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C H A P T E R 2 | Intel Express 460T Standalone Switch Users Guide |
What is a Switch?
A switch segments traffic, providing each port its own collision domain. This is different from a hub where all ports belong to the same collision domain.
Segments and Hubs
Hubs combine multiple wires so all attached devices behave like they are on the same wire. Because the devices share the same segment, data sent by one device is retransmitted to all devices on the same hub. This is equivalent to having all devices connected in a bus topology as illustrated below.
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| Signal sent to all ports |
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| Client A |
| Client B | |||||||
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| Client A sends |
| Client B |
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| signal to Client B | receives signal |
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The disadvantage is all devices must share the total available bandwidth. The more devices that are attached to the hub the less bandwidth for each user. Also, network performance suffers because all devices receive traffic and collisions from other users as the hub retransmits data across all ports.
Switches
Switches send traffic only to specific ports, rather than transmitting data across all ports. This means that each device attached to the switch receives fewer collisions and the entire bandwidth is available to the device.
MAC Address Port
006011FB34DB 2
00A027D36FAA 8
The signal is not sent to all ports
Client A sends | Client B |
signal to Client B | receives signal |
The switch maintains a table that associates a device’s MAC address to a port on the switch. When Client A communicates with Client B, the switch checks the table to determine which port Client B is attached to and then forwards the traffic to that port. If a device sends traffic to an address that is not in the table (or sends broadcast or multicast traffic) the switch sends the traffic out to all ports on the switch. When the switch receives a response it updates the table with the new address.
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