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rfc:rfc1043

Network Working Group A. Yasuda Request for Comments: 1043 T. Thompson

                                           Defense Intelligence Agency

Updates: RFC 732 February 1988

                 TELNET Data Entry Terminal Option
                       DODIIS Implementation

Status of this Memo

 This RFC suggests a proposed protocol on the TELNET Data Entry
 Terminal (DET) Option - DODIIS Implementation for the Internet
 community.  It is intended that this specification be compatible with
 the specification of DET Option in RFC-732.  Discussion and
 suggestions for improvements are encouraged.  Distribution of this
 memo is unlimited.

Introduction

 In the early 1980s, the Defense Intelligence Agency (DIA) undertook
 the tasks of developing a TELNET capability to access full screen
 applications across a packet switching network.  This effort was
 successful by implementing Data Entry Terminal (DET) options within
 the TELNET protocol based on RFC 732.  These DET options have been
 implemented on IAS, MVS, OS86 and UNIX operating systems.  DET
 options are being developed for VM and VMS operating systems.
 The Department of Defense Intelligence Information System (DODIIS) is
 a confederation of heterogeneous computer systems and remote
 terminals utilizing the Defense Data Network (DDN) as the
 communications backbone (namely the SCINET/DSNET-3).
 Although the reason for implementing a DET option specification was
 based upon data base application interfaces, the use of a full screen
 TELNET provides a method to achieve higher efficiency on the network.
 Most terminal to host applications on the ARPANET are character echo
 TELNETs.  This is both costly in time and network utilization, since
 one character pressed on the keyboard generates a datagram composed
 of TCP/IP headers plus the character sent to the host and the host
 echoes back a similar datagram.  In the DODIIS community, programmers
 are highly encouraged to implement full screen applications; line at
 a time is acceptable; and character remote echo mode is discouraged.
 This RFC in its final form will be implemented on SCINET.  During the
 interim period, the "DODIIS TELNET Network Virtual Data Entry
 Terminal (NVDET) Option Specification", DIA, April 1983, will be
 implemented.

Yasuda & Thompson [Page 1] RFC 1043 Data Entry Terminal - DODIIS February 1988

                           TABLE OF CONTENTS
                                                              Page No.
                                                              --------
 SECTION 1   COMMAND NAME AND OPTION CODE                          4
 SECTION 2   COMMAND MEANINGS                                      4
               Facilities Subcommands                              4
               Edit Subcommands                                    8
               Transmit Subcommands                                8
               Erase Subcommands                                  10
               Format Subcommands                                 10
               Miscellaneous Subcommands                          13
 SECTION 3   DEFAULT AND MINIMAL IMPLEMENTATION                   15
 SECTION 4   MOTIVATION FOR THE OPTION                            17
 SECTION 5   DESCRIPTION AND IMPLEMENTATION RULES                 17
               The DODIIS DET Model                               17
               Negotiating the DET Option                         18
               DET Facilities Negotiation                         18
               General DET Interaction                            19
               Form Construction                                  20
               Form response                                      21
               Function Keys                                      22
               Field Selection                                    22
               Out-Of-Context Data                                23
               Line Discipline                                    23
               Standard TELNET Control Functions                  24
               Other Implementation Notes                         24
 APPENDIX 1  DET OPCODES AND SUBCOMMAND SYNTAX                    25
 APPENDIX 2  DET ERROR CODES                                      26

Yasuda & Thompson [Page 2] RFC 1043 Data Entry Terminal - DODIIS February 1988

 The convention in the documentation of the TELNET NVDET Protocol is
 to express numbers in decimal.  Data fields are described left to
 right, with the most significant octet on the left and the least
 significant octet on the right.
 The order of transmission of the data described in this document is
 resolved to the octet level.  Whenever a diagram shows a group of
 octets, the order of transmission of those octets is the normal order
 in which they are read in English.  For example, in the following
 diagram the octets are transmitted in the order they are numbered.
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       1       |       2       |       3       |       4       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       5       |       6       |       7       |       8       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       9       |      10       |      11       |      12       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      Transmission Order of Bytes
 Whenever an octet represents a numeric quantity, the left most bit in
 the diagram is the high order or most significant bit.  That is, the
 bit labeled 0 is the most significant bit.  For example, the
 following diagram represents the value 170 (decimal).
                            0 1 2 3 4 5 6 7
                           +-+-+-+-+-+-+-+-+
                           |1 0 1 0 1 0 1 0|
                           +-+-+-+-+-+-+-+-+
                         Significance of Bits
 Similarly, whenever a multi-octet field represents a numeric
 quantity, the left most bit of the whole field is the most
 significant bit.  When a multi-octet quantity is transmitted the most
 significant octet is transmitted first.

