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Network Working Group                                         A. BhushanRequest for Comments: 114                                MIT Project MACNIC: 5823                                                  16 April 1971A FILE TRANSFER PROTOCOLI. Introduction   Computer network usage may be divided into two broad categories --   direct and indirect.  Direct usage implies that you, the network   user, are "logged" into a remote host and use it as a local user.   You interact with the remote system via a terminal (teletypewriter,   graphics console) or a computer.  Differences in terminal   characteristics are handled by host system programs, in accordance   with standard protocols (such as TELNET (RFC 97) for teletypewriter   communications, NETRJS (RFC 88) for remote job entry).  You, however,   have to know the different conventions of remote systems, in order to   use them.   Indirect usage, by contrast, does not require that you explicitly log   into a remote system or even know how to "use" the remote system.  An   intermediate process makes most of the differences in commands and   conventions invisible to you.  For example, you need only know a   standard set of network file transfer commands for your local system   in order to utilize remote file system.  This assumes the existence   of a network file transfer process at each host cooperating via a   common protocol.   Indirect use is not limited to file transfers.  It may include   execution of programs in remote hosts and the transfer of core   images.  The extended file transfer protocol would facilitate the   exchange of programs and data between computers, the use of storage   and file handling capabilities of other computers (possibly including   the trillion-bit store data computer), and have programs in remote   hosts operate on your input and return an output.   The protocol described herein has been developed for immediate   implementation on two hosts at MIT, the GE645/Multics and the PDP-   10/DM/CG-ITS (and possibly Harvard's PDP-10).  An interim version   with limited capabilities is currently in the debugging stage. [1]   Since our implementation involves two dissimilar systems (Multics is   a "service" system, ITS is not) with different file systems (Multics   provides elaborate access controls, ITS provides none), we feel that   the file transfer mechanisms proposed are generalizable.  In   addition, our specification reflects a consideration of other file   systems on the network.  We conducted a survey [2] of network hostBhushan                                                         [Page 1]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971   systems to determine the requirements and capabilities.  This paper   is a "first cut" at a protocol that will allow users at any host on   the network to use the file system of every cooperating host.II.  Discussion   A few definitions are in order before the discussion of the protocol.   A file is an ordered set consisting of computer instructions and/or   data.  A file can be of arbitrary length [3].  A named file is   uniquely identified in a system by its file name and directory name.   The directory name may be the name of a physical directory or it may   be the name of a physical device.  An example of physical directory   name is owner's project-programmer number and an example of physical   device name is tape number.   A file may or may not have access controls associated with it.  The   access controls designate the users' access privileges.  In the   absence of access controls, the files cannot be protected from   accidental or unauthorized usage.   A principal objective of the protocol is to promote the indirect use   of computers on the network.  Therefore, the user or his program   should have a simple and uniform interface to the file systems on the   network and be shielded from the variations in file and storage   systems of different host computers.  This is achieved by the   existence of a standard protocol in each host.   Criteria by which a user-level protocol may be judged were described   by Mealy inRFC 91, as involving the notion of logical records,   ability to access files without program modifications, and   implementability.  I would add to these efficiency, extendibility,   adaptability, and provision of error-recovery mechanisms.   The attempt in this specification has been to enable the reliable   transfer of network ASCII (7-bit ASCII in 8-bit field with leftmost   bit zero) as well as "binary" data files with relative ease.  The use   of other character codes, such as EBCDIC, and variously formatted   data (decimal, octal, ASCII characters packed differently) is   facilitated by inclusion of data type in descriptor headings.  An   alternative mechanism for defining data is also available in the form   of attributes in file headings.  The format control characters   reserved for the syntax of this protocol have identical code   representation in ASCII and EBCDIC.  (These character are SOH, STX,   ETX, DC1, DC2, DC3, US, RS, GS, and FS.)Bhushan                                                         [Page 2]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971   The notion of messages (the physical blocks of data communicated   between NCP's) is suppressed herein and that of "logical" records and   transactions is emphasized.  