Wi-Fi tracking systems are keeping track of people’s whereabouts by capturing the messages broadcasted by their Wi-Fi enable device. Smartphones use an active service discovery mechanism to search surrounding access points. In active service discovery mode, a smartphone periodically broadcast probe request frames. Upon reception of a probe request, an access point (AP) replies with a probe response, thus declaring its presence. The image below shows my iPhone mac address captured using Wireshark:

Wi-Fi tracking systems can track visitors in a retail space, because people’s smartphones are periodically broadcasting a unique identifier (MAC address). The Wi-Fi tracking systems record the MAC address, time-stamp, and sensor’s data for each received probe request. From this information, the Wi-Fi tracking systems can deduce the presence and the path of a Wi-Fi device across the area covered by the sensors.

Most Wi-Fi tracking systems do not fully disclose in their privacy policies how the data is collected, transferred from the sensors to the server, kept anonymous, and stored. Most Wi-Fi tracking systems companies rely on hashing the mac addresses method to anonymize MAC addressees in their databases. Nonetheless, how secure is our data if the database is compromised? According to French researchers Demir, Cunche, and Lauradoux, the hash-based anonymization use in Wi-Fi tracking systems can be defeated using free software tools such as, hashcat, in less than a day. They recommended to encrypt the MAC addresses entries obtained from a chain of hash with a master key. This master key is used once by the storage server and its known only by the entity computing the statistics. For each entry, a new key is generated using a cryptography one-way function and the previous key is erased. If a session key is compromised, the hacker will only know a single entry of an individual, instead of having access to all the entries in the database. Another element not mentioned clearly by Wi-Fi tracking companies is how individuals can opt-out when in proximity to the sensors. Retailers and businesses argue they can use the collected data to better tailor services to consumers; however, privacy, data protection, and human rights remain a significant concern.

Demir, L., Cunche, M., & Lauradoux, C. (2014, June). Analysing the privacy policies of Wi-Fi trackers. In Proceedings of the 2014 workshop on physical analytics (pp. 39-44). ACM.

This lack of education may cause even more widespread problems for companies with BYOD. Employees’ willingness to engage in unsafe behaviors is a concern, but what is much more troubling is when employees do share or interact with confidential data using unsecure technologies, such as Wi-Fi. In most cases, employee motives are not malicious, they are simply trying to do their jobs as efficiently and effectively as possible.

Wi-Fi is the most heavily used method to transport user data, according to multiple reports from analysis firms including Cisco, Aruba, and others. As a result, a company’s goal is not only to protect sensitive corporate information from unauthorized employees, but also from authorized employees accessing this information from an unsecure wireless network.

Perhaps one of the most shocking findings by Dell’s survey is that nearly two out of three employees who handle confidential data are being training on cybersecurity, but still don’t know how to keep sensitive information secure. The main issue is that company policies on confidential data usage and sharing are either unclear or not comprehensive enough to cover the spectrum of daily scenarios employees encounter in the workplace. Simple, concise, and clear security policies are key for preventing data breaches on Wi-Fi.

Wi-Fi networks often empower employees to share information; but first, organizations need to identify what is important data, and write down clear policies that define end-user access, types of data, who can have access to the data, and rules for its dissemination when using the corporate’s wireless networks. The goal is that at least 99 percent of employees understand why security is important, and do their best to use the corporate secure Wi-Fi network, no matter the device or location they are working on.

The following five foundational concepts are essential to implementing an effective WLAN:

Channels

There are more available channels to clients in 5Ghz than in the 2.4Ghz band; A reason why we should design the WLAN to operate primarily at 5Ghz. In the 2.4GHz band, we have a total of fourteen channels. However, the US is restricted to eleven channels (1 to 11).

