6048255EDA2290
 t?hy long grey beard and glittering eye,..Now wherefore stopp'st
 7367266662676726667626662666776766626762004672766766676277677277
 4F890CFE70725902512401E407C944529E70595CDAEF70785256F25034F00734
 ?thou me?...."The Bridegroom's doors are opened wide,..And I am
 2376672663000025662476666766627266677267626766662766620046624266
 0F48F50D5FDADA248502294572FFD7304FF2301250F05E5407945CDA1E40901D
 ?next of kin;..The guests are met, the feast is set:..May'st he
 2366772662666300566267677726762667227662666772672767300467277266
 0FE5840F60B9EBDA485075534301250D54C04850651340930354ADAD19734085
 a?r the merry din."....He holds him with his skinny hand,.."Ther
 6372766266777266622000046266667266627676266727666672666620025667
 1F204850D5229049EE2DADA8508FC43089D07948089303B9EE9081E4CDA24852
 e? was a ship," quoth he..."Hold off! unhand me, grey-beard loon
 6327672627667222776762662002466626662276666626622676726667626666
 5F07130103890C2015F48085EDA28FC40F66105E81E40D5C07259D251240CFFE
 !?"..Eftsoons his hand dropt he.....He holds him with his glitte
 2320046776667266726666267677266200004626666726662767626672666776
 1F2DA5643FFE30893081E4042F04085EDADA8508FC43089D07948089307C9445
 r?ing eye--..The Wedding-Guest stood still,..And listens like a
 7366626762200566256666662476772776662776662004662667766726666262
 2F9E70595DDDA485075449E7D75534034FF40349CCCDA1E40C9345E30C9B5010
 t?hree years; child:..The Mariner hath his will.....The Wedding-
 7367662766773266666300566246766672667626672766620000566256666662
 4F8255095123B0389C4ADA4850D129E52081480893079CCEDADA485075449E7D
 G?uest sat on a stone:..He cannot chuse but hear;..And thus spak
 4376772767266262776663004626666672667762677266673004662767727766
 7F553403140FE01034FE5ADA85031EEF4038535025408512BDA1E4048530301B
 e? on that ancient man,..The bright-eyed Mariner.....The ship wa
 6326627667266666672666200566267666726766246766672000056627667276
 5F0FE0481401E395E40D1ECDA4850229784D59540D129E52EDADA48503890071
 s? cheered, the harbour cleared,..Merrily did we drop..Below the
 7326666766227662667667726666766200467766726662762676700466672766
 3F03855254C048508122F5203C51254CDAD5229C90494075042F0DA25CF70485
 .kirk, below the hill,..Below the light-house top...
 2B667622666672766266662004666727662666672667762767200
 03B92BC025CF70485089CCCDA25CF704850C9784D8F53504F0EDA
Appendix B. ISO 646 Character Subset
 o-----------------------------------------------------------------o
 | | 7| 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 |
 | | B -+-----+-----+-----+-----+-----+-----+-----+-----|
 | | I 6| 0 | 0 | 1 | 1 | 0 | 0 | 1 | 1 |
 | | T -+-----+-----+-----+-----+-----+-----+-----+-----|
 | | 5| 0 | 1 | 0 | 1 | 0 | 1 | 0 | 1 |
 | |----+-----+-----+-----+-----+-----+-----+-----+-----|
 | | | | | | | | | | |
 | | | | | | | | | | |
 |------------| | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
 | BIT | | | | | | | | | |
 | 4 3 2 1 | | | | | | | | | |
 |============o====o=====+=====+=====+=====+=====+=====+=====+=====|
 | 0 0 0 0 | 0 | | | SP | 0 | | P | | |
 |------------|----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 0 0 0 1 | 1 | | | | 1 | A | Q | | |
 |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 0 0 1 0 | 2 | | | | 2 | B | R | | |
 |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 0 0 1 1 | 3 | | | | 3 | C | S | | |
 |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 0 1 0 0 | 4 | | | | 4 | D | T | | |
 |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 0 1 0 1 | 5 | | | | 5 | E | U | | |
 |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 0 1 1 0 | 6 | | | & | 6 | F | V | | |
 |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 0 1 1 1 | 7 | | | | 7 | G | W | | |
 |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 1 0 0 0 | 8 | | | ( | 8 | H | X | | |
 |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 1 0 0 1 | 9 | | | ) | 9 | I | Y | | |
 |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 1 0 1 0 | 10 | | | | | J | Z | | |
 |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 1 0 1 1 | 11 | | | | | K | | | |
 |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 1 1 0 0 | 12 | | | | | L | | | |
 |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 1 1 0 1 | 13 | | | - | | M | | | |
 |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 1 1 1 0 | 14 | | | . | | N | | | |
 |------------+----|-----+-----+-----+-----+-----+-----+-----+-----|
 | 1 1 1 1 | 15 | | | / | | O | | | |
 o-----------------------------------------------------------------o
Appendix C. X.25 Specific Information
 The International Organization for Standardization (ISO) Open Systems
 Interconnection (OSI) model is the basis for ODETTE-FTP.
 ODETTE-FTP covers levels 4 to 7, and originally CCITT X.25 was the
 only recommended telecommunication protocol for OSI's layers 1, 2, 3.
 ISO Reference Model:
 +------------------------------+ <==== File Service
 | Level-7 FTP application |
 |------------------------------|
 | Level-6 FTP presentation |
 |------------------------------|
 | Level-5 FTP session |
 |------------------------------|
 | Level-4 FTP transport |
 |------------------------------| <==== Network Service
 | Level-3 X.25 |
 |------------------------------|
 | Level-2 X.25 |
 |------------------------------|
 | Level-1 X.25 |
 +------------------------------+
C.1. X.25 Addressing Restrictions
 When an X.25 call is made over a PSDN, the Network User Address (NUA)
 of the destination must be specified in order that the PTT may route
 the call. The call placed is directed to the termination equipment
 upon the user's premises.
 It is possible to provide extra information in the Call Request
 Packet in addition to the mandatory NUA required by the PTT.
 This extra information may be of 2 kinds:
 (a) A subaddress:
 It is simply an extension to the address and it is put into the
 called address field of the Call Request Packet. This
 information (Address + Subaddress) is taken from the destination
 address field of the F_CONNECT_RQ; therefore, from the user's
 point of view, there is no distinction between the main address
 and subaddress parts.
