As per Relevance of the word terminal, we have this rfc below:
NWG/RFC# 732 DAY 13-Sep-77 18:38 41762
Data Entry Terminal
Network Working Group John
Request for Comments: 732
NIC: 41762 12 September 1977
Obsoletes: 731
Telnet Data Entry Terminal
1. Command Name and Code
DET 20
2. Command
IAC WILL
The sender of this command REQUESTS or AGREES to send and
subcommands to control the Data Entry Terminal
IAC WONT
The sender of this command REFUSES to send and receive
to control the Data Entry Terminal
IAC DO
The sender of this command REQUESTS or AGREES to send and
subcommands to control the Data Entry Terminal
IAC DONT
The sender of this command REFUSES to send and receive
to control the Data Entry Terminal
The DET option uses five classes of subcommands 1) to establish
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
are described below
The Network Virtual Data Entry Terminal (NVDET
The NVDET consists of a keyboard and a rectangular display.
keyboard is capable of generating all of the characters of the
character set. In addition, the keyboard may possess a number
function keys which when pressed cause a FN subcommand to be sent
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Data Entry Terminal
(Although most DET's will support one or more peripheral
such as a paper tape reader or a printer, this option does
consider their support. Support of peripheral devices should
treated by a is a separate option).
The screen of the data entry terminal is a rectangle M characters
N lines. The values of M and N are set by negotiating the
Line Width and Output Page Size options, respectively. The
writing position (x,y) on the screen (where x is the
position and y is the position of the line on the screen)
indicated by a special display character called the cursor.
cursor may be moved to any position on the screen without
any characters already on the screen. Cursor addressing in
terminals utilizes several topologies and addressing methods.
order to make the burden of implementaton as easy as possible
protocol supports two topologies (the finite plane and the
torus) and three addressing methods ((x,y); x and y, and
increments). Since the finite plane with absolute addressing is
least ambiguous and the easiest to translate to and from the others
it is the default scheme used by the NVDET. The torodial form
either relative or absolute addressing is provided for convience
Also the NVDET provides a mechanism for defining on the
fields with special attributes. For example, characters entered
these fields may be displayed with brighter intensity,
by reverse video or blinking, or protected from modification by
user. This latter feature is one of the most heavily used
applications where the DET displays a form to be filled out by
user
The definition of the NVDET uses Telnet option subnegotiations
accomplish all of its functions. Since none of the ASCII
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.
circumstances where the application program knows what kind
terminal is on the other end, it can send the ASCII
required to control functions not supported by the option or
implementation. In general keeping all NVDET functions out of
data stream provides better flexibility
Facility Functions (for detailed semantics see Section 5.)
IAC SB DET facility subcommand><facility map> IAC
where facility subcommand> is one 8-bit byte indicating
class of the facilities to be described, and <facility map> is
field of one or two 8-bit bytes containing flags describing
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Data Entry Terminal
facilities required or desired by the sender. The bits of
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.
values of the field are as follows
facility cmd: EDIT FACILITIES subcommand code: 1
facility map: bit
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
provides that the SKIP TO LINE and SKIP TO CHAR subcommands
supported
If the Incremental Cursor Addressing bit is set, the sender
or provides that the UP, DOWN, LEFT, and RIGHT subcommands
supported
If the Read Cursor bit is set, the sender requests or provides
READ CURSOR subcommand
If the Line Insert/Delete bit is set, the sender requests
provides that the LINE INSERT and LINE DELETE subcommands
supported
If the Char Insert/Delete bit is set, the sender requests
provides that the CHAR INSERT and CHAR DELETE subcommands
supported
If the Back Tab bit is set, the sender requests or provides that
BACK TAB subcommand be supported
If the Positive Addressing bit is set, then the sender is
the receiver that it can only move the cursor in the
direction. (Note: Terminals that have this property also have a
function to get back to the beginning.)