Figure 1

The Figure 1 show there is a 5Mhz separation between channels. For example, channel 1 centers on 2.412GHz and channel 2 centers on 2.417GHz. Protocols affect the number of possible non-overlapping channels depending on radio operation. Protocol requires 22MHz of channel separation to avoid adjacent channels to overlap and interfere with each other, resulting in three non-overlapping channels to be used to avoid interference. These channels are 1, 6, and 11. A quick scan of the WLAN 2.4GHz band will reveal which channels are utilized. Hopefully, channels 2, 3, 4, 5, 7, 8, 9, and 10 will not be present.

The limitation of three channels in the 2.4Ghz band, restrict how many access point can be deployed in a high-density scenario. A reason why many WLAN vendors recommend designing primarily at 5GHz. The 5GHz band has a total of twenty-five 20 MHz channels that can be utilized when designing a WLAN. The 802.11n standard introduce the concept of bonding two 20MHz channels together to form a larger channel 40MHz. And more recent the 802.11ac standard introduced the possibility to bond 4 channels together (80MHz) and 8 channels (160MHz). The 80MHz and 160MHz bonding of channels offer great capabilities and speed, however in real-world implementations they might not be beneficial due to high-density user requirements. Most enterprises will continue to use 20 or 40MHz channels. When we get into high density deployments, we want to stick with 20MHz channels.

If you understand your environment DFS (Dynamic Frequency Selection) channels can be used in the WLAN design. However, Access points must move off channel if they detect radar activity. Also, client’s devices must support DFS channels. If the majority of clients do not support DFS channels, then there’s not a whole lot of reason to take advantage of them. Leaving DFS channels out, we have nine non-overlapping channels (36, 40, 44, 48, 149, 153, 157, 161, and 165). 802.11ac standard introduced channel 144, but not too many clients offer support for it yet. Figure 2 show the channels available in the 5GHz band.

Figure 2

RF Behaviors

Many factors impair the successful transmission or reception of a radio signal. The most common issues are scattering, diffraction, reflection, refraction, and absorption.

Reflection is the RF signal reflecting or bouncing off reflective material that has a size greater than it wavelength. For example, a thick metal wall causes signals to reflect off. This results in poor signal penetration.

Absorption occurs when the RF energy is converted to heat. As the RF energy converts to heat it is absorbed, and therefore loss. There are a variety of household devices and electronics that can interfere with your RF signal, the most common being the microwave oven. Microwave ovens use radio waves at a specifically set frequency to agitate water molecules in food. As these water molecules get increasingly agitated they begin to vibrate at the atomic level and generate heat. This is possible due to the absorption and refraction behavior of radio waves.

Refraction occurs when the radio waves bend as they moves through a material. For example, take a butter knife and place it inside a water glass. If you look at the glass of water from the side, it would appear the knife breaks in the water. This kind of illusion occurs because the light waves are refracting as they pass through the water. Refraction can slightly change the path of an RF signal causing errors during the transmission or reception of a radio signal.

Scattering occurs when a RF signal hit an object and the signal scatter in all directions. Scattering is many reflections of the RF wave.

It is interesting that these RF behaviors were once bad for WLAN 802.11a/b/g, now are a good thanks to the introduction of Multiple Input/Multiple Output (MIMO) technology in 802.11n/ac. Dr. Raleigh, researcher and wireless pioneer, is known for his contribution in the development of MIMO smart antenna technology. Dr. Raleigh, has the best definition of how MIMO works:

MIMO systems divide a data stream into multiple unique streams, each of which is modulated and transmitted through a different radio-antenna chain at the same time in the same frequency channel. A revolutionary technique that reverses 100 years of thinking about how radio signals are transmitted, MIMO leverages environmental structures and takes advantage of multipath signal reflections to improve radio transmission performance.

