Understanding Wireless Network Devices > Complete Guide

Introduction to Wireless Networks

Understanding the Basics

Wireless networks have become an integral part of our lives, allowing us to connect and communicate without the constraints of physical cables.

Most of us rely on wireless technology daily, whether it's making phone calls, using our microwave ovens, or connecting our laptops to the internet. While we may take these wireless connections for granted, it's essential to understand the underlying technology to make the most of it and troubleshoot any issues that may arise.

Think of wireless networking as a set of black boxes that work seamlessly in the background. You can turn them on and use them without worrying about the technical details.

However, just like the early days of broadcast radio, understanding the inner workings of wireless networks can greatly enhance their performance.To fully grasp the potential of wireless networking, it's crucial to delve into the standards and specifications that govern these networks.

While the ultimate goal is for wireless connections to work effortlessly, having a basic knowledge of the technology can be invaluable when designing, building, or troubleshooting a network.

How Wireless Networks Operate

Wireless networks rely on three main elements: radio signals, data format, and network structure.

These elements work independently but must be defined to create a functional wireless network. In the OSI reference model, radio signals operate at the physical layer, while the data format controls the higher layers.

The network structure encompasses the wireless network interface adapters and base stations responsible for transmitting and receiving radio signals.

Each broadband wireless data service employs a unique combination of radio signals, data formats, and network structures. However, before diving into specifics, it's essential to understand some fundamental principles.

The Basics of Radio

Radio communication is made possible by Maxwell's equations, discovered by James Clerk Maxwell in 1864. These equations demonstrate that a changing magnetic field generates an electric field, and vice versa.

When alternating current (AC) flows through a conductor, it produces an alternating magnetic field that, in turn, creates an alternating electric field, resulting in the emission of electromagnetic radiation or radio waves.

Radio waves can be generated by a transmitter and detected by a receiver. Both devices employ antennas to focus and amplify the radio signals in specific directions.

By adjusting the frequency at which the transmitter sends the alternating current through the antenna, and by tuning the receiver to operate at that frequency, multiple signals can be transmitted and received simultaneously without interference. The range of frequencies utilised for radio communication is referred to as the radio spectrum.

Radio frequencies are measured in hertz (Hz), representing cycles per second. Depending on the application, radio signals operate at frequencies ranging from kilohertz (KHz) to gigahertz (GHz).

Modulation techniques, such as amplitude modulation (AM) and frequency modulation (FM), enable the transmission of voice, music, and other sounds over radio waves.

Wireless Data Networks

Different wireless data networks operate within specific radio frequency bands. For instance, Wi-Fi networks primarily utilize bands around 2.4 GHz or 5 GHz, reserved for unlicensed point-to-point spread spectrum radio services.

Unlicensed radio services allow anyone with compliant equipment to send and receive signals within those frequencies without a license. Spread spectrum technology, employed in wireless Ethernet networks, offers numerous advantages over conventional narrow-band signals.

Spread spectrum utilises wider frequency bands, making it less susceptible to interference and allowing for efficient transmission with low power consumption.

Spread spectrum radio encompasses various modulation techniques, including frequency-hopping spread spectrum (FHSS), direct-sequence spread spectrum (DSSS), and orthogonal frequency division multiplexing (OFDM). These techniques are utilised in different Wi-Fi standards.

Benefits of Wireless

Wireless broadband provides Internet access to mobile devices in addition to allowing network operators to extend their networks beyond the range of their wired connections.

For our purposes, two-way radio is the most sensible approach to wireless broadband, but other methods (such as infrared light or visible signaling) are also possible. Connecting your computer to the Internet (or a local network) by radio offers several advantages over connecting the same computer through a wired connection.

First, wireless provides convenient access for portable computers; it's not necessary to find a cable or network data outlet. And second, it allows a user to make a connection from more than one location and to maintain a connection as the user moves from place to place.

For network managers, a wireless connection makes it possible to distribute access to a network without the need to string wires or cut holes through walls.

In practice, access without cables means that the owner of a laptop or other portable computer can walk into a classroom, a coffee shop, or a library and connect to the Internet by simply turning on the computer and running a communication program.

Depending on the type of wireless network you're using, you might also be able to maintain the same connection in a moving vehicle. When you're installing your own network, it's often easier to use Wi-Fi links to extend your network and your Internet connection to other rooms because a wired system requires a physical path for the cables between the network router or switch and each computer.

Unless you can route those cables through a false ceiling or some other existing channel, this almost always means that you must cut holes in your walls for data connectors and feed wires inside the walls and under the floors.

A radio signal that passes through those same walls is often a lot neater and easier.

