Now that we’ve look briefly at cabling
I’d like to explain how network devices operate.
And the first device that we're going to look at is hub
a hub is a layer 1 device in the OSI model and you would use a Cat5
unshielded twisted pair cable with an RJ-45 connector
to connect your laptop as an example to a port on a hub.
hubs aren't very popular today and have been superseded by
switches and I'll explain in a few minutes why.
But for now lets assume that you are connecting your PC to a hub.
It’s important that you understand how a hub operate
however because wireless operates in the same way, like a physical hub would.
So when your connected to a wireless network you’ll often encounter
the same issues that you would encounter when connecting to a physical hub.
So for now lets assume that you are connecting your PC physically to a hub
hubs have multiple ports and thus multiple devices
can be connected to a hub at the same time.
The number of ports available depends on the hub model
but as you can see in both of this examples
a hub has various ports that you can connect devices to.
So in this topology let’s assume that you have 4 devices connected to a hub
on ports 1 to 4, it's important to realize that a hub is a physical layer device.
It’s not intelligent and does not understand the frames going through it.
It's basically a multi port repeater and it will amplify
or repeat the frames that it receives on 1 port out of all other ports.
So it's once again simply a multi port repeater with no intelligence.
The physical topology of a hub is a star topology.
In a star topology you have a central device
which in this case is a hub and devices hanging off that central device
as spokes which resemble the spokes in the bicycle wheel.
Each spoke devices connected to the central device with its own cable and all
transmission or communications between devices are through the central device.
In other words if A wants to communicate with C the traffic will flow
through the hub and will not flow directly between the 2 devices.
There were some major advantages to using hubs and UTP rather than 10base2.
The first advantage is a cable break, if a cable broke in this topology
it would only affect device A and it would not affect the rest of the network.
In a 10base2 if a cable broke it would affect all devices in that network.
Here however, other devices such as C and B can still communicate
even though the cable is broken to device A.
Another advantages that you can extend distances easily.
A bus topology is limited in size in a 10baseT environment
such as this, the distance between a device such as A and the hub
needs to be 100 meters but you can extend the distance by adding another hub.
In other words you add another multiple repeater and repeat or regenerate
the signal to extend the distance of the network to distances greater than 100 meters.
So in this example, E could be 100 meters away from its hub
and the 2 hubs could be 50 meters apart.
So in this example we've extended the network
further than the restriction of a 100 meters.
So device E could be 100 meters from its hub
it could be a cable length a 50 meters between the 2 hubs
and A could be a 100 meters away from its hub.
A network now has a length of 250 meters
which is well over the limitation of a 100 meters.
Now their are restriction on the number of hubs
that you can daisy chain together, but the point is, it's possible
to extend the topology by adding more hubs and more devices to the network.
These were therefore great reasons to move away from 10base2
and 10base5 and implement UTP or untwisted pair networks using hubs.
Another advantage is that UTP cabling is cheaper and easier to manage
and therefore it became common to use
hubs and 10baseT rather than 10base2 or 10base5 in the past.