Yasuda & Thompson [Page 3] RFC 1043 Data Entry Terminal - DODIIS February 1988

 1. Command Name and Option Code
    DET         20
 2. Command Meanings
    IAC WILL DET
       The sender of this command REQUESTS permission to begin, or
       AGREES that it will begin, sending and receiving Data Entry
       Terminal (DET) subcommands to control session interactions.
    IAC WONT DET
       If the connection is already operating in DET mode, the sender
       of this command DEMANDS that the connection stop operating in
       DET mode and begin operating in TELNET NVT mode.  If the
       connection is not operating in DET mode, the sender REFUSES to
       begin operating in DET mode.  A connection is operating in
       TELNET NVT mode when both parties are interpreting data as
       described by the TELNET SPECIFICATION, MIL-STD-1782.
    IAC DO DET
       The sender of this command REQUESTS permission to begin, or
       AGREES that it will begin, sending and receiving Data Entry
       Terminal (DET) subcommands to control session interactions.
    IAC DONT DET
       If the connection is already operating in DET mode, the sender
       of this command DEMANDS that the connection stop operating in
       DET mode and begin operating in TELNET NVT mode.  If the
       connection is not operating in DET mode, the sender REFUSES  to
       begin  operating in DET mode.    A connection is operating in
       TELNET NVT mode when both parties are interpreting data as
       described by the TELNET SPECIFICATION, MIL-STD-1782.
    DODIIS implementations of the DET option use the subcommands
    described in the remainder of Section 2.  A description of the
    DODIIS DET model and DET subcommand usage is contained in Section
    5.
 FACILITIES SUBCOMMANDS.  Facilities subcommands are used to negotiate
 DET facilities (subcommands and attributes).  The facility
 subcommands indicate the DET facilities the sender supports.
 Facility negotiation may be viewed as the terminal indicating the
 facilities it provides and the application indicating the facilities

Yasuda & Thompson [Page 4] RFC 1043 Data Entry Terminal - DODIIS February 1988

 it desires.  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.
    IAC SB DET EDIT-FACILITIES <facility map> IAC SE
       subcommand code:  1
       This subcommand indicates the edit facilities the sender
       supports.  The <facility map> parameter is one eight bit byte
       containing the following flags:
           Bits 5-7        Reserved
           Bit  4          Read Cursor
           Bits 0-3        Reserved
       where:
           If the Read-Cursor bit is set, the sender supports the
           READ-CURSOR and CURSOR-POSITION subcommands.
           Reserved bits represent edit facilities that are not
           defined for DODIIS implementations;  therefore, no
           descriptions are provided.  Reserved bits must be zeroed
           to indicate non support of the associated edit facilities.
    IAC SB DET ERASE-FACILITIES <facility map> IAC SE
       subcommand code:  2
       This subcommand indicates the erase facilities the sender
       supports.  The <facility map> parameter is one eight bit
       byte containing flags.  Since no erase facilities are
       defined for DODIIS implementations, no descriptions are
       provided.  The ERASE-FACILITIES subcommand is part of the
       minimal DET implementation and is included for that reason.
       DODISI implementors must declare non support of erase
       facilities by sending this subcommand with a zeroed facility
       map.
    IAC SB DET TRANSMIT-FACILITIES <facility map> IAC SE
       subcommand code:  3
       This subcommand indicates the transmit facilities the sender
       supports.  The <facility map> parameter is one eight bit byte
       containing the following flags:

Yasuda & Thompson [Page 5] RFC 1043 Data Entry Terminal - DODIIS February 1988

           Bits 6-7        Reserved
           Bit  5          Data Transmit
           Bits 0-4        Reserved
       where:
           If the Data-Transmit bit is set, the sender supports the
           DATA-TRANSMIT subcommand.
           Reserved bits represent transmit facilities that are not
           defined for DODIIS implementations; therefore, no
           descriptions are provided.  Reserved bits must be zeroed
           to indicate non support of the associated transmit
           facilities.
    IAC SB DET FORMAT-FACILITIES <facility map> IAC SE
       subcommand code:  4
       This subcommand indicates the format facilities the sender
       supports.  The <facility map> parameter is two eight bit bytes
       containing the following:
           Byte 0
              Bit  7       Function Key
              Bit  6       Modified
              Bit  5       Field Selection
              Bit  4       Repeat
              Bit  3       Blinking
              Bit  2       Reverse Video
              Bit  1       Right Justification
              Bit  0       Reserved
           Byte 1
              Bit  7       Reserved for color
              Bit  6       Reserved
              Bit  5       Protection
              Bit  4       Alphabetic-Only
              Bit  3       Numeric-Only
              Bits 0-2     Intensity
           where:
              If the Function-Key bit is set, the sender supports the
              FUNCTION-KEY and ENABLE-FUNCTION-KEY subcommands.
              If the Modified bit is set, the sender supports the
              FORMAT-DATA subcommand's Modified attribute and the

Yasuda & Thompson [Page 6] RFC 1043 Data Entry Terminal - DODIIS February 1988

              TRANSMIT-MODIFIED subcommand.
              If the Field-Selection bit is set, the sender supports
              the FORMAT-DATA subcommand's Selectable attribute and
              the SELECTED-FIELD subcommand.
              If the Repeat bit is set the sender supports the REPEAT
              subcommand.
              If the Blinking bit is set, the sender requests or
              provides the ability to emphasize a string of characters
              by causing them to blink when displayed.  (See the
              FORMAT-DATA subcommand.)
              If the Reverse-Video bit is set, the sender requests or
              provides the ability to emphasize a string of characters
              by "reversing their video image".  If characters are
              normally displayed as dark characters on a light
              background, they are reversed and displayed as light
              characters on a dark background, or
              vice versa.  (See the FORMAT-DATA subcommand.)
              If the Right-Justification bit is set, the sender
              requests or provides the ability to cause data entered
              in a field to be right justified within the field.  (See
              the FORMAT-DATA subcommand.)
              If the Protection bit is set, the sender requests or
              provides the ability to protect certain fields displayed
              on the DET screen from being altered by the user and
              supports the ERASE-UNPROTECTED, FIELD-SEPARATOR, and
              TRANSMIT-UNPROTECTED subcommands.  (See the FORMAT-DATA
              subcommand.)
              If the Alphabetic-Only bit is set, the sender requests
              or provides the ability to constrain the user of the DET
              such that only alphabetic data may be entered into
              certain fields.  (See the FORMAT-DATA subcommand.)
              If the Numeric-Only bit is set, the sender requests or
              provides the ability to constrain the user of the DET
              such that only numeric data may be entered into certain
              fields.  (See the FORMAT-DATA subcommand.)
              The Intensity parameter is three bits wide and is
              interpreted as a positive binary integer indicating the
              number of visible levels of intensity that the sender
              requests or provides for displaying data.  (See the

