Alan Klietz (ihnp4!meccts!mn-at1!alan@ucbvax.Berkeley.EDU)
4 Oct 87 18:48:39 GMT

In article <244@mitisft.Convergent.COM> andrew@mitisft.Convergent.COM (Andrew Knutsen) writes:
< It seems to me there are is a middle ground in here, between
<char-at-a-time and line- (or screen-) at-a-time, that can be implemented
<purely on the server side using the normal telnet protocol (ECHO negotiation).
<We are considering implementing this for support of low speed TCP links
<(eg async modems), and I'm curious if I'm going to run into some "common
<knowledge problem"...
< The basic idea is to have the kernel (virtual terminal driver) inform
<the telnet daemon when it *would be* doing immediate character echo, and
<not do it. The daemon turns this information into echo negotiation, which
<the client (hopefully) heeds. This results in speeded echo response in
<(for example) un*x "cooked" mode, plus a reduction in packet traffic.
< Has anyone tried this?

We modified the Cray-2 UNICOS kernel to signal a modified (kludged)
version of telnetd on a change in tty state. For example, when
the user typed "vi" on the Cray-2, the ioctl(TIOCSETA) call is sent
to the pty driver. The information in the call is stored in a dummy
kernel tty structure and the telnetd process is signaled. The telnetd
process wakes up and interrogates the terminal state by issuing an
ioctl(TIOCGETA) on the pseudo-tty. It picks up the info and says
"humm, this user wants raw mode". It then re-negotiates the ECHO
option with the client to switch to single character mode.

One problem with this approach is that the change of state is
asynchronous to the I/O.

Alan Klietz
Minnesota Supercomputer	Center (*)
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