 (b) User data:
 There is no standard for user data. Moreover, there is no
 information in the F_CONNECT_RQ from which the ODETTE-entity may
 derive user data to be put in the N_CONNECT_RQ; therefore, user
 data shall not be used.
C.2. Special Logic
 The SSID field SSIDSPEC specifies whether special logic must be
 applied (Y (yes) or N (no)) to the Data Exchange Buffer before the
 ODETTE-FTP moves the data into the NSDU (Network Service Data Unit)
 and passes control to the Network Service.
C.2.1. When Special Logic Is Not To Be Used
 This logic is not applied to SSRM and SSID commands.
C.2.2. The Need for "Enveloping" Exchange Buffers
 The "special-logic" parameter was created in order to allow the use
 of ODETTE-FTP over asynchronous links. The "special-logic" could be
 needed to enable terminals to access an X.25 network via an
 asynchronous entry (through a PAD: Packet Assembly / Disassembly).
 The "special-logic" is not needed in case of a whole X.25 connection.
 This "special-logic" realises a CRC function in order to detect
 errors due to the asynchronous medium.
 Negotiation of the "special-logic" parameter in the SSID command is
 as follows:
 SSID SSID
 -----------------------------------------------
 special-logic=yes --------------------->
 <------------------------------------ special-logic=yes
 or
 <------------------------------------ special-logic=no
 special-logic=no ---------------------->
 <------------------------------------ special-logic=no
 This logic is activated when the "special-logic" parameter in the
 SSID specifies Y (yes).
 Special logic processing, when activated, will function within level
 4 of the OSI model.
 +------------------------------+ <==== File Service
 | Level-7 FTP application |
 |------------------------------|
 | Level-6 FTP presentation |
 |------------------------------|
 | Level-5 FTP session |
 |------------------------------|
 | Level-4 FTP transport |
 | SPECIAL LOGIC PROCESSING |
 |------------------------------| <==== Network Service
 | Level-3 X.25 |
 |------------------------------|
 | Level-2 X.25 |
 |------------------------------|
 | Level-1 X.25 |
 +------------------------------+
C.2.3. Responsibilities of Special Logic
 When transmitting an Exchange Buffer and special logic is active,
 layer 4 will wrap the Exchange Buffer in synchronization and
 delineation characters, then protect the data integrity by means of a
 block checksum (BCS). When receiving an Exchange Buffer and special
 logic is active, layer 4 will remove such things as synchronization
 and delineation characters, etc., before passing the Exchange Buffer
 to the higher layers.
C.2.4. Extended Exchange Buffer Format
 Each envelope has a 1-byte header prefixed to it, and a 2-byte
 checksum appended to the end. The checksum is derived in a manner
 specified in the ISO DIS 8073 TRANSPORT LAYER documentation.
 The layout of the data buffer will be structured as follows:
 +------------------------------------------------------------------+
 | S | B | | B | C |
 | T | S | COMPLETE EXCHANGE BUFFER (CEB) | C | / |
 | X | N | | S | R |
 +------------------------------------------------------------------+
 A A A A
 | | | |
 | +------------- Block sequence number | |
 | | |
 +----------------- Synchronization character | |
 | |
 Block checksum -----------------------+ |
 |
 Delineation character --------------------+
 The envelope is initialised with an STX and the checksum variables
 are set to 0. The leading STX is not protected by the checksum
 calculation but is explicitly protected by a character compare at the
 receiver's end. The Exchange Buffer is processed character by
 character. As each character is removed from the Exchange Buffer, it
 is put through the checksum calculation and then, prior to its
 insertion in the envelope, it is put through the Shift-out
 transparency logic, which will result in either one or two characters
 being inserted. When the contents of the Exchange Buffer have been
 entirely processed, then the checksum variables are brought up to
 date by inserting two X'00's through the checksum calculator and the
 two resultant checksum characters forwarded to the Shift-out
 transparency logic for insertion into the envelope. Finally, a
 carriage return (CR) is appended to the envelope. The segment is now
 ready for transmission to line.
 Upon receipt of a valid envelope that has the correct sequence
 number, the host should increment his sequence number register ready
 for the next transmission.
 The receiver will initialise his receiving buffer area upon receipt
 of an STX character, place the STX at the beginning of the buffer,
 and reset checksum variables. All subsequent characters are
 processed using Shift-out logic before they are inserted into the
 buffer, at which point they will NOT be processed by the checksum
 calculator, although the character following the Shift-out (after
 subtracting X'20') will be. The checksum characters themselves will
 be processed by the checksum calculator by virtue of the design of
 the checksum algorithm.
C.2.5. Error recovery
C.2.5.1. Mechanism
 The error correction scheme is implemented by the definition of three
 timers and the use of an ASCII NAK (Negative Acknowledgement)
 character followed by a C/R. The <NAK><C/R> will flow between the
 two session partners, but only as a consequence of previous bad data.
 A user of the error recovery correcting extension must always work
 with a credit value of 1. This can be forced upon any session
 partner at SSID negotiation. The effect will be to force a simple
 half-duplex flip-flop protocol.
 Upon receipt of a bad block, send <NAK><C/R> to the session partner.
 Upon receipt of a <NAK><C/R>, a session partner should retransmit the
 last block in its entirety.
C.2.5.2. Timers
 The majority of error conditions will be detected by a bad BCS
 sequence. However, certain conditions cannot be so detected. For
 example, a corrupt C/R will mean that the receiver will not know that
 the end of a block has been reached. No matter how long he waits, no
 more data will come from the sender. Thus, a timer is the only way
 to detect this type of corruption. There are three timers needed to
 detect all possible malignant conditions of this type.
 T1 - Exchange Buffer Time Out (Inactivity or Response)
 T2 - Inter Character Time Out
 T3 - Data Carrier Detect Loss Time Out
 The three timers are in addition to the timer defined in the original
 protocol.
 TIMER T1 - RESPONSE TIME OUT (DEFAULT = 45 SECONDS):
 Used to detect a high-level block Time Out, e.g., the Time Out
 between an SFID and its associated SFPA or SFNA response.
 Started - It is started after the last character of an exchange
 buffer has been sent to the line.
 Stopped - It is stopped when an STX has been received.
 Expiry - Retransmit the whole block again, until such time as the
 retry limit has been reached.
