dchen@oliveb.UUCP (Dennis Chen) (05/17/86)
We have a very serious problem of 'telnet' program in our VAXen 11/{750,785}
4.2 BSD Unix. The symptom seems to me is flow control problem (lost
characters, gobble the screen when cat'ing file). The followings are
the tests dealt with the 'telnet' program:
Flow control problem occurs with any of following tests:
1. Use a VT100, "telnet" from VAX 11/{750,785} 4.2BSD Unix to
VAX 11/{750,785} 4.2BSD Unix
2. Use a VT100, "telnet" from VAX 11/(750,785} 4.2BSD Unix to
VAX 11/750 VMS with Wollongong Group TCP/IP
3. Use a VT100, "telnet" from VAX 11/{750,785} 4.2BSD Unix to
VALID workstation based 4.2BSD Unix. And vise versa.
NO flow control problem with any of following tests:
1. Use a VT100, "telnet" from VAX 11/750 VMS to VAX 11/750 4.2BSD Unix
2. Use an IBM PC or Olivetti M24 PC with kermit, "telnet" just
works fine between two VAXen running 4.2BSD Unix
3. Use an IBM PC or Olivetti M24 PC with kermit, "telnet" just
works fine between VAX 4.2BSD and VAX VMS.
4. Rlogin between two VAXen 4.2BSD Unix
From test 1. I can tell there is no problem with the telnet server, "telnetd".
Therefore, I would suspect there is flow control problem somewhere either in
"telnet" or serial line driver.
Note that all the serial interface cards we used are DH/DMs, and the
ethernet boards we used are either 3COM or Interlan.
Has anyone in the net has this problem ? Any suggestion would be greatly
appreciated ?
Thanks in advance
Dennis Chen
{allegra, fortune, glacier, hplabs, ihnp4}!oliveb!dchenjerry@wg3b20.UUCP (05/22/86)
> We have a very serious problem of 'telnet' program in our VAXen 11/{750,785} > 4.2 BSD Unix. The symptom seems to me is flow control problem (lost > characters, gobble the screen when cat'ing file). The followings are > the tests dealt with the 'telnet' program: > > Flow control problem occurs with any of following tests: > 1. Use a VT100, "telnet" from VAX 11/{750,785} 4.2BSD Unix to > VAX 11/{750,785} 4.2BSD Unix > 2. Use a VT100, "telnet" from VAX 11/(750,785} 4.2BSD Unix to > VAX 11/750 VMS with Wollongong Group TCP/IP > 3. Use a VT100, "telnet" from VAX 11/{750,785} 4.2BSD Unix to > VALID workstation based 4.2BSD Unix. And vise versa. > The "problem" has to do with the VT100 sending XON and XOFF as it tries to throttle output from the terminal driver. What happens in the above cases is that the XON is sent across the network where it reaches the telnet server who then gives it to the terminal driver who then stops output. However the beauty of TCP is that it can send a window of data at a time. So by the time the server side's terminal server stops output it is too late, the VT100 has been overriden. You can either set the terminal speed down to 4800 baud (or less) or make mods to the telnet program on the 4.2BSD side to do local XON/XOFF processing. I did this on Wollongong's VMS telnet and it works fine. VMS has the ability to set the terminal in a mode similar to RAW mode but ask to catch certain characters. I ask to catch CTRL-S and when I receive it buffer new characters over the net locally and send a XON across the net. When catching CTRL-Q I flush all characters and send a XOFF. Regards, Jerry Scott