Neil Harvey writes:

>Don't forget AICS Research's "Advanced Telnet" protocol, which is somewhere
>between telnet (each char echoed by host) and block mode (chars sent when
>you press enter), I think.

AICS is simply using local echo -- "half duplex" from the very old days
-- to eliminate the round-trip delay normally seen with Telnet. In normal
("full-duplex") Telnet, each keystroke generates a packet that's
transmitted to the remote machine. The remote machine echoes back the
character to your terminal session, which displays it on the screen. This
round trip can take a long time over the Internet.

Local echo operation means that the terminal displays each keystroke
immediately in addition to sending it to the remote machine. The remote
machine does not echo the character because it knows that the terminal
has already displayed it locally. This eliminates the sometimes-annoying
delay between keystroke and echo, and gives the illusion of instantaneous
data transmission. It's different from block mode, which buffers
characters and sends them in a single block. Characters are still sent
individually, one per packet, as they're typed.

NS/VT does use a block-oriented protocol. It buffers typed characters and
performs all character editing (e.g., character delete, line delete)
locally, and only sends the characters when you press Return (or whatever
key has been defined as the end-of-line character). The entire line is
sent as a single packet. The host keeps the terminal informed about how
it should do local editing: it tells the terminal what to echo for a
backspace or a line delete, what the current line termination characters
are, what the current subsystem break character is, and so on.

-- Bruce


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