Walt Haas (
Fri, 2 Oct 87 12:19:47 MDT

I've been following the discussion about TELNET echoing with some interest.
The problem has long since been solved in the big (public) network world.
A good example of how the solution works is represented by my X.25
implementation for the DEC-20 (RIP, sigh...). There were two cases worth

1) Minimum packet charge. In this case the PAD which was connected to the
   user's terminal did echoing of characters, and forwarded a packet only
   when there were enough characters to fill one, OR the user entered a
   transmission character, OR the user didn't type anything for a while.
   In this case the TOPS-20 system was set for page mode, half duplex
   operation. The PAD grabbed ^Q/^S to use for terminal flow control.

2) Screen editting. In this case characters were echoed by the host.
   The PAD forwarded soon after each character was keyed in. The TOPS-20
   system was set for full duplex, and passed ^Q/^S thru transparently to
   the applicateion (usually EMACS or some such).

I wrote a little command which switched between the two modes by sending
an X.29 packet from host to PAD and, at the same time, switching terminal
modes inside TOPS-20. With just a little more work this sequence could
have been built into EMACS.

So how did it work? Great! I had the pleasure of sitting in New York
running EMACS on UTAH-20 over Telenet, with good response. Then I could
quickly switch back to mode 1 (the default) for normal TOPS-20 command

One of the reasons this is hard to do with TELNET is that the TELNET
standard is worded in such a way that you don't have to implement these
functions in order to say you have a standard TELNET implementation.
The CCITT standard for PADs, in contrast, requires that you actually
implement a lot of functionality before you can say you conform.

Cheers -- Walt ARPA: uucp: ...utah-cs!haas

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