Re: HME resolved... at least for now.

On Fri, Apr 04, 2003 at 04:22:13PM +0100, Matthew Swabey wrote:
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mas01r> Allow me to add my 2c. AFAIK there is no standard for 10MBit Ethernet
mas01r> Full Duplex. You could do it but basically only using one manufacturers
mas01r> equipment or trusiting to luck.

10/full should work just fine between any manufacturer's equipment that
supports it.  Full duplex actually *removes* requirements from the
Ethernet protocol, stripping it of CSMA/CD completely, allowing either
link partner to transmit any time it wishes.  There is nothing to really
"screw up" when implementing full duplex Ethernet, since it is basically
a subset of half duplex Ethernet implementation-wise.  So reiterating
this, if the device supports manually placing the port into 10/full
mode, it should interoperate perfectly well with any other device that
has also been manually placed into 10/full mode.

Now Autonegotiation, on the other hand, is a completely different
animal.  There is plenty to screw up there, and it does often happen
that two different manufacturer's implementations don't interoperate
properly.  In that case it is absolutely imperative to manually
configure both ends for full duplex if either end is configured manually
for full duplex.  There is no way to "sense" the duplex setting of the
link partner like you can sense the speed.  Therein lies the difference
between Autonegotiation and Autosense.  The latter only deals with
passively sensing the speed based on the link pulses coming from the
other end, while the former is a complete two-way handshake protocol
that both ends must actively support and have enabled in order to
mutually agree on the best duplex (and speed) setting.  Most devices
will fall back to Autosense, with half duplex, if Autonegotiation is
disabled on the remote end or fails to negotiate properly.  So if the
remote end has been manually configured for full duplex, with
Autonegotiation disabled, while the local end has Autonegotiation
enabled, then you will be guaranteed to have a duplex mismatch and a
badly performing link.

-- 
Charles R. Anderson <[email protected]> / http://angus.ind.wpi.edu/~cra/
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