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RFC 731 - Telnet Data Entry Terminal option


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John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

                Telnet Data Entry Terminal Option

1.  Command Name and code:

        DET             20

2.  Command Meanings

     IAC WILL DET
     The sender of this command REQUESTS or AGREES  to  send  and
     receive subcommands to control the Data Entry Terminal.

     IAC WONT DET
     The sender of this  command  REFUSES  to  send  and  receive
     subcommands to control the Data Entry Terminal.

     IAC DO DET
     The sender of this command REQUESTS or AGREES  to  send  and
     receive subcommands to control the Data Entry Terminal.

     IAC DONT DET
     The sender of this  command  REFUSES  to  send  and  receive
     subcommands to control the Data Entry Terminal.

     The DET option  uses  five  classes  of  subcommands  1)  to
     establish   the   requirements   and   capabilities  of  the
     application and the terminal, 2) to format the  screen,  and
     to  control  the  3)  edit,  4) erasure, and 5) transmission
     functions.  The subcommands that perform these functions are
     described below.

     T__h_e_N__e_t_w_o_r_k_V__i_r_t_u_a_l_D__a_t_a_E__n_t_r_y_T__e_r_m_i_n_a_l(NVDET)

        The NVDET  consists  of  a  keyboard  and  a  rectangular
        display.   The  keyboard  is capable of generating all of
        the characters of the ASCII character set.  In  addition,
        the  keyboard may possess a number of function keys which
        when pressed cause a FN subcommand to be sent.  (Although
        most DET's will support one or  more  peripheral  devices
        such  as  a  paper  tape reader or a printer, this option

                                1

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

        does not consider their support.  Support  of  peripheral
        devices should be treated by a separate option.)

        The screen of the data entry terminal is  a  rectangle  M
        characters  by N lines.  The values of M and N are set by
        negotiating the Output Line Width and  Output  Page  Size
        options,  respectively.   The next writing position (x,y)
        on the screen (where x is the character position and y is
        the position of the line on the screen) is indicated by a
        special display character called the cursor.  The  cursor
        may  be  moved  to  any  position  on  the screen without
        disturbing any characters already on the screen.   Cursor
        addressing   in   existing   terminals  utilizes  several
        topologies and addressing methods.  In order to make  the
        burden of implementaton as easy as possible this protocol
        supports two topologies (the finite plane and the helical
        torus)  and three addressing methods ((x,y); x and y, and
        relative  increments).   Since  the  finite  plane   with
        absolute  addressing  is  the  least  ambiguous  and  the
        easiest to translate to and from the others,  it  is  the
        default scheme used by the NVDET.  The torodial form with
        either  relative  or  absolute addressing is provided for
        convience.

        Also  the NVDET provides a mechanism for defining on  the
        screen  fields  with  special  attributes.   For example,
        characters entered into these  fields  may  be  displayed
        with  brighter intensity, highlighted by reverse video or
        blinking, or protected from  modification  by  the  user.
        This  latter  feature is one of the most heavily used for
        applications where the DET displays a form to  be  filled
        out by the user.

        The  definition  of  the   NVDET   uses   Telnet   option
        subnegotiations  to  accomplish  all  of  its  functions.
        Since none of the  ASCII  characters  sent  in  the  data
        stream  have been used to define these functions, the DET
        option can be used in a "raw" or even  "rare"  mode.   In
        circumstances  where  the  application program knows what
        kind of terminal is on the other end,  it  can  send  the
        ASCII   characters  required  to  control  functions  not
        supported by the option or an implementation.  In general
        keeping all  NVDET  functions  out  of  the  data  stream
        provides better flexibility.

     F__a_c_i_l_i_t_y_F__u_n_c_t_i_o_n_s  (for detailed semantics see Section 5.)

     IAC SB DET <DET facility subcommand><facility map> IAC SE

        where  <DET  facility  subcommand>  is  one  8-bit   byte

                                2

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

        indicating  the  class of the facilities to be described,
        and <facility map> is a field of one or two  8-bit  bytes
        containing  flags  describing  the facilities required or
        desired by the sender.  The bits of the facility maps are
        numbered from the right starting at zero.  Thus, if bit 2
        is set the field will have a decimal  value  of  4.   The
        values of the field are as follows:

        facility cmd:  EDIT FACILITIES     subcommand code: 1
          facility map:                              bit numbers
             Toroidal Cursor Addressing                  6
             Incremental Cursor Addressing               5
             Read Cursor Address                         4
             Line Insert/Delete                          3
             Char Insert/Delete                          2
             Back Tab                                    1
             Positive Addressing only                    0

        where:

        If the Toroidal Cursor Addressing bit is set, the  sender
        requests  or  provides  that the SKIP TO LINE and SKIP TO
        CHAR subcommands be supported.

        If the Incremental Cursor  Addressing  bit  is  set,  the
        sender  requests or provides that the UP, DOWN, LEFT, and
        RIGHT subcommands be supported.

        If the Read Cursor bit is set,  the  sender  requests  or
        provides the READ CURSOR subcommand.

        If the Line Insert/Delete bit is set, the sender requests
        or  provides  that  the  LINE  INSERT  and  LINE   DELETE
        subcommands be supported.

        If the Char Insert/Delete bit is set, the sender requests
        or  provides  that  the  CHAR  INSERT  and  CHAR   DELETE
        subcommands be supported.

        If the Back Tab  bit  is  set,  the  sender  requests  or
        provides that the BACK TAB subcommand be supported.