Yasuda & Thompson [Page 7] RFC 1043 Data Entry Terminal - DODIIS February 1988

              FORMAT-DATA subcommand.)
              Reserved bits represent format facilities that are not
              defined for DODIIS implementations; therefore, no
              descriptions are provided.   Reserved bits must be
              zeroed to indicate non support of the associated format
              facilities.
 EDIT SUBCOMMANDS.  Edit subcommands are sent by the application to
 position the cursor on the DET screen.
    IAC SB DET MOVE-CURSOR <x><y> IAC SE
       subcommand code:  5
       This subcommand positions the DET cursor at screen location
       (x,y).  the <x> and <y> parameters are positive eight bit
       binary integers representing the character and line positions,
       respectively, of a DET screen location.  Values of x range
       from zero (0) through M-1, where M is the DET screen width in
       characters.  Values of y range from zero (0) through N-1,
       where N is the DET screen length in lines.
    IAC SB DET HOME-CURSOR IAC SE
       subcommand code: 12
       This subcommand positions the cursor at DET screen address
       (0,0).  It is equivalent to the MOVE-CURSOR subcommand, where
       x=0 and y=0.
 TRANSMIT SUBCOMMANDS.  Transmit subcommands are sent by the
 application to request data from the DET or by the terminal to
 identify data returned from the DET.
    IAC SB DET READ-CURSOR IAC SE
       subcommand code: 17
       This subcommand requests return of the DET cursor position.
       Use of this subcommand requires facility negotiation; see the
       EDITFACILITIES subcommand, Read-Cursor bit.
    IAC SB DET CURSOR-POSITION <x><y> IAC SE
       subcommand code: 18
       This subcommand returns cursor position in response to a

Yasuda & Thompson [Page 8] RFC 1043 Data Entry Terminal - DODIIS February 1988

       READCURSOR subcommand.  The <x> and <y> parameters are
       eight bit binary integers representing the cursor's position.
       The <x> and <y> parameters are positive eight bit binary
       integers representing the character and line positions,
       respectively, of a DET screen location.  Values of x range
       from zero (0) through M-1, where M is the DET screen width in
       characters.  Values of y range from zero (0) through N-1,
       where N is the DET screen length in lines.  Use of this
       subcommand requires facility negotiation; see the
       EDIT-FACILITIES subcommand, Read-Cursor bit.
    IAC SB DET TRANSMIT-SCREEN IAC SE
       subcommand code: 20
       This subcommand requests return of all characters on the DET
       screen beginning at cursor position (0,0).  M x N characters,
       where M is the DET screen width in characters and where N is
       the DET screen length in lines, are returned with a SPACE
       character returned for each character in the unwritten areas
       (the areas between defined fields).  FIELD-SEPARATOR and
       DATA-TRANSMIT subcommands are not required to delimit or
       identify fields.
    IAC SB DET TRANSMIT-UNPROTECTED IAC SE
       subcommand code: 21
       This subcommand requests return of all characters in
       unprotected fields.  Use of this subcommand requires facility
       negotiation; see the FORMAT-FACILITIES subcommand, Protection
       bit.
    IAC SB DET TRANSMIT-MODIFIED IAC SE
       subcommand code: 27
       This subcommand requests return of all characters in modified
       fields.  Modified fields are fields that have the Modified
       attribute set (see FORMAT-DATA subcommand) as well as fields
       actually modified by the user.  Use of this subcommand
       requires facility negotiation; see the FORMAT-FACILITIES
       subcommand, Modified bit.
    IAC SB DET DATA-TRANSMIT <x><y> IAC SE
       subcommand code: 28

Yasuda & Thompson [Page 9] RFC 1043 Data Entry Terminal - DODIIS February 1988

       This subcommand identifies a field returned in response to
       a TRANSMIT-MODIFIED subcommand.  The <x> and <y> parameters
       are positive eight bit binary integers indicating the cursor
       position of the field that follows the DATA-TRANSMIT
       subcommand.  This subcommand may precede the first field of
       a transmission with subsequent fields separated by the
       FIELD-SEPARATOR subcommand or it may precede each field.
       Use of this subcommand requires facility negotiation; see
       the TRANSMIT-FACILITIES subcommand, Data-Transmit bit.
 ERASE SUBCOMMANDS.  Erase subcommands are used by the application to
 erase the DET screen or selected DET screen areas.  In performing
 erase operations, the erased characters are replaced with SPACE
 characters.
    IAC SB DET ERASE-SCREEN IAC SE
       subcommand code: 29
       This subcommand erases all characters from the DET screen.
       All fields regardless of their attributes are deleted.  The
       cursor position after the operation is at (0,0).  If the
       protection attribute has been negotiated, the erased screen
       contains protected SPACE characters.
    IAC SB DET ERASE-UNPROTECTED IAC SE
       subcommand code: 35
       This subcommand erases all characters in the unprotected fields
       of the DET screen.  This subcommand replaces field contents
       with SPACE characters; field attributes and sizes are not
       changed.  The cursor position after the operation is at the
       beginning of the first unprotected field or, if there is no
       unprotected field, at (0,0).  Use of this subcommand requires
       facility negotiation; see the FORMAT-FACILITIES subcommand,
       Protection bit.
 FORMAT SUBCOMMANDS.  The format subcommands are used by the
 application to define the fields of a form and by the terminal to
 delimit fields sent from the DET.
    IAC SB DET FORMAT-DATA <format map><count> IAC SE
       subcommand code: 36
       This subcommand defines the attributes and size of a DET field.
       The <format map> parameter defines the field attributes and the