 TIMER T2 - INTER CHARACTER TIME OUT (DEFAULT = 7 SECONDS):
 Used to detect errors in the reception of individual characters.
 Started - For an asynchronous entity, it is started upon receipt
 of each character while in synchronisation mode. For an
 X.25 entity, it is started after a received block that
 did not terminate an Exchange Buffer.
 Stopped - Upon receipt of the next character.
 Expiry - Send a <NAK><C/R>, drop out of synchronised mode, and go
 back and listen to line.
 TIMER T3 - DATA CARRIER TEMPORARY LOSS (DEFAULT = 1 SECOND):
 Used by an asynchronous entity only and is used to detect a
 temporary carrier failure.
 Started - When DCD (Data Carrier Detect) is lost.
 Stopped - When DCD is regained.
 Expiry - Disconnect the session.
C.2.5.3. Types of Error
 Data corruption when it occurs can be categorised in one of five
 ways:
 (1) CORRUPT STX (START OF TEXT)
 In this situation the STX is not seen and synchronisation is not
 achieved. The terminating C/R is received out of synchronisation
 and hence the block is not seen by the receiver. A <NAK><C/R> is
 transmitted to the sender to indicate this. The sender should then
 retransmit the last block (each implementation will need to set a
 retry limit to be used for the number of consecutive times it
 attempts to retransmit a block -- a default limit of 5 is
 recommended). All data received outside synchronisation (except
 <NAK><C/R>) are ignored.
 (A) (B)
 Dropped Start of Text (STX)
 +-------------------------+
 | | B | | B | C |
 -----| | S | CEB | C | / |-----> Not sync
 | | N | | S | R |
 +-------------------------+
 +-------+
 | N | C |
 <-----| A | / |----- Not sync
 | K | R |
 +-------+
 Exchange Buffer Resent
 +-------------------------+
 | S | B | | B | C |
 -----| T | S | CEB | C | / |-----> Sync
 | X | N | | S | R |
 +-------------------------+
 (2) CORRUPT TERMINATION (C/R)
 This situation manifests itself as an extended period of
 synchronisation with no activity. The T2 timer will detect this
 condition.
 (A) (B)
 Corrupt Carriage Return
 +-------------------------+
 | S | B | | B | |
 -----| T | S | CEB | C | |-----> No activity
 | X | N | | S | |
 +-------------------------+
 +-------+
 | N | C | T2
 <-----| A | / |----- Timed out
 | K | R |
 +-------+
 Exchange Buffer Resent
 +-------------------------+
 | S | B | | B | C |
 -----| T | S | CEB | C | / |-----> Sync
 | X | N | | S | R |
 +-------------------------+
 (3) BAD DATA
 (4) BAD BCS (BLOCK CHECK SUM)
 In this situation, the receiver is unable to tell whether the error
 is bad data or bad BCS. In either case, the response is to discard
 the Exchange Buffer and send a <NAK><C/R>.
 (A) (B)
 Bad Data/BCS
 +-------------------------+
 | S | B | | B | C | Bad data
 -----| T | S | "%! | C | / |-----> detected
 | X | N | | S | R |
 +-------------------------+
 +-------+
 | N | C |
 <-----| A | / |----- Discard Block
 | K | R |
 +-------+
 Exchange Buffer Resent
 +-------------------------+
 | S | B | | B | C |
 -----| T | S | CEB | C | / |-----> Data OK
 | X | N | | S | R |
 +-------------------------+
 (5) BAD BLOCK SEQUENCE NUMBER (BSN)
 A circular sequential number (0 up to and including 9) is assigned
 to transmitted Exchange Buffers. This is to aid detection of
 duplicate or out-of-sequence Exchange Buffers. Once a duplicate
 block is detected, the Exchange Buffer in question is discarded.
 Once an out of sequence block is detected, this should result in a
 protocol violation.
 Example protocol sequence:
 (A) (B)
 Exchange Buffer Being Sent
 +-------------------------+
 | S | | | B | C | Expecting
 -----| T | 0 | EERP | C | / |-----> BSN=0
 | X | | | S | R | Transmission
 +-------------------------+
 Exchange Buffer Being Sent
 +-------------------------+
 | S | | | B | C | Response to
 <----| T | 0 | RTR | C | / |----- Previous
 | X | | | S | R | Block
 +-------------------------+
 Exchange Buffer Being Sent
 +-------------------------+ Expecting
 | S | | | B | C | BSN=1 (Block
 -----| T | 1 | SFID | C | / |- // -> lost in
 | X | | | S | R | Transmission)
 +-------------------------+ T1 Timed Out
 Exchange Buffer Being Sent
 +-------------------------+
 | S | | | B | C | Send last
 <----| T | 0 | RTR | C | / |----- Block
 | X | | | S | R | again
 +-------------------------+
 Discard Block
 and start
 Timer T1
 T1 Timed Out
 Exchange Buffer Resent
 +-------------------------+
 | S | | | B | C | Expecting
 -----| T | 1 | SFID | C | / |-----> BSN=1
 | X | | | S | R | Block OK
 +-------------------------+
 Exchange Buffer Being Sent
 +-------------------------+
 | S | | | B | C | Response
 <----| T | 1 | SFPA | C | / |----- BSN=1
 | X | | | S | R | Block OK
 +-------------------------+
 Exchange Buffer Being Sent
 +-------------------------+
 | S | | | B | C |
 -----| T | 2 | DATA | C | / |-----> Data OK
 | X | | | S | R |
 +-------------------------+
 Note: A credit value of 1 must be used to guarantee half-duplex
 flip-flop.
C.2.6. Sequence of Events for Special Logic Processing
 The following functions will be executed in sequence:
 1. Calculation of the Block Sequence Number (BSN):
 BSN is set to zero by SSID. First block will be sent with value
 zero. Value of BSN is increased by one for each data buffer to be
 transmitted. When BSN value exceeds 9, counter will be reset to
 zero.
 Format: numeric/1 pos.
 2. Calculation of the Block Checksum (BCS):
 Calculation is done as specified in the ISO DIS 8073 TRANSPORT
 LAYER document.
 Format: binary/2 pos.
