10 Introduction to Wireless Networks

How Wireless Networks Work

Wireless networking, or WiFi, is a very popular wireless networking technology today. There are more than several hundreds of millions of WiFi devices. In this chapter, we will explore the basics of wireless networking, including the different types of wireless networks, how they work, and the standards that govern them.

Essentially, a wireless network allows devices to remain linked to the network without any cables attached, providing greater convenience and mobility for the user.

Wireless networks operate using radio frequency (RF) technology, which generates an electromagnetic field when an RF current is supplied to an antenna. This field can then spread through space, allowing devices to communicate with each other wirelessly. The radio spectrum is a limited resource that must be shared by everyone. During most of the twentieth century, governments and international organizations have regulated most of the radio spectrum. This regulation controls the utilization of the radio spectrum, in order to prevent interference among different users. A company that wants to use a frequency range in a given region must apply for a license from the regulator. Most regulators charge a fee for the utilization of the radio spectrum and some governments have encouraged competition among companies bidding for the same frequency to increase the license fees.

For an introduction to wireless netoworking, watch this CertBros video (2023) [12:15].

Wireless Network Topologies

The two basic modes (also referred to as topologies) in which wireless networks operate are referred to as infrastructure and ad-hoc networks.

Source: http://www.e-cartouche.ch/content_reg/cartouche/LBStech/en/html/LBStechU2_wlantopo.html (CC-BY)

Infrastructure mode requires a physical structure to support it. This essentially means there should be a medium handling the network functions, creating an infrastructure around which the network sustains. In infrastructure-based wireless networks, the communication takes place between the wireless nodes (i.e., endpoints in the network such as your computer, your phone, etc.) and the access points (i.e., the router) only. There can be more than one access point on the same network handling different wireless nodes. A typical example of an infrastructure network would be cellular phone networks, which have to have a set infrastructure (i.e., network towers) to function.

You may use an infrastructure network if you can easily add more access points to boost the range, if you want to set up a more permanent network, and/or if you will need to bridge to other types of networks (e.g., you can connect to a wired network if required).

The one major downfall with infrastructure networks is that they are costly and time consuming to set up once. So, if you need your device to operate in remote areas where the infrastructure is weak or nonexistent, you cannot rely on infrastructure networks.

Ad-hoc wireless networks, on the other hand, do not require a set infrastructure to work. In ad-hoc networks, each node can communicate with other nodes, so no access point that provides access control is required. Whereas the routing in infrastructure networks is taken care of by the access point, in ad-hoc networks, the nodes in the network take care of routing to find the best possible path between the source and destination nodes to transfer data.

All the individual nodes in an ad-hoc network maintain a routing table, which contains the information about the other nodes. As the nature of the ad-hoc network is dynamic, this results in ever-changing router tables. An ad-hoc network is asymmetric by nature, meaning the path of data upload and download between two nodes in the network may be different.

A typical example of an ad-hoc network is connecting two or more laptops (or other supported devices) to each other directly without any central access point, either wirelessly or using a cable.

You may consider an ad-hoc network when you want to quickly set up a peer-to-peer (P2P) network between two devices, when creating a quick temporary network, and/or if there is no network infrastructure set up in the area (ad-hoc is the only network mode that can be used in areas like this). As the routing is handled by each node in the network, this uses more resources; as the number of devices connected in an ad-hoc network increases, the network interference increases, which may lead to slower networks.

Ranges of Wireless Networks

Wireless networks can be divided into four major types, based on their ranges.