The data passed by the NCP is parsed   into logical blocks by use of simple descriptors (code and count   mechanisms) as described in Section III.  The alternative to count is   fixed length blocks or standard end-of-file characters (scan data   stream).  Both seem less desirable than count.   The cooperating processes may be "daemon" processes which "listen" to   agreed-upon sockets, and follow the initial connection protocol much   in the same way as a "logger" does.  We recommend using a single   full-duplex connection for the exchange of both data and control   information [4], and using CLS to achieve synchronization when   necessary (a CLS is not transmitted until a RFNM is received).   The user may be identified by having the using process send at the   start of the connection the user's name information (either passed on   by user or known to the using system) [5].  This user name   information (a sequence of standard ASCII characters), along with the   host number (known to the NCP), positively identifies the user to the   serving process.   At present, more elaborate access control mechanisms, such as   passwords, are not suggested.  The user, however, will have the   security and protection provided by the serving system.  The serving   host, if it has access controls, can prevent unprivileged access by   users from other host sites.  It is up to the using host to prevent   its own users from violating access rules.   The files in a file system are identified by a pathname, similar to   the labels described inRFC 76 (Bouknight, Madden, and Grossman).   The pathname contains the essential information regarding the storage   and retrieval of data.   In order to facilitate use, default options should be provided.  For   example, the main file directory on disk would be the default on the   PDP-10/ITS, and a pool directory would be the default on Multics.   The file to be transferred may be a complete file or may consist of   smaller records.  It may or may not have a heading.  A heading should   contain ASCII or EBCDIC characters defining file attributes.  The   file attributes could be some simple agreed-upon types or they could   be described in a data reconfiguration or interpretation language   similar to that described inRFC 83 (Anderson, Haslern, and Heffner),   or a combination.Bhushan                                                         [Page 3]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971   The protocol does not restrict the nature of data in the file.  For   example, a file could contain ASCII text, binary core image, graphics   data or any other type of data.  The protocol includes an "execute"   request for files that are programs.  This is intended to facilitate   the execution of programs and subroutines in remote host computers   [6].III.  SPECIFICATIONS1. Transactions   1A.   The protocol is transaction-oriented.  A transaction is defined         to be an entity of information communicated between cooperating         processes.   1B.   Syntax         A transaction has three fields, a 72-bit descriptor field and         variable length (including zero) data and filler fields, as         shown below.  The total length of a transaction is (72 + data +         filler) bits.   | <code><filler count><NUL><data count><NUL> |    <data><filler>   |   | |____||____________||___||__________||___| |    |____________|   |   |   |         |         |        |       |   |          |          |   | 24-bits   8-bits    8-bits  24-bits  8-bits|    variable length  |   | <-------descriptor field 72-bits---------> |<--data and filler-->|   |                                            |                     |   1C.   Semantics         The code field has three 8-bit bytes.  The first byte is         interpreted as transaction type, the second byte as data type         and the third byte as extension of data type.         The filler count is a binary count of bits used as "filler"         (i.e., not information) at the end of a transaction [7].  As         the length of the filler count field is 8-bits, the number of         bits of filler shall not exceed 255 bits.         The data count is a binary count of the number of data (i.e.,         information) bits in the data field, not including filler bits.         The number of data bits is limited to (2^24-1), as there are 24         bits in the data count field.Bhushan                                                         [Page 4]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971         The NUL bytes are inserted primarily as fillers in the         descriptor field and allow the count information to appear at         convenient word boundaries for different word length machines         [8].2.  Transaction Types   2A.   A transaction may be of the following four basic types:         request, response, transfer and terminate.  Although large         number of request and transfer types are defined,         implementation of a subset is specifically permitted.  Host         computers, on which a particular transaction type is not         implemented, may refuse to accept that transaction by         responding with an unsuccessful terminate.         