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Welcome to Exam Notes by CertBlaster! This is our Free Study Guide Network Plus 5.4. In this installment, we will cover the topics addressed in objective 5.4 “Given a scenario, troubleshoot common wireless connectivity and performance issues.” The physical environment can impact wireless performance as much as some configuration problems. Dig in!
Reflection of a wireless signal is caused by solid objects in the signal path. Reflected signals bounce off large flat surfaces like walls, buildings, and large metallic objects.
Refraction is the diffusion of a signal’s wavelength, direction, and speed when traveling through glass or translucent materials.
Absorption occurs whenever a wireless signal encounters an object that absorbs some or all the signal strength. The degree of this impact depends on the object’s composition.
As you know latency is the delay between sending and receiving interfaces. Latency slows your overall wireless performance. The delay you will experience is measured in milliseconds and is usually fairly constant.
Jitter occurs when you have a condition where the latency varies, and the transmitted packets arrive in bursts or are out of sequence. This results in a delay as the data is reorganized.
As any signal travels away from the source the signal will weaken. This is especially true of wireless signals that can be affected by any physical obstacles in the signal path.
There are two types of wireless antennae unidirectional and omnidirectional. The omnidirectional antenna transmits the signal in all directions where the unidirectional antenna transmits in one direction. For example, you would place an omnidirectional in the center of your coverage area. A unidirectional antenna is especially effective in point to point wireless communication between two buildings.
To effectively serve your coverage area start by placing the antenna in the center of your area and survey the signal strength within this area. If the signal is weak in an area you can increase the transmitter radio power or relocate the antenna.
Power levels
Your wireless signal strength is measured in decibel-milliwatts (dBm). With dBm measurements being expressed in negative values. So, a -100 dBm signal is considerably weaker than a -10. On some access points, radio power can be increased to expand the coverage area. In situations where your signals reach outside the intended area, you can decrease the radio power.
Signal-to-noise ratio
With almost every device in your environment producing EMI at some level, these devices are combining to create interference that is called the noise floor. Compare the noise floor to a crowded restaurant where you must speak louder to compensate for the noise. Equally, your wireless signal must be stronger than the ambient noise floor. The difference between your signal strength and the noise floor is measured in dBm. If your signal is too close to the noise floor you risk corrupted data and the retransmissions created by this corruption.
An issue more relative to the crowded 2.4 GHz wireless band than the 5.0 GHz band is channel overlap. When choosing a 2.4 GHz channel the best practice is to use channels 1, 6 or 11. The channels are 22MHz wide and using the recommended channels there will be no overlap. In our example, you can see that transmissions seen on channel 4 (yellow) create interference with both channels 1 and 6. Channel 11 is your best choice here.
WiFi Analyzer
The WiFi Analyzer demonstrates the use of the 2.4GHz band. Note here that multiple devices can use the same channel by sharing the bandwidth. This, of course, reduces each client’s throughput. Having too many devices connected to a wireless network will seriously degrade performance. This is why your WiFi connections are so slow in places like airports.
Wireless devices communicate with each other on one frequency. Both the access point and the client must use the same frequency Certainly, if you were creating a new WiFi environment you would use 5 GHz technology to provide the best performance. The fact is that you will most likely be working in a mixed environment using the 2.4 GHz and 5 GHz frequencies. The wireless standards that cover these frequencies are 802.11ac in the 5 GHz range with Gigabit throughput capability and 802.11b/g/n at 2.4 GHz. 802.11n can operate in both frequency ranges with a throughput of 600 Mbps and is backward compatible with 802.11g at a speed of 54 MHz and 802.11b at 11 Mbps. The WLAN will slow to the lowest supported standard. To achieve the best performance, you would only allow 5 GHz connections to the access point. This setting would disregard all 2.4 GHz transmissions due to the frequency mismatch.
WLAN Interface Frequency Selection
Mismatched frequencies are not the only impediment to wireless connectivity. When configuring a wireless client, you must be sure that you are accessing the correct SSID (Security Set Identifier). The SSID will not be visible unless it is broadcasted.
Wireless signals are broadcast openly making them subject to interception. The signals are encrypted to secure communications. Early encryption types like WEP and WAP are insecure and your network should use at least WPA2. If the client security is set to something other than that of the access point it will not connect to the network.
Once you have the correct configuration you can attempt to connect. Your next challenge is using the correct Password/passphrase for authentication. A wrong passphrase will be denied.
That’s all for objective 5.4. See you in 5.5! We hope you enjoyed our free study guide Network plus 5.4 and good luck on the test!
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