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RFC 1415             FTP-FTAM Gateway Specification         January 1993


7. Functional Comparison of FTP and FTAM

   A comprehensive comparison of the services offered by FTP and FTAM is
   beyond the scope of this specification.  What follows is an analysis
   of several key points.  Refer to [NIST 86a] and [ROSE90] for a more
   complete discourse on this topic.

   FTAM is not a superset of FTP; each protocol has functions that only
   it performs.  The set of FTAM functions is, however, larger than the
   set of FTP functions.

   FTP combines file management and file transfer into one protocol
   engine, whereas FTAM separates management and transfer as they relate
   to files.

   The file transfer services of both FTP and FTAM expect a reliable
   underlying end-to-end service.  At a minimum, this service includes
   the capability to transfer entire files between remote hosts and to
   display remote filenames.

   In addition to this basic file transfer service, FTAM supports the
   capability to:  access a few records from a file server, create a
   network file system (similar to Sun's Network File System), handle
   printing and spooling, and access remote database records.  FTP does
   not support these additional capabilities.

   FTP uses TELNET services to set up a connection between the FTP
   Client and FTP Server.  A three-digit reply code followed by
   explanatory text indicates the status of the preceding request and
   provides diagnostic information explaining each transaction.

   FTAM relies on the Association Control Service Element (ACSE) to
   start and stop the network for network file interaction.  Generally,
   the ASCE establishes the application association and related
   application context needed to support the FTAM protocol.

   The FTAM protocol is modularized so as to keep the allowable number
   of actions in any particular state relatively small.  There are many
   more possible sequences of FTP operations than possible sequences of
   FTAM operations [NIST86].

   Because FTAM is more robust than FTP, FTAM allows greater flexibility
   for conveying information about files.  FTAM deals only with aspects
   of application processes, and leaves data representation and data
   management facilities to other OSI service elements.

   In contrast to the Client/Server model present in the FTP scheme,
   FTAM is based on the Initiator/Responder model.  The key distinction



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RFC 1415             FTP-FTAM Gateway Specification         January 1993


   is that once the FTAM Initiator has established a connection with a
   remote host, either the Initiator or Responder can request services
   of the other.  In the FTP realm, the Client both initiates a
   connection and requests all services.

   The FTP Client knows the real properties of the remote host
   filesystem.  FTAM, in contrast, embraces a conceptual model of a
   filesystem, labeled a virtual filestore model.  The virtual filestore
   is a collection of files, each of which has a name that uniquely
   identifies it.  Each file has a set of attributes, such as ownership
   information and contents, which is the data associated with the file.
   One file attribute is the <Contents Type> of the file, typically of
   value "FTAM-1", "FTAM-3", or "NBS-9".  The FTAM Initiator only knows
   the properties of the corresponding Responder and virtual filestore,
   not the real properties of the filesystem on the remote host.

7.1. Loss of Functionality

   As happens whenever two dissimilar protocols, or languages for that
   matter, are translated, some loss of functionality is inevitable.
   With reference to the FTP-FTAM gateway, several of the most blatant
   losses of functionality are:

        1. Diagnostics passed between protocols may not be precisely
           translated.

        2. The FTAM partial file (record) transfer may not be
           supported.

        3. Some FTAM attributes are not supported by FTP.

   The primary goal of the gateway protocol mappings are to minimize
   this loss of functionality. As this gateway specification and
   subsequent implementations evolve, means to partially overcome loss
   of functionality may become more obvious.  For example, the gateway
   may be able to emulate file record transfers between FTAM Initiators
   and FTP Servers.