By multipath, each MIMO receive antenna-radio chain is a linear combination of the multiple transmitted data streams. The data streams are separated at the receiver using MIMO algorithms that rely on estimates of all channels between each transmitter and each receiver. Each multipath route can then be treated as a separate channel creating multiple “virtual wires” over which to transmit signals. MIMO employs multiple, spatially separated antennas to take advantage of these “virtual wires” and transfer more data. In addition to multiplying throughput, range is increased because of an antenna diversity advantage, since each receive antenna has a measurement of each transmitted data stream. With MIMO, the maximum data rate per channel grows linearly with the number of different data streams that are transmitted in the same channel.

RF Measurements

RF measurement is an important concept to understand. Indoor WLAN range between 5 to 50mW of output power. Milliwatt, a common measurement, is one-thousandth of a watt. So, if we say we have a 1000 milliwatts signal, that means we have a 1 watt signal. In WLAN, we use dBm to express the signal strength at the receiver. dBm is defined as decibels relative to one milliwatt. The formula (dBm = 10 *log₁₀ ^{(power mW)}) helps us find the dBm when we know the power level (mW). Figure 3 shows the logarithmic relationship between power dBm and mW.

Figure 3

The RSSI stands for “Received Signal Strength Indicator” and it is a value that different vendors end up specifying differently. Technically, according to the 802.11 standard, RSSI is not equal to dBm and dBm is not equal to RSSI. Many times, when people are talking about signal strength, these terms are used interchangeably. Probably, the better term to use is “signal strength” rather than saying RSSI if we are going to equate it to dBm directly.

Noise floor is defined as the signal strength of the RF noise in the frequency space we are using. Usually, noise floor value is between -93 to -104 dBm. The difference between the received signal strength and the noise floor is what we call SNR (dB). For example, if the noise is -95 dBm and the signal strength is -70 dBm, then the SNR is 25 dB. So, there is 25 decibels difference between the signal and the noise floor. Notice we should use the right term dBm when referring to signal strength, dBm to noise floor, and dB to SNR.

Interference

WLAN Interference from multiple devices operating over the same frequency range, is a severe problem that greatly affects the ability for an RF receiver to interpret the data signal. Higher data rates require complex modulation techniques. As the modulation complexity increases, so does its susceptibility to interference. For example, 64-QAM (Quadrature Amplitude Modulation) would be more susceptible to interference than 256-QAM now in 802.11ac. As a result, we need a very good signal to be able to process the data signal, which is why RF interference is a key factor in obtaining good data rates.

A good RF spectrum analyzer will help you create a baseline of the known-interference in the environment. Typically, we would find low duty cycle and high duty cycle interferences. The low duty cycle often can be tolerated. However, we want to avoid high duty cycle interference in the channel. For instance, video devices operating in the 2.4GHz, often not 802.11, can have very high channel utilization. We are seeing several of these devices now operating in the 5GHz range as well. It is important to understand the level of interference in your environment.

Analysis

RF spectrum analyzers capture the RF energy and visually represent it in a lot of different ways. For example, swept spectrogram shows the RF energy over time and visually represents the signal strength in color. Figure 4 shows how a microwave oven is affecting channel 1.

Figure 4

If you are having high retry in your WLAN environment, and you suspect there may be interference, a spectrum analyzer will help you find non-802.11 devices operating in your environment. A protocol analyzer is very useful to troubleshoot WLAN problem, but it will only show you 802.11 frames. A spectrum analyzer will show you devices, such as video cameras, phones, microwave ovens, and bluetooth interferences.

Anyone that wants to deploy WLAN successfully, cannot ignore the importance of these five fundamentals of RF.

