rfc726.txt

RFC 相关的技术文档

     NWG/RFC# 726                          JBP DHC 8-MAR-77 08:29  39237
     Remote Controlled Transmission & Echoing Telnet Option



     Network Working Group             Jon Postel & Dave Crocker
     Request for Comments: 726            SRI-ARC      UC Irvine
     NIC: 39237                                     8 March 1977

     
     
       Remote Controlled Transmssion and Echoing Telnet Option


                                                                       1

     1.  Command name and code:                                        2

       RCTE 7                                                         2a

     2.  Command meanings:                                             3

       IAC WILL RCTE                                                  3a

         The sender of this command REQUESTS or AGREES to use
         the RCTE option, and will send instructions for
         controlling the other side's terminal printer.              3a1

       IAC WON'T RCTE                                                 3b

         The sender of this option REFUSES to send instructions
         for controlling the other side's terminal printer.          3b1

       IAC DO RCTE                                                    3c

         The sender REQUEST or AGREES to have the other side
         (sender of WILL RCTE) issue commands which will control
         his (sender of the DO) output to the terminal printer.      3c1

       IAC DON'T RCTE                                                 3d

         The sender of this command REFUSES to allow the other
         side to control his (sender of DON'T) terminal printer.     3d1

       IAC SB RCTE <cmd> [BC1 BC2] [TC1 TC2] IAC SE                   3e

         where:                                                      3e1

           <cmd> is one 8-bit byte having the following flags
           (bits are counted from the right):                       3e1a







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     NWG/RFC# 726                          JBP DHC 8-MAR-77 08:29  39237
     Remote Controlled Transmission & Echoing Telnet Option



           Bit  Meaning                                             3e1b

            0   0 = Ignore all other bits in this byte and
                    repeat the last <cmd> that was sent. Equals
                    a 'continue what you have been doing'.
                1 = Perform actions as indicated by other bits
                    in this byte.                                   3e1c

            1   0 = Print (echo) break character
                1 = Skip (don't echo) break character               3e1d

            2   0 = Print (echo) text up to break character
                1 = Skip (don't echo) text up to break character    3e1e

            3   0 = Continue using same classes of break
                    characters.
                1 = The two 8-bit bytes following this byte
                    contain flags for the new break classes.        3e1f

            4   0 = Continue using same classes of transmit
                    characters.
                1 = Reset transmit classes according to the two
                    bytes following 1) the break classes bytes,
                    if the break classes are also being reset,
                    or 2) this byte, if the break classes are
                    NOT also being reset.                           3e1g

           Value (decimal) of the <cmd> byte and its meaning:       3e1h

           0 = Continue what you have been doing                    3e1i

           Even numbers greater than zero (i.e. numbers with the
           right most bit off) are in error and should be
           interpreted as equal to zero. When the <cmd> is an
           even number greater than zero, classes bytes TC1 &
           TC2 and/or BC1 & BC2 must not be sent.                   3e1j

           1 = Print (echo) up to AND INCLUDING break character     3e1k

           3 = Print up to break character and SKIP (don't echo)
               break character                                      3e1l

           5 = Skip text (don't echo) up to break character, but
               PRINT break character                                3e1m

           7 = Skip up to and including break character             3e1n

           Add one of the previous non-zero values to one of the
           following values, to get the total decimal value for



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     NWG/RFC# 726                          JBP DHC 8-MAR-77 08:29  39237
     Remote Controlled Transmission & Echoing Telnet Option



           the byte (Note that classes may not be reset without
           also resetting the printing action; so an odd number
           is guaranteed):                                          3e1o

           8 = Set break classes (using the next two bytes [BC1
               BC2])                                                3e1p

           16 = Set transmission classes (using the next two
               bytes [TC1 TC2])                                     3e1q

           24 = Set break classes (using the next two bytes [BC1
               BC2]) and the transmission classes (using the two
               bytes after that [TC1 TC2]).                         3e1r

         Sub-commands (IAC SB RCTE...) are only sent by the
         controlling host and, in addition to other functions,
         functionally replace the Go-Ahead (IAC GA) Telnet
         feature. RCTE also functionally replaces the Echo (IAC
         ECHO) Telnet option. That is the Suppress Go-Ahead
         option should be in force and the Echo option should
         not be in force while the RCTE option is in use. The
         echo mode on terminating use of the RCTE option should
         be the default state, that is DON'T ECHO, WON'T ECHO.       3e2