Yasuda & Thompson [Page 10] RFC 1043 Data Entry Terminal - DODIIS February 1988

       <count> parameter defines the field size.  The field starts at
       the position of the cursor when the subcommand is acted upon.
       The next <count> data characters in the data stream fill the
       field.
       The <format map> parameter is two eight bit bytes and contains
       the following:
           Byte 0
              Bit  7             Blinking
              Bit  6             Reverse Video
              Bit  5             Right Justification
              Bits 3-4           Protection
              Bits 0-2           Intensity
           Byte 1
              Bits 5-7           Reserved
              Bits 2-4           Reserved for color
              Bit  1             Modified
              Bit  0             Selectable
           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, characters
              entered into the field by the user should be right
              justified.
              The Protection attribute is two bits wide and may take
              on the following values:
                0  No protection.  Any valid DET data character may
                   be entered in the field.
                1  Protected.  No data may be entered in the field.
                2  Alphabetic-only.  Only the alphabetic characters
                   (A-Z and a-z) or the space character may be
                   entered in the field.
                3  Numeric-only.  Only the numeric characters (0-9),

Yasuda & Thompson [Page 11] RFC 1043 Data Entry Terminal - DODIIS February 1988

                   the plus sign (+), the minus sign (-), the decimal
                   point (.) or the space character may be entered in
                   the field.
              The Intensity attribute is three bits wide and indicates
              the brightness to be used when displaying the characters
              in or entered into the field <count> characters wide.
              The available number of visible intensity levels should
              have been negotiated using the FORMAT-FACILITY
              subcommand. A value of zero (0) indicates that
              brightness should be OFF; that is, characters in or
              entered into the field should not be displayed.  The
              values 1-7 indicate relative brightness; the exact
              algorithm for mapping these values to the available
              levels of intensity is left to the implementors.
              If the Modified bit is set, the field is considered to
              have been modified and will be returned, along with any
              user modified fields.
              If the Selectable bit is set, the field is a candidate
              for field selection using the DET field selection
              device.
    The <count> parameter is two bytes and should be interpreted as a
    positive 16-bit binary integer that defines the field size.  The
    high order bit is transmitted first.  Data, not in the scope of
    the count of a FORMAT-DATA subcommand, should be displayed with
    the default field attributes (no blinking, no reverse video, no
    justification, no protection, not modified, not selectable, and a
    visible intensity).  Minimum field size is one (1) character.
    Maximum field size is determined by a field's starting location
    and the end of the screen or the start of the next field.
    Use of field attributes requires facility negotiation; see the
    FORMAT-FACILITIES subcommand.
 IAC SB DET REPEAT <count><char> IAC SE
       subcommand code: 37
       This subcommand permits compression of DET data by encoding
       strings of identical characters as the character and a repeat
       count.  The <count> parameter is a positive 8-bit binary
       integer.  The <char> parameter is a valid DET data character.
       Use of this subcommand requires facility negotiation; see
       the FORMAT-FACILITIES subcommand, Repeat bit.

Yasuda & Thompson [Page 12] RFC 1043 Data Entry Terminal - DODIIS February 1988

    IAC SB DET FIELD-SEPARATOR IAC SE
       subcommand code: 39
       This subcommand separates fields returned by the DET in
       response to TRANSMIT-MODIFIED or TRANSMIT-UNPROTECTED
       subcommands.  Use of this subcommand requires facility
       negotiation; see the FORMAT-FACILITIES subcommand,
       Protection bit.

MISCELLANEOUS SUBCOMMANDS

    IAC SB DET FUNCTION-KEY <code> IAC SE
       subcommand code: 40
       This subcommand transmits a user entered function key code.
       The <code> parameter is one byte that identifies the virtual
       function key entered.  Function key <code> values range from
       0 to 255.  This subcommand is used in conjunction with the
       ENABLE-FUNCTION-KEY subcommand.  Use of this subcommand
       requires facility negotiation; see the FORMAT-FACILITIES
       subcommand, Function-Key bit.
    IAC SB DET ERROR <cmd><error code> IAC SE
       subcommand code: 41
       This subcommand allows a DET option implementation to report
       errors it detects to the corresponding TELNET process.  The
       <cmd> parameter is one byte containing the subcommand code
       of the subcommand causing the error.  The <error code>
       parameter is one byte containing a DET error code.  (See
       Appendix 2 for DET error codes.)
       Errors should be reported when detected.  However, the
       implementation should attempt to carry out the intent of
       the subcommand or data in error.
    IAC SB DET START-OUT-OF-CONTEXT-DATA IAC SE
       subcommand code: 42
       This subcommand precedes out-of-context data.  The data
       following this subcommand and prior to the
       END-OUT-OF-CONTEXT-DATA subcommand is NOT part of the current
       form.  The out-out-of-context data should be interpreted as
       NVT mode data (i.e., it may contain carriage return and line