In WPA and WPA2 PSK all clients share a common security key. Potential security issues arise because all stations in the wireless network share the same security key. Although WPA and WPA2 PSK offer many advantages, it should not be used for an enterprise wireless network. The recommended solution for most corporate environments is WPA2 Enterprise. The three primary authentication components of WPA2-Enterprise are: Remote Authentication Dial-In User Service (RADIUS), IEEE 802.1X (port based access control), and Extensive Authentication Protocol (EAP). RADIUS allows for centralized authentication services and acts as the authentication server. In the enterprise, RADIUS is used to query an external user database, such as Active Directory (AD). IEEE 802.1X is the standard that defines port-based access control, which specifies the following three components:

• The supplicant (Client device seeking authentication)
• The authenticator (The AP or wireless controller, which provides the wireless connection)
• The authentication server (The RADIUS server that validate the user credentials)

In addition to improved encryption and integrity algorithms, the 802.1X/EAP provide user authentication and dynamic key distribution. EAP is a Layer 2 authentication protocol that can be applied to wired and wireless networks. The 802.1X/EAP Authentication Process consists of the following steps:

The first step for a client is to become 802.11 authenticated and associated, during which each station receives the other’s capabilities and requirements. An Open System Authentication must take place first, without this association, 802.1X/EAP cannot start. Open System Authentication is like connecting an Ethernet cable between a switch and a PC to confirm physical link.

The second step is for the client (supplicant) and authentication server (AS) to complete the mutual 802.1X/EAP authentication and for the AS to pass the Pairwise Master Key (PMK) to the Authenticator.

The third step is for the two stations to have matching PMK. The PMK will be used to generate the pairwise transient key (PTK) for encryption purposes. The shared PMK by the stations is obtained during the 802.1X/EAP authentication process.

The fourth step is the 4-way handshake. The 4-way handshake is the final step used to generate pairwise transient keys (PTK) for encryption of unicast transmissions and a group temporal key (GTK) for encryption of broadcast/multicast transmissions. Each station in the wireless network will have a unique PTK. Upon a successful 4-Way handshake, the authenticator and supplicant have authenticated each other and traffic will be allowed to flow.

EAP is an authentication framework, and does not mandate the use of a specific authentication method. For this reason, multiple EAP types can be used in a WLAN security deployment. The following list shows the most common types of EAP types:

• EAP-TLS (Client and server certificates required)
• TTLS (EAP-MSCHAPv2 – only server certificate is required)
• PEAPv0 (EAP-MSCHAPv2 – only server certificate is required)
• PEAPv0 (EAP-TLS – Client and server certificates required)
• PEAPv1 (EAP-GTC – used with token card and directory-based authentication systems)

The EAP types such as EAP-TLS and PEAP (EAP-TLS) require the use of a digital certificate on both the authentication server and the clients, which can become expensive and increase management overhead. The most common EAP type use is PEAP (EAP-MSCHAPv2) because it is included in the Windows operating system, and doesn’t require the validation of the supplicant certificate.

The following images show the steps in the 802.1X/EAP authentication flow:

Step 1: 802.11 Authentication and Association

Step 2/3: PEAP General Authentication Flow

Step 4: 4-way handshakeThe following explains the main points during the 802.1X/EAP Authentication:   

1. The supplicant sends an authentication request to the authenticator.
2. The authenticator sends an authentication success to the supplicant.
3. The supplicant sends an association request to the authenticator.
4. The authenticator sends an association success to the supplicant.
5. EAP Start message.
6. The authenticator sends an EAP frame requesting the identity of the supplicant.
7. The supplicant responds with an EAP frame with the clear-text outer identity that is not the real username. At this point, the authenticator forwards the outer identity to the authenticator server (AS). All other traffic remains blocked. The outer identity simply informs the AS that a supplicant wants to be validated.
8. The AS sends the server certificate to the supplicant. The supplicant validates the server-side certificate and therefore authenticates the authentication server.
9. An encrypted point-to-point TLS tunnel is created between the supplicant and the authentication server.
10. Once the TLS tunnel is established, the AS requests the real identity of the supplicant. The supplicant responds with the inner identity, which is the real credential. The credential is now hidden because it is encrypted inside the TLS Tunnel.
11. The AS server sends a RADIUS Accept or Failure message to the authenticator.
12. The authenticator will send an EAP Success or Failure message to the supplicant. If the supplicant credentials were valid, then a 4-way handshake is conducted to generate the pairwise transient key (PTK) for encryption purposes.
13. The authenticator sends an EAPoL-Key frame containing an ANonce to the supplicant. The supplicant derives the PTK from the PMK, ANonce, SNonce, and MAC addresses.
14. The supplicant send an EAPoL-Key frame SNonce to the authenticator with a message integrity code (MIC). The authenticator derives a PTK from the PMK, ANonce, SNonce, and MAC addresses. At this point, both the supplicant and authenticator have a PTK that can be used to encrypt unicast traffic.
15. If necessary, the authenticator send EAPoL-Key frame containing the GTK. The GTK is used to encrypt broadcast/multicast traffic.
16. The supplicant sends a final EAPoL-Key frame to confirm to the authenticator that the temporal keys were installed.