        If the Positive Addressing bit is set, then the sender is
        informing the receiver that it can only move  the  cursor
        in  the  positive direction.  (Note:  Terminals that have
        this property also have a Home function to  get  back  to
        the beginning.)

        facility cmd:  ERASE FACILITIES     subcommand code:  2
          facility map:                                bit numbers

                                3

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

             Erase Field                                     4
             Erase Line                                      3
             Erase Rest of Screen                            2
             Erase Rest of Line                              1
             Erase Rest of Field                             0

        where:

        If a bit of the facility map for this facility command is
        set,  the  sender  requests  or  provides  the   facility
        indicated by the bit.  For a more complete description of
        each  of  these functions see the Erase Functions section
        below.

        facility cmd:  TRANSMIT FACILITIES     subcommand code:  3
          facility map:                      bit numbers
             Data Transmit                         5
             Transmit Line                         4
             Transmit Field                        3
             Transmit Rest of Screen               2
             Transmit Rest of Line                 1
             Transmit Rest of Field                0

        where:

        If a bit of the facility map for this facility command is
        set,  the  sender  requests  or  provides  the   facility
        indicated by the bit.  For a more complete description of
        each  of  these  functions  see  the  Transmit  Functions
        section below.

        facility cmd:  FORMAT FACILITIES     subcommand code:  4
          facility map:                               bit numbers
                                        byte 0
             Repeat                                         4
             Blinking                                       3
             Reverse Video                                  2
             Right Justification                            1
             Overstrike                                     0

                                        byte 1
             Protection On/Off                              6
             Protection                                     5
             Alphabetic-only Protection                     4
             Numeric-only Protection                        3
             Intensity                                      0-2

        where:

        If the Repeat bit is set the sender requests or  provides

                                4

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

        the REPEAT subcommand.

        If the Blinking  bit  is  set,  the  sender  requests  or
        provides  the ability to highlight a string of characters
        by causing them to blink.

        If the Reverse Video bit is set, the sender  requests  or
        provides  the ability to highlight a string of characters
        by "reversing the video image," i.e., if  the  characters
        are  normally  displayed  as  black characters on a white
        background, this is reversed to be white characters on  a
        black background, or vice versa.

        If  the  Right  Justification  bit  is  set,  the  sender
        requests or provides the ability to cause entries of data
        to be right justified in the field.

        If the Overstrike bit is  set,  the  sender  requests  or
        provides  the  ability  to superimpose one character over
        another on the screen much  like  a  hard  copy  terminal
        would  do if the print mechanism struck the same position
        on the paper with different characters.

        If the Protection On/Off bit is set, the sender  requests
        or  provides  the  ability  to  turn  on  and  off  field
        protection.

        If the Protection bit is  set,  the  sender  requests  or
        provides  the  ability  to  protect  certain  strings  of
        characters displayed on the screen from being altered  by
        the  user of the terminal.  Setting this bit also implies
        that   ERASE   UNPROTECTED   and   TRANSMIT   UNPROTECTED
        subcommands (see below) are supported.

        If the Alphabetic-only Protection bit is set, the  sender
        requests or provides the ability to constrain the user of
        the  terminal such that he may only enter alphabetic data
        into certain areas of the screen.

        If the Numeric-only Protection bit  is  set,  the  sender
        requests or provides the ability to constrain the user of
        the  terminal  such that he may only enter numerical data
        into certain areas of the screen.

        The three bits of the  Intensity  field  will  contain  a
        positive  binary  integer indicating the number of levels
        of intensity that the sender  requests  or  provides  for
        displaying the data.  The value of the 3 bit field should
        be interpreted in the following way:

                                5

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

           1        one visible intensity
           2        two intensities; normal and bright
           3        three intensities; off, normal, and bright
          >3        >3 intensities; off, and the remaining levels
                    proportioned from dimmest to brightest intensity.

        For the all of the above commands, if the appropriate bit
        in <facility map> is not set, then the  sender  does  not
        request or provide that facility.

     E__d_i_t_i_n_g_F__u_n_c_t_i_o_n_s

        IAC SB DET MOVE CURSOR <x><y> IAC SE  subcommand code: 5

        where <x> is an 8-bit byte containing a  positive  binary
        integer   representing  the  character  position  of  the
        cursor, <y> is an 8-bit byte containing a positive binary
        integer representing the line position of the cursor.

        This subcommand moves the cursor to the  absolute  screen
        address (x,y) with the following boundary conditions:

          if x>M-1, set x=M-1 and send an ERROR subcommand
          if y>N-1, set y=N-1 and send an  ERROR subcommand

        This describes a finite plane topology on the screen.

        IAC SB DET SKIP TO LINE <y> IAC SE    subcommand code: 6

        where <y> is a positive 8-bit binary number.

        This subcommand moves the cursor to the  absolute  screen
        line y.  x remains constant.  For values of y>N-1
          y = y mod N.

        IAC SB DET SKIP TO CHAR <x> IAC SE   subcommand code: 7

        where <x> is a positive 8-bit binary number.

        This  subcommand  moves  the  cursor  to   the   absolute
        character  position  x.  y remains constant, unless x>M-1
        in which case:
          x' = (x mod M)
          y' = (y+(x DIV N))
          where x' and y' are the new values of  the cursor.

        These last two subcommands define a toroidal topology  on
        the screen.

                                6

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

        IAC SB DET UP IAC SE            subcommand code:  8
        IAC SB DET DOWN IAC SE          subcommand code:  9
        IAC SB DET LEFT IAC SE          subcommand code: 10
        IAC SB DET RIGHT IAC SE         subcommand code: 11

        These subcommands are provided as a convenience for  some
        terminals.   The  commands  UP, DOWN, LEFT, and RIGHT are
        defined as

        UP:         (x,y)=(x, y-1 mod N)
        DOWN:       (x,y)=(x, y+1 mod N)
        LEFT:       (x,y)=(x-1, y); if x=0 then x-1 = 0
        RIGHT:      (x,y)=(x+1 mod M, y) and y = y+1 if x+1>M-1

        Note:  DOWN, LEFT, and RIGHT cannot always be replaced by
        the  ASCII  codes  for  linefeed,  backspace,  and  space
        respectively.   The latter are format effectors while the
        former are cursor controls.

        IAC SB DET HOME IAC SE      subcommand code:  12

        This subcommand positions the cursor to (0,0).   This  is
        equivalent  to  a MOVE CURSOR 0,0 or the sequence SKIP TO
        LINE 0, SKIP TO CHAR 0.  This subcommand is provided  for
        convenience,  since  most terminals have it as a separate
        control.

