Switches and collisions

Discussion in 'Cisco' started by Liam, Sep 9, 2004.

  1. Liam

    Liam Guest

    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
     
    Liam, Sep 9, 2004
    #1
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  2. Liam

    Ivan Ostres Guest

    In article <chpkoj$pdu$1.nb.home.nl>,
    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 ***
     
    Ivan Ostres, Sep 9, 2004
    #2
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  3. Liam

    paul blitz Guest

    "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" <> wrote in message
    news:chpkoj$pdu$1.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, Sep 9, 2004
    #3
  4. Liam

    paul blitz Guest

    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" <> wrote in message
    news:414069d4$0$20250$...
    > "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" <> wrote in message
    > news:chpkoj$pdu$1.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, Sep 9, 2004
    #4
  5. Liam

    Scooby Guest

    "paul blitz" <> wrote in message
    news:414069d4$0$20250$...
    > "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" <> wrote in message
    > news:chpkoj$pdu$1.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.
     
    Scooby, Sep 9, 2004
    #5
  6. Liam

    paul blitz Guest


    > 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 blitz, Sep 10, 2004
    #6
  7. Liam

    Scooby Guest

    "paul blitz" <> wrote in message
    news:414178ce$0$20243$...
    >
    > > 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.
     
    Scooby, Sep 10, 2004
    #7
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