Finally, the supplicant can send encrypted unicast traffic to the destination. The authentication and encryption key generation processes are necessary to provide data privacy, as well as protection when connecting to the WLAN.

When designing a new wireless LAN, the variables to coverage are; the power settings (which are Country dependent), antenna gain, and the physical environment. The newer enterprise grade access points on the market will automatically adjust their settings for optimal coverage, but planning a wireless network has, unfortunately, never been as simple as drawing circles on a floor plan. Wireless surveys, and the documentation to understand the results, can go a long way to help creating a network that matches the initial expectations of your project. You will stand more of a chance implementing an effective WLAN when including heat maps and spectrum analysis from a professional survey, especially when VOIP is going to be a feature.

Wireless Capacity:

The location and number of access points required nowadays, depends on how many wireless clients will be using the network simultaneously, what they will be using the bandwidth for, and in where in the building (for density coverage). Looking at the design and layout of your project, you will know of the main areas that will be using wireless. For example, in Schools, there are large classrooms, assembly halls, canteens, and playgrounds where students will gather using mobiles, tablets and possibly laptops. These environments have the potential to be a high density area for WLAN clients. We can no longer install an access point in a hallway, and record the signal while walking away until the final lingering strains of signal fade. Now you design for capacity as well (or at least you should).

It’s always good to plan for the users at the edge of the coverage area as well, as depending on the access point manufacturer you have chosen, they can experience a diminished performance and the overall capacity will suffer, even if you have great coverage to start off with. If you cut lower data rates out and decrease the coverage area, you can potentially increase throughput. If you allow the lower data rates, you can increase the coverage area of each access point but users will notice the difference as they walk half way between access points placed further away than usual. This then leaves you with the difficult conundrum of whose desk to put in this black spot as a punishment.

Planning for Capacity, not just Coverage:

Providing access to a service that does not live up to expectations might be as bad as providing no service at all. In planning capacity per user, you must begin with the usable capacity of a WLAN channel and an estimate of how many users will be sharing it. One 11-Mbps 802.11b wireless LAN channel provides a real throughput of about 5.5 Mbps after we net out the impact of protocol headers, acknowledgements, retransmissions, and other network overhead. The 802.11a and g networks provide a maximum throughput of 30 Mbps, though that is reduced significantly if the 802.11g users are sharing a channel with 802.11b users. So, the estimated throughput of a WLAN channel is roughly 50% to 55% of the raw data rate. That estimate assumes all users are in fairly close proximity to the access point and so are operating at the maximum data rate.

Proper design involves providing signal coverage in all areas, but also insuring that the network delivers adequate performance for all users in a cell. It should also be noted that wireless LAN design is an ongoing process, so these capacity issues must be revisited as usage grows and more access points/cells are added to the network. Of course, adding more access points also increases the cost of the network.