 3. Shift-out transparency (See TRANSMIT/RECEIVE logic.)
 To avoid appearance of any control characters in the data stream,
 all the characters of the extended Exchange Buffer (with exception
 of the STX and carriage return characters enveloping the buffer)
 are put through a Shift-out logic, which result in a character
 being inserted (SO) and adding hex value '20' to the control
 character.
 4. The carriage return is inserted at the end of the data buffer.
 Note: After adding STX, BSN, BCS, CR, and SO-logic, the data buffer
 may exceed the Data Exchange Buffer size.
C.2.7. Checksum Creation Algorithm
 These follow the ISO DIS 8073 TRANSPORT LAYER standard.
 SYMBOLS:
 The following symbols are used:
 C0,C1 Variables used in the algorithm
 L Length of the complete NSDU
 X Value of the first octet of the checksum parameter
 Y Value of the second octet of the checksum parameter
 ARITHMETIC CONVENTIONS:
 Addition is performed in one of the two following modes:
 a) modulo 255 arithmetic
 b) one's complement arithmetic in which if any of the variables
 has the value minus zero (i.e., 255) it shall be regarded as
 though if was plus zero (i.e., 0).
 ALGORITHM FOR GENERATING CHECKSUM PARAMETERS:
 . Set up the complete NSDU with the value of the checksum parameter
 field set to zero.
 . Initialise C0 and C1 to zero.
 . Process each octet sequentially from i=1 to L by
 a) adding the value of the octet to C0, then
 b) adding the value of C0 to C1.
 . Calculate X and Y such that
 X = C0 - C1
 Y = C1 - 2*C0
 . Place the values X and Y in the checksum bytes 1 and 2,
 respectively.
C.2.8. Algorithm for checking checksum parameters
 . Initialise parameters C0 and C1 to zero.
 . Process each octet of NSDU sequentially from i=1 to L by
 a) adding the value of the octet to C0, then
 b) adding the value of C0 to C1.
 . If, when all the octets have been processed, either or both C0
 and C1 does not have the value zero, then the checksum formulas
 have not been satisfied.
 Note that the nature of the algorithm is such that it is not
 necessary to compare explicitly the stored checksum bytes.
C.2.9. Shift-out Processing
 (Transparency for all control characters)
 TRANSMIT LOGIC (values SO: X'0E' or X'8E')
 Buffer(1), ... , (n) is a character in the buffer to be sent.
 FOR i=1 to n /* for all octets of the buffer */
 IF ((buffer(i) & X'7F') < X'20')
 THEN output (SO)
 output (buffer(i) + X'20')
 ELSE output (buffer(i))
 NEXT:
 RECEIVE LOGIC (values SO: X'0E' or X'8E')
 Buffer(1), ... , (n) is a character in the received buffer.
 drop = false
 FOR i=1 to n /* for all octets of the buffer */
 IF drop = true
 THEN output (buffer(i) - X'20')
 drop = false
 ELSE IF buffer(i) = (X'0D' or X'8D')
 THEN Stop
 ELSE IF buffer(i) = SO
 THEN drop = true
 ELSE output (buffer(i))
 NEXT:
C.3. PAD Parameter Profile
 Before an (ODETTE-FTP) asynchronous entity --> Modem --> PAD -->
 (ODETTE-FTP) native X.25 link can be established, the target PAD
 parameters must be set such that correct communication is
 established. It is strongly recommended that the PAD parameters are
 set by the X.25 entity. CCITT recommendations X.3, X.28, and X.29
 define the PAD parameters and procedures for exchange of control
 information and user data between a PAD and a packet mode Data
 Terminal Equipment (DTE).
 Following is the Parameter list and values used to set the PAD for
 ODETTE-FTP communication. For further detailed information see the
 specification for CCITT X.25, X.28, X.29 and X.3.
 No. Description Value Meaning
 ---------------------------------------------------------------
 1 Escape from Data Transfer 0 Controlled by host
 2 Echo 0 No Echo
 3 Data Forwarding Signal 2 Carriage Return
 4 Selection of Idle Timer Delay 20 1 second
 5 Ancillary Device Control 0 X-ON, X-OFF not used
 6 PAD Service Signals 1 All except prompt
 7 Procedure on Break 2 Reset
 8 Discard Output 0 Do not discard
 9 Padding after Carriage Return 0 No padding
 10 Line Folding 0 No line folding
 11 Terminal Data Rate - Read only
 12 Flow Control of the PAD 0 No flow control used
 13 Linefeed Insertion after C/R 0 No linefeed
 14 Linefeed Padding 0 No linefeed padding
 15 Editing 0 No editing
 16 Character Delete 127 Delete
 17 Line Delete 24 <CTRL>X
 18 Line Display 18 <CTRL>R
 19 Editing PAD Service Signals 0 No service signal
 20 Echo Mask 0 No echo mask
 21 Parity Treatment 0 No parity check
 22 Page Wait 0 No page wait
 Note 1:
 Refer to CCITT (1984)
 - Parameters 1 - 12 are mandatory and available internationally.
 - Parameters 13 - 22 may be available on certain networks and may
 also be available internationally.
 - A parameter value may be mandatory or optional.
 The ODETTE profile refers only to parameter values which must be
 internationally implemented if the parameter is made available
 internationally.
 The ODETTE-FTP "special-logic" parameter may be impossible on some
 PADs because they do not support of some of the parameters (13 - 22).
 (If the PAD is supporting parity check (21) by default, ODETTE-FTP
 special logic would be impossible.)
 It is a user responsibility to ensure special logic consistency when
 making the PAD subscription.
 Note 2:
 Some parameters may have to be set differently depending on:
 - Make and function of the start-stop mode DTE entity.
 - Start-stop mode DTE entity ODETTE-FTP monitor function.
 - PAD services implemented.
 - Packet mode DTE entity ODETTE-FTP monitor function.
Appendix D. OFTP X.25 over ISDN Recommendation
 This appendix describes the recommendation of ODETTE Group 4 (1) for
 the use of OFTP (2) over X.25 over ISDN.
 (1) ODETTE Group 4 is responsible for the specification of
 Telecommunications standards and recommendations for use
 within the Automotive Industry.
 (2) OFTP (ODETTE File Transfer Protocol) is the communications
 standard specified by ODETTE Group 4 designed for the transfer
 of both EDI and non-EDI data.
 This document offers an introductory overview of a technical subject.
 It is structured to contain the ODETTE recommendation, together with
 introductory information for the person not familiar with ISDN, and
 notes on the issues associated with the implementation of the
 recommendation.
