From: Drew (apt@dcs-success.com)
Date: Thu Jul 18 2002 - 11:12:25 EDT
Here is my 2 cents, I haven't been following the thread and I know you have
just about had it but...here it goes. Sorry if some of this is sounds basic
but give me a chance.
Let's start with 10baseT and 100baseT.
Ethernet needs to work on CSMA/CD Carrirer Sense Multiple Access with
Collision Detection), which means each device must "check the wire" (or
broadcast domain) to see if any other computer is communicating and if so,
it must wait a random amount of nano-seconds and then try again.
Communication is strictly one way. Only one node at a time communicating in
only one direction at a time. Traffic is ONE way. Each computer (at least
with TCP) must periodically let the other computer know that it has received
packets 1,2,3,4 etc before the other computer will send packets 5,6,7,8 etc.
If this response does not occur then the first computer will try to resend,
and if it has to keep resending, all of a sudden, the transfer will slow to
a major crawl.
Then, out of the clear blue, Full Duplex Ethernet cards are announced and
advertises that it will allow two way communication! What a great thing!
However, how does that work with CSMA/CD? Well, if you are all plugged into
a switch that will allow two way communication (by reducing the broadcast
domain down to only the two nodes communicating, and buffering in transit)
then all is well and the equipment is working as advertised.
But, If you are plugged into a hub that does not allow for two way
communication and/or you have your cards set to full duplex, and maybe a
card or two on the LAN are set to autonegotiate or even 10 baseT, then you
will have major issues as the cards try to negotiate a communication
channel. You can even experience problems with all new cards going 100 full
duplex through a hub by itself.
When I'm setting up a LAN that may have multiple NICs going through a hub, I
usually try to set them all at a common speed and at half Duplex. I only go
full duplex through switches.
Hope this helps
Drew
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