Factors to Assure Adequate Capacity:

There are four basic factors in the design that we can control to ensure adequate capacity as well as adequate radio coverage:

1. Radio link interface: First we can choose the radio link interface that will be used, 802.11a, b, or g.
2. Cell layout/channel assignment: The designers then select the placement of access points, antennas, and radio repeaters to provide coverage and to limit interference.
3. Power levels: With a limited number of available channels, the same channels must be reused in different parts of the facility. When a channel is reused, we must reduce the transmit power of the other access points using that channel to limit co-channel interference (i.e. the interference created by access points in different parts of the facility that are assigned the same channel). However, reducing transmit power also reduces the range, so more access points may be required to provide the same coverage.
4. Limit association rates: One last technique to keep low-speed users from impacting the overall performance is to limit the range of rates at which users will be allowed to associate. For example, in an 802.11b installation, you can limit association rates to users whose signal strength will support data rates ¡Ý5.5 Mbps. Higher transmission rates require a stronger received signal, so supporting only the higher data rates will mean more cells have to be provided or there will be dead spots in the coverage area.

Wi-Fi stands for Wireless Fidelity and is the same thing as saying WLAN which stands for “Wireless Local Area Network.”

Wi-Fi is a networking technology that uses radio waves to allow high-speed data transfer over short distances. Wi-Fi works off of the same principal as other wireless devices – it uses radio frequencies to send signals between devices. The radio frequencies are completely different say from walkie talkies, car radios, cell phones, and weather radios. For example, your car stereo receives frequencies in Kilohertz and Megahertz range (AM and FM stations), and Wi-Fi transmits and receives data in the Gigahertz range.

Interesting Fact:

For Wi-Fi, the frequency happens to be 2.4Ghz and 5Ghz. These waves are very similar to the frequency found in your microwave! Your microwave uses 2.450Ghz to heat up food and your router uses 2.412 GHz to 2.472 GHz to transmit your data over Wi-Fi. This is why some people with old or faulty microwaves experience a problem with their Wi-Fi signal when they try to make popcorn.

How to Properly Design a Wireless Network:

When designing and deploying a wireless network, there are several factors to consider. Most manufacturers of wireless access points and routers indicate a typical range that their equipment can provide. Depending on the type of antenna used and the physical location of the access point or router, the range may vary significantly. It is important to consider obstacles such as walls, ceilings, furniture, and electronic interference from machinery, power lines and even microwave ovens as these all play a role in wireless signal reception. In wireless transmissions, reflections (when wireless signals “bounce” off objects) and multipath (when wireless signals travel in multiple paths arriving at the receiver at different times) are as important as signal strength in determining the success of an installation. A signal will also exhibit peaks and nulls in its amplitude and alteration of its polarization (vertical or horizontal) when propagating through walls, ceilings, and reflecting off metallic objects.

Wireless radios have special hardware and software to deal with multipath and signal level nulls, but if the antenna is in a poor location, the radio will not be able to communicate. When trying to get the best performance in a location with a lot of barriers or reflections, it is important to be able to move the antenna in all three axes in order to minimize the effects of multipath and optimize the signal strength. A good first step is to obtain a layout of the floor plan and then draw in access point locations. You will want to “overlap” the range of the access points so you have complete coverage.

Antenna Position for Directional:

Yagi and parabolic grid antennas, typically used for point to point line of sight applications, must point directly at one another for maximum signal strength. Be sure to clear all obstructions that could distort or block the antenna beam.

Antenna Position for Omni-Directional:

Omni-directional antennas should be mounted as far away as possible from all surfaces including walls, floors, ceilings etc. Additionally, all Omni-directional antennas should be mounted at the same height for maximum performance and signal strength.

Guidelines for a Better Wireless Network Design:

The following tips will help you and your business design a secure wireless network that accommodate a multitude of devices now and into the future:

1. Include capacity or total number of devices and application performance into your network plan.
2. Use dual radio access points.
3. Load balance wireless users.
4. Include network access control as part of the total system.
5. Keep your firmware or network adapter driver for your wireless network devices updated.
6. Consider a hi-gain antenna.
7. Design to the lowest common denominator on your network.