Yasuda & Thompson [Page 13] RFC 1043 Data Entry Terminal - DODIIS February 1988

       feed characters) and should be displayed in a timely and
       non-destructive fashion.
    IAC SB DET END-OUT-OF-CONTEXT-DATA IAC SE
       subcommand code: 43
       This subcommand indicates the end of the out-of-context data.
    IAC SB DET ENABLE-FUNCTION-KEYS <key-map>IAC SE
       subcommand code: 44
       This subcommand enables (or disables) virtual function keys and
       indicates the application's data requirements on function key
       selection.  The <key-map> parameter is a variable length byte
       string.  Each byte contains four bit-pairs and each bit-pair
       represents a single function key.  The first byte represents
       function keys zero (0) through three (3); the second byte,
       function keys four (4) through seven (7); and so on.  Bit-pair
       values and there meanings are as follows:
           0  The virtual function key is disabled (i.e., locked).
           1  The virtual function key is enabled.  Only the FUNCTION-
              KEY subcommand is returned on function key selection.
           2  The  virtual  function  key  is  enabled.  All requested
              screen data and/or cursor position, as well as, the
              FUNCTION-KEY subcommand are returned on function key
              selection.
           3  Undefined.
       Function keys not explicitly represented in the bitmap are
       disabled (i.e., they are assumed to have a bit-pair value of
       zero (0)).
       Use of this subcommand requires facility negotiation; see the
       FORMAT-FACILITIES subcommand; Function-Key bit.
    IAC SB DET SELECTED-FIELD <x><y> IAC SE
       subcommand code: 45
       This subcommand identifies a user selected field.  The <x> and
       <y> parameters are the cursor position of the character
       selected from within a selectable field (see the FORMAT-DATA

Yasuda & Thompson [Page 14] RFC 1043 Data Entry Terminal - DODIIS February 1988

       subcommand, Selectable attribute.)  Use of this subcommand
       requires negotiation; see the FORMAT-FACILITIES subcommand,
       Field-Selection bit.

3. Default and Minimal Implementation

    Default.
       WONT DET -- DONT DET
       If the DET option cannot be negotiated, the connection is
       not operated in DET mode.
    Minimal DET Implementation.
       The minimal DET implementation consists of all DET subcommands
       that may be used without prior negotiation.  These subcommands
       are as follows:
           EDIT-FACILITIES
           ERASE-FACILITIES
           TRANSMIT-FACILITIES
           FORMAT-FACILITIES
           MOVE-CURSOR
           HOME-CURSOR
           ERASE-SCREEN
           TRANSMIT-SCREEN
           FORMAT-DATA
           ERROR
           START-OUT-OF-CONTEXT-DATA
           END-OUT-OF-CONTEXT-DATA
    DODIIS DET implementation requirements.
       The minimal DET implementation set of subcommands is not broad
       enough to support forms interactions between DODIIS terminals
       and DODIIS applications.  Therefore, DODIIS implementations of
       the DET option must support additional DET subcommands.
       DODIIS terminal (User Host) implementations must implement and
       support all of the DET subcommands contained in Section 2, as
       well as those DET attributes supported by the terminal hardware
       and any DET attributes easily emulated in software.  DODIIS
       application (Server Host) implementations must implement and
       support those DET subcommands and attributes required by its
       applications.

Yasuda & Thompson [Page 15] RFC 1043 Data Entry Terminal - DODIIS February 1988

       DODIIS implementation recommendations are contained in the
       table that follows.  DODIIS implementors are cautioned that
       failure to provide recommended support may limit
       interoperability.
       Recommended DET support levels for DODIIS implementations
                                    USER HOST           SERVER HOST
    DET SUBCOMMANDS                 SUPPORT LEVEL       SUPPORT LEVEL
    ---------------                 -------------       -------------
    EDIT-FACILITIES                 send & receive      send & receive
    ERASE-FACILITIES                send & receive      send & receive
    TRANSMIT-FACILITIES             send & receive      send & receive
    FORMAT-FACILITIES               send & receive      send & receive
    REPEAT                          send & receive      send & receive
    ERROR                           send & receive      send & receive
    MOVE-CURSOR                     receive only        send only
    HOME-CURSOR                     receive only        send only
    READ-CURSOR                     receive only        send only
    TRANSMIT-SCREEN                 receive only        send only
    TRANSMIT-UNPROTECTED            receive only        send only
    TRANSMIT-MODIFIED               receive only        send only
    ERASE-SCREEN                    receive only        send only
    ERASE-UNPROTECTED               receive only        send only
    FORMAT-DATA                     receive only        send only
    START-OUT-OF-CONTEXT-DATA       receive only        send only
    END-OUT-OF-CONTEXT-DATA         receive only        send only
    ENABLE-FUNCTION-KEYS            receive only        send only
    CURSOR-POSITION                 send only           receive only
    DATA-TRANSMIT                   send only           receive only
    FIELD-SEPARATOR                 send only           receive only
    FUNCTION-KEY                    send only           receive only
    SELECTED-FIELD                  send only           receive only
    DET ATTRIBUTES
    --------------
    Blinking                        (1)                 (2)
    Reverse video                   (1)                 (2)
    Right justification             (1)                 (2)
    Protection                      required            (2)
    Alphabetic-only protection      (1)                 (2)
    Numeric-only protection         (1)                 (2)
    Intensity level > 1             (1)                 (2)
    OTHER
    -----
    Page size (lines)               24-48
    Line size (characters)          80

Yasuda & Thompson [Page 16] RFC 1043 Data Entry Terminal - DODIIS February 1988

    Function keys (number)          64
       (1)   Implement if supported by terminal hardware.
       (2)   Implement if required by the application.