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Data Entry Terminal
facility cmd: ERASE FACILITIES subcommand code: 2
facility map: bit
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,
sender requests or provides the facility indicated by the bit. For
more complete description of each of these functions see the
Functions section below
facility cmd: TRANSMIT FACILITIES subcommand code: 3
facility map: bit
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,
sender requests or provides the facility indicated by the bit. For
more complete description of each of these functions see
Transmit Functions section below
facility cmd: FORMAT FACILITIES subcommand code: 4
facility map: bit
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
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
subcommand
If the Modified bit is set, the sender requests or provides
ability to indicate fields that are modified and supports
TRANSMIT MODIFIED subcommand
If the Light Pen bit is set, the sender requests or provides
support of a light pen, including the Pen Selectable attribute
the DATA FORMAT subcommand
If the Repeat bit is set the sender requests or provides the
subcommand
If the Blinking bit is set, the sender requests or provides
ability to highlight a string of characters by causing them
blink
If the Reverse Video bit is set, the sender requests or provides
ability to highlight a string of characters by "reversing the
image," i.e., if the characters are normally displayed as
characters on a white background, this is reversed to be
characters on a black background, or vice versa
If the Right Justification bit is set, the sender requests
provides the ability to cause entries of data to be right
in the field
If the Overstrike bit is set, the sender requests or provides
ability to superimpose one character over another on the screen
like a hard copy terminal would do if the print mechanism struck
same position on the paper with different characters
If the Protection On/Off bit is set, the sender requests or
the ability to turn on and off field protection
If the Protection bit is set, the sender requests or provides
ability to protect certain strings
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Data Entry Terminal
characters displayed on the screen from being altered by the user
the terminal. Setting this bit also implies that ERASE UNPROTECTED
DATA TRANSMIT, FIELD SEPARATOR, and TRANSMIT UNPROTECTED
(see below) are supported
If the Alphabetic-only Protection bit is set, the sender requests
provides the ability to constrain the user of the terminal such
he may only enter alphabetic data into certain areas of the screen
If the Numeric-only Protection bit is set, the sender requests
provides the ability to constrain the user of the terminal such
he may only enter numerical data into certain areas of the screen
The three bits of the Intensity field will contain a positive
integer indicating the number of levels of intensity that the
requests or provides for displaying the data. The value of the 3
field should be interpreted in the following way
1 one visible
2 two intensities; normal and
3 three intensities; off, normal, and
>3 >3 intensities; off, and the remaining
proportioned from dimmest to brightest intensity
For the all of the above commands, if the appropriate bit
<facility map> is not set, then the sender does not request
provide that facility
Editing
IAC SB DET MOVE CURSOR IAC SE subcommand code: 5
where is an 8-bit byte containing a positive binary
representing the character position of the cursor, is an 8-
byte containing a positive binary integer representing the
position of the cursor
This subcommand moves the cursor to the absolute screen
(x,y) with the following boundary conditions
if x>M-1, set x=M-1 and send an ERROR
if y>N-1, set y=N-1 and send an ERROR
This describes a finite plane topology on the screen
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Data Entry Terminal
IAC SB DET SKIP TO LINE IAC SE subcommand code: 6
where is a positive 8-bit binary number
This subcommand moves the cursor to the absolute screen line y.
remains constant. For values of y>N-1
y = y mod N
IAC SB DET SKIP TO CHAR IAC SE subcommand code: 7
where is a positive 8-bit binary number
This subcommand moves the cursor to the absolute character
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
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
codes for linefeed, backspace, and space respectively. The
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
a MOVE CURSOR 0,0 or the sequence SKIP TO LINE 0, SKIP TO CHAR 0.
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Data Entry Terminal
This subcommand is provided for convenience, since most
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 (
current line, determined by the position of the cursor) and
y-1. Lines y through N-2 move down one line, i.e. line y
line y+1; y+1 becomes y+2, ...; N-2 becomes N-1. Line N-1 is
off the bottom of the screen. The position of the cursor
unchanged
IAC SB DET LINE DELETE IAC SE subcommand code: 14
This subcommand deletes line y where y is the current line
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-1
line position is set to all spaces. The cursor position
unchanged
IAC SB DET CHAR INSERT IAC SE subcommand code: 15
This subcommand inserts the next character in the data
between the xth and x-1st characters, where x is the
character position of the cursor. The xth through M-2nd
on the line are shifted one character positon to the right. The
character is inserted at the vacated xth position. The M-1
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-
position. The x-th character is removed and the characters x+1
through M-1 are shifted one character position to the left to
the x-th through M-2nd characters. The M-1st character position
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
of the cursor to the sender
IAC SB DET CURSOR POSITION IAC SE subcommand code: 18
where and are positive 8-bit binary integers
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Data Entry Terminal
This subcommand is sent by a Telnet implementation in response to
READ CURSOR subcommand to convey the coordinates of the cursor
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
position. If none exists on the present line, the cursor moves
the previous line and so on until a tab is found or the
(0,0) is encountered. When field protection is in effect the
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
the screen from position (0,0) to (M-1,N-1). The cursor will be
(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
unprotected fields from position (0,0) to (M-1,N-1). The
fields are separated by the field separator subcommand. The
will be at (0,0) or at the beginning of the first unprotected
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
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
position (M-1,y) whichever comes first. The cursor position
the transmission is one character position after the end of
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
field presently occupied by the cursor. The cursor position
the operation is complete is one character position after the end
the field or, if
position is protected, at the beginning of the next
field
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Data Entry Terminal
IAC SB DET TRANSMIT REST OF SCREEN IAC SE subcommand code: 24
This subcommand causes the terminal to transmit all characters
the screen from position (x,y) to (M-1,N-1) or until the end
text. (x,y) is the current cursor position. The cursor
after the operation is one character position after the last
character, or (0,0) if the last filled character position
(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
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.