802.11ac (aka 5G Wi-Fi) is the next step after 802.11n (aka N or Wireless-N, which is currently is the most popular Wi-Fi standard). It’s backward-compatible with N, meaning that a 5G Wi-Fi router will support N clients and 5G Wi-Fi clients will also be able to connect to an N router. Wireless-N, in turn, is backward compatible with the rest of the wireless standards, including 802.11g, 802.11b, and 802.11a.

How 802.11ac is different from 802.11n

The biggest difference, other than the improved speeds, that 802.11ac has over Wireless-N is the fact that 5G Wi-Fi works solely on the 5Ghz band and supports channel width, for now, up to 80Mhz (as opposed to 20Mhz of N).

To make 802.11ac hardware truly backward-compatible with N devices, which are available in both 2.4Ghz and 5Ghz bands, all 5G Wi-Fi devices will come with 802.11n on the 2.4Ghz band.

What is 802.11ac good for?

Everything. I can’t imagine how the faster connection speed would hurt you. However, the new standard is especially good for high-def streaming within a local network. In arecent demo, Netgear showed that it could instantly play back four different 1080p movies wirelessly to four HDTVs using 802.11ac connections, something not possible with Wireless-N.

802.11ac clients are also supposed to offer much better battery life than N clients. This is mostly thanks to the improved speed. The fact that 5G Wi-Fi clients can finish transmitting the same amount of data in just around 1 third of the time, compared to N clients, translates into less energy being used.

A wavelength is the distance between two successive peaks. In simpler words, a wavelength is the distance that a single cycle of an RF signal travels.  It is important to understand that there is an inverse relationship between wavelength and frequency (λ = c/f). The formula demonstrates that the higher the frequency of an RF signal, the smaller the wavelength of that signal.

Higher frequency waves have shorter wavelengths and lower frequency waves have longer wavelengths. This is important for a wireless engineer to know for two reasons. First, the coverage distance is dependent on the attenuation through the air. Second, the higher the frequency the less the signal will penetrate obstacles such as walls, windows, and doors. 

Frequency is the number of times a specified event occurs within a specified time interval. It can also be defined as “how often an RF wave cycles per second,” as pictured in Figure 1. So, when we are talking about 2.4GHz WLAN radio cards, the RF signal is oscillating 2.4 billion times per second. Although wavelength and frequency do not cause attenuation, the perception is that higher frequency signals with smaller wavelengths attenuate faster than signals with a larger wavelength.

Figure 1

Access points using 5GHz radio cards will have shorter range and coverage area than access points operating at 2.4GHz. This is important for a wireless engineer to know because more 5GHz access points may have to be installed to provide the same coverage that can be achieved by a lesser number of 2.4Ghz access points.

Amplitude is often referenced as how loud or strong the signal is. In figure 2, we can see that the wavelength (λ) and amplitude of the RF signal. When an access point transmit at 100 mW, that is referred as transmit amplitude. When a radio receives an RF signal, the received signal strength is most often referred to as received amplitude.

Figure 2

Phase is another important property of an RF signal. When two waves are in phase, they strengthen the signal received. When two waves are 180 degrees out of phase, they can completely cancel the signal. In figure 3, we can see two waves in phase.

Figure 3

RF Behaviors

Absorption is the most common RF behavior. If a RF signal that does not pass through an object, then 100% absorption has occurred.

Reflection is when a wave hits a smooth object that is larger than the wave itself. In an enterprise environment, waves can reflect out of smooth surfaces such as doors, walls, and file cabinets. Anything made of metal, glass, and concrete may cause reflection as well.

Scattering is often referred as multiple reflections. This behavior occurs when an RF signal encounters some type of uneven surface and is reflected into multiple directions.

Refraction is when a RF signal bends as it passes through a medium, thus causing the direction of the wave to change. RF refraction most commonly occurs because of atmospheric conditions.

