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In this section of the course,

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we're going to discuss wireless issues.

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For the purposes of this section,

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whenever I talk about wireless, I'm specifically referring

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to wifi or the 802.11 family of standards

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and not Bluetooth, cellular, satellite

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near field communication or RFID.

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Even though some of those topics we cover,

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like interference antennas

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and attenuation also will be applicable

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to those technologies too.

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Now, before we jump into this section, it's important for us

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to do a quick review of different specifications

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and limitations that are involved with wireless networks.

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First, you need to consider the different speeds

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and throughputs of our various 802.11 wireless networks.

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When we talk about the speed, we're normally referring

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to the bandwidth of a given connection.

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Bandwidth refers to the theoretical speed

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of data going across the network, where throughput,

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on the other hand, is the actual speed

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of the data crossing that network.

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If you're using 802.11a,

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you're going to have a maximum bandwidth

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or theoretical speed of 54 megabits per second.

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Now, while that theoretical maximum does exist, in reality,

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it's much more common to see throughput of only 20

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to 30 megabits per second when using a wireless A network.

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Now, if you're using 802.11b,

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you're going to see a maximum bandwidth

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or theoretical speed of only 11 megabits per second.

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Now, this is the theoretical maximum,

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but in reality, it's more common to see about five

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to seven megabits per second of throughput.

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If you're using 802.11g,

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you're going to find a maximum bandwidth

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or theoretical speed of 54 megabits per second.

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Now, in reality, it's going to be more common

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to see throughputs of around 30 to 32 megabits per second.

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If you're using 802.11n,

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you're going to find a maximum bandwidth

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or theoretical speed is around 600 megabits per second,

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but in reality, it's more common to see ranges around 140

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to 150 megabits per second.

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If you move into 802.11ac,

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you have a maximum bandwidth

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or theoretical speed of 1300 megabits per second,

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or 1.3 gigabits per second.

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Now, sometimes you're going to see wireless AC advertised

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with speeds of up to 1900 megabits per second,

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but that is adding together the 1300 megabits per second

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for the five gigahertz radio

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and another 600 megabits

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for backwards compatibility using wireless N

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and embedded 2.4 gigahertz radio inside of the access point.

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Now, the theoretical maximum is somewhere between 1300

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and 1900 megabits per second depending

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on the model you're purchasing.

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But in reality, you'll usually see 100

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to 500 megabits per second in speeds of real throughput.

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Now, if you're using 802.11ax

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as your wireless network, your maximum bandwidth

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or theoretical speed will be up to 10 gigabits per second.

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Now, that is a theoretical maximum,

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but in the real world, we usually see throughputs of

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around 600 to 900 megabits per second.

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Next, let's consider the distance associated

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with each variant of wifi that you may come across

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when working in the field.

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Wireless, A, B and G could all reach distances of

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around 35 meters indoors at

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around 100 meters outdoors.

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Wireless N, on the other hand, can reach 70 meters indoors

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and up to 250 meters outdoors.

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Wireless AC and AX networks can reach distances

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of about 50 meters indoors and around 100 meters outdoors.

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Now, you may be wondering, do I need

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to memorize all of those distances?

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And the answer here is no,

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but you should be aware that wireless N has doubled

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the distance over earlier wireless A, B and G networks.

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Also, you should be aware that wireless AC

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and wireless AX will cover a distance between wireless N

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and the other earlier technologies of A, B, and G,

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but at vastly improved speeds and throughputs.

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Now, when it comes to distance,

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we're really worried mostly about

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how strong the signal will be when it's received

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by our client,

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and we measure this in terms of the RSSI

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or the received signal strength indicator.

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Now, sometimes you're going to hear people call this

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signal strength as well.

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RSSI is simply an estimated measure of the power level

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that a radio frequency client device is going

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to be receiving from a wireless access point

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or wireless router.

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As the distance increases, the signal will get weaker

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and weaker, and the data rates

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and throughput experience by your users

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will get slower and slower.