cursor position after the operation is one character position
the last character of the line or the first character of the
line
IAC SB DET TRANSMIT REST OF FIELD IAC SE subcommand code: 26
This subcommand causes the receiver to transmit the rest of
characters in the field currently occupied by the cursor. The
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
which have the modified attribute set. The cursor position after
operation is unchanged
IAC SB DET DATA TRANSMIT IAC SE subcommand code: 28
This subcommand is used to preface data sent from the terminal
response to a user action or a TRANSMIT command. The parameters
and indicate the initial position of the cursor. See
Transmit Subcommands subsection in Section 5 for more details.
DATA TRANSMIT subcommand may precede an entire transmission
each field being delineated by the FIELD SEPARATOR subcommand
would be the case in a response
TRANSMIT UNPROTECTED. Or, it may precede each field as would be
case in a response to a TRANSMIT MODIFIED
Erase
IAC SB DET ERASE SCREEN IAC SE subcommand code: 29
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Data Entry Terminal
This subcommand causes all characters to be removed from the screen
All fields regardless of their attributes are deleted. The
position after the operation will be (0,0). Most terminals set
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
from the screen, where y is the line of the current cursor position
All fields regardless of their attributes are deleted. The
position after this operation will be (0,y). Note: This
can be easily simulated by the sequence: LINE DELETE, LINE INSERT
However, the order is important to insure that no data is lost
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
cursor to be removed. The cursor position after the operation is
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)
(M-1,N-1) to be removed from the screen. All fields regardless
their attributes are deleted. The cursor position after
operation is unchanged. This is equivalent to doing an ERASE REST
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
attributes are deleted. The cursor position after the operation
unchanged
IAC SB DET ERASE REST OF FIELD IAC SE subcommand code: 34
This subcommand causes all characters from position (x,y) to the
of the current field to be removed from the screen. The
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
fields to be removed from the screen. The cursor position after
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Data Entry Terminal
operation is at (0,0) or, if that position is protected, at
beginning of the first unprotected field
Format
IAC SB DET FORMAT DATA IAC
subcommand code: 36
where is a two byte field containing the
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
characters should have the Blinking attribute applied to it by
receiver
If the Reverse Video bit is set, the following field of
characters should be displayed by the receiver with video reversed
If the Right Justification bit is set, the input entered into
field of characters should be right justified
The Protection field is two bits wide and may take on
following values
0 no
1
2 alphabetic
3 numeric
The protection attribute specifies that the other side may
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)
the following field of bytes
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Data Entry Terminal
The Intensity field is 3 bits wide and should be interpreted in
following way
The values 0-6 should be used as an indication of the
brightness to be used when displaying the characters in or
into the following field characters wide. The number
levels of brightness available should have been
previously by the Format Facility subcommand. The exact
for mapping these values to the available levels of intensity
left to the implementors. A value of 7 in the intensity
indicates that the brightness should be off, and any characters
or entered into the field should not be displayed
If the Modified bit is set, the field is considered to have
modified and will be transmitted in response to a TRANSMIT
subcommand
If the Pen Selectable bit is set, the field can be selected with
light pen. Note: Use of the light pen should be the subject
another Telnet option
is 2 bytes that should be interpreted as a positive 16-
binary integer representing the number of characters following
command which are affected by it
Data sent to the terminal or the Using Host for unwritten areas
the screen not in the scope of the count should be displayed
the default values of the format map. The default values are
Blinking, Normal Video, No Justification, No Protection and
Intensity. For example, suppose a FORMAT DATA subcommand was sent
the terminal with attributes Blinking and Protected and
count of 5 followed by the string "Name: John Doe". The
"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
of the terminal. The describes the attributes that
field bytes wide should have. This field is to start at
position of the cursor when the command is acted upon. The
displayable characters in the data stream are used to
the field. Subsequent REPEAT subcommands may be used to specify
contents of this field. If the sender specifies attributes that
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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Data Entry Terminal
IAC SB DET REPEAT IAC SE subcommand code: 37
where is a positive 8-bit binary integer. is an 8-
byte containing an ASCII character
This subcommand is used to perform data compression on data
transferred to the terminal by encoding strings of
characters as the character and a count. The repeated characters
be part of a field
IAC SB DET SUPPRESS PROTECTION <negotiation> IAC
subcommand code: 38
where <negotiation> may have the values of the Telnet
negotiation
251
252
253
254
This subcommand is used to suppress the field protection in
non-destructive manner. Many data entry terminals provide the
by which protection may be turned on and off without modifying
contents of the screen or the terminal's memory. Thus,
protection may be turned off and back on without retransmitting
form
The default setting of the option is that protection is on, in
IAC SB DET SUPPRESS PROTECTION WONT IAC
IAC SB DET SUPPRESS PROTECTION DONT IAC
Negotiation of this subcommand follows the same rules
negotiations of the Telnet options
IAC SB DET FIELD SEPARATOR IAC SE subcommand code: 39
It is necessary when transmitting only the unprotected portion
the screen to provide a means for delimiting the fields.
