I have a situation where I am using xterm to run a telnet session to a 
server over the Internet (don't worry its all behind some very 
aggressive firewalls and non-standard ports).

As you are probably aware each keystroke is a flurry of TCP packets 
with high overhead for each keystroke, and zero data ACK packets.

However, as xterm does the VT100 emulation then when a cursor key is 
pressed, a string of characters rather than a single character gets 
transmitted, eg. when an up cursor is pressed then the ANSI string 
<ESC>[A gets sent.

In most cases this does not present a problem with the three characters 
being transmitted in one packet and the application understanding what 
the string is about, but occasionally the <ESC> gets sent in one packet 
and the [A gets sent in a separate packet.  The receiving application 
thinks that something has gone missing and does not recognise these as a 
logical string.

There definitely isn't an MTU problem with such small packets and the 
DF flag is set.

I don't know why these strings are being broken up or where the 
problem lies, whether in xterm, or in the TCP stack.  It appears that 
the problem is more prevalent with slower hardware, but I cannot be 
objective about that.

As you can imagine it is very frustrating for the operators and 
embarrassing for me as this client has placed great faith in Linux.

Any ideas?
-- 
Howard.
LANNet Computing Associates <http://www.lannet.com.au>






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