In this lesson,
we're going to discuss interference in wireless networks.
If you remember, anytime you have multiple wireless networks
communicating on the same channel,
you can have interference
because they're all talking at the same frequency.
To avoid interference in the 2.4 gigahertz spectrum,
we always use the three channels of one, six, and 11.
If I'm using channel six
and you're using channel four, though,
we're going to have an overlap
and we're going to interfere with each other's networks.
This interference can lead to retransmissions
and this will slow down both of our networks.
So when you're conducting your site survey,
you're always going to want to make sure you see what channels
and frequencies are already being used in your area.
If you create an extended service set wireless network,
you need to plan the locations of your access points
and the channels they're going to use.
Remember, in a 2.4 gigahertz network,
you always want to make sure
you're using channels one, six, and 11,
and you never want two of the same channel number
sitting next to each other and overlapping.
This way, I can make sure that I have good coverage.
For example, let's say I was installing access points
down a long hallway.
I would install them as 1, 6, 11, 1, 6, and 11.
Notice that I skipped each one to a different number.
This ensures there's no overlapping zones.
They're touching one another of the same type of number.
Also, you want to ensure you have 10 to 15% overlap
between the two access points
to make sure you have sufficient coverage
and time for the devices to hand off.
Now, if you're using a newer 5 gigahertz network,
you're going to utilize a honeycomb pattern
for your access points as they're being installed,
and you should always ensure that each channel
is not repeated until you're at least two zones away.
This will ensure adequate coverage
and minimize interference.
Next, let's cover attenuation.
Attenuation is a reduction of signal strength
between the transmission and receipt of the wireless signal.
Attenuation can occur for lots of different reasons,
such as increasing the distance between the transmitter
and the receiver, hitting a wall or other physical obstacle
or signal interference
that's reducing the overall signal strength
because of more noise
in the environment causing interference.
Attenuation can occur within the antenna's cable itself
or in the radio frequency wave
as it's traveling away from the transmitter
and towards the receiver.
When the attenuation is occurring
inside the antenna's cable,
it's normally going to be caused by the materials
and the construction of that antenna.
If low quality components were used to make that antenna
or the cables inside of it,
there are going to be more resistance inside that wire
and that leads to more attenuation.
To increase the signal strength
and reduce the attenuation,
you can replace the cable
or the antenna with a higher quality,
lower-resistant component.
With radio frequency wave signal attenuation,
one of the causes of this is multi-path reception.
Now, this occurs when the transmitted signal
starts bouncing off walls and other physical objects,
and then it eventually gets redirected back to the receiver.
Now, for example, let's say I was standing
on one side of the room and you're standing
on the other side of the room
and there's a big support column
standing right between us.
If I wanted to send a ball to you
that's going to signify my radio waves,
I couldn't throw it directly to you
because if I did that, it's going to hit the column
and bounce back towards me.
So instead, I would need an omnidirectional antenna
to throw out a lot of different balls simultaneously.
Some those will bounce off the sidewalls
and they'll eventually reach you.
Some will hit the pole in front of me and bounce back to me.
But because of all this different balance,
we're going to have slower
and weaker signals by the time they get to you
because I had to bounce off the wall first, right?
Well, the same thing happens with our radio frequency waves.
They may bounce around the room
and they'll eventually get to you,
but they may be attenuated and weaker than before.
And it's going to lead to a lower RSSI value for you
and lower throughput for the data being sent
over these networks.