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rfc:rfc114

Network Working Group A. Bhushan Request for Comments: 114 MIT Project MAC NIC: 5823 16 April 1971

                      A FILE TRANSFER PROTOCOL

I. 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 host

Bhushan [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 in RFC 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 in RFC 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 in RFC 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. SPECIFICATIONS

1. 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     2D

Bhushan [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 2

Bhushan [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 in section 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 in Section 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 the

Bhushan [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     Extension

ASCII character, bit8=0 (network) 8 A NUL

ASCII characters, bit8=1 8 A 1

ASCII characters, bit8=even parity 8 A E

ASCII characters, bit8=odd parity 8 A O

ASCII characters, 8th bit info. 8 A 8

ASCII characters, 7 bits 7 A 7

ASCII characters, in 9-bit field 9 A 9 ASCII formatted files (with SOH,

      STX, ETX, etc.)                 8             A          F

DEC-packed ASCII (5 7-bit char.,

      36th bit 1 or 0)                36            A          D

EBCDIC characters 8 E NUL SIXBIT characters 6 S NUL Binary data 1 B NUL Binary bytes (size is binary ext.) 1-255 B (any) Decimal numbers, net ASCII 8 D A Decimal numbers, EBCDIC 8 D E Decimal numbers, sixbit 6 D S Decimal numbers, BCD (binary coded) 4 D B Octal numbers, net. ASCII 8 O A Octal numbers, EBCDIC 8 O E Octal numbers, SIXBIT 6 O S Hexadecimal numbers, net. ASCII 8 H A Hexadecimal numbers, EBCDIC 8 H E Hexadecimal numbers, SIXBIT 6 H S Unsigned 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 I Floating point (PDP-10) 36 F D Status codes 8 S NUL

Bhushan [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 of RFC 66 as modified by RFC 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 a

Bhushan [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 or

Bhushan [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 in RFC 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 in RFC 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
 in RFC 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 in RFC 83
 and NIC5772.  In fact, it complements the reconfiguration.  For

Bhushan [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]

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