between a pair of hosts utilizing the same file transfer protocol.   The latter, more transparent method does not necessarily require that   the user determine which gateway is most appropriate for their   respective source-destination pair.  In fact, filestore service   providers are registered using the address of a predetermined   gateway.  With this approach, the user:       1. Must be aware that a gateway is required to reach the          destination FTP or FTAM host.       2. Need not determine which gateway is most appropriate to          access their ultimate destination host.       3. Need not explicitly connect to the gateway prior to          connecting to the destination FTP or FTAM host.5. Gateway State Variables and Transitions   As described, the FTP-FTAM gateway provides two sets of services:   FTP-Initiated and FTAM-Initiated.  Each service has its own mutually   exclusive set of state variables and transitions that   deterministically define the actions of the gateway.  Gateway support   for these state variables and transitions is required.   For conciseness in this discussion, FTP-Initiated will be abbreviated   with "FTP-I", and FTAM-Initiated will be abbreviated with "FTAM-I".   Concerning error conditions, if a connection is dropped when the   gateway is in any state other than FTP-I:Initial-State or FTAM-   I:Initial-State, then the gateway will issue a fatal error message to   the host with the remaining connection, and then drop that   connection.  If the remaining host is an FTP Client, then the gateway   will send an ABOR, QUIT, and 426 reply code (Connection closed,Mindel & Slaski                                                [Page 13]RFC 1415             FTP-FTAM Gateway Specification         January 1993   transfer aborted).  If it is an FTAM Initiator, then the gateway will   send an F-P-ABORT with a <Diagnostic> value with identifier 1011   (Lower layer failure), as well as any known <Further Details>.   Other error conditions are not addressed in this discussion.5.1. FTP-Initiated Gateway Service   The set of state variables for the FTP-Initiated Gateway service   follow:  State Variable                State Definition  ----------------------------------------------------------------  FTP-I:Initial-State           Initial state of FTP-Initiated Gateway                                service.                                Gateway is waiting for an FTP Client to                                issue a USER command in order to                                proceed with connection establishment                                with remote FTAM Responder.  If SITE or                                ACCT commands are sent while waiting                                for USER command, save arguments for                                subsequent use.  FTP-I:Wait-for-PASS           Gateway has already received USER                                command from FTP Client, as well as                                userid and destination host DN.                                Gateway is waiting for the FTAM                                Responder logon password.  FTP-I:Wait-for-PAddress       Gateway has already received PASS                                command from FTP Client.  Gateway is                                resolving the provided FTAM Responder's                                address to a Presentation Address.  The                                provided address may be a Distinguished                                Name, User Friendly Name, or Domain                                Name.  Resolution will typically be                                done using X.500 directory services.  FTP-I:Wait-for-Connection     Gateway has initiated a connection to                                the FTAM Responder and is waiting for                                notification as to whether or not the                                logon is successful.  FTP-I:Wait-for-ClientCmd      Connection exists between FTP Client                                and FTAM Responder.  Gateway is waiting                                for next command or response from FTPMindel & Slaski                                                [Page 14]RFC 1415             FTP-FTAM Gateway Specification         January 1993                                Client.  Commands and responses are                                mapped as they are received.  FTP-I:Wait-for-RespondrCmd    Connection exists between FTP Client                                and FTAM Responder.  Gateway is waiting                                for next command or response from FTAM                                Responder.  Commands and responses are                                mapped as they are received.   Each of the possible state transitions is provided in the remainder   of Section 5.1.  For each state transition, the actions causing the   transition are listed.5.1.1. FTP-I:Initial-State   -->   FTP-I:Initial-State        1. Gateway receives SITE or ACCT command from FTP Client.           SITE argument includes Distinguish Name of FTAM Responder.5.1.2. FTP-I:Initial-State   -->   FTP-I:Wait-for-PASS        1. Gateway receives USER command from FTP Client.  Arguments           include Distinguished Name of FTAM Responder and userid on           FTAM responder.5.1.3. FTP-I:Wait-for-PASS   -->   FTP-I:Wait-for-PAddress        1. Gateway receives PASS command from FTP Client.5.1.4. FTP-I:Wait-for-PAddress   -->   FTP-I:Wait-for-Connection        1. Gateway resolves received Distinguished Name, User Friendly           Name, or Domain Name of FTAM Responder to OSI Presentation           address.        2. Gateway sends F-INITIALIZE to FTAM Responder with           Presentation Address in <Called Presentation Address>,           userid in <Initiator Identity>, and password in <Filestore           Password>.5.1.5. FTP-I:Wait-for-Connection   -->   FTP-I:Wait-for-NextMapping        1. Gateway receives <State Result> of "Success" .        