The following transaction type codes are tentatively defined:         Transaction Type                       Transaction Type Code                                             ASCII   Octal   Hexidecimal         Request                 Identify                        I       111     49                 Retrieve                        R       122     52                 Store                           S       123     53                 Append                          A       101     41                 Delete                          D       104     44                 Rename                          N       116     4E                 addname (Plus)                  P       120     50                 deletename (Minus)              M       115     4D                 Lookup                          L       114     4C                 Open                            O       117     4F                 Close                           C       103     43                 Execute [9]                     E       105     45         Response                 ready-to-receive (rr)           <       074     3C                 ready-to-send (rs)              >       076     3E         Transfer                 complete_file                   *       052                 heading                         #       043     23                 part_of_file                    '       054     2C                 last_part                       .       056     2E         Terminate                 successful (pos.)               +       053     2B                 unsuccessful (neg.)             -       055     2DBhushan                                                         [Page 5]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971   2B.   Syntax         In the following discussion US, RS, GS, FS, DC1, DC2, and DC3         are the ASCII characters, unit separator (octal 037), record         separator (octal 036), group separator (octal 035), file         separator (octal 034), device control 1 (octal 021), device         control 2 (octal 022), and device control 3 (octal 023),         respectively.  These have an identical interpretation in         EBCDIC.   2B.1  Requests         Identify, retrieve, store, append, delete, open, lookup and         execute requests have the following data field:                       <path name>                Rename request has the data field:                       <path name> GS <name>                Addname and deletename requests have the data field:                       <path name> GS <filenames>         where pathname [10], name and filenames have the following         syntax (expressed in BNF, the metalanguage of the ALGOL 60         report):         <pathname> ::= <device name>|<name>|<pathname>US<name>         <device name> ::= DC1<name>         <name> ::= <char> | <name> <char>         <char> ::= All 8-bit ASCII or EBCDIC characters except                 US, RS, GS, FS, DC1, DC2, AND DC3.         <filenames> ::= <name>|<filenames> RS <name>         The data type for the request transaction shall be either A         (octal 101 for ASCII, or E (octal 105) for EBCDIC [11].         Some examples of pathname are:         DC1 MT08         DC1 DSK 1.2 US Net<3> US J.Doe US Foo         udd US proj. US h,n/x US user US file         filename 1 filename 2Bhushan                                                         [Page 6]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971   2B.2  Responses         The response transactions shall normally have an empty data         field.   2B.3  Transfers         The data types defined insection 4 will govern the syntax of         the data field in transfer transactions.  No other syntactical         restrictions exist.   2B.4  Terminates         The successful terminate shall normally have an empty data         field.  The unsuccessful terminate may have a data field         defined by the data types A (octal 101) for ASCII, E (octal         105) for EBCDIC, or S (octal 123) for status.         A data type code of 'S' would imply byte oriented error return         status codes in the data field.  The following error return         status codes are defined tentatively:         Error Code Meaning                        Error Code                                             ASCII   Octal  Hexadecimal         Undefined error                       U       125     55         Transaction type error                T       124     54         Syntax error                          S       123     53         File search failed                    F       106     46         Data type error                       D       104     44         Access denied                         A       101     41         Improper transaction sequence         I       111     49         Time-out error                        O       117     4F         Error condition by system             E       105     45   2C.   Semantics   2C.1  Requests         Requests are always sent by using host.  In absence of a device         name or complete pathname, default options should be provided         for all types of requests.         _Identify_ request identifies the user as indicated by         <pathname> from serving to using host.         _Retrieve_ request achieves the transfer of file specified in         <pathname> from serving to using host.Bhushan                                                         [Page 7]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971         _Store_  request achieves the transfer of file specified in         <pathname> from using to serving host.         _Append_ request causes data to be added to file specified in         pathname.         _Rename_ request causes name of file specified in <pathname> to         be replaced by name specified in <name>.         _Delete_ request causes file specified in <pathname> to be         deleted.  If an extra level of protection for delete is desired         (such as the query 'Do you wish to delete file x?'), it is to         be a local implementation option.         _Addname_ and _deletename_ requests cause names in <filenames>         to be added or deleted to existing names of file specified in         <pathname>.  These requests are useful in systems such as         Multics which allow multiple names to be associated with a         file.         _Lookup_ request achieves the transfer of attributes (such as         date last modified, access list, etc) of file specified in         <pathname>, instead of the file itself.         _Open_ request does not cause a data transfer, instead file         specified in <pathname> is "opened" for retrieve (read) or         store (write).  Subsequent requests are then treated as         requests pertaining to the file that is opened till such a time         that a close request is received.         _Execute_ request achieves the execution of file specified in         <pathname>, which must be an executable program.  Upon receipt         of rr response, using host will transmit the necessary input         data (parameters, arguments, etc).  Upon completion of         execution serving host will send the results to using host and         terminate [12].   2C.2  Response         Responses are always sent by serving host.  The rr response         indicates that serving host is ready to receive the file         indicated in the preceding request.  The rs response indicates         that the next transaction from serving host will be the         transfer of file indicated in the preceding request.Bhushan                                                         [Page 8]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971   2C.3  Transfers         Transfers may be sent by either host.  Transfer transactions         indicate the transfer of file indicated by a request.  Files         can be transferred either as complete_file transactions or as         part_of_file transactions followed by last_part transactions.         The file may also have a heading transaction in the beginning.         The syntax of a file, therefore, may be defined as:         <file> ::= <text> | <heading> <text>         <text> ::= <complete_file> | <parts> <last_part>         <parts> ::= <part_of_file> | <parts> <part_of_file>         Headings may be used to communicate the attributes of files.         The form of headings is not formally specified but is discussed         in Section IV as possible extension to this protocol.   2C.4  Terminates         The successful terminate is always sent by serving host.  It         indicates to using host that serving host has been successful         in serving the request and has gone to an initial state.  Using         host will then inform user that his request is successfully         served, and go to an initial state.         The unsuccessful terminate may be sent by either host.  It         indicates that sender of the terminate is unable to (or does         not not wish to) go through with the request.  Both hosts will         then go to their initial states.  The using host will inform         the user that his request was aborted.  If any reasons for the         unsuccessful terminate (either as text or as error return         status codes) are received, these shall be communicated to the         user.3.    Transaction Sequence   3A.   The transaction sequence may be defined as an instance of file         transfer, initiated by a request and ended by a terminate [13].         The exact sequence in which transactions occur depends on the         type of request.  A transaction sequence may be aborted anytime         by either host, as explained inSection 3C.   3B.   Examples         The identify request doesn't require a response or terminate         and constitutes a transaction sequence by itself.Bhushan                                                         [Page 9]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971         Rename, delete, addname, deletename and open requests involve         no data transfer but require terminates.  The user sends the         request and the server sends a successful or an unsuccessful         terminate depending on whether or not he is successful in         complying with the request.         Retrieve and Lookup requests involve data transfer from the         server to the user.  The user sends the request, the server         responds with a rs, and transfers the data specified by the         request.  Upon completion of the data transfer, the server         terminates the transaction sequence with a successful terminate         if all goes well, or with an unsuccessful terminate is errors         were detected.         Store and Append requests involve data transfer from the user         to server.  The user sends the request and the server responds         with a rr.  The user then transfers the data.  Upon receiving         the data, the server terminates the sequence.         