8. Mapping of Protocol Functions and Representations

   The mappings presented are based upon the FTAM protocol
   implementation as defined in Stable Implementation Agreements for
   Open Systems Interconnection Protocols:  Part 9 - FTAM Phase 2,
   produced by the March 1992 Open Systems Environment Implementors'
   Workshop [NIST92], and in [ISO8571-1], [ISO8571-2],[ISO8571-
   3],[ISO8571-4], and [ISO8571-5].  The FTP protocol as defined in
   Request for Comments [RFC959].   The mappings are strongly influenced
   by the work of M. A. Wallace et. al. at NIST [NIST86] and John Scott



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RFC 1415             FTP-FTAM Gateway Specification         January 1993


   at MITRE [MITRE87].

   A key goal of the mappings presented in this document is to minimize
   the loss of functionality between the two protocols.  The specific
   approach taken to implement the mappings is left to the discretion of
   the gateway implementor.  The focus of the protocol function and
   representation mappings is on non-error encumbered processing.  The
   mapping of diagnostic and error messages is treated separately in
   section 9.

   At a minimum, the FTAM implementation in the FTP-FTAM gateway support
   for Implementation Profiles T1 (Simple File Transfer) and M1
   (Management), as defined in [NIST92], is required.  These
   Implementation Profiles correspond to the A/111 and A/13 Profiles of
   Standards Promotion and Application Group in Europe, respectively
   [NIST92].

   At a minimum, the gateway support for the following is required:

      ASCII and 8 bit binary file types.  It should also support FTP
      File Stream Mode.

      The following FTAM document types: FTAM-1 (unstructured text
      file), FTAM-3 (unstructured binary file), and NBS-9 (set of
      directory entries).

   POSIX file naming and organization conventions are assumed in these
   mappings; i.e., files in the systems are assumed to be organized in a
   hierarchical structure in which all of the non-terminal nodes are
   directories and all of the terminal nodes are any other type of file.

   The following terminology is used in the mapping specifications:

      argument .......FTP Service Command argument, as used in [RFC959].

      parameter ......FTAM Service Primitive parameters and attributes,
                      as enumerated in Tables 6, 50, and 51 of [ISO8571-
                      3].

   The following notation is used in the mapping specifications:

      Arguments and parameters are enclosed in angle brackets; e.g.,
      <Action Result>

      Values of arguments and parameters are enclosed in quotation
      marks; e.g., "Success"





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RFC 1415             FTP-FTAM Gateway Specification         January 1993


      FTP Service Commands and FTAM Primitives are in uppercase; e.g., F-
      INITIALIZE

8.1.  FTP-Initiated Gateway Service

   The protocol mapping between FTP and FTAM may be one-to-zero (i.e.,
   not mappable), one-to-one, or one-to-many.

   The general steps taken by the FTP-FTAM gateway to provide the FTP-
   Initiated service are:

        1. Accept an FTP Client request at the FTP Server side of the
           gateway service.

        2. Map the request to the (set of) corresponding FTAM
           Initiator function(s).

        3. Acting as an FTAM Initiator, send the FTAM Initiator
           function(s) to the FTAM Responder.

        4. Accept information returned to the FTAM Initiator side of
           the gateway.  This information originated at the FTAM
           Responder.

        5. Map this returned information to the protocol form
           understood by the FTP Server side of the gateway.

        6. Send this returned information from the FTP Server side of
           the gateway to the FTP Client.

   For each FTP protocol function, the FTAM protocol functions required
   to map it are identified:

   FTP       FTAM

   ------------------------------------------------------------------

   ABOR      F-BEGIN-GROUP, F-CANCEL, F-CLOSE, F-DESELECT, F-END-GROUP

   ACCT      F-INITIALIZE,

   ALLO      none

   APPE      F-BEGIN-GROUP, F-CLOSE, F-CREATE, F-DATA, F-DATA-END, F-
             DESELECT, F-END-GROUP, F-OPEN, F-READ-ATTRIBUTES, F-SELECT,
             F-TRANSFER-END, F-WRITE

   CDUP      F-BEGIN-GROUP, F-DESELECT, F-END-GROUP, F-SELECT



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RFC 1415             FTP-FTAM Gateway Specification         January 1993


