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Liam 09-09-2004 01:15 PM

Switches and collisions
 
Is it true that a full duplex switch can't have any collision?
My instructor tells me it is not possible, only i think it could happen.

Anyone any ideas or documents on this one?

Thnx,

Liam



Ivan Ostres 09-09-2004 02:17 PM

Re: Switches and collisions
 
In article <chpkoj$pdu$1@news2.tilbu1.nb.home.nl>, wannabe@hotmail.com
says...
> Is it true that a full duplex switch can't have any collision?
> My instructor tells me it is not possible, only i think it could happen.
>
> Anyone any ideas or documents on this one?
>
>


There's no colisions in full duplex connection by definition. The only
way you can see colisions is if you have duplex mismatch (and then it
will be 'late collisions') but that is not a normal state of the
operation.

--
-Ivan.

*** Use Rot13 to see my eMail address ***

paul blitz 09-09-2004 02:33 PM

Re: Switches and collisions
 
"Full Duplex" means that you can send AND receive at the same time... so if
you are "talking to" another switch port, then you can never colide with
their reply.

But, what happens if someone ELSE is also talking to that switchport already
when you send a packet?....I'm guessing that as the port is already in use,
your data doesn't go through. But it's not actually a collision (as you
would see on a half-duplex setup), its more of a discard.


Paul


"Liam" <wannabe@hotmail.com> wrote in message
news:chpkoj$pdu$1@news2.tilbu1.nb.home.nl...
> Is it true that a full duplex switch can't have any collision?
> My instructor tells me it is not possible, only i think it could happen.
>
> Anyone any ideas or documents on this one?
>
> Thnx,
>
> Liam
>
>




paul blitz 09-09-2004 02:39 PM

Re: Switches and collisions
 
Ok, thinking about it, I guess the answer - at least for a limited amout of
data - is that the data gets buffered, and then released when the port is
free. But if the buffer capacity gets exceeded (lots of hosts talking to a
busy server maybe?) then I guess there is still the posibility of data
simply being discarded.... but still no actual collisions!


Paul


"paul blitz" <paul.blitz@centia.co.uk> wrote in message
news:414069d4$0$20250$ed9e5944@reading.news.pipex. net...
> "Full Duplex" means that you can send AND receive at the same time... so

if
> you are "talking to" another switch port, then you can never colide with
> their reply.
>
> But, what happens if someone ELSE is also talking to that switchport

already
> when you send a packet?....I'm guessing that as the port is already in

use,
> your data doesn't go through. But it's not actually a collision (as you
> would see on a half-duplex setup), its more of a discard.
>
>
> Paul
>
>
> "Liam" <wannabe@hotmail.com> wrote in message
> news:chpkoj$pdu$1@news2.tilbu1.nb.home.nl...
> > Is it true that a full duplex switch can't have any collision?
> > My instructor tells me it is not possible, only i think it could happen.
> >
> > Anyone any ideas or documents on this one?
> >
> > Thnx,
> >
> > Liam
> >
> >

>
>




Scooby 09-09-2004 09:27 PM

Re: Switches and collisions
 
"paul blitz" <paul.blitz@centia.co.uk> wrote in message
news:414069d4$0$20250$ed9e5944@reading.news.pipex. net...
> "Full Duplex" means that you can send AND receive at the same time... so

if
> you are "talking to" another switch port, then you can never colide with
> their reply.
>
> But, what happens if someone ELSE is also talking to that switchport

already
> when you send a packet?....I'm guessing that as the port is already in

use,
> your data doesn't go through. But it's not actually a collision (as you
> would see on a half-duplex setup), its more of a discard.
>
>
> Paul
>
>
> "Liam" <wannabe@hotmail.com> wrote in message
> news:chpkoj$pdu$1@news2.tilbu1.nb.home.nl...
> > Is it true that a full duplex switch can't have any collision?
> > My instructor tells me it is not possible, only i think it could happen.
> >
> > Anyone any ideas or documents on this one?
> >
> > Thnx,
> >
> > Liam
> >
> >

>
>


How do you suggest that someone else could be talking on the same port? The
only way this could happen is having some other multiple access device
(switch or hub), since you can't plug multiple devices into one switchport.
Another switch will queue the outgoing data, so no collisions there. A hub
will only speak half duplex - possible collisions.




paul blitz 09-10-2004 09:49 AM

Re: Switches and collisions
 

> How do you suggest that someone else could be talking on the same port?

The
> only way this could happen is having some other multiple access device
> (switch or hub), since you can't plug multiple devices into one

switchport.
> Another switch will queue the outgoing data, so no collisions there. A

hub
> will only speak half duplex - possible collisions.


I was thinking about 2 hosts (on their own switch ports!) both talking to
the same host on a third port.... so the switch has 2 packets to go to the
same outgoing port... obviously it can send only one, so I guess (as long as
it has buffer space) it buffers the second packet until the first one has
been sent.

Paul




Scooby 09-10-2004 11:16 AM

Re: Switches and collisions
 
"paul blitz" <paul.blitz@centia.co.uk> wrote in message
news:414178ce$0$20243$ed9e5944@reading.news.pipex. net...
>
> > How do you suggest that someone else could be talking on the same port?

> The
> > only way this could happen is having some other multiple access device
> > (switch or hub), since you can't plug multiple devices into one

> switchport.
> > Another switch will queue the outgoing data, so no collisions there. A

> hub
> > will only speak half duplex - possible collisions.

>
> I was thinking about 2 hosts (on their own switch ports!) both talking to
> the same host on a third port.... so the switch has 2 packets to go to the
> same outgoing port... obviously it can send only one, so I guess (as long

as
> it has buffer space) it buffers the second packet until the first one has
> been sent.
>
> Paul
>
>


Paul, that is correct. There is actually an awful lot (potentially) that
goes on in a switch from the time it starts coming in one port and then goes
out another. Packets are queued before being sent. It is much different
than a hub that just passes the signal along the wire. And, you were
correct, if too much data is coming in, then packets will get dropped before
ever being sent out a port.




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