Execute request involves transfer of inputs from user to         server, and transfer of outputs from server to user.  The user         sends the request to which the server responds with rr.  The         user then transfers the necessary inputs.  The server         "executes" the program or subroutine and transfers the outputs         to the user.  Upon completion of the output transfer, the         server terminates the transaction sequence.   3C.   Aborts         Either host may abort the transaction sequence at any time by         sending an unsuccessful terminate, or by closing the connection         (NCP to transmit a CLS for the connection).  The CLS is a more         drastic type of abort and shall be used when there is a         catastrophic failure or when an abort is desired in the middle         of a long file transfer.  The abort indicates to the receiving         host that the other host wishes to terminate the transaction         sequence and is now in the initial state.  When CLS is used to         abort, the using host will reopen the connection.4.    Data Types   4A.   The data type code together with the extension code defines the         manner in which the data field is to be parsed and interpreted         [14].  Although a large number of data types are defined,         specific implementations may handle only a limited subset of         data types.  It is recommended that all host sites accept theBhushan                                                        [Page 10]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971         "network ASCII" and "binary" data types.  Host computers which         do not "recognize" particular data types may abort the         transaction sequence and return a data type error status code.   4B.   The following data types are tentatively defined.  The code in         the type and extension field is represented by its ASCII         equivalent with 8th bit as zero.Bhushan                                                        [Page 11]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971        Data Type                                    Code                                     Byte Size       Type     ExtensionASCII character, bit8=0 (network)       8             A          NULASCII characters, bit8=1                8             A          1ASCII characters, bit8=even parity      8             A          EASCII characters, bit8=odd parity       8             A          OASCII characters, 8th bit info.         8             A          8ASCII characters, 7 bits                7             A          7ASCII characters, in 9-bit field        9             A          9ASCII formatted files (with SOH,        STX, ETX, etc.)                 8             A          FDEC-packed ASCII (5 7-bit char.,        36th bit 1 or 0)                36            A          DEBCDIC characters                       8             E         NULSIXBIT characters                       6             S         NULBinary data                             1             B         NULBinary bytes (size is binary ext.)      1-255         B        (any)Decimal numbers, net ASCII              8             D          ADecimal numbers, EBCDIC                 8             D          EDecimal numbers, sixbit                 6             D          SDecimal numbers, BCD (binary coded)     4             D          BOctal numbers, net. ASCII               8             O          AOctal numbers, EBCDIC                   8             O          EOctal numbers, SIXBIT                   6             O          SHexadecimal numbers, net. ASCII         8             H          AHexadecimal numbers, EBCDIC             8             H          EHexadecimal numbers, SIXBIT             6             H          SUnsigned integers, binary (ext.        field is byte size)             1-225         U        (any)Sign magnitude integers (field is        binary size)                    1-255         I        (any)2's complement integers (ext.        field is byte size)             1-255         2        (any)1's complement integers (ext.        field is byte size)             1-255         1        (any)Floating point (IBM360)                 32            F          IFloating point (PDP-10)                 36            F          DStatus codes                            8             S         NULBhushan                                                        [Page 12]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971   4C.   The data type information is intended to be interpretive.  If a         host accepts a data type, it can interpret it to a form suited         to its internal representation of characters or numbers [15].         Specifically when no conversion is to be performed, the data         type used will be binary.  The implicit or explicit byte size         is useful as it facilitates storing of data.  For example, if a         PDP-10 receives data types A, A1, AE, or A7, it can store the         ASCII characters five to a word (DEC-packed ASCII).  If the         datatype is A8 or A9, it would store the characters four to a         word.  Sixbit characters would be stored six to a word.  If         conversion routines are available on a system, the use of         system program could convert the data from one form to another         (such as EBCDIC to ASCII, IBM floating point to DEC floating         point, Decimal ASCII to integers, etc.).5. Initial Connection, CLS, and Identifying Users   5A.   