DET's use a variety of ASCII characters such as Tab,
Separator, Unit Separator, etc. In order to maintain transparency
the NVDET this subcommand is used to separate the fields. Clearly
this incurs rather high overhead. This overhead can be avoided
using the Byte Macro Option (see Appendix 3).
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Data Entry Terminal
Miscellaneous
IAC SB DET FN IAC SE subcommand code: 40
where: is one byte
Many data-entry terminals provide a set of "function" keys
when pressed send a one-character command to the server.
subcommand describes such a facility. The values of the
are defined by the user and server. The option merely provides
means to transfer the information
IAC SB DET ERROR IAC SE subcommand code: 41
where
is a byte containing the subcommand code of the
in error
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
report errors they detect to the corresponding Telnet process.
this point it is worth reiterating that the philosophy of
option is that when an error is detected it should be reported
however, the implementation should attempt its best effort to
out the intent of the subcommand or data in error
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Data Entry Terminal
3. Default and Minimal Implementation
WON'T DET -- DON'T
Neither host wishes to use the Data Entry Terminal option
Minimal
DET EDIT
DET ERASE
DET TRANSMIT
DET FORMAT
DET MOVE CURSOR
DET
DET ERASE
DET TRANSMIT
DET FORMAT
DET ERROR
In the case of formatting the data, the minimal
should be able to support a low and high level of intensity
protection for all or no characters in a field. These functions
however, are not required
The minimal implementation also requires that the Output Line
and Output Page Size Telnet options be supported
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Data Entry Terminal
4.
The Telnet protocol was originally designed to provide a means
scroll-mode terminals, such as the standard teletype, to
with processes through the network. This was suitable for the
majority of terminals and users at that time. However, as use of
network has increased into other areas, especially areas where
network is considered to provide a production environment for
work, the desires and requirements of the user community have changed
Therefore, it is necessary to consider supporting facilities that
not initially supported. This Telnet option attempts to do that
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
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
functions that are either common to all or can be easily simulated
the more sophisticated functions supplied in some terminals
Unlike most real data entry terminals where the terminal functions
encoded into one or more characters of the native character set,
option performs all such controls within the Telnet
mechanism. This allows programs that are intimately familiar with
kind of terminal they are communicating with to send commands that
not be supported by either the option or the implementation. In
words, it is possible to operate in a "raw" or at least "rare"
using as much of the option as necessary
Although many data entry terminals support a variety of
devices such as printers, cassettes, etc. it is beyond the scope
this option to entertain such considerations. A separate option
be defined to handle this aspect of these devices
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Data Entry Terminal
5.
General
All implementations of this option are required to support a
minimal set of the subcommands for this option. Section 3 contains
complete list of the subcommands in this minimal set. In
with the Telnet protocol philosophy that an implementation
not have to be able to parse commands it does not implement,
subcommand of this option is either in the minimal set or is
by one of the facility subcommands. An implementation
"negotiate" with its correspondent for permission to use
not in the minimal set before using them. For details of
negotiation process see the section below on facility subcommands
Most data entry terminals are used in a half duplex mode. (
most DET's on the market can be used either as data entry
or as standard interactive terminals, we are only concerned
with their use as DET's.) When this option is used, it is
that the following Telnet options be refused: Echo,
Controlled Transmission and Echoing, and Suppress Go-Ahead. However
this option could be used to support a simple full duplex CRT
application using the basic cursor control functions provided here
For these cases, one or more of the above list of options might
required. (Support of sophisticated interactive
applications is beyond the scope of this option and should be
by another option or the Network Graphics Protocol.)