   CWD       F-BEGIN-GROUP, F-END-GROUP, F-DESELECT, F-SELECT

   DELE      F-BEGIN-GROUP, F-DELETE, F-END-GROUP, F-SELECT

   HELP      none

   LIST      F-BEGIN-GROUP, F-CLOSE, F-DATA, F-DATA-END, F-DESELECT, F-
             END-GROUP, F-OPEN, F-READ, F-READ-ATTRIBUTES, F-SELECT, F-
             TRANSFER-END

   MKD       none

   MODE      none

   NLST      F-BEGIN-GROUP, F-CLOSE, F-DATA, F-DATA-END, F-DESELECT, F-
             END-GROUP, F-OPEN, F-READ, F-SELECT, F-TRANSFER-END

   NOOP      none

   PASS      F-INITIALIZE

   PASV      none

   PORT      none

   PWD       F-BEGIN-GROUP, F-DESELECT, F-END-GROUP, F-READ-ATTRIBUTES,
             F-SELECT

   QUIT      F-P-ABORT or F-U-ABORT, F-TERMINATE

   REIN      F-BEGIN-GROUP, F-CANCEL, F-CLOSE, F-DESELECT, F-END-GROUP

   REST      F-CHECK, F-RESTART

   RETR      F-BEGIN-GROUP, F-CLOSE, F-DATA, F-DATA-END, F-DESELECT, F-
             END-GROUP, F-OPEN, F-READ, F-SELECT, F-TRANSFER-END

   RMD       none

   RNFR      F-BEGIN-GROUP, F-DESELECT, F-END-GROUP, F-SELECT

   RNTO      F-BEGIN-GROUP, F-CHANGE-ATTRIBUTES, F-DESELECT, F-END-
             GROUP, F-SELECT

   SITE      F-INITIALIZE

   SMNT      none




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RFC 1415             FTP-FTAM Gateway Specification         January 1993


   STAT      none

   STOR      F-BEGIN-GROUP,F-CLOSE, F-CREATE, F-DATA, F-DATA-END, F-
             DESELECT, F-END-GROUP, F-OPEN, F-READ-ATTRIBUTES, F-SELECT,
             F-TRANSFER-END, F-WRITE

   STOU      F-BEGIN-GROUP, F-CLOSE, F-CREATE, F-DATA, F-DATA-END, F-
             DESELECT, F-END-GROUP, F-OPEN, F-READ-ATTRIBUTES, F-SELECT,
             F-TRANSFER-END, F-WRITE

   STRU      none

   TYPE      none

   USER      F-INITIALIZE

   The remainder of this section presents detailed mapping procedures
   for each of the FTP protocol functions.  Gateway support for these
   mappings is required.

8.1.1. ABOR

        1. Send F-CANCEL to FTAM Responder.
        2. Send the following grouped request to the FTAM Responder.
           F-BEGIN-GROUP
           F-CLOSE
           F-DESELECT
           F-END-GROUP
        3. Translate FTAM Responder <Action Result> and <Diagnostic>
           parameters to equivalent FTP reply code(s) and send reply
           codes to FTP Client.
        4. Translate FTP Client reply codes to equivalent FTAM <Action
           Result> and <Diagnostic> parameters and send parameters to
           FTAM Responder.

8.1.2. ACCT

        1. Set <Account> parameter value for issuing F-INITIALIZE to
           FTAM Responder.
        2. If <Called Presentation Address>, <Initiator Identity>, and
           <Filestore Password> parameters are available, attempt
           connection with FTAM Responder;
           Otherwise wait for additional ACCT commands.
        3. Translate FTAM Responder <Action Result> and <Diagnostic>
           parameters to equivalent FTP reply code(s) and send reply
           codes to FTP Client.
        4. Translate FTP Client reply codes to equivalent FTAM <Action
           Result> and <Diagnostic> parameters and send parameters to



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RFC 1415             FTP-FTAM Gateway Specification         January 1993