There will be a prearranged socket number [16] for the         cooperating process on the serving host.  The connection         establishment will be in accordance with the initial connection         protocol ofRFC 66 as modified byRFC 80.  The NCP dialog would         be:              user to server:    RTS<us><3><p>         if accepted, server to user:    STR<3><us><CLS><3><us>              server to user on link p:  <ss>              server to user:    STR<ss+1><us>RTS<ss><us+1><q>              user to server:    STR<us><ss+1>RTS<us+1><ss><r>         This sets up a full-duplex connection between user and server         processes, with server receiving through local socket ss from         remote socket us+1 via link q, and sending to remote socket us         through local socket ss+1 via link r.   5B.   The connection will be broken by trading a CLS between the         NCP'S for each of the two connections.  Normally the user will         initiate the CLS.         CLS may also be used by either the user or the server to abort         a data transmission in the middle.  If a CLS is received in the         middle of a transaction sequence, the whole transaction         sequence will be aborted.  The using host will then reopen the         connection.   5C.   The first transaction from the user to server will be the         identify transaction.  The users will be identified by the         pathname in data field of the transaction which should be aBhushan                                                        [Page 13]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971         form acceptable to the server.  The server is at liberty to         truncate pathnames for its own use.  Since the identify         transaction does not require a response or terminate, the user         can proceed directly with other requests.IV.  Extensions to Protocol   The protocol specified above has been designed to be extendable.  The   obvious extensions would be in the area of transaction types (new   types of requests), error return status words, and data types.  Some   of the non-obvious extensions, that I can visualize are provisions of   access control mechanisms, developing a uniform way of specifying   file attributes in headings of files, increasing the scope of the   execute command to include subroutine mediation, and the provision of   transaction sequence identification numbers to facilitate handling of   multiple requests over the same connection pair.   Users of protected file systems should be able to have a reasonable   degree of confidence in the ability of the serving process to   identify remote users correctly.  In the absence of such confidence,   some users would not be willing to give access to the serving process   (especially write access).  Inclusion of access control mechanisms   such as passwords, is likely to enhance the indirect use of network   by users who are concerned about privacy and security.  A simple   extension to the protocol would be to have the serving host sent a   transaction type "password?" after it receives user name.  Upon   receipt of "password?" the using host will transmit the password,   which when successfully acknowledged, would indicate to the user that   requests may proceed.   There are a number of file attributes which properly belong in the   heading of a file rather than the file itself or the data type in   descriptors of transactions.  Such attributes include access control   lists, date file was last modified, information about the nature of   file, and description of its contents in a data description or data   reconfiguration language.  Some uniformity in the way file attributes   are specified would be useful.  Until then, the interpretation of the   heading would be up to the user or the using process.  For example,   the heading of files which are input to a data reconfiguration (form)   machine may be the desired transformations expressed in the   reconfiguration language.   The "execute" command which achieves the execution of programs   resident in remote hosts is a vital part of indirect use of remote   hosts.  The present scope of the execute command, as outlined in the   specifications, is somewhat limited.  It assumes that the user orBhushan                                                        [Page 14]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971   using process is aware of the manner in which the arguments and   results should be exchanged.  One could broaden the scope of the   execute command by introducing a program mediation protocol [17].   The present specification of the protocol does not allow the   simultaneous transfer and processing of multiple requests over the   same pair of connections.  If such a capability is desired, there is   an easy way to implement it which only involves a minor change.  A   transaction sequence identification number (TSid) could replace a NUL   field in the descriptor of transactions.  The TSid would facilitate   the coordination of transactions, related to a particular transaction   sequence.  The 256 code combinations permitted by the TSid would be   used in a round-robin manner (I can't see more than 256 outstanding   requests between two user-processes in any practical implementation).   