To better understand the normal traffic pattern, we should be aware of the various usual factors that govern the performance of a wireless network. For example, data packets, associations, and disassociations, signal strength with/without interferences. Our objective while analyzing preceding parameters is to form a baseline that can prove worthy when comparing the traffic patterns with unusual ones. The factor that affects the network performance the most is a different form of interference, which is caused due to various factors such as physical obstructions such as thick walls, roofs; and electronic appliances, such as microwave, cordless phones, and so on.

While dealing with wireless networks, the integrity of data becomes more important because the packets are simply traveling in the air, and anyone with some basic hardware and knowledge of how wireless networks work can sniff and capture these packets easily. Wireless networks don't have any rescue options to protect the integrity, so using them, you cannot be 100% assured regarding the security of data.

Let's say, for example, you are listening to a particular channel in the spectrum. Normally, you can sniff only one channel at a time, but if the channels start overlapping each other, than it is quite possible that you will see other channel packets in the list pane. As per the normal functioning of a wireless spectrum, the networks that operate close to each other are supposed to choose non-overlapping channels such as 1,6,11,14 to avoid any issues. Refer to the following figure that best illustrates channel overlapping (I used from the same from Wikipedia):

The strength of the wireless network is totally dependent on Radio Frequency (RF) signals that carry the traffic. Once the wireless signal starts traveling, the strength is supposed to lessen eventually, as it travels farther because of the obstructions that come in between. The device that works over the same RF energy is also responsible for reducing the wireless signal strength. If you are also dealing with such issues, then just using Wireshark to listen on an interface in the monitor mode won't solve the purpose. You need a spectrum analyzer, such as Wi-Spy+Channelyzer, that is paired with a USB (refer to http://metageek.com) adapter and gives you an extra eye over the RF energy form; otherwise, you won't be able to see them. Most of the time, the device emitting high RF energy can be the cause of poor network performance.

To inspect the environment for RF energy, you need to walk down the office on your own with your laptop running a spectrum analyzer, which would be able to detect the RF anomalies that can affect your wireless network performance. The placement of these analyzers does play an important role in solving the problem. If a host in your office is not able to connect then the best option is to place your analyzer as close to the host as possible in order to perceive the situation from the host's perspective. If various hosts in your office experience a similar problem, then the best option would be to place the analyzer near the access point they are trying to connect to. Depending on the scenario you are dealing with, you can dynamically decide and even manually scan through the office premises to get to know whether there is any RF energy interfering.

I don't have any special hardware to show you RF energy, but I will use an inbuilt tool from the Kali Linux OS, which will help us fetch various granular details regarding different WLANs available around my premises and all the devices that are connected to Wi-Fi (if paired with a hardware used for spectrum analysis, this can prove really useful). The name of the tool is Kismet, and it is quite efficient in representing details in graphical and various available statistical formats, thus enabling us to know more about the neighborhood (use it for ethical purposes). Follow these steps to use the Kismet tool on Kali Linux:

Now, let's see what does each pointer in the preceding screenshot signifies:

In the bottom-right corner of the window, the interface used to capture details is shown: mon0 (a monitor mode activated interface). Through this tool, we are not able to capture any RF energy that can distort the traffic shape, which lessens our network performance. But the same tool, when paired with Wi-Spy or Ubertooth hardware, will show the RF energy spectrum. If you are one of those professionals who needs to deal with Wi-Fi troubleshooting in day-to-day working, then you should use this—if not now, then someday you will.

The RF energy emitted from the devices won't be the problem every time; sometimes, you would be required to look at the packet level like checking authentication and association packets, that is, you can match your normal traffic pattern with the anomaly you might be facing.

These are one of those essential components of WLAN data transfers that avoid collisions from happening and ensure the integrity of the data that is sent. The following illustration determines the four-step process that takes place to follow a 100% fail-proof delivery:

First, the AP sends a request to the STA to gain medium access; once the STA approves the AP's request, the AP starts sending data. As soon as the data transfer is completed, the STA sends an ACK packet to acknowledge error-free delivery. If the ACK is not sent, then then the AP will start retransmission after some time.