        IAC SB DET LINE INSERT IAC SE     subcommand code:  13

        This subcommand inserts a line of spaces between lines  y
        (the  current  line,  determined  by  the position of the
        cursor) and line y-1.  Lines y through N-2 move down  one
        line,  i.e.  line  y  becomes line y+1;  y+1 becomes y+2,
        ...; N-2 becomes N-1.  Line N-1 is lost off the bottom of
        the  screen.   The  position  of   the   cursor   remains
        unchanged.

        IAC SB DET LINE DELETE IAC SE     subcommand code:  14

        This subcommand deletes line y where  y  is  the  current
        line  position of the cursor.  Lines y+1 through N-1 move
        up one line, i.e.  line y+1 becomes line y;  y+2  becomes
        y+1;  ...;  N-1  becomes N-2.  The N-1st line position is
        set  to  all  spaces.   The   cursor   position   remains
        unchanged.

        IAC SB DET CHAR INSERT IAC SE     subcommand code: 15

        This subcommand inserts the next character  in  the  data
        stream  between  the xth and x-1st characters, where x is

                                7

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

        the current character position of the  cursor.   The  xth
        through  M-2nd  characters  on  the  line are shifted one
        character positon to the right.   The  new  character  is
        inserted   at   the  vacated  xth  position.   The  M-1st
        character is lost.  The position of  the  cursor  remains
        unchanged.

        IAC SB DET CHAR DELETE IAC SE     subcommand code:  16

        This subcommand deletes the character on  the  screen  at
        the x-th position.  The x-th character is removed and the
        characters  x+1  through  M-1  are  shifted one character
        position to the left to become  the  x-th  through  M-2nd
        characters.   The M-1st character position is left empty.
        (For most terminals it will be set to a  NUL  or  space.)
        The cursor position remains unchanged.

        IAC SB DET READ CURSOR IAC SE     subcommand code:  17

        This subcommand requests the receiver to send the present
        position of the cursor to the sender.

        IAC SB DET CURSOR POSITION <x><y> IAC SE
                                          subcommand code:  18

        where <x> and <y> are positive 8-bit binary integers.

        This subcommand is sent by  a  Telnet  implementation  in
        response  to  a  READ  CURSOR  subcommand  to  convey the
        coordinates of the cursor to the other side.  Note: x  is
        less than  M and y is less than  N.

        IAC  SB DET REVERSE TAB IAC SE     subcommand code:  19

        This subcommand causes the cursor to move to the previous
        tab position.  If none exists on the  present  line,  the
        cursor  moves  to the previous line and so on until a tab
        is found or the address (0,0) is encountered.  When field
        protection is in effect the cursor moves to the beginning
        of the preceding unprotected field.

     T__r_a_n_s_m_i_t_F__u_n_c_t_i_o_n_s  (For detailed semantics see Section 5.)

        IAC SB DET TRANSMIT SCREEN IAC SE     subcommand code: 20

        This subcommand  causes  the  terminal  to  transmit  all
        characters   on   the   screen  from  position  (0,0)  to
        (M-1,N-1).   The  cursor  will  be  at  (0,0)  after  the
        operation is complete.

                                8

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

        IAC SB DET TRANSMIT UNPROTECTED IAC SE
                                        subcommand code:  21

        This subcommand  causes  the  terminal  to  transmit  all
        characters  in  unprotected fields from position (0,0) to
        (M-1,N-1).  The unprotected fields are separated  by  the
        field  separator subcommand.  The cursor will be at (0,0)
        or at the beginning of the first unprotected field  after
        the operation is complete.

        IAC SB DET TRANSMIT LINE IAC SE      subcommand code:  22

        This subcommand causes the terminal to transmit all  data
        on  the  yth  line  where  y is determined by the present
        position of the cursor.   Data  is  sent  from  character
        position  (0,y)  to  the  end-of-line or position (M-1,y)
        whichever comes first.  The  cursor  position  after  the
        transmission  is  one character position after the end of
        line  condition  or  the  beginning  of  the  next  line,
        (0,y+1).

        IAC SB DET TRANSMIT FIELD IAC SE     subcommand code:  23

        This subcommand causes the terminal to transmit all  data
        in  the  field  presently  occupied  by  the cursor.  The
        cursor position after the operation is  complete  is  one
        character position after the end of the field or, if that
        position  is  protected,  at  the  beginning  of the next
        unprotected field.

        IAC SB DET TRANSMIT REST OF SCREEN IAC SE
                                        subcommand code:  24

        This subcommand  causes  the  terminal  to  transmit  all
        characters on the screen from position (x,y) to (M-1,N-1)
        or  until  the end of text.   (x,y) is the current cursor
        position.  The cursor position after the operation is one
        character position after  the  last  text  character,  or
        (0,0) if the last filled character position is (M-1,N-1).

        IAC SB DET TRANSMIT REST OF LINE IAC SE
                                        subcommand code:  25

        This subcommand  causes  the  terminal  to  transmit  all
        characters on the yth line from position (x,y) to the end
        of  line  or (M-1,y) whichever comes first.  (x,y) is the
        current cursor position.  The cursor position  after  the
        operation  is  one  character  position  after  the  last
        character of the line or the first character of the  next
        line.

                                9

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

        IAC SB DET TRANSMIT REST OF FIELD IAC SE
                                        subcommand code:  26

        This subcommand causes the receiver to transmit the  rest
        of  the characters in the field currently occupied by the
        cursor.  The cursor position after the  operation  is  at
        the beginning of the next field.

        IAC SB DET DATA TRANSMIT <x><y> IAC SE
                                        subcommand code:  27

        This subcommand is used to preface  data  sent  from  the
        terminal  in  response  to  a  user  action or a TRANSMIT
        command.  The parameters <x> and <y> indicate the initial
        position of the cursor.   See  the  Transmit  Subcommands
        subsection in Section 5 for more details.

     E__r_a_s_e_F__u_n_c_t_i_o_n_s

        IAC SB DET ERASE SCREEN IAC SE     subcommand code: 28

        This subcommand causes all characters to be removed  from
        the  screen.   All  fields regardless of their attributes
        are deleted.  The cursor  position  after  the  operation
        will  be (0,0).  Most terminals set the erased characters
        to either NUL or space characters.