 The first section provides the detailed ODETTE recommendation, which
 is followed by a general discussion. If you are not familiar with
 the terminology, please read the subsequent sections first.
 How far an existing X.25 Line adapter may be replaced by an ISDN line
 adapter in an installation depends on the opportunities in view of
 connections (X.25 or ISDN) of the involved partners for file
 transfer.
 Companies that keep many connections to external partners (for
 example, car manufacturing companies) may use the OFTP file transfer
 in view of compatibility, which must always be considered anyway only
 in parallel to the X.25 network.
 It is not the aim of this recommendation to remove the OFTP file
 transfer generally from the X.25 network to the ISDN network. This
 will not always be possible for international connections because of
 technical reasons, and this does not always make sense for
 connections with a low size of data to be transmitted.
 Certainly, the use of ISDN, when exchanging a high volume of data
 (for example, CAD/CAM files), is very much cheaper than the use of an
 X.25 network. For such cases, this recommendation shall provide a
 cost-effective possibility for file transfer.
 This appendix is organized as follows. D.1 defines the ODETTE
 recommendation in these terms, D.2 introduces the ISDN environment to
 the unfamiliar reader, D.3 describes the various methods of
 connecting to ISDN, and D.4 covers implementation issues.
D.1. ODETTE ISDN Recommendation
 X.25: Level 2 ISO 7776
 Protocol
 Level 3 ISO 8208
 Protocol
 Packet Size 128
 Level 2 7
 Window Size
 Level 3 7
 Window Size
 First LCN 1
 Number of LCNs 1
 Facilities Window Size and Packet Size
 negotiation shall be supported
 by everybody. Call User Data
 should not be required.
 Calling NUA Optionally provided by the call
 initiator.
 Called NUA Should be set to a value where
 the last 'n' digits can be
 specified by the called party.
 ISDN: Apart from requesting a 64K unrestricted digital
 call, no ISDN features shall be required.
 Timeout control: To avoid connections (B channels) within the
 circuit-switched ISDN network remaining active
 but unused for a long time, the adapter should
 include a timeout control.
 An ISDN connection (B channel) should be released
 if no X.25 packets have been transmitted on this
 connection for a longer time. For flexibility a
 variable user definable timer should be
 incorporated into the adapter.
 In the event of a timeout situation the adapter
 has to release the ISDN connection and notify the
 local OFTP by the transmission of a clear packet.
 The pages that follow are informational and do not form part of this
 recommendation.
D.2. Introduction to ISDN
 The use of digital encoding techniques over such high-quality,
 error-free backbone networks has allowed the PTTs to offer high
 bandwidths to the end user. The service is named ISDN (Integrated
 Services Digital Network).
 The increasing need to transfer larger volumes of EDI data, in
 particular CAD/CAM drawings, has focused attention upon high-speed,
 low-cost communication. The traditional X.25 over a Packet Switched
 Data Network (PSDN) has been a good general purpose communications
 subsystem. Unfortunately, its cost and transfer speed make PSDN
 expensive for the new requirement.
 X.25 over the new ISDN provides both the transfer speed and cost
 benefits to satisfy the new requirements.
 We include the following terminology because for us to make sense of
 ISDN and X.25, it is important that we use definitions precisely and
 avoid the abuses of the past.
 ISDN: Integrated Services Digital Network
 X.25: X.25 is a communications protocol. It defines the
 structure of data packets that comprise the protocol and
 the manner in which they are used.
 PSDN: A PSDN (Packet Switched Data Network) is a network over
 which the X.25 protocol is operated.
 PSPDN: A PSPDN (Packet Switched Public Data Network) is a PSDN
 operated by the PTTs. PSPDNs are given trade names,
 such as PSS in the UK, Datex-P in Germany, and Transpac
 in France.
 BRI: Basic Rate Interface, also known as Basic Rate Access,
 defines an ISDN facility with 2 x 64 K B channels.
 PRI: Primary Rate Interface, also known as Primary Rate
 Access, defines an ISDN facility with 30 x 64 K B
 channels.
 Channels: ISDN is typically brought into a consumer's premises
 using a twisted pair of wire. Over this wire, data can
 be transmitted in frequency bands. These frequency
 bands are allocated as channels.
 B channels: The B channels are the data channels and operate at 64
 Kb. The two end users of a connection will communicate
 over a B channel.
 D channel: Signalling on ISDN is performed over the D channel.
 Signalling is used to set up and release connections on
 the B channels. In some countries, the D channel can
 also be used for limited X.25 access to the PTTs' PSDN.
 The D channel operates at the lower speed of 16 Kb as it
 is normally used only at the beginning and end of a
 connection.
 Bandwidth Allocation:
 2 Wire B2 - 64 Kb
 Twisted Pair B1 - 64 Kb
 D Channel - 16 Kb
 The standard for the operation of the D channel is
 called ETSI and is used in most European countries.
 However, some countries that started the introduction
 very early used proprietary standards, for example:
 1TR6 - Used in Germany
 BTNR - Used in the UK
 Although there are D channel variations, this will not
 affect communications over the B channels as the
 communication over the D channel is between the
 subscriber and the ISDN service provider.
 However, the consumer's equipment must be able to handle
 the channel D signalling operated by the ISDN service
 provider and so there may be a problem of equipment
 availability and certification.
 All the PTTs have committed to migrate to ETSI (also
 known as EURO-ISDN and Q.931) and many are currently
 supporting both their national variant and ETSI. It is
 advisable that in this situation the subscriber select
 the ETSI variant to avoid unnecessary equipment
 obsolescence.
 Services: The high-speed service is provided in two forms, Basic
 and Primary.
 Basic: 2+D, the D 2B channel operates at 16 Kb. The
 Basic Rate access is normally provided to the subscriber
 over simple twisted pair cable.
 Primary: 30B+D, the D channel operates at 64 Kb.
 Primary Rate access is normally provided to the
 subscriber over shielded coaxial cable. Note that the
 bandwidth for Primary is 2.048 Mbit/s.
 Protocols: The B channel is a binary channel and is transparent to
 the flow of data. Therefore, all of the currently
 available protocols can operate over a B channel. The
 most common protocol is X.25.
 X.25: The X.25 protocol is a primary protocol for open
 computer-to-computer communication.