An alternate way of simultaneous processing of requests is to open   new pairs of connection.  I am not sure as to how useful simultaneous   processing of requests is, and which of the two is a more reasonable   approach.V. Conclusions   I tried to present a user-level protocol that will permit users and   using programs to make indirect use of remote host computers.  The   protocol facilitates not only file system operations but also program   execution in remote hosts.  This is achieved by defining requests   which are handled by cooperating processes.  The transaction sequence   orientation provides greater assurance and would facilitate error   control.  The notion of data types is introduced to facilitate the   interpretation, reconfiguration and storage of simple and limited   forms of data at individual host sites.  The protocol is readily   extendible.Endnotes   [1] The interim version of the protocol, limited to transfer of ASCII   files, was developed by Chander Ramchandani and Howard Brodie of   Project MAC.  The ideas of transactions, descriptors, error recovery,   aborts, file headings and attributes, execution of programs, and use   of data types, pathnames, and default mechanisms are new here.   Howard Brodie and Neal Ryan have coded the interim protocol in the   PDP-10 and the 645, respectively.   [2] The network system survey was conducted last fall by Howard   Brodie of Project MAC, primarily by telephone.   [3] PDP-10 Reference Handbook, page 306.Bhushan                                                        [Page 15]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971   [4] We considered using two full-duplex links, one for control   information, the other for data.  The use of a separate control link   between the cooperating processes would simplify aborts, error   recoveries and synchronization.  The synchronization function may   alternatively be performed by closing the connection (in the middle   of a transaction sequence) and reopening it with an abort message.   (The use of INR and INS transmitted via the NCP control link has   problems as mentioned by Kalin inRFC 103.)  We prefer the latter   approach.   [5] Identifying users through use of socket numbers is not practical,   as unique user identification numbers have not been implemented, and   file systems identify users by name, not number.   [6] This subject is considered in detail by Bob Metcalfe in a   forthcoming paper.   [7] Filler bits may be necessary as particular implementations of   NCP's may not allow the free communication of bits.  Instead the   NCP's may only accept bytes, as suggested inRFC 102.  The filler   count is needed to determine the boundary between transactions.   [8] 72-bits in descriptor field are convenient as 72 is the least   common multiple of 6, 8, 9, 18, 24 and 30, the commonly encountered   byte sizes on the ARPA network host computers.   [9] The execute request is intended to facilitate the indirect   execution of programs and subroutines.  However, this request in its   present form may have only limited use.  A subroutine or program   mediation protocol would be required for broader use of the execute   feature.  Metcalfe considers this problem in a forthcoming paper.   [10] The pathname idea used in Multics is similar to that of labels   inRFC 76 by Bouknight, Madden and Grossman.   [11] We, however, urge the use of standard network ASCII.   [12] The exact manner in which the input and output are transmitted   would depend on specific mediation conventions.  Names of input and   output files may be transmitted instead of data itself.   [13] The transactions (including terminate) are not "echoed", as   echoing does not solve any "hung" conditions.  Instead time-out   mechanisms are recommended for avoiding hang-ups.   [14] The data type mechanism suggested here does not replace data   reconfiguration service suggested by Harslem and Heafner inRFC 83   and NIC5772.  In fact, it complements the reconfiguration.  ForBhushan                                                        [Page 16]

RFC 114                 A FILE TRANSFER PROTOCOL           16 April 1971   example, data reconfiguration language can be expressed in EBCDIC,   Network ASCII or any other code that form machine may "recognize".   Subsequent data may be transmitted binary, and the form machine would   reconfigure it to the required form.  I have included in data types,   a large number suggested by Harslem and Heafner, as I do not wish to   preclude interpretation, reconfiguration and storage of simple forms   of data at individual host sites.   [15] The internal character representation in the hosts may be   different even in ASCII.  For example PDP-10 stores 7-bit characters,   five per word with 36th bit as don't care, while Multics stores them   four per word, right-justified in 9-bit fields.   [16] It seems that socket 1 has been assigned to logger and socket 5   to NETRJS.  Socket 3 seems a reasonable choice for the file transfer   process.   [17] The term program mediation was suggested by Bob Metcalfe who is   intending to write a paper on this subject.         [ This RFC was put into machine readable form for entry ]             [ into the online RFC archives by Ryan Kato 6/01]Bhushan                                                        [Page 17]