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Now, when you look at

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the received signal strength indication for your client,

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you're going to see that it's somewhere between -60

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and -65 decibels or dBs most of the time

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if you have a strong signal.

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This indicates you have a good strong signal

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and it can support heavy network-based applications

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like Voice over IP, video streaming,

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and other bandwidth intensive applications.

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The RSSI value will actually be measured

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as a value from zero to -100.

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The closer the signal is to zero,

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the stronger the signal will be

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that's being received by that client.

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For example, my computer is currently showing an RSSI value

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of -38 dB, which is extremely strong, and that's

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because my wireless access point is located about

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five feet from my computer.

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Now, when you're looking at RSSI,

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anything over around -90 decibels is considered

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to be extremely weak.

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If your signals around -65 decibels,

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this is considered fairly strong.

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If you have an RSSI of -55 decibels,

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this is a strong signal, and as RSSI of -30

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or above is considered extremely strong,

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and you're probably sitting right next

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to your wireless access point.

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Finally, let's talk about

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the effective equivalent isotropic radiated power or EIRP.

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Now, the effective equivalent isotropic radiated power is

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the maximum amount of power

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that could be radiated from an ideal isotropic antenna

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given its antenna gain

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and the transmitting power of the radio frequency system.

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This is usually going to be measured in dBi

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or decibels over isotropic.

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An omnidirectional antenna is an isotropic antenna,

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and it distributes its power equally out in all directions.

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Now, why should you care about EIRP levels?

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Well, because these EIRP levels will tell you

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how strong the signal is being rated out

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of your wireless access point towards your client.

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Now, this is the other half of

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RSSI that we just talked about.

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Remember, RSSI is used to measure the amount

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of signal being received

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by the client from that access point.

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But when you're dealing with EIRP,

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you're really talking about the signal being sent

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from the access point.

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So if you're having signal issues

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with your wireless network, you can look at the RSSI

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and the clients to determine if they're having

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an issue receiving the data.

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Or you can look at the EIRP level

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and determine if the issue is instead

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being caused by the access point,

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its antennas or its power levels not being high enough.

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Now, we just covered a lot of key terms

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and information that you need to know

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as we move forward into this section

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on wireless networking troubleshooting.

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So in this section, we're really going to be focused again

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on domain five network troubleshooting,

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and this time we'll be looking at objective 5.4.

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Objective 5.4 states that given a scenario,

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you must be able to troubleshoot common performance issues.

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First, we're going to look at wireless coverage issues.

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Wireless coverage issues can arise from factors like

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physical obstructions, signal range limitations,

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and the positioning of your access points,

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which can lead to areas with weak or no wireless signal.

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Then we'll discuss interference issues.

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Interference issues in wireless networks are often going to be

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caused by overlapping channels,

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electronic devices in the area,

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or other physical barriers

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that disrupt the radio frequency

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signals from being transmitted.

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Next, we're going to learn about client disassociation issues.

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Now, client disassociation issues occur when wireless

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clients unexpectedly disconnect from the network.

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This can be caused by having too much distance

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between your client and the access point from power saving

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modes being turned on or from network congestion.

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After that, we're going to explore incorrect

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wireless configurations.

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Now, incorrect wireless configurations such

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as mismatched security settings, incorrect SSIDs

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or improperly set channels can all prevent your client

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devices from connecting to the network

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or lead to an unstable wireless network connection.

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Then we're going to cover captive portal issues.

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Captive portal issues may involve authentication problems,

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misconfigured access policies,

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or connection timeouts

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that impede users from successfully logging

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into a wireless network.

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Next, we're going to look at some other considerations

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that you need to think about when you're troubleshooting

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your wireless network problems.

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And finally, we'll take a short quiz to see what you learned

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during this section of the course

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and review your answers fully

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to ensure you know why the right answers were right

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and the wrong answers were wrong.

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So if you're ready, let's get started

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troubleshooting wireless issues in this section

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of the course.