  • WPANs (Wireless Personal Area Networks) are short-range wireless networks that connect devices within a few meters, such as Bluetooth headphones, keyboards, mice, and smartwatches. WPANs use low-power radio waves and have a data rate of up to 25 Mbps. WPANs are suitable for personal use and small-scale applications, such as wireless printing, file sharing, and health monitoring.
  • WLANs (Wireless Local Area Networks) are medium-range wireless networks that connect devices within a few hundred meters, such as Wi-Fi routers, laptops, smartphones, and tablets. WLANs use radio waves in the 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz, and 5.9 GHz bands and have a data rate of up to 10 Gbps. WPANs are suitable for personal use and small-scale applications, such as wireless printing, file sharing, and health monitoring. WLANs are suitable for home and office use and provide internet access, network security, and multimedia streaming.
  • WMANs (Wireless Metropolitan Area Networks) are long-range wireless networks that connect devices within a few kilometers, such as WiMAX base stations, antennas, and modems. WMANs use radio waves in the 2.3 GHz, 2.5 GHz, 3.5 GHz, and 5.8 GHz bands and have a data rate of up to 1 Gbps. WMANs are suitable for urban and rural use and provide broadband access, voice over IP, and video conferencing.
  • WWANs (Wireless Wide Area Networks) are very long-range wireless networks that connect devices across the globe, such as cellular towers, satellites, and mobile phones. WWANs use radio waves in the 700 MHz, 800 MHz, 900 MHz, 1.8 GHz, 1.9 GHz, 2.1 GHz, 2.6 GHz, and 3.5 GHz bands and have a data rate of up to 100 Mbps. WWANs are suitable for mobile and remote use and provide voice, text, email, web browsing, and GPS services.

Wireless Networking Standards

Several wireless networking standards are included in the 802.11 family of standards. These standards are developed by the Institute of Electrical and Electronics Engineers (IEEE) and define the specifications for a range of wireless LAN (Wi-Fi) technologies, some of which are designed for short-range communication, while others are optimized for longer ranges. The range of an 802.11 technology depends on factors such as frequency band, modulation schemes, transmit power, and the environment in which it is deployed. The table below provides a summary of the main 802.11 standards.

Standard Frequency Typical throughput Max bandwidth Range (m) indoor/outdoor Year of development
802.11a 5 GHz 25 Mbps 54 Mbps 35/120 1999
802.11b 2.4 GHz 6.5 Mbps 11 Mbps 38/140 1999
802.11g 2.4 GHz 20 Mbps 54 Mbps 38/140 2003
802.11n 2.4/5 GHz 100 Mbps 600 Mbps 70/250 2009
802.11ac 5 GHz 210 Mbps 6.9 Gbps 35/150 2014
802.11ad 60 GHz 800 Mbps 7 Gbps 10/100 2012
802.11ah 0.9 GHz 150 Kbps 18 Mbps 1000/1000 2017
802.11ax 2.4/5 GHz 600 Mbps 10 Gbps 50/200 2021
802.11be 2.4/5 GHz 2.4 Gbps 40 Gbps 50/200 2024 (estimated)

All IEEE 802.11 standard amendments are constructed in a manner such that devices that operate according to their specifications will be backward compatible with earlier versions so that any modern IEEE 802.11-based device can communicate with older products. The 802.11 working group defined the basic service set (BSS) as a group of devices that communicate with each other. We continue to use network when referring to a set of devices that communicate.

While most of the frequency ranges of the radio spectrum are reserved for specific applications and require a special license, there are a few exceptions. These exceptions are known as the Industrial, Scientific, and Medical (ISM) radio bands. These bands can be used for industrial, scientific and medical applications without requiring a license from the regulator. For example, some radio-controlled models use the 27 MHz ISM band and some cordless telephones operate in the 915 MHz ISM. In 1985, the 2.400-2.500 GHz band was added to the list of ISM bands. This frequency range corresponds to the frequencies that are emitted by microwave ovens. Sharing this band with licensed applications would have likely caused interference, given the large number of microwave ovens that are used. Despite the risk of interference with microwave ovens, the opening of the 2.400-2.500 GHz allowed the networking industry to develop several wireless network techniques to allow computers to exchange data without using cables.

When developing its family of standards, the IEEE 802.11 working group took a similar approach as the IEEE 802.3 working group that developed various types of physical layers for Ethernet networks. 802.11 networks use the CSMA/CA Medium Access Control technique described earlier and they all assume the same architecture and use the same frame format.

For more information on the current status of the project, see The Evolution of Wi-Fi Technology and Standards (IEEE Standards Association, 16 May 2023).

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.

Source: File:2.4 GHz Wi-Fi channels (802.11b,g WLAN).png – Wikimedia Commons

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.