        IAC SB DET ERASE LINE IAC SE     subcommand code:  29

        This subcommand causes all characters on the yth line  to
        be  removed  from  the screen, where y is the line of the
        current cursor position.  All fields regardless of  their
        attributes  are  deleted.  The cursor position after this
        operation will be (0,y).  Note:  This  operation  can  be
        easily  simulated  by  the  sequence:   LINE DELETE, LINE
        INSERT.  However, the order is important to  insure  that
        no data is lost off the bottom of the screen.

        IAC SB DET ERASE FIELD IAC SE     subcommand code:  30

        This  subcommand  causes  all  characters  in  the  field
        occupied  by  the  cursor  to  be  removed.   The  cursor
        position after the operation is at the beginning  of  the
        field.

        IAC SB DET ERASE REST OF SCREEN IAC SE
                                        subcommand code:  31

                               10

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

        This subcommand causes all characters from position (x,y)
        to (M-1,N-1) to be removed from the screen.   All  fields
        regardless  of  their attributes are deleted.  The cursor
        position after  the  operation  is  unchanged.   This  is
        equivalent  to  doing  an  ERASE REST OF LINE plus a LINE
        DELETE for lines greater than y.

        IAC SB DET ERASE REST OF LINE IAC SE
                                        subcommand code:  32

        This subcommand causes all characters from position (x,y)
        to (M-1,y) to be  removed  from  the  screen  All  fields
        regardless  of  their attributes are deleted.  The cursor
        position after the operation is unchanged.

        IAC SB DET ERASE REST OF FIELD IAC SE
                                        subcommand code:  33

        This subcommand causes all characters from position (x,y)
        to the end of the current field to be  removed  from  the
        screen.   The  cursor  position  after  the  operation is
        unchanged.

        IAC SB DET ERASE UNPROTECTED IAC SE
                                        subcommand code:  34

        This subcommand causes all characters on  the  screen  in
        unprotected  fields  to  be removed from the screen.  The
        cursor position after the operation is at  (0,0)  or,  if
        that position is protected, at the beginning of the first
        unprotected field.

     F__o_r_m_a_t_F__u_n_c_t_i_o_n_s

        IAC SB DET FORMAT DATA <format map><count> IAC SE
                                        subcommand code:  35

        where <format  map>  is  an  8-bit  byte  containing  the
        following flags:

          Blinking                                 7
          Reverse Video                            6
          Right Justification                      5
          Protection                              3-4
          Intensity                               0-2

        where:

        If the Blinking  bit  is  set,  the  following  field  of
        <count>  characters  should  have  the Blinking attribute

                               11

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

        applied  to it by the receiver.

        If the Reverse Video bit is set, the following  field  of
        <count>  characters  should  be displayed by the receiver
        with video reversed.

        If the Right Justification bit is set, the input  entered
        into  the  field  of  <count>  characters should be right
        justified.

        The Protection field is two bits wide and may take on the
        following values:

          0         no protection
          1         protected
          2         alphabetic only
          3         numeric only

        The protection attribute specifies that  the  other  side
        may  modify  any  character  (no  protection),  modify no
        characters   (protected),   enter    only    alphabetical
        characters  (A-Z,  and  a-z)  (alphabetic only), or enter
        only numerical characters (0-9,+,.,and -) (numeric  only)
        in the following field of <count> bytes.

        The  Intensity  field  is  3  bits  wide  and  should  be
        interpreted in the following way:

        The values 0-6 should be used as  an  indication  of  the
        relative  brightness  to  be  used  when  displaying  the
        characters in or entered into the following field <count>
        characters wide.  The  number  of  levels  of  brightness
        available  should  have  been  obtained previously by the
        Format Facility  subcommand.   The  exact  algorithm  for
        mapping these values to the available levels of intensity
        is  left  to  the  implementors.   A  value  of  7 in the
        intensity field indicates that the brightness  should  be
        off,  and  any  characters  in  or entered into the field
        should not be displayed.

        <count> is 2  bytes  that  should  be  interpreted  as  a
        positive 16-bit binary integer representing the number of
        characters  following  this command which are affected by
        it.

        Data sent to the terminal or the Using Host for unwritten
        areas of the screen not in the scope of the count  should
        be  displayed  with the default values of the format map.
        The default values are  No  Blinking,  Normal  Video,  No
        Justification, No Protection and Normal Intensity.

                               12

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

        This subcommand is used to format data to be displayed on
        the screen of the terminal.  The <format  map>  describes
        the  attributes  that the field <count> bytes wide should
        have.  This field is to start  at  the  position  of  the
        cursor  when the command is acted upon.  The next <count>
        displayable characters in the data  stream  are  used  to
        fill  the  field.   Subsequent  REPEAT subcommands may be
        used to specify the  contents  of  this  field.   If  the
        sender  specifies  attributes  that  have not been agreed
        upon by the use of the Format  Facility  subcommand,  the
        Telnet  process  should  send  an Error Subcommand to the
        sender, but format the screen as if the bit had not  been
        set.

        IAC SB DET REPEAT <count><char> IAC SE
                                        subcommand code:  36

        where  <count>  is  a  positive  8-bit  binary   integer.
        <char> is an 8-bit byte containing an ASCII character.

        This subcommand is used to perform  data  compression  on
        data  being  transferred  to  the  terminal  by  encoding
        strings of identical characters as the  character  and  a
        count.   The  repeated  characters may be part of a field
        specified

        IAC SB DET SUPPRESS PROTECTION <negotiation> IAC SE
                                            subcommand code:  37

        where <negotiation> may have the  values  of  the  Telnet
        option negotiation:

                    251                 WILL
                    252                 WONT
                    253                 DO
                    254                 DONT

        This subcommand is used to suppress the field  protection
        in  a  non-destructive manner.  Many data entry terminals
        provide the means by which protection may  be  turned  on
        and  off  without modifying the contents of the screen or
        the terminal's  memory.   Thus,  the  protection  may  be
        turned  off  and back on without retransmitting the form.
        The default setting of the option is that  protection  is
        on, in other words

                    IAC SB DET SUPPRESS PROTECTION WONT IAC SE
                    IAC SB DET SUPPRESS PROTECTION DONT IAC SE

                               13

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

        Negotiation of this subcommand follows the same rules  as
        negotiations of the Telnet options.

