<excessive Cc's to other mailing lists removed>
On Fri, 2 Apr 1999, Dave Mielke wrote:
> On Fri, 2 Apr 1999, Admin-Eng wrote:
> >Why full duplex whould be off ? I though in operate faster in full duplex
> >mode
>
> Full duplex only makes sense if you have a dedicated link between
> exactly two systems. It then lets each of those two systems send
> to the other concurrently. When you have more than two systems,
> and they all send to each other one, it is necessary to use half
> duplex.
Err Dave,
Imagine three systems, A, B and C, on a switch, S, and all are capable
of 10mbps full-duplex:
A--------+-+
| |
B--------|S|----<the world>
| |
C--------+-+
Consider A sending a 100 megabyte file to B, and C sending a 100
megabyte file to A.
A can transmit continuously to B at 10mpbs, while receiving the
file from C at 10mpbs. The transfer of both files therefore takes 100
seconds.[1]
If you have only half-duplex between A and the switch, then in my
example, it takes twice the time (200 seconds) to move the files
between the machines, because the link to machine A is congested.
So, in summary, full-duplex is useful in more cases than just a fixed
link with 2 machines on it (provided your switch/hub can do full
duplex too).
Best regards,
Mark
[1] Okay - so I didn't account for ACK traffic back from B to A and A
to C, nor congestion backoff, but that's fairly negligable effect and
not relevent for the point I was making.
+-------------------------------------------------------------------------+
Mark Cooke The views expressed above are mine and are not
Systems Programmer necessarily representative of university policy
University Of Birmingham URL: http://www.sr.bham.ac.uk/~mpc/
+-------------------------------------------------------------------------+
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