 Passive Bus: It is possible to have an ISDN service enter a building
 and then have an 8-core cable laid within the building
 with multiple ISDN junction points, in the same way as
 one would have multiple telephone points (extensions)
 for a particular external telephone line.
 Connection Setup
 The adapter is responsible for analysing the outgoing X.25 call
 request and making an ISDN call to a derived ISDN address,
 establishing a new X.25 level-2 and level-3, and then propagating
 the X.25 Call Request Packet.
 Connection Termination
 The termination phase of the X.25 call is made with a Clear
 Request and finalised with a Clear Confirmation. The recipient of
 the Clear Confirm should then close down the ISDN connection.
 The clear down of the ISDN connection should only be made if there
 are no other Switched Virtual Circuits (SVCs) active on the ISDN
 connection; note that the usage of multiple simultaneous SVCs is
 only by virtue of bilateral agreement.
D.3. Equipment Types
 There are a number of ways in which ISDN/X.25 access can be made.
 Integrated Adapter
 This is normally a PC-based ISDN adapter inside a PC. It is
 normal in such an environment that the OFTP application has the
 ability to manipulate the ISDN and X.25 aspects of the session
 independently and therefore have complete control.
 Equally important is that the speed of communication between the
 adapter and the application are at PC BUS speeds. It is
 therefore more likely that the effective transmission speed will
 be nearer the 64K limit.
 The other benefit of such a direct linkage is that both 64K B
 channels may be used in parallel and both able to operate at
 64Kb.
 Elementary Terminal Adapter
 In this scenario, the computer has an integral X.25 adapter
 communicating X.21 with a Terminal Adapter that fronts the ISDN
 network. This allows a host with a X.25 capability to interface
 to ISDN, normally on a one-to-one basis.
 The interface between the Terminal Adapter and the PC will
 typically only support one 64K B channel. This is obviously an
 inefficient usage of the ISDN service.
 Because the linkage between the computer and the Terminal Adapter
 is only X.25, then some modification/configuration may be needed
 inside the Terminal Adapter when new users are added.
 X.25 Switch
 This solution is normally found inside the larger corporates
 where an internal X.25 network is operated or where dual X.25 and
 ISDN is required.
 The main benefit of a switch is to support both PSDN and ISDN
 simultaneously. Also, multiple X.21 lines may be implemented
 between the X.25 switch and the computer.
 This solution normally requires more effort to configure and may
 require obligations to be placed upon how incoming callers
 specify routing.
D.4. Implementation
 The adoption of ISDN as an additional subsystem to support OFTP
 communications has associated implementation problems, which can be
 categorised as below:
 X.25/ISDN Addressing
 Making a Call
 Receiving a Call
 Logical Channel Assignment
 Facilities Negotiation
 ISDN Call Attributes
 Homologation Issues
 Growth
 Performance
D.4.1. X.25/ISDN Addressing
 The original OFTP was designed to work over the X.25 networks
 provided by the PTTs (PSPDNs). The national X.25 networks were
 interconnected to provide a global X.25 network, and a common
 addressing scheme was adopted by all. Although there were a few
 differences in addressing within a national network, the interface to
 other countries was quite rigid and normalised.
 PSPDN Numbering
 The addressing scheme adopted in X.25 is a 15-digit number
 (Network User Address, NUA) where the first three identify the
 country, the fourth digit identifies the network within the
 country, and the remainder specify the individual subscriber plus
 an optional subaddress. In the UK where a full X.25 numbering
 scheme is adopted, a NUA is, e.g., 234221200170, where 2342 is the
 DNIC (Data Network Identification Code) and 21200170 is the
 subscriber number.
 ISDN Numbering
 ISDN is an extension of the normal telephone system; consequently,
 it adopts (or rather is) the same numbering scheme as the
 telephone system (PSTN).
 The Numbering Conflict
 The PSDN and PSTN numbering schemes are two totally different
 numbering schemes. There is no relationship between them. It is
 this conflict that is at the heart of the matter.
D.4.2. Making a Call
 It is a consequence of PSDN and PSTN being based upon different and
 unconnected numbering schemes that the key problem arises.
 For X.25 to work over ISDN, three main methods of addressing are
 available:
 Un-mapped: The X.25 called NUA is used as the PSTN number. Thus,
 an X.25 call to 0733394023 will result in a PSTN call
 to 0733394023 and the call request that consequently
 flows will also be to 0733394023.
 Manipulated: The X.25 called NUA is manipulated by the subtraction
 and/or addition of digits to derive a resultant PSTN
 number. Thus, 2394023 could be manipulated to derive
 a PSTN number of 00944733394023, where the prefix 2 is
 deleted and replaced by 00944733.
 Mapped: The X.25 called NUA is used as a look-up into a table
 of PSTN numbers. Thus, an X.25 call to 234221200170
 could be mapped to and result in a PSTN call to
 0733394023 and the call request that consequently
 flows will remain as 234221200170.
 Un-mapped Calls
 Un-mapped calls are where the host-specified X.25 NUA is converted
 directly to the corresponding ISDN number.
 Thus, an X.25 call issued by the host to X.25 NUA 0733394023 will
 result in an ISDN call to the PSTN number 0733394023. After the
 call has been established, then HDLC/X.25 protocol setup will be
 established after which an X.25 call request will be transferred
 with the NUA 0733394023.
 When a PSTN call is made, the number of digits in the called
 number vary depending upon the location of the called party.
 When a number is called, it may be local, national, or
 international.
 local: 394023
 national: 0733 394023
 international: 009 44 733 394023
 Depending upon where a call originates, the corresponding X.25 NUA
 in the call request packet will vary dramatically.
 Such variation of X.25 NUA, in particular the changing prefix, can
 be difficult to be accommodated by X.25 routing logic in many
 products.
 When an international PSTN call is being made, then it is likely
 that the PSTN number exceeds 15 digits, which is the maximum
 length of an X.25 NUA. Therefore, using un-mapped addressing may
 make some international calls impossible to make.
 Manipulated Calls
 The X.25 called NUA is manipulated by the subtraction and/or
 addition of digits to derive a resultant PSTN number.
 Let us assume that by internal convention we have identified the
 prefix '2' to indicate an international ISDN call. Thus, an X.25
 call request of 244733394023 could be manipulated to derive a PSTN
 number of 00944733394023, where the prefix '2' is deleted and
 replaced by '009' (the international prefix).
