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In this lesson,

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we're going to discuss interference in wireless networks.

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If you remember, anytime you have multiple wireless networks

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communicating on the same channel,

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you can have interference

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because they're all talking at the same frequency.

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To avoid interference in the 2.4 gigahertz spectrum,

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we always use the three channels of one, six, and 11.

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If I'm using channel six

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and you're using channel four, though,

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we're going to have an overlap

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and we're going to interfere with each other's networks.

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This interference can lead to retransmissions

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and this will slow down both of our networks.

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So when you're conducting your site survey,

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you're always going to want to make sure you see what channels

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and frequencies are already being used in your area.

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If you create an extended service set wireless network,

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you need to plan the locations of your access points

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and the channels they're going to use.

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Remember, in a 2.4 gigahertz network,

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you always want to make sure

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you're using channels one, six, and 11,

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and you never want two of the same channel number

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sitting next to each other and overlapping.

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This way, I can make sure that I have good coverage.

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For example, let's say I was installing access points

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down a long hallway.

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I would install them as 1, 6, 11, 1, 6, and 11.

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Notice that I skipped each one to a different number.

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This ensures there's no overlapping zones.

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They're touching one another of the same type of number.

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Also, you want to ensure you have 10 to 15% overlap

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between the two access points

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to make sure you have sufficient coverage

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and time for the devices to hand off.

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Now, if you're using a newer 5 gigahertz network,

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you're going to utilize a honeycomb pattern

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for your access points as they're being installed,

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and you should always ensure that each channel

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is not repeated until you're at least two zones away.

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This will ensure adequate coverage

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and minimize interference.

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Next, let's cover attenuation.

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Attenuation is a reduction of signal strength

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between the transmission and receipt of the wireless signal.

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Attenuation can occur for lots of different reasons,

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such as increasing the distance between the transmitter

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and the receiver, hitting a wall or other physical obstacle

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or signal interference

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that's reducing the overall signal strength

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because of more noise

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in the environment causing interference.

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Attenuation can occur within the antenna's cable itself

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or in the radio frequency wave

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as it's traveling away from the transmitter

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and towards the receiver.

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When the attenuation is occurring

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inside the antenna's cable,

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it's normally going to be caused by the materials

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and the construction of that antenna.

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If low quality components were used to make that antenna

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or the cables inside of it,

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there are going to be more resistance inside that wire

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and that leads to more attenuation.

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To increase the signal strength

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and reduce the attenuation,

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you can replace the cable

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or the antenna with a higher quality,

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lower-resistant component.

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With radio frequency wave signal attenuation,

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one of the causes of this is multi-path reception.

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Now, this occurs when the transmitted signal

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starts bouncing off walls and other physical objects,

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and then it eventually gets redirected back to the receiver.

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Now, for example, let's say I was standing

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on one side of the room and you're standing

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on the other side of the room

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and there's a big support column

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standing right between us.

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If I wanted to send a ball to you

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that's going to signify my radio waves,

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I couldn't throw it directly to you

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because if I did that, it's going to hit the column

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and bounce back towards me.

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So instead, I would need an omnidirectional antenna

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to throw out a lot of different balls simultaneously.

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Some those will bounce off the sidewalls

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and they'll eventually reach you.

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Some will hit the pole in front of me and bounce back to me.

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But because of all this different balance,

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we're going to have slower

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and weaker signals by the time they get to you

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because I had to bounce off the wall first, right?

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Well, the same thing happens with our radio frequency waves.

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They may bounce around the room

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and they'll eventually get to you,

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but they may be attenuated and weaker than before.

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And it's going to lead to a lower RSSI value for you

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and lower throughput for the data being sent

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over these networks.