In RFC 728, it was noted that a synch sequence can cause
interactions between Telnet Control functions and the data stream.
synch sequence causes data but not control functions to be flushed
If a control function which has an effect on the data
following it is present in the data stream when a synch
occurs, the control function will have its effect not on
intended data but on the data immediately following the Data Mark
The following DET subcommands are susceptible to this pitfall
CHAR
DATA
FORMAT
The undesired interactions are best avoided by the
of the synch sequence deleting these subcommands and all
associated with them before continuing to process the
functions. This implies that the Data Mark should not occur in
middle of the data associated with these subcommands
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Data Entry Terminal
Facility
These four subcommands are used by the User and
implementations to negotiate the subcommands and attributes of
terminal that may be utilized. This negotiation can be viewed as
terminal (User Host) indicating what facilities are provided and
Server Host (or application program) indicating what facilities
desired
When Sent: A Server Telnet implementation using the DET option
send a facility subcommand requesting the use of a
subcommand or terminal attribute not in the minimal
before the first use of that subcommand or attribute. The
Telnet implementation should respond as quickly as possible with
reply. Neither the User nor Server are required to negotiate
subcommand at a time. Also, a Telnet implementation responding to
facility subcommand is not required to give permission only for
subcommand. It may send a format map indicating all facilities
that class which it supports. However, a Telnet
requesting facilities must send a facility subcommand before
first use of the subcommand regardless of whether
negotiations have indicated the facility is provided. The
cannot be used until a corresponding facility subcommand has
received. There are no other constraints on when the
subcommands may be sent. In particular, it is not necessary for
application to know at the beginning of a session all
that it will use
Action When Recieved: There are two possible actions that may
taken when a facility subcommand is received depending on
the receiver is a requestor or a provider (User).
Requestor: When a facility subcommand is received by a requestor
it is in the state of Waiting for a Reply, it should go into
state of Not Waiting. It should then take the facility map it
sent and form the logical intersection with the facility
received. (For the Intensity attribute, one should take the
of the number received and the number requested.) The
indicates the facilities successfully negotiated. Note:
the receiver is not in the Waiting for Reply state, then this is
provider case described next
Provider: When a facility subcommand is received, it should send
facility subcommand with a facility map of the facilities
provides as soon as possible. It should then determine what
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facilities it is providing for the Requestor by forming the
intersection of the facility map received and the one sent
Note: Although in most cases the requestor will be the Server
and the provider will be the User Host supporting the terminal,
distinction may not always be true
Transmit
There are two kinds of transmit subcommands: those used to
that data be sent to the requestor, and one to preface data sent
the requestor. The first kind allow the requestor to control when
from where and to some degree how much data is transmitted from
terminal. Their explanation is straightforward and may be found
Section 2.
Data may be sent from the terminal as a result of two events:
user of the terminal caused the transmission or in response to
transmit subcommand. Some programs may wish to know from where
the screen the transmission began. (This is reasonable, since
terminal user may move the cursor around considerably
transmitting.) Other programs may not need such information.
DATA TRANSMIT subcommand is provided in case this function
needed. When used this subcommand prefaces data coming from
terminal. The parameters and give the screen coordinates
the beginning of the transmission. must be less than or equal
M-1 and must be less than or equal to N-1. It is assumed
all data between this DATA TRANSMIT and the next one starts at
coordinates given by the first subcommand and continues filling
line thereafter according to the constraints of the screen and
format effectors in the data. Thus an intelligent or
user-host DET implementation (depending on your point of view)
only include a DATA TRANSMIT subcommand when the new starting
is different from the last ending point
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6. Sample
The nomenclature of RFC 726 will be used to describe this example.
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.
surrounded by angle brackets (<>) is to be taken as a single unit
E.g, carriage return is , and the decimal value 27
represented <27>.
We assume that the user has established the Telnet connection
logged on, and an application program has just been started
by the user directly or through a canned start up procedure.
presentation on the page is meant to merely group entities
and does not imply the position of message boundaries. One
assume that any part of the dialogue may be sent as one or
messages. The first action of the program or Telnet is to
the DET option
S:
U:
S: