RFC 857 (rfc857) - Page 2 of 5
Telnet Echo Option
Alternative Format: Original Text Document
RFC 857 May 1983
The NVT has a printer and a keyboard which are nominally
interconnected so that "echoes" need never traverse the network; that
is to say, the NVT nominally operates in a mode where characters
typed on the keyboard are (by some means) locally turned around and
printed on the printer. In highly interactive situations it is
appropriate for the remote process (command language interpreter,
etc.) to which the characters are being sent to control the way they
are echoed on the printer. In order to support such interactive
situations, it is necessary that there be a TELNET option to allow
the parties at the two ends of the TELNET connection to agree that
characters typed on an NVT keyboard are to be echoed by the party at
the other end of the TELNET connection.
5. Description of the Option
When the echoing option is in effect, the party at the end performing
the echoing is expected to transmit (echo) data characters it
receives back to the sender of the data characters. The option does
not require that the characters echoed be exactly the characters
received (for example, a number of systems echo the ASCII ESC
character with something other than the ESC character). When the
echoing option is not in effect, the receiver of data characters
should not echo them back to the sender; this, of course, does not
prevent the receiver from responding to data characters received.
The normal TELNET connection is two way. That is, data flows in each
direction on the connection independently; and neither, either, or
both directions may be operating simultaneously in echo mode. There
are five reasonable modes of operation for echoing on a connection
pair:
Neither end echoes
One end echoes for itself
Postel & Reynolds