4. Motivation for the option

 In 1981, the TELNET DET option (RFC 732) was selected as the protocol
 to support interactions between DODIIS forms applications and DODIIS
 forms terminals.  The intent was to foster a high degree of
 interoperability between DODIIS hosts with forms applications and
 terminals.  Since that time, the DET option has been and is being
 implemented by several independent organizations within the DODIIS
 community.
 Motivated by concern that the independently developed implementations
 of the DET option may not interoperate with one another, DODIIS
 implementors met to identify DODIIS implementation requirements and
 to resolve implementation issues that affect interoperability.
 This document attempts to present the agreements and recommendations
 of the DODIIS implementors.

5. Description and Implementation Rules

 The DODIIS DET model.
 The conceptual model of the DODIIS DET is that of a half-duplex,
 forms oriented device with the following:
    a.  A rectangular screen for displaying protected and unprotected
       data (a form) and optional capability to support blinking,
       reverse video, and up to seven display intensity levels.
    b.  A keyboard and onboard mechanisms for editing unprotected
       fields of a form and returning the modified fields.
    c.  Function keys that may be enabled and disabled on a key-by-key
       basis by the application.
    d.  A field selection device, similar to a light pen, that permits
       user selection of characters within appropriately identified
       "selectable" fields.
 The DODIIS DET screen has default sizes of 80 characters and 24
 lines.  These defaults may be changed through negotiation using the
 Output Line Width and the Output Page Size options.  When the parties

Yasuda & Thompson [Page 17] RFC 1043 Data Entry Terminal - DODIIS February 1988

 cannot agree on screen size through negotiation, the default values
 will be used.  By agreement, DODIIS terminal (User Host)
 implementations of DET will support page sizes of 24 to 48 lines.
 The next writing position (x,y) on the DET screen is indicated by a
 special display character called the cursor, where x is the position
 of a character on a line and y is the line position on the DET
 screen.  Values of x range from 0 (the left most character position
 on the line) to M-1, where M is the line length.  Values of y range
 from 0 (the top most line on the screen) to N-1, where N is the page
 length.  The cursor may be moved to any position on the DET screen
 without disturbing the characters already displayed.
 Valid field data for DET forms are the displayable ASCII character
 codes in the range 32 through 126 decimal and character 7 "BELL".
 Negotiating the DET option
    The DET option is negotiated when either party REQUESTS use of the
    DET option and the other party AGREES to its use.  The DET option
    is requested by sending a DO DET and WILL DET and is accepted by
    sending a WILL DET and DO DET.  (In the spirit of TELNET
    negotiation, the DET option must be negotiated for both directions
    on the connection.)
    Several TELNET options conflict with the DET option.  Therefore,
    when the DET option is negotiated, the following TELNET options
    should be refused (or explicitly terminated):  Echo, Suppress Go-
    Ahead, and Binary.  (The Suppress Go-Ahead is the default state of
    DODIIS TELNET connections when they are first established.)
 DET facilities negotiation
    All implementations of the DET option are required to support the
    minimal DET implementation described in Section 3.  In addition,
    DODIIS implementations are required to support subcommands and
    attributes that are consistent with DODIIS implementation
    requirements.  Before any of these additional DET facilities may
    be used, an implementation must negotiate with its correspondent
    for permission to use them.
    The four facility subcommands (EDIT-FACILITIES, ERASE-FACILITIES,
    TRANSMIT-FACILITIES, and FORMAT-FACILITIES) are used to negotiate
    DET subcommands and attributes.  This negotiation consists of an
    exchange of facility subcommands and may be viewed as the terminal
    (User Host) indicating the facilities it provides and the
    application program (Server Host) indicating the facilities it
    desires.  The facilities that are jointly supported (and may be

Yasuda & Thompson [Page 18] RFC 1043 Data Entry Terminal - DODIIS February 1988

    used) are arrived at by forming the logical intersection of the
    facility map that was sent with the facility map that was
    received.  (For the intensity attribute, the lesser of the number
    of intensity levels sent and the number of intensity levels
    received will be used.)  An implementation must record the
    currently agreed upon set of subcommands and attributes.  Only
    subcommands and attributes reflected in that set may be used
    without further exchange of facility subcommands.
    Either party or both parties may initiate facilities negotiation
    without confusion as long as care is taken to avoid non-
    terminating negotiation loops.  In particular, if you initiate
    negotiation by sending a facility subcommand, you must remember
    that you did initiate the negotiation.  On receipt of a facility
    subcommand; if you initiated the negotiation, no response is
    required and the negotiation is complete; if you did not initiate
    the negotiation, you must respond by sending the appropriate
    facility subcommand to the requester.  (Note that there is no
    requirement to negotiate facilities one class at a time and that
    the awareness of who initiated the negotiation must be maintained
    for each of the facility subcommands.)
    A TELNET implementation responding to a facility subcommand is not
    required to compute the logical intersection of the maps before
    responding.  It should respond as quickly as possible with a
    facility map indicating all facilities of that class that it
    supports.  There is no confusion since both parties compute the
    set of supported subcommands and attributes in the same fashion.
    Note that while both parties must agree to the use of the optional
    subcommands and attributes, either party may disable use at any
    time by merely sending the appropriate facility subcommand.
    Further, there are no restrictions on when facilities may be sent.
                                 CAUTION:
               All facilities maps contain reserved bits.
               These reserved bits must be zeroed when
               facility maps are sent to indicate non
               support and/or ignorance of the associated
               facility.  The reserved bits may be defined
               in the future.
 General DET Interaction
    In the general interaction, the application implementation
    constructs a form, negotiates the desired options, indicates the
    required responses, and sends the TELNET GO-AHEAD.  The GO-AHEAD
    signals that the form construction is complete and that the DET