         Classes for break and transmission (the right-most bit
         of the second byte (TC2 or BC2) represents class 1; the
         left-most bit of the first byte (TC1 or BC1) represents
         the currently undefined class 16:                           3e3

           1: Upper-Case Letter (A-Z)                               3e3a

           2: Lower-case Letters (a-z)                              3e3b

           3: Numbers (0-9)                                         3e3c

           4: Format Effectors (<BS> <CR> <LF> <FF> <HT> <VT>)      3e3d

             The sequence <cr><lf> counts as one character when
                processed as the Telnet end of line, and is a
                single break character when class 4 is set. The
                sequence <cr><nul> counts as one character and
                is a break character if and only if <cr> is a
                break character (i.e. class 4 is set).

           5: Non-format Effector Control Characters including
              <DEL> and <ESC>                                       3e3e

           6: . , ; : ? !                                           3e3f




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     NWG/RFC# 726                          JBP DHC 8-MAR-77 08:29  39237
     Remote Controlled Transmission & Echoing Telnet Option



           7: { [ ( < > ) ] }                                       3e3g

           8: ' "  / \ % @ $ & # + - * = ^ _ | ~                    3e3h

           9: <Space>                                               3e3i

           And Telnet commands (IAC . . .) sent by the user are
           always to have the effect of a break character. That
           is, every instance of an IAC is to be treated as a
           break character, except the sequence IAC IAC.            3e3j

         The representation to be displayed when printing is
         called for is the obvious one for the visible
         characters (classes 1, 2, 3, 6, 7, and 8). Space (class
         9) is represented by a blank space. The format
         effectors (class 4) by their format effect. The
         non-format effector controls (class 5) print nothing
         (no space).                                                 3e4

         Initially no break classes or transmission classes are
         in effect.                                                  3e5

         Please note that if all the bits are set in a Telnet
         subcommand argument byte such as TC2 or BC2 then that
         byte must be preceeded by an <IAC> flag byte. This is
         the common convention of doubling the escape character
         to use its value as data.                                   3e6

         Sub-commands (IAC SB RCTE...) are refered to as "break
         reset commands".                                            3e7

     3.  Default:                                                      4

       WON'T RCTE -- DON'T RCTE                                       4a

         Neither host asserts special control over the other
         host's terminal printer.                                    4a1

     4.  Motivation for the option:                                    5

       RFC's 1, 5 and 51 discuss Network and process efficiency
       and smoothness.                                                5a

       RFC 357, by John Davidson, introduces the problem of
       echoing delay that occurs when a remote user accesses a
       full-duplex host, thru a satellite link. In order to save
       the many thousands of miles of transit time for each
       echoed character, while still permitting full server
       responsiveness and clean terminal output, an echo control



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     NWG/RFC# 726                          JBP DHC 8-MAR-77 08:29  39237
     Remote Controlled Transmission & Echoing Telnet Option



       similar to that used by some time-sharing systems is
       suggested for the entire Network.                              5b

         In effect, the option described in this document
         involves making a using host carefully regulate the
         local terminal printer according to explicit
         instructions from the remote (serving) host.                5b1

       An important additional issue is efficient Network
       transmission. Implementation of the Davidson Echoing
       Scheme will eliminate almost all server-to-user echoing.       5c

         The option described in this document also requests
         using hosts to buffer a terminal's input to the serving
         host until it forms a useful unit (with "useful unit"
         delimited by break or transmission characters as
         described below). Therefore, fewer messages are sent on
         the user-to-server path.                                    5c1

       N.B.:  This option is only intended for use with
       full-duplex hosts. The Go-Ahead Telnet feature is
       completely adequate for half-duplex server hosts. Also,
       RCTE should be used in place of the ECHO Telnet option.
       That is the Suppress Go-Ahead option should be in force
       and the Echo option should not be in force while the RCTE
       option is in use.                                              5d


























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     NWG/RFC# 726                          JBP DHC 8-MAR-77 08:29  39237
     Remote Controlled Transmission & Echoing Telnet Option



     5.  Explicit description of control mechanism:                    6

       User Terminal Printing Action & Control Procedure              6a

         Negotiate the use of the RCTE option. Once the option
         is in force the user Telnet follows the following
         procedure.                                                  6a1

         1) Read an item from the network.                           6a2

           If the item is data, then print it and go to 1.          6a2a

           If the item is a command, then set the classes and go
           to 2.                                                    6a2b