📄 rfc726.txt
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2) If the terminal input buffer is empty, then go to 3,
else go to 4. 6a3
3) Wait for an item to appear either from the terminal
or from the network. 6a4
If an item appears from the terminal, then go to 4. 6a4a
If a data item appears from the network, then print
it and go to 3. 6a4b
If a command appears from the network, then an error
has occured. 6a4c
4) Read an item from the terminal input buffer. 6a5
If the item is not a break, then print/skip it and go
to 2. 6a5a
If the item is a break, then print/skip it and go to
1. 6a5b
Note: Output from the server host may occur at any
time, such "spontaneous output" is printed in step 3. 6a6
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Remote Controlled Transmission & Echoing Telnet Option
Explanation: 6b
Both Hosts agree to use the RCTE option. After that,
the using host (IAC DO RCTE) merely acts upon the
controlling (serving) host's commands and does not
issue any RCTE commands unless and until it (using
host) decides to stop allowing use of the option (by
sending IAC DON'T RCTE). 6b1
1) The using host is synchronized with the server by
initially and when ever it returns to step 1 suspending
terminal echo printing until it receives a command from
the server. 6b2
The server may send either output to the terminal
printer or a command, and usually sends a both. 6b3
The server may send output to the terminal printer
either in response to user input or spontaneously. In
the former case, the output is processed in step 1. In
the latter case, the output is processed in step 3. 6b4
Server sends an RCTE command. The command may redefine
break and transmission classes, action to be performed
on break characters, and action to be performed on
text. Each of these independent functions is controlled
by separate bits in the <cmd> byte. 6b5
A transmission character is one which RECOMMENDS that
the using host transmit all text accumulated up to
and including its occurrence. (For network
efficiency, using hosts are DISCOURAGED (but not
prohibited) from sending before the occurrence of a
transmission character, as defined at the moment the
character is typed). 6b5a
If the transmission classes bit (bit 4) is on, the
two bytes following the two break classes bytes (or
immediately following the <cmd> byte, if the break
classes bit is not on) will indicate what classes
are to be enabled.
If the bit is OFF, the transmission classes remain
unchanged. When the RCTE option is first initiated,
NO CLASSES are in effect. That is, no character
will be considered a transmission character. (As if
both TC1 and TC2 are zero.)
A break character REQUIRES that the using host
[page 7]
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Remote Controlled Transmission & Echoing Telnet Option
transmit all text accumulated up to and including its
occurrence and also causes the using host to stop its
print/discard action upon the user's input text,
until directed to do otherwise by another IAC SB RCTE
<cmd> IAC SE command from the serving host. Break
characters therefore define printing units. "Break
character" as used in this document does NOT mean
Telnet Break character. 6b5b
If the break classes bit (bit 3) is on, the two
bytes following <cmd> will indicate what classes
are to be enabled. There are currently nine (9)
classes defined, with room for expansion.
If the bit is OFF, the break classes remain
unchanged. When the RCTE option is initiated, NO
CLASSES are to be in effect. That is, no
transmission will take place in the user to server
direction until the first break reset command is
received by the user from the server.
The list of character classes, used to define break
and transmission classes are listed at the end of
this document, in the Tables Section. 6b5c
Because break characters are special, the
print/discard action that should be performed upon
them is not always the same as should be performed
upon the rest of the input text. 6b5d
For example, while typing a filename to TENEX, I
want the text of the filename to be printed
(echoed); but I do not want the <escape> (if I use
the name completion feature) to be printed.
If bit 1 is ON the break character is NOT to be
printed.