Yasuda & Thompson [Page 19] RFC 1043 Data Entry Terminal - DODIIS February 1988

    keyboard may be unlocked to permit a user response.
    The user normally responds by editing the unprotected areas of the
    form and signaling "form-complete", entering a function key,
    electing a field, or performing a combination of the preceding.
    In each case, the terminal implementation sends the DET
    subcommands indicating the user's response and returns the GO-
    AHEAD.  The GO-AHEAD signals the end of the user response.
    The form, as edited by the user, remains on the virtual screen so
    the application may continue the interaction by altering the form.
 Form construction
    The application implementation constructs a form on an erased
    screen by defining each of the fields in the form.  The DET fields
    are defined by their starting cursor position, size, attributes,
    and contents (data).
    A field's starting cursor position is the cursor position of the
    first character in the field.  The cursor may be positioned
    explicitly by the MOVE-CURSOR subcommand or it may be positioned
    implicitly by field data or other DET subcommands (e.g.,
    ERASESCREEN and ERASE-UNPROTECTED).
    Field size, attributes, and contents may be defined using the
    FORMAT-DATA subcommand followed by field data.  Alternatively, a
    field with default attributes may be defined using only the field
    data.  In this case, field size is the data string length.  The
    data string is terminated by the GO-AHEAD or any DET subcommand,
    except the REPEAT subcommand.
    There are no restrictions on attribute combinations that might be
    applied to a field even though some combinations may not be
    supported by terminal hardware.  The terminal implementation
    should display the field with a "reasonable" combination of
    attributes.  There is an error code that might be returned when an
    "unsupported combination of format attributes" is detected.  It is
    not clear what the application should do about the error.  In any
    event, this condition should not provoke session termination.
    Field contents (data) are restricted to printable ASCII characters
    and "BELL" (codes 32 through 126 and 7 decimal).  It is the
    responsibility of the application implementation to properly
    translate carriage returns, line feeds, tabs, etc.  to the
    appropriate DET subcommands.
    The maximum number of fields a screen might contain is the screen

Yasuda & Thompson [Page 20] RFC 1043 Data Entry Terminal - DODIIS February 1988

    size in characters (the product of characters per line and lines
    per screen).
    Fields may not overlap.  That is, a new field may not start or end
    within a previously defined field.  However, overwriting of a
    field to change its attributes or contents is permitted.
    There are no restrictions on the order in which a form is built
    (e.g., left-to-right and top-to-bottom); the terminal
    implementation must be prepared to handle any order.  Terminal
    implementations are encouraged to display data as it arrives to
    accommodate applications that persist in displaying status updates
    on the task(s) they are performing.
    If an application elects to modify a user edited form, it must
    properly position the cursor making no assumptions about where the
    user might have left the cursor.  Further it must exactly
    overwrite the existing fields.
    When form construction is complete, the application indicates its
    response requirements by sending the appropriate transmit
    subcommand.  It may send TRANSMIT-SCREEN, TRANSMIT-UNPROTECTED, or
    TRANSMIT-MODIFIED to request data and/or it may send READ-CURSOR
    to request cursor position.  TRANSMIT-MODIFIED should be used
    whenever possible to minimize the volume of data transmitted
    between user and server hosts.
 Form response
    A form response is generated by the terminal implementation when
    the user signals "form-complete" or enters an enabled function
    key.  The data returned are determined by the application through
    the transmit subcommands.  If no transmit subcommand was sent the
    Modified and Protection attributes are used to determine an
    implied transmit subcommand.  If the Modified attribute has been
    negotiated, assume TRANSMIT-MODIFIED.  If the Protection attribute
    has been negotiated but the Modified has not, assume
    TRANSMITUNPROTECTED.  If neither has been negotiated, assume
    TRANSMITSCREEN.  (The intent is to achieve transmission efficiency
    by returning the smallest amount of data permitted by the in-force
    DET attributes.)
                                 CAUTION:
            With TRANSMIT-MODIFIED the terminal implementation
            must return all fields marked with the Modified
            attribute in addition to fields actually modified by
            the terminal user.

Yasuda & Thompson [Page 21] RFC 1043 Data Entry Terminal - DODIIS February 1988

    Returned fields are identified and delimited using the
    DATATRANSMIT and/or FIELD-SEPARATOR subcommands.  The DATA-
    TRANSMIT subcommand indicates the cursor address of the field that
    follows it and there are no restrictions on the order in which
    fields are returned.  The FIELD-SEPARATOR subcommand conveys
    left-to-right and top-to-bottom field ordering.  Data not preceded
    by one of these subcommands is assumed to be the first unprotected
    field in the form.  A FIELD-SEPARATOR followed by FIELD-SEPARATOR
    indicates a field was unchanged and not returned.
    Unless otherwise restricted by Numeric-only or Alphabetic-only
    attributes, data entered into unprotected fields is restricted to
    the printable ASCII characters and "BELL" (codes 32 through 126
    and 7 decimal); no other characters are permitted.
 Function keys
    By general agreement, DODIIS terminal implementations will support
    64 function keys (key values 0 through 63).  Information on
    mapping function keys to application functions is the
    responsibility of the application and should be provided to the
    terminal user in the form of user documentation.
    The application enables and disables the function keys and
    indicates its form response requirements by sending the
    ENABLEFUNCTION-KEY subcommand.  The terminal implementation
    validates function key selections based on information received in
    the ENABLE-FUNCTION-KEY bitmap.  When an enabled function key is
    entered, the terminal returns a form response (if indicated in the
    bitmap), a FUNCTION-KEY subcommand, and the GO-AHEAD.
    Virtual function keys are part of the DET's virtual keyboard and
    are "locked" when the application has the GO-AHEAD.  Since the
    terminal sends the GO-AHEAD when a function key is entered,
    entering a function key "re-locks" all function keys until the
    GO-AHEAD is returned.
 Field selection
    Any character within a field having the Selectable attribute is a
    candidate for selection.  When selection is made, the terminal
    returns a SELECTED-FIELD subcommand identifying the character
    position selected.  Multiple selections are permitted; however,
    the ordering of the selections need not be preserved.  Field
    selection does not cause the GO-AHEAD to be sent.  The GO-AHEAD
    must be sent as a result of another user action such as a function
    key entry or "form-complete" indication.  Field selection is
    disabled when the application has the GO-AHEAD.