 The X.25 called NUA would typically be left in its un-manipulated
 state. As individual internal conventions vary, the X.25 called
 NUA will vary. In the case above, it would be 244733394023, but
 another installation might have the convention where a prefix of
 '56' specifies the UK and so the NUA will be 56733394023, where
 the '56' is deleted and replaced with '00944' to derive the PSTN
 number.
 Mapped Calls
 The mapped method offers maximum flexibility in that:
 The PSTN number can exceed 15 digits.
 The X.25 NUA and PSTN number can be totally different.
 The problem with mapped calls is administrative. IBM mainframes
 can't handle X.25 over ISDN at all, let alone support mapping.
 For the mainframe solution to work, an external X.25/ISDN router
 box is required and it is the responsibility of the external box
 to provide any mapping necessary.
 This means that any changes or addition of OFTP partners over ISDN
 will require access to the computer room or special configuration
 equipment to change the tables inside the external X.25/ISDN
 router box.
D.4.3. Receiving a Call
 We have seen from the previous section that the called X.25 NUA
 from an ISDN incoming call may vary considerably. If ISDN/X.25 is
 confined to a national boundary, then such variation will not be
 so great as most calls will have matching called X.25 NUA and PSTN
 numbers.
 X.25 switches and X.25 adapters normally route/accept/reject calls
 based upon their X.25 called NUA. In particular, routing is made
 upon the X.25 called NUA subaddress.
 To derive this subaddress, there are 2 methods:
 1) the last 'n' digits are analysed.
 2) the base X.25 NUA of the line is removed from the called NUA.
 For example, if the called X.25 NUA is 23422120017010 and the
 PSDN subscriber NUA is 234221200170, then the subaddress
 derived from subtraction is 10.
 Obviously, the second method will not work if the incoming NUA
 varies.
 ISDN Features
 ISDN, like X.25, has a core set of features that are then enriched
 with options. In the original OFTP X.25 specification, it was
 decided that the Q-bit and D-bit options were not common to all
 networks or applications; they were therefore positively excluded
 from the specification.
 It is proposed that apart from the core ISDN features necessary to
 establish a call, no other features be used.
 Subaddressing
 There are two forms of ISDN subaddressing, overdialled and specific.
 The overdial method allows an ISDN number to be artificially
 extended. A typical case would be where a private exchange has been
 installed in a larger company. Assume that the base number is
 394023 and the computer is on internal extension 1234, then by
 specifying an ISDN number of 3940231234, direct access may be made
 to the internal extension.
 The problem with this method is that it extends to called number and
 may, especially for international access, exceed the ISDN numbering
 limits between countries.
 The other method of subaddressing is where a discrete subaddress is
 placed in a specific field in the ISDN call setup.
 The problem with this method, is that it requires the caller to
 place the subaddress in the ISDN call setup. Not all ISDN
 implementations will allow this insertion.
 In conclusion, subaddressing of any kind should be avoided.
D.4.4. Logical Channel Assignment
 An X.25 dataline will have associated with it a number of logical
 channels.
 The number of channels is a part of the agreement between the PTT
 and the subscriber. The number of channels subscribed to is
 important; call failure and similar problems will result if the
 number of logical channels defined at the two remote ends are
 different.
 If a DTE makes a call out, then the highest defined logical channel
 number will be selected. If the remote Data Communications
 Equipment (DCE) does not have the same number of logical channels
 defined, then an invalid logical channel is being used from the
 perspective of the recipient DCE and the call will be rejected.
D.4.5. Facilities Negotiation
 In the PSPDN environment, it is possible to subscribe to negotiation
 of window size and packet size. Although this negotiation requested
 by the originator's DTE may be propagated to the remote DTE at the
 discretion of the originator's DCE, it is a local responsibility
 between the DTE and DCE pair.
 In the ISDN scenario where it is a DTE-DTE type connection, the
 window size and packet size may be left at the default value and
 consequently the values may be omitted from the call request. If no
 values are specified, then it is vital that both DTEs have
 configured themselves to the recommended defaults.
 The symptom of a window size mismatch is a hang situation without
 any informational error codes.
 The symptoms of a packet size mismatch could work in some scenarios,
 but would otherwise issue error codes indicating invalid packet
 sizes.
 Window Size
 The CCITT X.25 window size has a default value of '2', although
 subscribers may have other default window sizes, e.g., '7', by
 virtue of agreement with the PTT.
 Window size negotiation can be explicitly requested by specifying
 the requested window size in the Facilities fields in the Call
 Request packet.
 Packet Size
 The CCITT X.25 packet size has a default value of '128' octets,
 although subscribers may have other default values, e.g., '1024',
 agreed with the PTT.
D.4.6. ISDN Call Setup
 The initial setup of an ISDN call is initiated with the
 transmission of a Q.931 SETUP command. Apart from requesting that
 a call be established, the SETUP command can optionally carry
 information about the calling party, the called party, routing
 information, the type of circuit required (e.g., voice or data),
 and information about the protocols that are requested to be
 established.
 Setup Parameters:
 Bearer capability Information transfer and
 access attributes
 Called Party number Destination's network address
 Called Party subaddress Destination's complete
 address
 Calling Party number Source's network address
 Low-layer compatibility Layer 1-3 indication
 High-layer compatibility Layer 4-7 indication
D.4.7. Homologation Issues
 Homologation procedures were adopted and vigorously enforced by the
 PTTs with respect to the quality and conformance of communications
 equipment connected to the services provided by the PTTs.
 In particular, commercial X.25 products had to be tested and approved
 before they could be connected to the PTTs' PSPDN. The advantage of
 this to the subscriber was that there was very little chance of the
 approved equipment not working.
 With ISDN, similar approval standards are still enforced. So the
 subscriber has the same confidence in their ISDN equipment. Wrong,
 the ISDN equipment itself is approved, but the X.15 protocol that
 operates on top of ISDN is now outside of the scope of approval
 services.
 This means that quality of conformance to standards of X.25 over ISDN
 is subject to the variable quality procedures within the various ISDN
 equipment manufacturers.
 Although it is likely that commercial reputation will place pressure
 upon the manufacturers with a programming bug to correct such errors,
 it still requires the subscribers that do not communicate well to put
 time and effort into finding the party with the error.
