Re: why my RH6.0 does not support PCI modem, modem info

[Alan Shutko <ats acm org>]

"Tony Johnson" <gjohnson showmaster com> writes:

> Standard phone lines weren't designed to transmit data for larger
> sizes like ethernet is.  Some Macintosh computers cannot handle the
> standard mtu size of 1500 bytes that ethernet has.

Could you explain what you mean?  A phone line transmits the same
amount of data at the same speed regardless of the size of the
packet.  It's just that the data is broken up at the PPP layer into
different size chunks, and thus application data will have a lower
ratio to protocol data as the packet size goes down.  (If phone lines
weren't able to handle 1500 byte mtus, how did they ever manage with
large kermit packets or zmodem?)

Now, if you start looking at very lossy lines, a smaller packet size might
be faster because you have lost less when you lose part of a packet,
but with error-correcting modems I find that I need _really_ big
problems to lose something between the ends of a PPP.

(It used to be conventional wisdom five years ago that if you wanted
your ftps to approach the speed of zmodem, you'd up the mtu, but if
you wanted interactive telnets during ftps, you'd decrease this.  Were
we all wrong?  Of course, that was in they days when a 1500 byte
packet would take longer than a second to xmit....)


-- 
Alan Shutko <ats acm org> - Looking for a job in Long Island!
Check http://rescomp.wustl.edu/~ats/ for a resume.
IBM: Ici Beaucoup Merde