ttydX and xterm size (LINES and COLUMNS understanding)

[Emanuel Strobl]

Dear console gurus,

when I open a xterm on the local machine, say with 100x37, vi and man 
recognizes the size and display the content correctly.
If I use cu/tip in a 100x37 xterm "ls" works fine (uses all lines) as long as 
I start vi but man doesn't work (no scrolling possible). After the vi session 
only 24 lines (or whatever type I set in /etc/ttys) are used, but man works 
correctly.
Why can I use different terminal sizes on the local machine and in ssh 
sessions but not over a serial console?
If I set "setenv LINES 37" and "setenv COLUMNS 100" it works also on the 
serial line but why or how can vi and others know what size my terminal is 
via ssh session? I'm sure this behaviour is adoptable to serial consoles too.

Thanks,

-Harry
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