Yup, makes sense. I can only speak for 3Com on this one, but I believe
Cisco implements similar features. On a 3Com Corebuilder (as well as their
Workgroup Switches) they use fake collisions as a flow control mechanism.
In other words if there was contention at the server or switch and they
couldn't handle the load then a collision (a JAM) will be sent. Now, that
said after we all just agreed that collisions can not happen on a full
duplex Ethernet segment:) If you notice in Cisco texts that Collision
Detection is disabled on full duplex links, this is not true. Collision
detection is still there, at least on a 5000 and can be simulated by loading
up a server at 10MB FD with a few 100MB FD clients on the other end of the
Cat, you will see this in action. 3Com does the same thing, I thought this
was kinda interesting.
Shawn
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Priscilla Oppenheimer
Sent: Tuesday, December 26, 2000 2:06 PM
To: Andy Walden; John lay
Cc: [EMAIL PROTECTED]
Subject: Re: Confused (was Re: is this statement true ??)
I think what John is getting at is that there is still contention. In his
example with two clients trying to reach one server, there's contention at
the switch, and at the server possibly. There's no contention on the medium
itself. There's only one device trying to send at any one time. The switch
has its transmit pair and the server has its own transmit pair. If the
switch has two frames to send to the server, the backup happens at the
switch. Does that make sense?
Priscilla
At 08:33 AM 12/26/00, Andy Walden wrote:
>This is correct. You don't use full duplex if you are competing for
>bandwidth, ie, plugged into a hub. But if you are plugged into a switch,
>there is only one bandwidth domain between the device and switch and
>with nothing competing for the bandwidth on that link so you can go full
>duplex.
>
>andy
>
>On Tue, 26 Dec 2000, John lay wrote:
>
> > Priscilla, everybody,
> >
> > I am confused. Ethernet and FastEthernet uses the CSMA/CD as a channel
> > allocation techinque in a shared media access envoiroment.
> > Here it comes the confusion, when you are saying that the Full-duplex
does
> > not support CSMA/CD because the transmit and receive are on different
> wires.
> > This implies that in this case there is no shared media, how come if
you
> > have two clients competing to talk to the same server
simultaneously....!!
> >
> > Thanx
> >
> >
> > On Mon, 25 Dec 2000 16:36:11 -0800, Priscilla Oppenheimer wrote:
> >
> > > It's true for Ethernet because Ethernet's CSMA/CD media access
control
> > > method has strict timing requirements, which result in strict length
> > > restrictions. Half-duplex uses CSMA/CD. Full-duplex does not.
> > >
> > > I wouldn't say it's true in general, however.
> > >
> > > Priscilla
> > >
> > > At 05:32 PM 12/25/00, Li Song wrote:
> > > >"full-duplex can be used over longer distance than
> > > >half-duplex" ??
> > > >what 's your opinion ??
> > > >
> > > >
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