Source: NonOverlappingChannels2.4GHz802.11-en – List of WLAN channels – Wikipedia

The 802.11 Data Frame Format

802.11 devices exchange variable length frames, which have a slightly different structure than the simple frame format used in Ethernet LANs. Details may be found in [IEEE802.11] and [Gast2002] . An 802.11 frame contains a fixed length header, a variable length payload that may contain up 2324 bytes of user data and a 32 bits CRC. Although the payload can contain up to 2324 bytes, most 802.11 deployments use a maximum payload size of 1500 bytes as they are used in infrastructure networks attached to Ethernet LANs. An 802.11 data frame is shown below.Source: NIST SP 800-97, Establishing Wireless Robust Security Networks: A Guide to IEEE 802.11l
The 802.11 data frame format consists of the following fields:

  • Frame Control: This is a 2-byte field that contains 11 subfields. It specifies the type, subtype, and other control information of the frame. The subfields are:
    • Protocol Version: This is a 2-bit field that indicates the revision level of the WLAN standard. It is set to 0 for WLAN (PV0) and 1 for PV1 (IEEE 802.11ah).
    • Type: This is a 2-bit field that indicates the type of the frame. It can be 00 for management, 01 for control, 10 for data, or 11 for extension.
    • Subtype: This is a 4-bit field that indicates the subtype of the frame. It depends on the type field and can have different values for different types of frames.
    • To DS: This is a 1-bit field that is set to 1 if the frame is destined to the distribution system (DS), which is the network infrastructure that connects wireless access points.
    • From DS: This is a 1-bit field that is set to 1 if the frame is originated from the distribution system.
    • More Fragments: This is a 1-bit field that is set to 1 if the frame is part of a fragmented data unit and more fragments follow.
    • Retry: This is a 1-bit field that is set to 1 if the frame is a retransmission of an earlier frame.
    • Power Management: This is a 1-bit field that indicates the power management mode of the sender. It can be 0 for active mode or 1 for power save mode.
    • More Data: This is a 1-bit field that indicates whether the sender has more data to send. It can be 0 for no more data or 1 for more data.
    • Protected Frame: This is a 1-bit field that indicates whether the frame body is encrypted. It can be 0 for clear text or 1 for encrypted.
    • Order: This is a 1-bit field that is used for two purposes. It can indicate whether the frame contains a High Throughput Control (HTC) field or whether the frame is strictly ordered.
  • Duration/ID: This is a 2-byte field that specifies the time period for which the frame and its acknowledgment occupy the channel. It can also be used as an identification field for some control frames.
  • Address 1: This is a 6-byte field that contains the MAC address of the immediate destination of the frame. It can be the receiver address (RA) or the BSSID (Basic Service Set Identifier).
  • Address 2: This is a 6-byte field that contains the MAC address of the immediate source of the frame. It can be the transmitter address (TA) or the source address (SA).
  • Address 3: This is a 6-byte field that contains the MAC address of the final destination or the original source of the frame. It can be the destination address (DA) or the source address (SA).
  • Sequence Control: This is a 2-byte field that contains two subfields. It is used to identify and order the fragments of a data unit. The subfields are:
  • Fragment Number: This is a 4-bit field that indicates the fragment number of the current frame. It ranges from 0 to 15.
  • Sequence Number: This is a 12-bit field that indicates the sequence number of the current data unit. It ranges from 0 to 4095.
  • Address 4: This is an optional 6-byte field that contains the MAC address of the final source or the original destination of the frame. It can be the source address (SA) or the destination address (DA). It is only present when both To DS and From DS are set to 1.
  • QoS Control: This is an optional 2-byte field that contains quality of service information for the frame. It is only present when the subtype is QoS data or QoS null.
  • HT Control: This is an optional 4-byte field that contains high throughput control information for the frame. It is only present when the Order bit is set to 1 and the subtype is not QoS null.
  • Frame Body: This is a variable-length field that contains the actual data or payload of the frame. It can be up to 2304 bytes long. It can also be encrypted if the Protected Frame bit is set to 1.
  • FCS: This is a 4-byte field that contains the frame check sequence, which is a cyclic redundancy check (CRC) value used to detect errors in the frame.

For a deeper dive into how wireless networking works, watch this ComputerPhile video:

Wireless Security Standards

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.

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