Yasuda & Thompson [Page 22] RFC 1043 Data Entry Terminal - DODIIS February 1988

 Out-of-context data
    The out-of-context-data subcommands identify data that is clearly
    not in the context of the form interaction.  It is a convenient
    not in the mechanism for sending ARE-YOU-THERE responses or host
    advisory messages to the user without disturbing the DET's virtual
    screen or altering the context of the form interaction.
    The application may send out-of-context data at anytime.  The data
    must be preceded by the START-OUT-OF-CONTEXT-DATA subcommand and
    followed immediately by the END-OUT-OF-CONTEXT-DATA subcommand.
    The out-of-context data should contain carriage returns and line
    feeds to facilitate formatting.  The sender should limit the
    amount of data sent, since most terminal implementations must
    buffer the data prior to displaying it.  The terminal
    implementation should display the data to the user in a timely
    fashion.  The data is for display only, no user response is
    required, and there is no mechanism for user response.
 Line Discipline
    The subject of DET and line discipline (controlling the connection
    using the GO-AHEAD) causes a bit of confusion.  The following
    rules apply to GO-AHEAD and the DET option:
       When DET is negotiated, the application assumes the GO-AHEAD.
       GO-AHEAD is never passed implicitly; it is always passed
       explicitly.
       When the application has the GO-AHEAD, the terminal
       implementation may send TELNET commands (INTERRUPT-PROCESS,
       ABORT-OUTPUT, BREAK, and ARE-YOU-THERE).  Nothing else is
       valid.
       When the terminal has the GO-AHEAD, the application may send
       out-of-context data or MOVE-CURSOR and FORMAT-DATA subcommands
       to update protected fields.  Nothing else is valid.  (The
       terminal implementation must display the out-of-context data
       and the field updates as soon as convenient.)
       The terminal implementation sends the GO-AHEAD, without further
       action on the part of the terminal user, when an enabled
       function key or a "form-complete" is entered.
    Since the terminal user must take explicit action to return the
    GO-AHEAD to the application, instances will occur when the user
    has the GO-AHEAD but the application needs it to display a new
    form.  (This is most likely to occur when the user enters an

Yasuda & Thompson [Page 23] RFC 1043 Data Entry Terminal - DODIIS February 1988

    INTERRUPT PROCESS.)  When it does occur, the application should
    send an out-of-context-context message requesting the user to
    enter a "form-complete".  If the user cooperates, the application
    can ignore any associated form response and regain control of the
    connection to display its form.
    The line discipline described here is more rigorous than that
    described for NVT in MIL-STD-1782.  These rules apply only when
    operating in DET mode.  At other times, the descriptions contained
    in MIL-STD-1782 apply.  This distinction is necessary to ensure
    interoperability with non-DET implementations of TELNET.
 Standard TELNET control functions
    The TELNET control functions, ERASE CHARACTER and ERASE LINE, are
    NOT required and should not be sent in DET mode.
 Other implementation notes
    a. The DODIIS DET conceptual model does not support character
       editors or basic scrolling applications.
    b. Implementors are cautioned that DET subcommand parameters
       (e.g., facilities maps) may take on the value of the IAC
       character and must be replicated if they are to be properly
       interpreted.
    c. Principle of Robustness:  "Be conservative in what you send; be
       liberal in what you accept from others."

Yasuda & Thompson [Page 24] RFC 1043 Data Entry Terminal - DODIIS February 1988

APPENDIX 1 - DET OPCODES AND SUBCOMMAND SYNTAX.

           OPCODE    SUBCOMMAND SYNTAX
           ------    -----------------
            1     EDIT-FACILITIES <facility 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>
           12     HOME-CURSOR
           17     READ-CURSOR
           18     CURSOR-POSITION <x><y>
           20     TRANSMIT-SCREEN
           21     TRANSMIT-UNPROTECTED
           27     TRANSMIT-MODIFIED
           28     DATA-TRANSMIT <x><y>
           29     ERASE-SCREEN
           35     ERASE-UNPROTECTED
           36     FORMAT-DATA <format map><count>
           37     REPEAT <count><character>
           39     FIELD-SEPARATOR
           40     FUNCTION-KEY <code>
           41     ERROR <cmd><error code>
           42     START-OUT-OF-CONTEXT-DATA
           43     END-OUT-OF-CONTEXT-DATA
           44     ENABLE-FUNCTION-KEYS <key-map>
           45     SELECTED-FIELD <x><y>

Yasuda & Thompson [Page 25] RFC 1043 Data Entry Terminal - DODIIS February 1988

APPENDIX 2 - DET ERROR CODES

            1        Facility not previously negotiated.
            2        Illegal subcommand code.
            3        Cursor Address Out of Bounds.
            4        Undefined FUNCTION-KEY 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.
           13        Invalid field - overlap detected.

Yasuda & Thompson [Page 26]

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