        IAC SB DET FIELD SEPARATOR IAC SE    subcommand code:  38

        It is necessary when transmitting  only  the  unprotected
        portion  of  the screen to provide a means for delimiting
        the fields.   Existing  DET's  use  a  variety  of  ASCII
        characters  such as Tab, Group Separator, Unit Separator,
        etc.  In order to maintain transparency of the NVDET this
        subcommand is used to separate the fields.  Clearly, this
        incurs  rather  high  overhead.   This  overhead  can  be
        avoided by using the Byte Macro Option (see Appendix 3).

     M__i_s_c_e_l_l_a_n_e_o_u_s_C__o_m_m_a_n_d_s

        IAC SB DET FN <code> IAC SE     subcommand code:  39

        where:  <code> is one byte.

        Many data-entry terminals provide  a  set  of  "function"
        keys  which  when pressed send a one-character command to
        the server.  This subcommand describes such  a  facility.
        The  values  of  the <code> field are defined by the user
        and server.  The option  merely  provides  the  means  to
        transfer the information.

        IAC SB DET ERROR <cmd> <error code> IAC SE
                                        subcommand code:  40

        where:
               <cmd> is a byte containing the subcommand code  of
        the subcommand in error.
                <error code> is a byte containing an error  code.
        (For a list of the defined error codes see Appendix 2.)

        This  subcommand  is   provided  to  allow   DET   option
        implementations  to  report  errors  they  detect  to the
        corresponding Telnet process.  At this point it is  worth
        reiterating  that  the  philosophy of this option is that
        when an error is detected it should be reported; however,
        the implementation should  attempt  its  best  effort  to
        carry out the intent of the subcommand or data in error.

                               14

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

3.  Default and Minimal Implementation Specifications

     D__e_f_a_u_l_t

        WON'T DET -- DON'T DET

        Neither host wishes to use the Data Entry Terminal option.

     M__i_n_i_m_a_l_I__m_p_l_e_m_e_n_t_a_t_i_o_n

          DET EDIT FACILITIES
          DET ERASE FACILITIES
          DET TRANSMIT FACILITIES
          DET FORMAT FACILITIES
          DET MOVE CURSOR <x><y>
          DET HOME
          DET ERASE SCREEN
          DET TRANSMIT SCREEN
          DET FORMAT DATA
          DET ERROR <cmd> <error code>

        In  the  case  of  formatting  the  data,   the   minimal
        implementation  should  be able to support a low and high
        level  of  intensity  and  protection  for  all   or   no
        characters in a field.  These functions, however, are not
        required.

        The minimal implementation also requires that the  Output
        Line  Width  and  Output  Page  Size  Telnet  options  be
        supported.

                               15

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

4.  Motivation

     The Telnet protocol was originally  designed  to  provide  a
     means  for  scroll-mode  terminals,  such  as  the  standard
     teletype, to communicate with processes through the network.
     This was suitable for the vast  majority  of  terminals  and
     users  at  that  time.   However,  as use of the network has
     increased into  other  areas,  especially  areas  where  the
     network  is  considered  to provide a production environment
     for other work, the desires and  requirements  of  the  user
     community  have  changed.   Therefore,  it  is  necessary to
     consider  supporting  facilities  that  were  not  initially
     supported.   This  Telnet  option  attempts  to  do that for
     applications that require data entry terminals.

     This option in effect defines the Network Virtual Data Entry
     Terminal.  Although the description of this option is  quite
     long, this does not imply that the Telnet protocol is a poor
     vehicle  for this facility.  Data Entry Terminals are rather
     complex and varied in their abilities.  This option attempts
     to support both the minimal set of useful functions that are
     either common to all or can be easily simulated and the more
     sophisticated functions supplied in some terminals.

     Unlike most real data entry  terminals  where  the  terminal
     functions  are  encoded  into  one or more characters of the
     native character set, this option performs all such controls
     within the Telnet  subnegotiation  mechanism.   This  allows
     programs  that  are  intimately  familiar  with  the kind of
     terminal they are communicating with to send  commands  that
     may   not   be   supported  by  either  the  option  or  the
     implementation.  In other words, it is possible  to  operate
     in  a  "raw"  or  at  least "rare" mode using as much of the
     option as necessary.

     Although many data entry  terminals  support  a  variety  of
     peripheral  devices such as printers, cassettes, etc.  it is
     beyond  the  scope  of  this  option   to   entertain   such
     considerations.   A  separate  option  should  be defined to
     handle this aspect of these devices.

                               16

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

5.  Description

G__e_n_e_r_a_l_N__o_t_e_s

     All implementations of this option are required to support a
     certain minimal set of  the  subcommands  for  this  option.
     Section  3  contains  a  complete list of the subcommands in
     this minimal set.   In  keeping  with  the  Telnet  protocol
     philosophy that an implementation should not have to be able
     to parse commands it does not implement, every subcommand of
     this  option  is  either in the minimal set or is covered by
     one of the facility  subcommands.   An  implementation  must
     "negotiate"  with  its  correspondent  for permission to use
     subcommands not in the minimal set before using  them.   For
     details of this negotiation process see the section below on
     facility subcommands.

     Most data entry terminals are used in a  half  duplex  mode.
     (Although  most  DET's  on  the market can be used either as
     data entry terminals or as standard  interactive  terminals,
     we  are  only concerned here with their use as DET's.)  When
     this option is used, it  is  suggested  that  the  following
     Telnet   options   be   refused:   Echo,  Remote  Controlled
     Transmission and Echoing, and Suppress  Go-Ahead.   However,
     this  option  could  be used to support a simple full duplex
     CRT  based  application  using  the  basic  cursor   control
     functions  provided  here.   For these cases, one or more of
     the above list of  options might be required.   (Support  of
     sophisticated   interactive   calligraphic  applications  is
     beyond the scope of this   option  and  should  be  done  by
     another option or the Network Graphics Protocol.)

