Hubs and Switches
 The
difference between hubs and switches is clear - a hub is a cheap
imitation.
Both hubs and switches act as a "point of
convergence" on a Local Area Network (LAN), allowing one computer
to talk to another on the same network. However a hub is very generic
in it's task - if it receives a message from one PC to another,
it broadcasts it to all computers on the network. It is then up
to an individual PC to realise the data is intended for it and accept
that data.
A switch on the other hand is completely aware
of the network it is connected to. It understands what computers
are where, the source and destination of each data packet and ensures
that packets are delivered to the correct PC first time.
Hubs
Hubs uses several ports to connect multiple computers
to the same LAN. Each computer network card occupies a port on the
hub. Most modern hubs can operate on 100-BaseT networks, and allow
2-16 computers to be connected on the same LAN using Cat5 connections.
Some hubs also include an extra port to "piggyback"
hubs on top of each other. This means you can expand an existing
4-port hub network to allow 7 computers by purchasing another 4-port
hub. This extra port can also be used to connect to other active
network components such as printers or switches.
Hubs are known as "multiport repeaters"
- they simply receive data on one port and re-transmit, or repeat
it on the other ports.
Due to the lack of it's intelligence, hubs can
very quickly be bogged down with unnecessary traffic and are only
suitable for small home/office networks that require a cost-effective
solution.
Hubs function at the physical layer of the OSI
Reference Model. They are not considered part of the cabling infrastructure
and are most often used for multiplexing, multi-port bridging functions,
switching and test access.
Most suitable cabling for hubs: Shielded
Cables, UTP Cables
Switches
A switch looks very similar to a hub - it accepts
Cat5 and fibre connections from network devices and allows them
all to communicate. However switches work very differently from
hubs as outlined below.
When a device is first connected to a switch,
it needs to identify the device against all others connected to
it. It does this by MAC address - a unique identifier given to all
networkable devices at manufacture (computers, MP3 players, fridges,
games consoles and so on). The switch then issues a unique IP address
to that particular device to allow it to be easily identified on
the network. Only the switch is aware of the MAC address - from
here the IP address is used to direct data to that device.
The switch is now aware of all devices attached
to it. When one device sends data destined for a particular IP address,
the switch knows the MAC address and hence which port that device
is connected to. The data goes directly to that device, as opposed
to being transmitted over the entire network waiting for a recipient.
Switches can also be "piggybacked" to
expand a LAN. Special ports will be supplied to allow switches to
be connected together as an easy method to expand an existing network.
Most suitable cabling for switches: Shielded
Cable, UTP Cables, Fibre
Optic
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