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  1. xjx
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    #1

    Default hub=layer 2 devices ?

    Are hub layer 1 or 2 devices?
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  3. Ancient Relic.......
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    #2
    A hub resides at layer 1. reference
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  4. Johan Hiemstra Site Admin Webmaster's Avatar
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    #3
    I edited your post, as we do not allow questions from other sites, books, or other copyright protected study material to be discussed in these forums. Instead, try to reword the question in to a simple technical question.

    You can find the answer to 'your' question here:
    http://www.techexams.net/technotes/n...mponents.shtml
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  5. Senior Member
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    #4
    Hubs do reside in the physical layer, here's why. I hope it can make sense somewhat.

    Here's the OSI model. As you send data, it moves down the OSI model. It changes it's form as you go down. As you recieve data, it goes up. Understand as you go down the OSI model, you can pretend it keeps getting "enveloped" with address'. As you go up the OSI model, the envelopes gets opened and it reads the address

    Layer 7 -- Protocol Data Unit
    Layer 6 -- Protocol Data Unit
    Layer 5 -- Protocol Data Unit
    Layer 4 -- Packet - Get's broken/fragmented into packets
    Layer 3 -- Packet - IP address is added to Packet
    Layer 2 -- Frame - Turns the packet into a frame, MAC address is added
    Layer 1 -- Electrical pulses - turns into electrical pulses on the wire

    Hubs - Hub's are dumb, no intelligence, just repeat to every computer
    Pretend you have 5 computers connected via a hub. If computer 1 sends data to computer 5, computers 2, 3, 4, 5 (All the computers connected) would get that data sent to them. This is known as a broadcast. Refer to the OSI model, hubs only repeat the electric pulses to every computer connected

    Switches - Switches are not dumb, they sit on Layer 2. Switches analyzes the "FRAME" and and looks at the MAC address. Computer 1 sends data to computer 5, only computer 5 recieves it because the switch knows the MAC address of computers 1 - 5. Understand the fact that the switch sits at layer two because it reads MAC address. MAC address are added when the packet is turned into a FRAME.


    Routers are layer 3, they read IP address'
    IP address' are stated in the network layer on the packet. This means the router first needs to get the electrical pulses, then "convert back to frame", then "convert back to a packet" then read the IP address on it.

    This is why a router is slower then a hub. Hub doesn't do anything other then repeats the electical signal it gets at the physical layer.

    Switches can send data to a correct person in the lan because they can read mac address' which are at layer 2. So in order to read a mac address, you would have to collect the electric pulses turn it into a frame, then read the mac address. Then turn it back into electrical pulses and send it to the MAC address it's destined to.

    Routers need to turn the electrical pulses at physical layer into a frame which is at a datalink layer then it needs to turn it into a packet. read the destination IP address, turn the packet into a frame, turn the frame into electrical pulses on the wire.

    This is why routers are more smart then switches, switches are more smart the hubs.

    This should hopefully give you somewhat an understanding, feel free to ask questions. Someone feel free to correct me if I'm wrong. I know probably in my OSI model, from 7 - 5. PDU's get changed into something else.
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