
NWG/RFC# 732                                  DAY 13-Sep-77 18:38  41762
Data Entry Terminal Option



Network Working Group                                           John Day
Request for Comments: 732                                               
NIC: 41762                                             12 September 1977

Obsoletes: 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.

  The Network Virtual Data Entry Terminal (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.





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Data Entry Terminal Option



    (Although most DET's will support one or more peripheral devices
    such as a paper tape reader or a printer, this option does not
    consider their support. Support of peripheral devices should be
    treated by a is 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.

  Facility Functions  (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 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





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Data Entry Terminal Option



    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.)







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    facility cmd:  ERASE FACILITIES                  subcommand code:  2

      facility map:                                bit numbers

        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

        FN                                 byte 0      7
        Modified                                       6
        Light Pen                                      5
        Repeat                                         4
        Blinking                                       3
        Reverse Video                                  2
        Right Justification                            1
        Overstrike                                     0





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Data Entry Terminal Option



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

    where:

    If the FN bit is set, the sender requests or provides the FN
    subcommand.

    If the Modified bit is set, the sender requests or provides the
    ability to indicate fields that are modified and supports the
    TRANSMIT MODIFIED subcommand.

    If the Light Pen bit is set, the sender requests or provides the
    support of a light pen, including the Pen Selectable attribute of
    the DATA FORMAT subcommand.

    If the Repeat bit is set the sender requests or provides 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






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Data Entry Terminal Option



    characters displayed on the screen from being altered by the user of
    the terminal. Setting this bit also implies that ERASE UNPROTECTED,
    DATA TRANSMIT, FIELD SEPARATOR, 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:

      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.

  Editing Functions

    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.







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Data Entry Terminal Option



    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.

    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.





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Data Entry Terminal Option



    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 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.






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    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.

  Transmit Functions (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.

    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.






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    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.

    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 TRANSMIT MODIFIED IAC SE              subcommand code: 27

    This subcommand causes the receiver to transmit only those fields
    which have the modified attribute set. The cursor position after the
    operation is unchanged.

    IAC SB DET DATA TRANSMIT <x><y> IAC SE           subcommand code: 28

    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. A
    DATA TRANSMIT subcommand may precede an entire transmission with
    each field being delineated by the FIELD SEPARATOR subcommand as
    would be the case in a response toa

    TRANSMIT UNPROTECTED. Or, it may precede each field as would be the
    case in a response to a TRANSMIT MODIFIED.

  Erase Functions

    IAC SB DET ERASE SCREEN IAC SE                   subcommand code: 29






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Data Entry Terminal Option



    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: 30

    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: 31

    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: 32

    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: 33

    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: 34

    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: 35

    This subcommand causes all characters on the screen in unprotected
    fields to be removed from the screen. The cursor position after the






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    operation is at (0,0) or, if that position is protected, at the
    beginning of the first unprotected field.

  Format Functions

    IAC SB DET FORMAT DATA <format map><count> IAC SE
                                                     subcommand code: 36

    where <format map> is a two byte field containing the following
    flags:

      Byte 0
        Blinking                                 7
        Reverse Video                            6
        Right Justification                      5
        Protection                              3-4
        Intensity                               0-2
      Byte 1
        Modified                                1
        Pen Selectable                          0

    where:

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





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    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.

    If the Modified bit is set, the field is considered to have been
    modified and will be transmitted in response to a TRANSMIT MODIFIED
    subcommand.

    If the Pen Selectable bit is set, the field can be selected with the
    light pen. Note: Use of the light pen should be the subject of
    another Telnet option.

    <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. For example, suppose a FORMAT DATA subcommand was sent to
    the terminal with attributes Blinking and Protected and a

    count of 5 followed by the string "Name: John Doe". The string
    "Name:" would be protected and blinking, but the string "John Doe"
    would not be.

    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.






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    IAC SB DET REPEAT <count><char> IAC SE           subcommand code: 37

    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: 38

    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

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

    IAC SB DET FIELD SEPARATOR IAC SE                subcommand code: 39

    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).






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Data Entry Terminal Option



  Miscellaneous Commands

    IAC SB DET FN <code> IAC SE                      subcommand code: 40

    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: 41

    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.























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Data Entry Terminal Option



3. Default and Minimal Implementation Specifications

  Default

    WON'T DET -- DON'T DET

    Neither host wishes to use the Data Entry Terminal option.

  Minimal Implementation

    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.
























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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.


















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5. Description

  General Notes

    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

    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.





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  Facility Subcommands

    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.

    When Sent: 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.

    Action When Recieved: 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

    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






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    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.

  Transmit Subcommands

    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.


















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Data Entry Terminal Option



6.  Sample Interaction

  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
                                             asking the user the size of
                                             the terminal.  This could
                                             have been done before the
                                             DET option was negotiated.]

  U:<IAC><WILL><NAOP>

  U:<IAC><SB><NAOP><DR><25><IAC><SE>

  S:<IAC><SB><NAOP><DS><0><IAC><SE>

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










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  U:<IAC><SB><NAOL><DR><80><IAC><SE>         [Defines the screen to be
                                             25 lines by 80 characters.
                                             The server may use this
                                             information when formatting
                                             the screen.]

  S:<IAC><SB><NAOL><DS><0><IAC><SE>

  S:<IAC><SB><DET><FORMAT FACILITIES>
  <Repeat><Protection, 3 Levels
  Intensity><IAC><SE>                        [Now set the terminal
                                             attributes.]

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





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Data Entry Terminal Option



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

    <IAC><SB><DET><FORMAT FACILITIES>
    <Blinking><0><IAC><SE>                   [Get permission to use
                                             Blinking 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>
    <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 (see Appendix
                                             3)]







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Data Entry Terminal Option



  U:<IAC><SB><BM><DEFINE>
  <166><6><IAC SB DET FIELD
  SEPARATOR IAC SE><IAC><SE>

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

  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.





































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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        TRANSMIT MODIFIED
  28        DATA TRANSMIT <x><y>
  29        ERASE SCREEN
  30        ERASE LINE
  31        ERASE FIELD
  32        ERASE REST OF SCREEN
  33        ERASE REST OF LINE
  34        ERASE REST OF FIELD
  35        ERASE UNPROTECTED
  36        FORMAT DATA <format map>
  37        REPEAT     <count><char>
  38        SUPPRESS PROTECTION <negotiation>
  39        FIELD SEPARATOR
  40        FN <code>
  41        ERROR  <cmd><error code>









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Appendix 2 - Error Codes

  1         Facility not previously negotiated.

  2         Illegal subcommand code.

  3         Cursor Address Out of Bounds.

  4         Undefined FN value.

  5         Can't negotiate acceptable line width.

  6         Can't negotiate acceptable page length.

  7         Illegal parameter in subcommand.

  8         Syntax error in parsing subcommand.

  9         Too many parameters in subcommand.

  10        Too few parameters in subcommand.

  11        Undefined parameter value

  12        Unsupported combination of Format Attributes



























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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:

    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:





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    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.










































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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.

  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.







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  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.









































John Day                                                       [page 30]