In this section of the course,
we're going to discuss wireless issues.
For the purposes of this section,
whenever I talk about wireless, I'm specifically referring
to wifi or the 802.11 family of standards
and not Bluetooth, cellular, satellite
near field communication or RFID.
Even though some of those topics we cover,
like interference antennas
and attenuation also will be applicable
to those technologies too.
Now, before we jump into this section, it's important for us
to do a quick review of different specifications
and limitations that are involved with wireless networks.
First, you need to consider the different speeds
and throughputs of our various 802.11 wireless networks.
When we talk about the speed, we're normally referring
to the bandwidth of a given connection.
Bandwidth refers to the theoretical speed
of data going across the network, where throughput,
on the other hand, is the actual speed
of the data crossing that network.
If you're using 802.11a,
you're going to have a maximum bandwidth
or theoretical speed of 54 megabits per second.
Now, while that theoretical maximum does exist, in reality,
it's much more common to see throughput of only 20
to 30 megabits per second when using a wireless A network.
Now, if you're using 802.11b,
you're going to see a maximum bandwidth
or theoretical speed of only 11 megabits per second.
Now, this is the theoretical maximum,
but in reality, it's more common to see about five
to seven megabits per second of throughput.
If you're using 802.11g,
you're going to find a maximum bandwidth
or theoretical speed of 54 megabits per second.
Now, in reality, it's going to be more common
to see throughputs of around 30 to 32 megabits per second.
If you're using 802.11n,
you're going to find a maximum bandwidth
or theoretical speed is around 600 megabits per second,
but in reality, it's more common to see ranges around 140
to 150 megabits per second.
If you move into 802.11ac,
you have a maximum bandwidth
or theoretical speed of 1300 megabits per second,
or 1.3 gigabits per second.
Now, sometimes you're going to see wireless AC advertised
with speeds of up to 1900 megabits per second,
but that is adding together the 1300 megabits per second
for the five gigahertz radio
and another 600 megabits
for backwards compatibility using wireless N
and embedded 2.4 gigahertz radio inside of the access point.
Now, the theoretical maximum is somewhere between 1300
and 1900 megabits per second depending
on the model you're purchasing.
But in reality, you'll usually see 100
to 500 megabits per second in speeds of real throughput.
Now, if you're using 802.11ax
as your wireless network, your maximum bandwidth
or theoretical speed will be up to 10 gigabits per second.
Now, that is a theoretical maximum,
but in the real world, we usually see throughputs of
around 600 to 900 megabits per second.
Next, let's consider the distance associated
with each variant of wifi that you may come across
when working in the field.
Wireless, A, B and G could all reach distances of
around 35 meters indoors at
around 100 meters outdoors.
Wireless N, on the other hand, can reach 70 meters indoors
and up to 250 meters outdoors.
Wireless AC and AX networks can reach distances
of about 50 meters indoors and around 100 meters outdoors.
Now, you may be wondering, do I need
to memorize all of those distances?
And the answer here is no,
but you should be aware that wireless N has doubled
the distance over earlier wireless A, B and G networks.
Also, you should be aware that wireless AC
and wireless AX will cover a distance between wireless N
and the other earlier technologies of A, B, and G,
but at vastly improved speeds and throughputs.
Now, when it comes to distance,
we're really worried mostly about
how strong the signal will be when it's received
by our client,
and we measure this in terms of the RSSI
or the received signal strength indicator.
Now, sometimes you're going to hear people call this
signal strength as well.
RSSI is simply an estimated measure of the power level
that a radio frequency client device is going
to be receiving from a wireless access point
or wireless router.
As the distance increases, the signal will get weaker
and weaker, and the data rates
and throughput experience by your users
will get slower and slower.
Now, when you look at
the received signal strength indication for your client,
you're going to see that it's somewhere between -60
and -65 decibels or dBs most of the time
if you have a strong signal.
This indicates you have a good strong signal
and it can support heavy network-based applications
like Voice over IP, video streaming,
and other bandwidth intensive applications.
The RSSI value will actually be measured
as a value from zero to -100.
The closer the signal is to zero,
the stronger the signal will be
that's being received by that client.
For example, my computer is currently showing an RSSI value
of -38 dB, which is extremely strong, and that's
because my wireless access point is located about
five feet from my computer.
Now, when you're looking at RSSI,
anything over around -90 decibels is considered
to be extremely weak.
If your signals around -65 decibels,
this is considered fairly strong.
If you have an RSSI of -55 decibels,
this is a strong signal, and as RSSI of -30
or above is considered extremely strong,
and you're probably sitting right next
to your wireless access point.
Finally, let's talk about
the effective equivalent isotropic radiated power or EIRP.
Now, the effective equivalent isotropic radiated power is
the maximum amount of power
that could be radiated from an ideal isotropic antenna
given its antenna gain
and the transmitting power of the radio frequency system.
This is usually going to be measured in dBi
or decibels over isotropic.
An omnidirectional antenna is an isotropic antenna,
and it distributes its power equally out in all directions.
Now, why should you care about EIRP levels?
Well, because these EIRP levels will tell you
how strong the signal is being rated out
of your wireless access point towards your client.
Now, this is the other half of
RSSI that we just talked about.
Remember, RSSI is used to measure the amount
of signal being received
by the client from that access point.
But when you're dealing with EIRP,
you're really talking about the signal being sent
from the access point.
So if you're having signal issues
with your wireless network, you can look at the RSSI
and the clients to determine if they're having
an issue receiving the data.
Or you can look at the EIRP level
and determine if the issue is instead
being caused by the access point,
its antennas or its power levels not being high enough.
Now, we just covered a lot of key terms
and information that you need to know
as we move forward into this section
on wireless networking troubleshooting.
So in this section, we're really going to be focused again
on domain five network troubleshooting,
and this time we'll be looking at objective 5.4.
Objective 5.4 states that given a scenario,
you must be able to troubleshoot common performance issues.
First, we're going to look at wireless coverage issues.
Wireless coverage issues can arise from factors like
physical obstructions, signal range limitations,
and the positioning of your access points,
which can lead to areas with weak or no wireless signal.
Then we'll discuss interference issues.
Interference issues in wireless networks are often going to be
caused by overlapping channels,
electronic devices in the area,
or other physical barriers
that disrupt the radio frequency
signals from being transmitted.
Next, we're going to learn about client disassociation issues.
Now, client disassociation issues occur when wireless
clients unexpectedly disconnect from the network.
This can be caused by having too much distance
between your client and the access point from power saving
modes being turned on or from network congestion.
After that, we're going to explore incorrect
wireless configurations.
Now, incorrect wireless configurations such
as mismatched security settings, incorrect SSIDs
or improperly set channels can all prevent your client
devices from connecting to the network
or lead to an unstable wireless network connection.
Then we're going to cover captive portal issues.
Captive portal issues may involve authentication problems,
misconfigured access policies,
or connection timeouts
that impede users from successfully logging
into a wireless network.
Next, we're going to look at some other considerations
that you need to think about when you're troubleshooting
your wireless network problems.
And finally, we'll take a short quiz to see what you learned
during this section of the course
and review your answers fully
to ensure you know why the right answers were right
and the wrong answers were wrong.
So if you're ready, let's get started
troubleshooting wireless issues in this section
of the course.