How Wi-Fi Works

Wi-Fi, short for Wireless Ethernet, which employs spread-spectrum radio signals to transmit computer data across local area networks (LANs).

Wi-Fi Network Protocols

Wi-Fi specifications govern the movement of data through the physical layer, which comprises the radio link. Additionally, these specifications define a media access control (MAC) layer responsible for managing the interface between the physical layer and the rest of the network structure.

The Physical Layer

Within an 802.11 network, each packet transmitted via radio includes a 144-bit preamble. This preamble encompasses 128 bits used for receiver-transmitter synchronisation, along with a 16-bit start-of-frame field.

Following the preamble, there is a 48-bit header that carries essential information such as the data transfer speed, packet length, and error-checking sequence. Referred to as the PHY preamble, this header governs the physical layer of the communication link based on the ISO model.

Since the header specifies the data speed that follows it, both the preamble and the header are always transmitted at a constant rate of 1 Mbps. Consequently, even if the network link operates at the full 11 Mbps, the effective data transfer speed is notably slower.

In practice, one can expect around 85 percent of the nominal speed, as various forms of overhead in data packets further reduce the actual speed.

The 144-bit preamble originated from older and slower DSSS systems, and it remains in the specification to ensure compatibility with those legacy standards.

However, it does not serve any practical purpose. An optional alternative is a shorter 72-bit preamble. In the case of a short preamble, the synchronisation field contains 56 bits combined with the same 16-bit start-of-frame field used in long preambles.

Although, the 72-bit preamble is incompatible with very old 802.11 hardware, it is inconsequential in modern Wi-Fi networks, as all devices can recognise the short preamble format.

Functionally, a short preamble performs equally well compared to a long preamble. A long preamble requires a maximum of 192 milliseconds to process, whereas a short preamble completes the task in 96 milliseconds.

In essence, the short preamble reduces the overhead on each packet by half. This significant reduction positively impacts actual data transmission speed, especially for activities like streaming audio and video, as well as voice over Internet services.

Manufacturers may default to using either a long or short preamble. However, it is typically possible to modify the preamble length through the configuration software of network adapters and access points.

For most users, the preamble length falls into the category of technical details that need not be comprehended, as long as it remains consistent across all devices within the network. In contrast, around fifteen years ago, when telephone modems were the prevalent means of connecting computers, individuals had to concern themselves with configuring data bits and stop bits for each modem call.

While many people might not have precisely understood what a stop bit is (it represents the time required for an old mechanical Teletype printer to return to the idle state after sending or receiving each byte), they recognised the need for consistency at both ends.

Similarly, preamble length serves as an obscure setting that must match on every node within a network, although most individuals neither know nor care about its underlying significance.

The MAC Layer

Within the ISO model, the MAC layer, which is typically considered a subset of the data link layer, governs the traffic flow through the radio network. It ensures data collisions and conflicts are minimised through a set of rules known as carrier sense multiple access/collision avoidance (CSMA/CA).

Additionally, the MAC layer supports security functions outlined in the 802.11 standards. When multiple access points exist within a network, the MAC layer associates each network client with the access point that offers the strongest signal quality.

In situations where multiple nodes in the network attempt to transmit data simultaneously, CSMA/CA directs all but one of the conflicting nodes to defer their transmissions and retry later, enabling the remaining node to send its packet. CSMA/CA operates as follows: When a network node intends to send a packet, it first listens for other signals.

If no signals are detected, it waits for a brief random interval before checking again. Should it still sense no signals, it proceeds to transmit the packet. The receiving device evaluates the packet and, if intact, sends an acknowledgment back to the sender.

However, if the sending node does not receive the acknowledgment, it assumes a collision occurred with another packet, causing data corruption. In such cases, it waits for another random interval before attempting another transmission.

CSMA/CA offers an optional feature wherein an access point can be designated as a point coordinator, granting priority to a network node transmitting time-critical data types like voice or streaming media.

The MAC layer supports two forms of authentication to verify that a network device is authorised to join the network: open authentication and shared key authentication.

During network configuration, all nodes within the network must utilise the same type of authentication. The MAC layer handles these authentication mechanisms and other administrative functions by exchanging control frames before permitting the higher layers to transmit data.

It also configures several options on the network adapter:

Power modes:

Continuous aware mode and power save polling mode. In continuous aware mode, the radio receiver remains active, consuming power constantly.

Conversely, in power save polling mode, the radio remains idle for extended periods but periodically polls the access point for new messages. Power save polling mode reduces battery drain on portable devices such as laptops and PDAs.

