For an overview of 802.11, watch this CBT Nuggets video (2022) [10:19].

Wireless Frequency Bands

The frequency of a radio wave is the number of cycles it completes in one second, measured in hertz (Hz). The wavelength of a radio wave is the distance it travels in one cycle, measured in meters (m). Different radio waves have different properties and applications. For example, radio waves with lower frequencies can travel farther and penetrate through walls and other obstacles, but they carry less information and are more prone to interference. Radio waves with higher frequencies can carry more information and are less affected by interference, but they have shorter range and are more easily blocked by obstacles.

To organize and regulate the use of radio waves, frequency ranges are grouped into bands. A frequency band is a range of frequencies that have similar characteristics and are allocated for specific purposes. For example, the 2.4 GHz band is a frequency band that ranges from 2.4 to 2.4835 GHz. This band is widely used for wireless networking, as well as other devices such as Bluetooth, microwave ovens, and cordless phones.

Within each frequency band, there are multiple channels that can be used for wireless communication. A channel is a subset of a frequency band that has a defined center frequency and bandwidth. The center frequency is the midpoint of the channel, and the bandwidth is the width of the channel, measured in megahertz (MHz). For example, in the 2.4 GHz band, there are 14 channels, each with a bandwidth of 22 MHz and a center frequency that is 5 MHz apart from the adjacent channels. The first channel has a center frequency of 2.412 GHz, the second channel has a center frequency of 2.417 GHz, and so on.

The choice of frequency band and channel affects the performance and interference of wireless networks. Performance refers to the speed and quality of wireless communication, while interference refers to the unwanted signals that disrupt or degrade wireless communication. As mentioned before, higher frequency bands and channels offer higher performance, and lower frequency bands and channels offer lower interference. Wireless network administrators balance these factors and choose the best frequency band and channel for their network. Some of the factors that influence this decision are listed below.

• The number and type of devices that use the same frequency band and channel: If there are too many devices that use the same frequency band and channel, they will compete for the limited radio resources and cause congestion and collisions. This will reduce the performance and reliability of wireless communication. You may want to select a frequency band and channel that is less crowded and has less overlap with other devices.
• The distance and obstacles between the wireless devices: If the wireless devices are too far apart or there are walls or other obstacles between them, the radio signals will become weaker and more distorted. This will reduce the performance and quality of wireless communication. In this case, you may want to select a frequency band and channel that has longer range and better penetration.
• The regulatory and legal restrictions of the frequency band and channel: Different countries and regions have different rules and regulations for the use of radio waves. Some frequency bands and channels may be restricted or prohibited for certain purposes or users. Select a frequency band and channel that is allowed and compatible with the local laws and standards.

 

Concepts Corner

Let’s think of 802.11 channels like traffic lanes on a highway:

1. Frequency Bands as Highways: Imagine the 2.4 GHz and 5 GHz frequency bands as two separate highways. Each highway has multiple lanes (channels) that cars (data packets) can travel on.
2. Channel Width as Lane Width: On the 2.4 GHz highway, each lane is 20 feet wide, while on the 5 GHz highway, lanes can be 20, 40, 80, or even 160 feet wide. Wider lanes allow more cars to travel side by side, increasing the overall traffic flow (data rate).
3. Channel Spacing as Lane Markings: On the 2.4 GHz highway, lanes are spaced 5 feet apart, but since each lane is 20 feet wide, they overlap. This overlap can cause traffic jams (interference). To avoid this, drivers are advised to use non-overlapping lanes (channels 1, 6, and 11).
4. Channel Access as Traffic Rules: Cars use a rule called CSMA/CA (like a traffic light system) to avoid collisions. Before entering a lane, a car checks if it’s clear. If it’s not, the car waits until the lane is free.
5. Channel Planning as Traffic Management: In a busy city with many highways (access points), proper traffic management is crucial. This involves assigning lanes (channels) to minimize overlap and avoid traffic jams (interference).

The 802.11 Data Frame Format

Although wireless networks are convenient and popular, they can pose security challenges and risks. Wireless data and devices can be intercepted, eavesdropped, tampered, or compromised by unauthorized parties who are within the range of the wireless signals. Therefore, wireless networks need to implement security methods and protocols that protect the confidentiality, integrity, and availability of wireless communication.

Wireless security methods and protocols are standards and techniques that provide authentication, encryption, and access control for wireless networks. Authentication verifies the identity of wireless devices and users before allowing them to join the network. Encryption scrambles the wireless data so that only authorized parties can read it. Access control regulates the permissions and privileges of wireless devices and users on the network.

Below is a history of the most common wireless security methods and protocols:

• Wired Equivalent Privacy (WEP): This was the first wireless security protocol, introduced in 1999. It uses a static encryption key that is shared between the wireless devices and the access point (AP). However, WEP has many security flaws and weaknesses, such as the use of a weak encryption algorithm (RC4), the reuse of the same encryption key for all packets, and the lack of authentication and integrity mechanisms. WEP can be easily cracked and hacked by various tools and methods. WEP is no longer recommended and should never be used.
• Wi-Fi Protected Access (WPA): This was an interim wireless security protocol, developed in 2003 to replace WEP. It uses a dynamic encryption key that changes for each packet, based on the Temporal Key Integrity Protocol (TKIP). It also provides authentication and integrity features, such as the use of a pre-shared key (PSK) or an authentication server (802.1X). WPA is more secure than WEP, but it still has some vulnerabilities and limitations, such as the use of a weak encryption algorithm (RC4), the susceptibility to dictionary attacks, and the lack of backward compatibility with some older devices. WPA is also obsolete and should be avoided.
• Wi-Fi Protected Access 2 (WPA2): This is the current industry standard for wireless security, established in 2004. It uses a strong encryption algorithm (AES) that is considered unbreakable by today’s standards. It also supports two modes of authentication and access control: WPA2-Personal (PSK) and WPA2-Enterprise (802.1X). WPA2-Personal is suitable for home and small office networks, where a common passphrase is used to authenticate all wireless devices and users. WPA2-Enterprise is suitable for large and complex networks, where a dedicated authentication server is used to verify the credentials of each wireless device and user. WPA2 is the most secure and recommended wireless security protocol.
• Wi-Fi Protected Access 3 (WPA3): This is the latest and most advanced wireless security protocol, introduced in 2018. It is designed to address some of the remaining issues and challenges of WPA2, such as the vulnerability to offline dictionary attacks, the lack of forward secrecy, and the difficulty of configuring secure settings. WPA3 offers several enhancements and features, such as the use of a more robust encryption algorithm (SAE), the support for simultaneous authentication of equals (SAE), the provision of individualized encryption for open networks, and the protection of legacy devices with weak passwords. WPA3 is still in the process of adoption and deployment, but it is expected to become the new standard for wireless security in the near future.

For an overview of WPA3, watch the presentation “Secure Wi-Fi Migrations: A WPA3 How-To | Jennifer Minella | WLPC Phoenix 2023” (Wireless LANS Professionals, 2023) [27:56].

​This chapter is adapted from “Computer Networking : Principles, Protocols and Practice, 3rd Edition” by Olivier Bonaventure (2019), Université catholique de Louvain (UCL), licensed under CC BY-NC-SA 4.0 as a derivative from this page and this page of the original work; and “Connectivity of the Internet of Things” by SparkFun licensed under CC BY-NC-SA 4.0.