 So far, tests have shown a number of subtle errors, such as timing
 problems, that have taken many days to find, prove, and fix.
D.4.8. Growth
 Primary Rate Access
 If a user decides to plan for growth from the beginning, then the
 Primary Rate Access has apparent financial benefits. Such
 apparent savings are usually lost due to the increased cost of
 user hardware to support such an interface. The BRI for data
 usage is very common and cards/adapters are low in cost, whereas
 the PRI cards/adapters are few and far between and consequently
 highly priced.
 Basic Rate Access
 One way to grow with ISDN is to buy multiple BRI lines, increasing
 slowly in units of 2 x B channels. The PTTs will be able to
 provide the same subscriber number for all the lines provided in a
 similar way to the traditional hunting group associated with PSTN
 type working.
D.4.9. Performance
 The obvious benefit of ISDN is speed; unfortunately, the majority
 of computer systems in use today have a finite amount of computing
 power available. The attachment of multiple active high-speed
 communication lines used in file transfer mode could take a
 significant amount of CPU resource to the detriment of other users
 on the system.
 Connecting an ISDN line with the default 2 B channels to your
 computer using an X.21 interface is going to give a consistent 64
 Kb throughput only if one of the B channels is active at any one
 time.
 If there are two 64 Kb channels active and contending for a single
 64 Kb X.21 interface, then effective throughput will be reduced
 significantly to just over 50%.
 Mainframe issues:
 Users with a mainframe front-end are also going to find cost an
 issue. The scanners that scan the communications interfaces are
 based upon aggregate throughput. A 64 Kb interface takes up a lot
 of cycles.
 Determining 'DTE' or 'DCE' Characteristics
 The following section is an extract from the ISO/IEC 8208
 (International Standards Organization, International
 Electrotechnical Commission) (1990年03月15日) standard, which is an
 ISO extension of the CCITT X.25 standard.
 The restart procedure can be used to determine whether the DTE
 acts as a DCE or maintains its role as a DTE with respect to the
 logical channel selection during Virtual Call establishment and
 resolution of Virtual Call collision.
 When prepared to initialise the Packet Layer, the DTE shall
 initiate the restart procedure (i.e., transmit a RESTART REQUEST
 packet). The determination is based on the response received from
 the data exchange equipment (DXE) as outlined below.
 a) If the DTE receives a RESTART INDICATION packet with a
 restarting cause code that is not 'DTE Originated' (i.e., it
 came from a DCE), then the DTE shall maintain its role as a DTE.
 b) If the DTE receives a RESTART INDICATION packet with a
 restarting cause code of 'DTE Originated' (i.e., it came from
 another DTE), then the DTE shall confirm the restart and act as
 a DCE.
 c) If the DTE receives a RESTART INDICATION packet with a
 restarting cause code of 'DTE Originated' (i.e., it came from
 another DTE) and it does not have an unconfirmed RESTART REQUEST
 packet outstanding (i.e., a restart collision), then the DTE
 shall consider this restart procedure completed but shall take
 no further action except to transmit another RESTART REQUEST
 packet after some randomly chosen time delay.
 d) If the DTE issues a RESTART REQUEST packet that is subsequently
 confirmed with a RESTART CONFIRMATION packet, then the DTE shall
 maintain its role as a DTE.
Acknowledgements
 This document draws extensively on revision 1.4 of the ODETTE File
 Transfer Specification [OFTP].
 Many people have contributed to the development of this protocol and
 their work is hereby acknowledged.
Normative References
 [CMS-Compression]
 Gutmann, P., "Compressed Data Content Type for
 Cryptographic Message Syntax (CMS)", RFC 3274, June 2002.
 [CMS] Housley, R., "Cryptographic Message Syntax (CMS)", RFC
 3852, July 2004.
 [ISO-646] International Organisation for Standardisation, ISO
 Standard 646:1991, "Information technology -- ISO 7-bit
 coded character set for information interchange", 1991.
 [PKCS#1] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
 Standards (PKCS) #1: RSA Cryptography Specifications
 Version 2.1", RFC 3447, February 2003.
 [TLS] Dierks, T. and E. Rescorla, "The Transport Layer Security
 (TLS) Protocol Version 1.1", RFC 4346, April 2006.
 [UTF-8] Yergeau, F., "UTF-8, A Transformation Format of ISO
 10646", STD 63, RFC 3629, November 2003.
 [ZLIB] Deutsch, P. and J-L. Gailly, "ZLIB Compressed Data Format
 Specification version 3.3", RFC 1950, May 1996.
Informative References
 [ISO-6523] International Organisation for Standardisation, ISO
 Standard 6523:1984, "Data interchange -- Structures for
 the identification of organisations", 1984.
 [OFTP] Organisation for Data Exchange by Tele Transmission in
 Europe, Odette File Transfer Protocol, Revision 1.4, April
 2000.
 [FTP] Postel, J. and J. Reynolds, "File Transfer Protocol", STD
 9, RFC 959, October 1985.
 [RFC793] Postel, J., "Transmission Control Protocol", STD 7, RFC
 793, September 1981.
 [RIME] Coleridge, Samuel Taylor, "The Rime of the Ancient
 Mariner", 1817.
 [X.509] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
 X.509 Public Key Infrastructure Certificate and
 Certificate Revocation List (CRL) Profile", RFC 3280,
 April 2002.
 [RFC3850] Ramsdell, B., "Secure/Multipurpose Internet Mail
 Extensions (S/MIME) Version 3.1 Certificate Handling", RFC
 3850, July 2004.
ODETTE Address
 The ODETTE File Transfer Protocol is a product of the Technology
 Committee of Odette International. The Technology Committee can be
 contacted via the ODETTE Central Office:
 ODETTE INTERNATIONAL Limited
 Forbes House
 Halkin Street
 London
 SW1X 7DS
 United Kingdom
 Phone: +44 (0)171 344 9227
 Fax: +44 (0)171 235 7112
 EMail: info@odette.org
 URL: http://www.odette.org
Author's Address
 Ieuan Friend
 Data Interchange Plc
 Rhys House
 The Minerva Business Park
 Lynchwood
 Peterborough
 PE2 6FT
 United Kingdom
 Phone: +44 (0)1733 371 311
 EMail: ieuan.friend@dip.co.uk
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 ietf-ipr@ietf.org.