2. Gateway sends 230 reply code (User Logged In) to FTP           Client.5.1.6. FTP-I:Wait-for-ClientCmd   -->   FTP-I:Wait-for-RespondrCmd        1. Gateway receives command or response from FTP Client and           maps it to FTAM protocol, as defined in section 8.1.Mindel & Slaski                                                [Page 15]RFC 1415             FTP-FTAM Gateway Specification         January 19935.1.7. FTP-I:Wait-for-RespondrCmd   -->   FTP-I:Wait-for-ClientCmd        1. Gateway receives command or response from FTAM Responder           and maps it to FTP protocol, as defined in section 8.1.5.1.8. FTP-I:Wait-for-ClientCmd   -->   FTP-I:Wait-for-USER        1. Gateway receives QUIT command from FTP Client; maps QUIT as           per Section 8.1.5.2. FTAM-Initiated Gateway Service   The set of state variables for the FTAM-Initiated Gateway service   follow:  State Variable                State Definition  ----------------------------------------------------------------  FTAM-I:Initial-State          Initial state of FTAM-Initiated Gateway                                Service.                                Gateway is waiting for an FTAM                                Initiator to issue an F-INITIALIZE                                command in order to proceed with                                connection establishment with remote                                FTP Server.  FTAM-I:Wait-for-IPAddress     Gateway has already received F-                                INITIALIZE from FTAM Initiator.                                Gateway is resolving the provided FTP                                Server's address to an IP address.  The                                provided address may be a Domain Name,                                Distinguished Name, or User Friendly                                Name.  FTAM-I:Wait-for-Connection    Gateway has initiated a connection to                                the FTP Server and is waiting for                                notification as to whether or not the                                logon is successful.  FTAM-I:Wait-for-InitiatrCmd   Connection exists between FTAM                                Initiator and FTP Server.  Gateway is                                waiting for next command or response                                from FTAM Initiator.  Commands and                                responses are mapped as they are                                received.Mindel & Slaski                                                [Page 16]RFC 1415             FTP-FTAM Gateway Specification         January 1993  FTP-I:Wait-for-ServerCmd      Connection exists between FTAM                                Initiator and FTP Server.  Gateway is                                waiting for next command or response                                from FTP Server.  Commands and                                responses are mapped as they are                                received.   Each of the possible state transitions is provided in the remainder   of Section 5.2.  For each state transition, the actions causing the   transition are listed.5.2.1. FTAM-I:Initial-State   -->   FTAM-I:Wait-for-IPAddress        1. Gateway receives F-INITIALIZE from FTAM Initiator.  Domain           Name of FTP Server is either in <Responding Presentation           Address> or in the "@host" portion of the <Initiator           Identity> parameter.  The userid is in <Initiator           Identity>, and password is in <Filestore Password>           parameter.5.2.2. FTAM-I:Wait-for-IPAddress   -->   FTAM-I:Wait-for-Connection        1. Gateway resolves received Domain Name, Distinguished Name,           or User Friendly Name of FTP Server to IP address.        2. Gateway sends USER to FTP Server.        3. Gateway sends PASS to FTP Server.5.2.3. FTAM-I:Wait-for-Connection  -->   FTAM-I:Wait-for-NextMapping        1. Gateway receives 230 reply code (User Logged In) from FTP           Server.        2. Gateway sends <State Result> of "Success" to FTAM           Initiator.5.2.4  FTAM-I:Wait-for-InitiatrCmd   -->   FTAM-I:Wait-for-ServerCmd        1. Gateway receives command or response from FTAM Initiator           and maps it to FTP protocol, as defined in section 8.2.5.2.5. FTAM-I:Wait-for-ServerCmd   -->   FTAM-I:Wait-for-InitiatrCmd        1. Gateway receives command or response from FTP Server and           maps it to FTAM protocol, as defined in section 8.2.5.2.6. FTAM-I:Wait-for-InitiatrCmd  -->  FTAM-I:Wait-for-INITIALIZE        1. Gateway receives F-CLOSE primitive from FTAM Initiator;           maps F-CLOSE as per Section 8.2.Mindel & Slaski                                                [Page 17]RFC 1415             FTP-FTAM Gateway Specification         January 19936. Document Type Support   The set of FTAM document types supported by the FTP-FTAM gateway is a   subset of the document types identified in the Stable Implementation   Agreements for Open Systems Interconnection Protocols:  Part 9 - FTAM   Phase 2, produced by the March 1992 Open Systems Environment   Implementors' Workshop [NIST92].  This subset was chosen for its   equivalence to those document types supported by FTP.  The set   includes:                FTAM-1    "ISO FTAM Unstructured text file                FTAM-3    "ISO FTAM Unstructured binary file                NBS-9     "NBS-9 FTAM File directory file"      FTAM document types map to FTP document types as follows:                FTAM      <->       FTP                ----------------------------------                FTAM-1    <->       ASCII                FTAM-3    <->       8 bit binary                NBS-9     <->       Directory   Gateway support for FTAM-1 and FTAM-2 is required, whereas support   for NBS-9 is recommended.6.1. Notes on NBS-9   NBS-9 is optional in GOSIP versions 1 and 2 [NIST91].  NBS-9 will be   superseded by its replacement when ISO/IEC ISP 10607-2 and ISO/IEC   ISP 10607-2/Amendment 1 are published [NIST92].   For conformance to NBS-9, an FTAM Responder is only required to   return the <Filename> file attribute, subject to local security and   access control.  All other requested attributes need not be returned.   Systems supporting the NBS-9 document type shall make available an   NBS-9 document called 'DIRLIS'.  This document can be used to obtain   a listing of files and their associated attributes from a remote   Filestore.Mindel & Slaski                                                [Page 18]RFC 1415             FTP-FTAM Gateway Specification         January 19937. 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