A separate bit (bit 2) signals whether or not the
text itself should be printed (echoed) to the
terminal. If bit 2 = 0, then the text IS to be
printed. 6b5e
Yet another bit (bit 0 - right-most bit) signals
whether or not any of the other bits of the command
should be checked. If this bit is OFF, then the
command should be interpreted to mean "continue
whatever echoing strategy you have been following,
using the same break and transmission classes." 6b5f
[page 8]
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Remote Controlled Transmission & Echoing Telnet Option
2) The user Telnet now checks the terminal input
buffer, if it contains data it is processed in step 4,
otherwise the user Telnet waits in step 3 for further
developments. 6b6
3) The user Telnet waits until either the human user
enters some data in which case Telnet proceeeds to step
4, or an item is received from the network. If the item
from the network is data it is spontaneous output and
is printed, Telnet then continues to wait. If the item
from the network is a command then an error has
occured. In this case the user Telnet may attempt to
resynchronize the use of RCTE as indicated below. 6b7
4) Items from the terminal are processed with printing
controlled by the settings of the latest break reset
command. When a break character is processed, the cycle
of control is complete and action re-commences at step
1. 6b8
Input from the terminal is (hopefully) buffered into
units ending with a transmission or break character;
and echoing of input text is suspended after the
occurrence of a break character and until receipt of a
break reset command from the serving host. The most
recent break reset command determines the break
actions. 6b9
In summary, what is required is that for every break
character sent in the user to server direction there be
a break reset command sent in the server to user
direction. The user host initially has no knowledge of
which characters are break characters and so starts in
a state that assumes that there are no break characters
and also that no echoing is to be provided. The server
host is expected to send a break reset command to
establish the break classes and the echoing mode before
it receives any data from the user. 6b10
Synchronization and Resynchronization: 6c
The serving and using hosts must carefully synchronize
break reset commands with the transmission of break
characters. Except at the beginning of an interaction,
the serving host may only send a break reset command in
response to the Using host's having sent a break
character as defined at that time. This should
establish a one-to-one correspondence between them. (A
<cmd> value of zero, in this context, is interpreted as
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NWG/RFC# 726 JBP DHC 8-MAR-77 08:29 39237
Remote Controlled Transmission & Echoing Telnet Option
a break classes reset to the same class(es) as before.)
The break reset command may be preceded by terminal
output. 6c1
The re-synchronization of the break characters and the
break reset commands is done via the exchange of the
Telnet signal Abort Output (AO) in the server to user
direction and the SYNCH in the user to server
direction. 6c2
Suppose the server wants to resynchronize the break
characters and the break reset commands. 6c3
a. The server should be sure all output to the
terminal has been printed by using, for example, the
Timing Mark Option. 6c3a
b. The server sends the AO signal. 6c3b
c. The user receives the AO signal. The user flushes
all user to server data wheather it has been echoed
or not. The user sends a SYNCH to the server. [The
SYNCH consists of the Telnet Data Mark (DM) and the
host-to-host interrupt (INS).] The user now enters
the initial state at step 1. 6c3c
d. The server receives the SYNCH and flushes any
data preceeding the DM (as always). The server now
sends a break reset command. (Actually the break
reset command could be sent at any time following the
AO.) 6c3d
Suppose the user wants to resynchronize the break
characters and the break reset commands. 6c4
a. The user should discard all user to server data
wheather it has been echoed or not. 6c4a
b. The user sends the AO signal. The user now enters
the algorithm at step 1. 6c4b
c. The server receives the AO signal. The server
discards all data buffered but not yet sent to the
user. The server sends a SYNCH to the user. The
server sends a break reset command to the user. 6c4c
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Remote Controlled Transmission & Echoing Telnet Option
Notes and Comments: 6d
Even-numbered commands, greater than zero, are in
error, since they will have the low-order bit off. The
command should be interpreted as equal to zero, which
means that any classes reset bytes ([TC1 TC2] [BC1
BC2]) will be in error. (The IAC SE, at the end of the
command, eliminates any parsing problems due to this
error.) 6d1
Serving hosts will generally instruct using hosts not
to echo break characters, even though it might be
alright to echo most break characters. For example,
<cr> is usually a safe character to echo but <esc> is
not. TENEX Exec is willing to accept either, during
filename specification. Therefore, the using host must
be instructed not to echo any break characters. 6d2
This is generally a tolerable problem, since the
serving host has to send an RCTE command at this
point, anyhow. Adding an echo for the break character
to the message will not cause any extra network
traffic. 6d2a
The RCTE Option entails a rather large overhead. In a
true character-at-a-time situation, this overhead is
not justified. But on the average, it should result in
significant savings, both in network traffic and host
wake-ups. 6d3
Buffering Problems and Transmission vs. Printing
Constraints: 6d4
There are NO mandatory transmission constraints. The
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