     In RFC 728, it was noted that a  synch  sequence  can  cause
     undesired  interactions between Telnet Control functions and
     the data stream.  A  synch  sequence  causes  data  but  not
     control  functions  to  be  flushed.   If a control function
     which has an effect on the  data immediately following it is
     present in the data stream when a synch sequence occurs, the
     control function will have its effect not  on  the  intended
     data  but  on  the data immediately following the Data Mark.
     The  following  DET  subcommands  are  susceptible  to  this
     pitfall:

                    CHAR INSERT
                    DATA TRANSMIT
                    FORMAT DATA

     The undesired interactions are best avoided by the  receiver

                               17

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

     of  the  synch  sequence  deleting these subcommands and all
     data associated with them before continuing to  process  the
     control  functions.   This implies that the Data Mark should
     not occur in the middle of the data  associated  with  these
     subcommands.

F__a_c_i_l_i_t_y_S__u_b_c_o_m_m_a_n_d_s

     These four subcommands are  used  by  the  User  and  Server
     implementations  to negotiate the subcommands and attributes
     of the terminal that may be utilized.  This negotiation  can
     be  viewed  as  the  terminal  (User  Host)  indicating what
     facilities are provided and the Server Host (or  application
     program) indicating what facilities are desired.

     W__h_e_n_S__e_n_t:_  A Server Telnet  implementation  using  the  DET
     option must send a facility subcommand requesting the use of
     a  particular  subcommand  or  terminal attribute not in the
     minimal  implementation  before  the  first  use   of   that
     subcommand  or  attribute.   The  User Telnet implementation
     should respond  as  quickly  as  possible  with  its  reply.
     Neither  the  User  nor Server are required to negotiate one
     subcommand  at  a  time.   Also,  a  Telnet   implementation
     responding  to a facility subcommand is not required to give
     permission only for that subcommand.   It may send a  format
     map  indicating  all  facilities  of  that  class  which  it
     supports.   However,  a  Telnet  implementation   requesting
     facilities  must send a facility subcommand before its first
     use  of  the  subcommand  regardless  of   whether   earlier
     negotiations  have  indicated the facility is provided.  The
     facility cannot  be  used  until  a  corresponding  facility
     subcommand   has   been   received.    There  are  no  other
     constraints on when the facility subcommands  may  be  sent.
     In  particular,  it  is  not necessary for an application to
     know at the beginning of a session all  facilities  that  it
     will use.

     A__c_t_i_o_n_W__h_e_n_R__e_c_i_e_v_e_d:_  There are two possible  actions  that
     may   be  taken  when  a  facility  subcommand  is  received
     depending on whether  the  receiver  is  a  requestor  or  a
     provider (User).

     Requestor:  When a facility  subcommand  is  received  by  a
     requestor  and it is in the state of Waiting for a Reply, it
     should go into the state of Not  Waiting.   It  should  then
     take  the  facility  map   it  had sent and form the logical
     intersection with  the  facility  map  received.   (For  the
     Intensity  attribute,  one  should  take  the minimum of the
     number received  and  the  number  requested.)   The  result
     indicates  the facilities successfully negotiated.  Note: if

                               18

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

     the receiver is not in the Waiting  for  Reply  state,  then
     this is the provider case described next.

     Provider:  When  a  facility  subcommand   is  received,  it
     should send a facility subcommand with a facility map of the
     facilities  it provides as soon as possible.  It should then
     determine what  new  facilities  it  is  providing  for  the
     Requestor   by  forming  the  logical  intersection  of  the
     facility map received and the one sent.

     Note:  Although in most cases  the  requestor  will  be  the
     Server   Host  and  the  provider  will  be  the  User  Host
     supporting the terminal, this distinction may not always  be
     true.

T__r_a_n_s_m_i_t_S__u_b_c_o_m_m_a_n_d_s

     There are two kinds of transmit subcommands:  those used  to
     request  that  data  be  sent  to  the requestor, and one to
     preface data sent to the requestor.  The  first  kind  allow
     the requestor to control when, from where and to some degree
     how  much  data  is  transmitted  from  the terminal.  Their
     explanation is straightforward and may be found  in  Section
     2.

     Data may be sent from  the  terminal  as  a  result  of  two
     events:  the user of the terminal caused the transmission or
     in  response  to  a  transmit subcommand.  Some programs may
     wish to know from  where  on  the  screen  the  transmission
     began.   (This  is  reasonable,  since the terminal user may
     move the cursor around  considerably  before  transmitting.)
     Other  programs  may  not  need  such information.  The DATA
     TRANSMIT subcommand is provided in  case  this  function  is
     needed.  When used this subcommand prefaces data coming from
     the  terminal.   The parameters  <x> and <y> give the screen
     coordinates of the beginning of the transmission.  <x>  must
     be  less  than or equal to M-1 and  <y> must be less than or
     equal to N-1.  It is assumed that all data between this DATA
     TRANSMIT and the  next one starts at the  coordinates  given
     by  the  first  subcommand   and continues filling each line
     thereafter according to the constraints of  the  screen  and
     the  format  effectors  in the data.  Thus an intelligent or
     sloppy user-host DET implementation (depending on your point
     of view) need only include a DATA TRANSMIT  subcommand  when
     the  new  starting  point  is different from the last ending
     point.

6.  Sample Interaction

                               19

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

The nomenclature of RFC 726 will be used to describe this  example.   To
quote that RFC:

     "S:"  is sent from serving host to using host.
     "U:"  is sent from using host to serving host.
     "T:"  is entered by the terminal user.
     "P:"  is printed on the terminal.

     Text  surrounded  by  square  brackets([])  is  commentary.    Text
     surrounded  by angle brackets (<>) is to be taken as a single unit.
     E.g,  carriage  return  is  <cr>,  and  the  decimal  value  27  is
     represented <27>.

     We assume that the user  has  established  the  Telnet  connection,
     logged  on, and an application program has just been started either
     by the user directly or through a canned start up  procedure.   The
     presentation on the page is meant to merely group entities together
     and  does not imply the position of message boundaries.  One should
     assume that any part of the dialogue may be sent  as  one  or  many
     messages.   The  first  action  of  the  program  or  Telnet  is to
     negotiate the DET option:

S: <IAC><DO><DET>

U:  <IAC><WILL><DET>

S:<IAC><DO><OUTPUT PAGE SIZE>           [First negotiate the screen
                                        size.  In this case we are
U:<IAC><WILL><NAOP>                     asking the user the size of the
                                        terminal.  This could have been
U:<IAC><SB><NAOP><DR><25><IAC><SE>      done before the DET option was
                                        negotiated.]
S:<IAC><SB><NAOP><DS><0><IAC><SE>

S:<IAC><DO><OUTPUT LINE WIDTH>

U:<IAC><SB><NAOL><DR><80><IAC><SE>      [Defines the screen to be 25
                                        lines by 80 characters.
S:<IAC><SB><NAOL><DS><0><IAC><SE>       The server may use this
                                        information when formatting
                                        the screen.]
S:<IAC><SB><DET><FORMAT FACILITIES>     [Now set the terminal attributes.]
  <Repeat><Protection, 3 Levels
  Intensity><IAC><SE>

U:<IAC><SB><DET><FORMAT FACILITIES>
  <Repeat, Blinking><Protection, 3
  Levels Intensity><IAC><SE>

S:<IAC><SB><DET><ERASE SCREEN><IAC><SE>     [Erase the screen and

                               20

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

                                            start sending the form.]
  <IAC><SB><DET><FORMAT DATA>
  <Protection=1, Intensity=1><0>
  <5><IAC><SE>Name:

  <IAC><SB><DET><MOVE CURSOR><0><1>
    <IAC><SE>

  <IAC><SB><DET><FORMAT DATA>
    Protection=1, Intensity=1><0>
    <8><IAC><SE>

  Address:
  <IAC><SB><MOVE CURSOR><0><4><IAC>
    <SE>

  <IAC><SB><DET><FORMAT DATA>
    Protection=1, Intensity=1><0>
    <17><IAC><SE>
  Telephone number:

  <IAC><SB><DET><MOVE CURSOR><32><4>
  <IAC><SE>

  <IAC><SB><DET><FORMAT DATA>
    Protection=1, Intensity=1><0>
    <24><IAC><SE>
  Social Security Number:

  <IAC><SB><DET><FORMAT DATA>           [Establish a field that doesn't
    <Protection=1, Intensity=7>         display what is typed into it.]
    <0><11><IAC><SE>

  <IAC><SB><DET><MOVE CURSOR><32>
    <5><IAC><SE>

  <IAC><SB><DET><FORMAT FACILITIES>     [Get permission to use Blinking
    <Blinking><0><IAC><SE>              Attribute.]

U:<IAC><SB><DET><FORMAT FACILITIES>
    <Repeat, Blinking><Protection,
    3 Levels Intensity><IAC><SE>

S:<IAC><SB><DET><FORMAT DATA>
  <Blinking=1, Protection=1,
  Intensity=1><0><29><IAC><SE>

  Your SSN will not be printed.

  <IAC><SB><DET><HOME><IAC><SE>

                               21

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

  <IAC><GA>

The previous exchange has placed a form on the screen that looks like:

Name:
Address:

Telephone Number:                       Social Security Number:
                                   "Your SSN will not be printed."

where the quoted string is blinking.

The terminal user is  now  free  to  fill  in  the  form  provided.   He
positions  the  cursor at the beginning of the first field (this usually
is done by hitting the tab key) and begins typing.  We do not show  this
interaction  since  it  does  not generate any interaction with the User
Telnet program or the network.  After the terminal  user  has  completed
filling in the form, he strikes the transmit key to send the unprotected
part  of the form, but first the User Telnet program negotiates the Byte
Macro Option to condense the Field Separator subcommand:

U:<IAC><DO><BM>                         [Negotiate Byte Macro Option.]

S:<IAC><WILL><BM>                       [Define decimal 166 to be the
                                        Field Separator subcommand
U:<IAC><SB><BM><DEFINE>                 (see Appendix 3)]
  <166><6><IAC SB DET FIELD
  SEPARATOR IAC SE><IAC><SE>

S:<IAC><SB><BM><ACCEPT><166>            [The server accepts the macro.]
  <IAC><SE>

U:<IAC><SB><DET><DATA TRANSMIT><0><6>
  <IAC><SE>
  John Doe <166> 1515 Elm St., Urbana, Il 61801
  <166> 217-333-9999 <166> 123-45-6789 <166>

S:<IAC><SB><DET><ERASE SCREEN><IAC><SE>
  Thank you.

And so on.

                               22

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

Appendix 1 - Subcommands, opcodes and syntax

               1    EDIT FACILITIES     <Facilty map>
               2    ERASE FACILITIES    <Facility map>
               3    TRANSMIT FACILITIES <Facility map>
               4    FORMAT FACILITIES    <Facility map 1> <Facility map 2>
               5    MOVE CURSOR          <x> <y>
               6    SKIP TO LINE         <y>
               7    SKIP TO CHAR         <x>
               8    UP
               9    DOWN
               10   LEFT
               11   RIGHT
               12   HOME
               13   LINE INSERT
               14   LINE DELETE
               15   CHAR INSERT
               16   CHAR DELETE
               17   READ CURSOR
               18   CURSOR POSITION      <x><y>
               19   REVERSE TAB
               20   TRANSMIT SCREEN
               21   TRANSMIT UNPROTECTED
               22   TRANSMIT LINE
               23   TRANSMIT FIELD
               24   TRANSMIT REST OF SCREEN
               25   TRANSMIT REST OF LINE
               26   TRANSMIT REST OF FIELD
               27   DATA TRANSMIT <x><y>
               28   ERASE SCREEN
               29   ERASE LINE
               30   ERASE FIELD
               31   ERASE REST OF SCREEN
               32   ERASE REST OF LINE
               33   ERASE REST OF FIELD
               34   ERASE UNPROTECTED
               35   FORMAT DATA <format map>
               36   REPEAT     <count><char>
               37   SUPPRESS PROTECTION <negotiation>
               38   FIELD SEPARATOR
               39   FN <code>
               40   ERROR  <cmd><error code>