Diffraction is the bending of an RF signal around an object. Typically, diffraction is caused by partial blockage of the RF signal. These blockage areas can become dead zones or blind spots.

The five phenomena (Reflection, Refraction, Diffraction, Scattering, and Absorption) cause multiple copies of the signal to arrive at the receiver at slightly at different times. This is important to consider and it is one thing that we take advantage of in our modern WLAN with 802.11n and 802.11ac using what is called MIMO (Multiple-Input Multiple-Output). We’re taking advantage of these phase variations and using them to transmit multiple space streams.

When troubleshooting wired networks, engineers usually start at the layer 1, the Physical layer. The same best practice applies to WLAN troubleshooting. Learning the RF fundamentals is an essential step to properly troubleshoot, design, and manage wireless networks. 

Note: The terms definitions were obtained from the CWNA official study guide book.

Most businesses deploy wireless networks to meet the strong employee demands for access anywhere, anytime. Employees claim having greater mobility will allow them to increase their productivity. However, having a Wi-Fi network that is poorly designed will not only frustrate employees, but also result in a decrease in productivity. These three major fails represent challenges to businesses when implementing wireless networks.

Fail # 1 “Design”

Wi-Fi Design is the foundation to having an operational, usable, and reliable Wi-Fi network. The time spent gathering the user requirements and conducting wireless surveys is worthwhile, as it directly affects the implementation’s success.  I will create multiple series that will dive deeper into this subject, but for now one should remember the “Placement” of the access points. Several times the correction of the placement has been the fix for user’s wireless complaints. Most access points will provide you with documentation on the antenna patterns. For instance, an access point built with downtilt omnidirectional antennas is better suited to be installed horizontal to the floor.  Another important area of design is the “Frequency” and “Channels”. Today, most devices will prefer the frequency 5Ghz; however, 2.4Ghz remains relevant due to legacy devices and spread limitation of 5Ghz. Most vendors will automate the selection of channels, but the software not always makes the best decision. It is important to verify the channels of your access points. As a rule, access points in the 2.4Ghz are set to channels 1, 6, or 11. In the 5Ghz frequency, there are 20 more non-overlapping channels than the 2.4Ghz band, which can be use in the channel plan. Another area of design is “Power” levels. As a rule, access points should not be configured to use 100% of power levels. Administrators may want to increase the coverage cells, but doing so contributes to a higher co-channel interference, degrading the Wi-Fi network.

Fail #2 “Security”

The recommendation is to migrate from TKIP (Temporal Key Integrity Protocol) encryption in favor of the newer, and more secure, AES encryption (Advanced Encryption Standard). While TKIP offers a significant security upgrade over WEP, it has become a depreciated technology that is no longer considered secure enough to protect your Wi-Fi network from hackers. There are multiple well-known vulnerability attacks that can intercept and decipher the keys. Another consideration is speed. If you have a legacy Wi-Fi network configured with TKIP in the security options, then clients (including 802.11ac) will be limited to 54Mbps to ensure interoperability.

Fail #3 “Surveys”

Failure to conduct a wireless survey is not uncommon, as businesses want to save in costs. However, as the saying goes “If you fail to plan, you are planning to fail” or rather, in this case, administrators who fail to plan survey are planning to fail. At a minimum, a pre and post passive surveys should be conducted. A pre-survey will help determine the placement of the access points, understand the physical layout (obstructions, interference, and user locations), as well as to generate accurate heat maps.  The post survey will help measure the signal coverage and how well the Wi-Fi network is meeting the end user requirements. An active survey is always preferred over a passive survey, as it will help measure throughput and behavior of data packets.

These “Three Major Fails” may cause unreliable performance of wireless networks, spotty coverage, lack of throughput due to interference, not enough access points to cater for concurrent users, or too many access points (causing co-channel interference). Although small failures are inevitable, the three major fails discussed can be averted by following best practices.