C H A P T E R 2 Intel
®
Express 530T Switch Users Guide
12
What is a Switch?
A switch segments traffic, providing each port its own collision domain.
This is different than a hub where all ports belong to the same collision
domain.
Segments and hubs
Hubs combine multiple wires so all attached devices behave as though
they are on the same wire. Since 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.
The disadvantage is all devices must share the total available bandwidth.
The more devices that are attached to the hub results in less bandwidth
for each user. Also, network performance suffers since all devices
receive traffic and collisions from other users because the hub
retransmits data across all ports.
Switches
Switches send traffic only to specific ports, rather than transmit 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.
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 looks in 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.
Client A sends
signal to Client B
Client B
receives signal
Client A
Client B
Signal sent to all ports
Client A sends
signal to Client B
Client B
receives signal
The signal is not
sent to all ports
MAC Address
Port
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530-Chapter2.fm Page 12 Monday, September 11, 2000 4:14 PM