                               23

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

Appendix 2 - Error Codes

               1    Facility not previously negotiated.
               2    Illegal subcommand code.
               3    Cursor Address Out of Bounds.
               4    Undefined FN value.
               4    Can't negotiate acceptable line width.
               5    Can't negotiate acceptable page length.
               6    Illegal parameter in subcommand.
               7    Syntax error in parsing subcommand.
               8    Too many parameters in subcommand.
               9    Too few parameters in subcommand.
               10   Undefined parameter value
               11   Unsupported combination of Format Attributes

                               24

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

               Appendix 3 - Use of the Byte Macro Option

     One of the major drawbacks of the DET option is  that  because  the
     functions  are  encoded  as  Telnet option subnegotiations a fairly
     high overhead is incurred.  A function like Character Insert  which
     is encoded as a single byte in most terminals requires six bytes in
     the DET option.  Originally the only other solution that would have
     accomplished  the  same  transparency  that  the use of subcommands
     provides would  have  been  to  define  additional  Telnet  control
     functions.   However,  since  this would entail modification of the
     Telnet protocol itself, it was  felt  that  this  was  not  a  wise
     solution.    Since  then the Telnet Byte Macro Option (RFC 729) has
     been defined.  This option allows the user and  server  Telnets  to
     map  an arbitrary character string into a single byte which is then
     transferred over the net.  Thus the Byte Macro Option provides  the
     means  for  implementations  to avoid the overhead for heavily used
     subcommands.  The rest of this appendix suggests how the Byte Macro
     Option should be applied to the DET option.

     In keeping with the specification of the Byte Macro Option,   macro
     bytes  will  be  chosen  from  the  range 128 to 239.   For the DET
     option, it is suggested that macro  bytes be chosen by  adding  the
     subcommand  code to 128.  In addition, an unofficial DET subcommand
     might be defined indicating that each side was willing  to  support
     macro bytes for all subcommands (but not necessarily support all of
     the  subcommands  themselves)  according  to  this algorithm.  This
     subcommand would be:

     IAC SB DET DET-MACRO <negotiation> IAC SE
                                        subcommand code:  254

     where <negotiation> may  have  the  values  of  the  Telnet  option
     negotiation:
                    251       WILL
                    252       WONT
                    253       DO
                    254       DONT

     This subcommand is sent by a Telnet implementation to  indicate its
     willingness to adopt byte macros for all  of  the  DET  subcommands
     according to the following algorithm:

                               25

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

        The macro byte for subcommand i will be i+128 and will represent
        the following string for parameterless subcommands:

        IAC SB DET <subcommand code> IAC SE

        and the following string for subcommands  with  parameters:

        IAC SB DET <subcommand code>

        The default setting for this subcommand is that the  macros  are
        not in effect, in other words,

             IAC SB DET DET-MACRO WONT IAC SE
             IAC SB DET DET-MACRO DONT IAC SE

        Negotiation  of  this  subcommand  follows  the  same  rules  as
        negotiations of the Telnet options.

                               26

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

                               References

     1.  ADM-1 Interactive Display Terminal Operator's Handbook
           Lear-Siegler, Inc. 7410-31.

     2.  ADM-Interactive Display Terminal Operator's Handbook
            Lear-Siegler, Inc. EID, 1974.

     3.  Burroughs TD 700/800 Reference Manual, Burroughs Corp., 1973

     4.  Burroughs TD 820 Reference Manual, Burroughs Corp. 1975.

     5.  CC-40  Communications Station:  General Information Manual.
           Computer Communication, Inc.  Pub. No. MI-1100. 1974.

     6.  Crocker, David.  "Telnet Byte Macro Option," RFC 729, 1977.

     7.  Data Entry Virtual Terminal Protocol for Euronet, DRAFT, 1977.

     8.  Day, John.  "A Minor Pitfall in the Telnet Protocol,"
           RFC 728, 1977.

     9.  Hazeltine 2000 Desk Top Display Operating Instructions.
           Hazeltine IB-1866A, 1870.

     10.  How to Use the Consul 980:  A Terminal Operator's Guide
           and Interface Manual.  Applied Digital Data Systems, Inc.
            98-3000.

     11.  How to Use the Consul 520:  A Terminal Operator's Guide
           and Interface Manual.  Applied Digital Data Systems, Inc.
           52-3000.

     12.  Honeywell 7700 Series Visual Information Projection (VIP)
            Systems:  Preliminary Edition. 1973.

     13.  An Introduction to the IBM 3270 Information Display System.
            IBM GA27-2739-4. 1973.

     14.  Naffah, N.  "Protocole Appareil Virtuel type Ecran"
            Reseau Cyclades.  TER 536. 1976.

                               27

John Day                               Data Entry Terminal Option
June 27,1977                                            NIC 40652
                                                          RFC 731

     15.  Postel, Jon and Crocker, David.  "Remote Controlled
            Transmission and Echoing Telnet Option", RFC 726
            NIC 39237, Mar. 1977.

     16.  Schicker, Peter.  "Virtual Terminal Protocol (Proposal 2).
            INWG Protocol Note #32., 1976.

     17.  UNISCOPE Display Terminal :  Programmer Reference .  Sperry-
            Univac UP-7807 Rev. 2, 1975.

     18.  Universal Terminal System 400:  System Description.  Sperry-
            Univac UP-8357, 1976.

     19.  Walden, David C. "Telnet Output Line Width Option."
            NIC # 20196, 1973, also in ARPANET Protocol Handbook, 1976.

     20.  Walden, David C.  "Telnet Output Page Size"  NIC # 20197,
            1973, also in ARPANET Protocol Handbook, 1976.

                               28

 

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