Hub:
- A hub is a device that connects a number of computers together to make a LAN.
- The typical use of a hub is at the centre of a star network (or as part of a hybrid network).
- The hub has cables plugged into it from each computer.
The hub has a number of ports (usually 4, 8, 16 or 32).
How a hub operates?
1. The hub receives the message to send from the source machine.
2. This hub broadcast the message(with the address of the destination and source) to all stations connected to it.
3. All devices connected to the hub receive the message but only the destination device can read it.
More information...
- We can increase the number of hubs to expand the network.
- If a message sent on that network, it will be broadcast on all ports of the different hubs.
- When several workstations send a data packet at the same time, a collision occurs in the hub and it spreads.
- In fact, a hub that receives a message on one of its ports will send it on all other ports including where is connected the second hub, which itself will broadcast the same message on his own and so on. All stations connected to various hubs will receive the message.
- We can increase the number of hubs to expand the network.
- If a message sent on that network, it will be broadcast on all ports of the different hubs.
- When several workstations send a data packet at the same time, a collision occurs in the hub and it spreads.
- In fact, a hub that receives a message on one of its ports will send it on all other ports including where is connected the second hub, which itself will broadcast the same message on his own and so on. All stations connected to various hubs will receive the message.
Activity:
1. Machine 1 wants to send a message to machine 2, This message reach the machine 10 or not?
2. The machines 1 and 10 want to send a message at the same time as follows:
2. The machines 1 and 10 want to send a message at the same time as follows:
Machine 1 --> Machine 9 and
Machine 10 -->Machine 2
3. What will happen?
Switch:
A switch is a smart hub, it has the same role of a hub but it eliminates the broadcast to all stations and it selects exactly the specific machine.
Except if it doesn't know the address of the destination.
B. How a switch operates?
1. The switch receives the message to send from the source machine and save the address of the latter.
2. If he does not know the address of the destination, the switch proceeds by the broadcast, otherwise it sends the message only to the destination.
C. More information...
During the learning phase, the switch operates like a hub (by broadcast). Once it has identified the workstations, it sent the message only to the destination.
The difference between hubs and switches:
Activity:
1. If a data packet is sent by the machine A, which
machines will receive this package? Justify ?
1. 2. If a data packet is transmitted by the machine
A in the direction of the machine C, which
machines will receive this package? Justify ?
1.
3. If a data packet is sent by the machine A in
the
direction of the machine E, which
machines will receive this package? Justify ?
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