Access control:

This feature ensures unauthorized users are kept out of the network. A Wi-Fi network can employ two access control methods: the SSID (network name) and the MAC address (a unique character string identifying each network node).

Each network node must have the correct SSID programmed into it; otherwise, the access point will not associate with that node. An optional table of MAC addresses can further restrict access to radios whose addresses are listed.

The MAC layer also manages the wired equivalent privacy (WEP) or Wi-Fi protected access (WPA) encryption function. WEP encryption uses either a 64-bit or a 128-bit encryption key to encode and decode data transmitted via the radio link, while WPA employs a 128-bit key and a 48-bit initialisation vector.

Other Control Layers

All the activities specified in the 802.11 standards occur at the PHY and MAC layers. Higher layers handle tasks such as addressing, routing, data integrity, syntax, and data format within each packet.

These layers are agnostic to the medium of transmission, whether it be wires, fiber optic lines, or radio links. Consequently, wireless networks can be used with any type of LAN or network protocol.

The same radios can seamlessly handle TCP/IP, Novell NetWare, and other network protocols integrated into Windows, Unix, Macintosh, and other operating systems.

Wi-Fi Network Protocols

Wi-Fi network protocols are sets of rules and specifications that govern the operation of Wi-Fi networks. These protocols define how data is transmitted over the wireless medium and ensure compatibility and efficient communication between devices.

The first widely adopted Wi-Fi protocol was 802.11b, introduced in 1999. It operated in the 2.4 GHz frequency band and provided a data transfer speed of up to 11 Mbps.

Shortly after, 802.11a was released, operating in the 5 GHz frequency band and offering faster speeds but with a shorter signal range. In 2003, the 802.11g specification combined the best features of both 802.11b and 802.11a, providing a data transfer speed of 54 Mbps while maintaining compatibility with 802.11b devices.

The latest major Wi-Fi protocol is 802.11n, which offers even higher speeds and improved security compared to earlier versions. It utilises multiple antennas and advanced techniques to achieve data transfer rates of up to several hundred Mbps. Importantly, devices that support 802.11n can also work with older 802.11b and 802.11g devices.

It's worth noting that there are additional Wi-Fi specifications, such as 802.11c, d, e, and f, which deal with specific functionalities like bridge operation and Quality of Service (QoS). These specifications are typically relevant only to manufacturers and network administrators.

When using Wi-Fi to connect to the internet, it's essential to understand that the speed of the wireless link is not the sole determining factor for data transfer speed.

The maximum bandwidth of the Wi-Fi signal is constrained by the speed of the internet connection that the Wi-Fi access point is connected to, such as a T-1 line, cable modem, or DSL line.

Even if the Wi-Fi network supports high-speed signaling, the actual speed you experience will be limited by the internet connection's maximum speed, which is often around 5 Mbps or less.

Wi-Fi Radio Frequencies

Wi-Fi radio frequencies refer to the specific bands of the radio spectrum that are used for wireless communication in Wi-Fi networks. These frequencies are divided into different bands and channels, and their allocation varies slightly between countries and regions.

One commonly used band is the 2.4 GHz band, which is designated for unlicensed industrial, scientific, and medical (ISM) services.

Wi-Fi protocols like 802.11b, 802.11g, and 802.11n operate within this band. Another band, known as the unlicensed national information infrastructure (U-NII), is located near 5.3 GHz and is used by 802.11a.

Although the frequency allocations differ slightly worldwide, most countries and regions utilise the same frequency bands. These minor variations are generally not significant since most networks operate within a single country or region, and the signal range typically spans only a few hundred feet.

The overlap among national standards allows Wi-Fi equipment to be used legally worldwide, with the available channels usually predetermined by the country of sale or set by the manufacturer.

Wireless networks operate on specific channels within the frequency bands. In North America, Wi-Fi devices commonly use 11 channels for 802.11b/g, while other countries authorize 13 channels. Japan, however, uses 14 channels, and France allows only 4 channels.

The channels are numbered universally, meaning that channel 9 in one country corresponds to the same frequency as channel 9 in another. To minimise interference, it is recommended to coordinate channel usage with neighboring networks, including home Wi-Fi networks.

Ideally, each network should use channels that are at least 25 MHz or five channel numbers apart. Networks that aim to avoid interference can choose high and low channel numbers, with channels 1, 6, and 11 being popular choices.

When more than three networks are present, some interference may occur, but assigning a new channel in the middle of an existing pair can help minimise it. Interference can also arise from other devices operating in the 2.4 GHz band, such as cordless telephones and microwave ovens.

It is important to note that the frequencies listed for each channel represent the center frequency of a 22 MHz channel, and neighboring channels overlap. Therefore, having widely separated channels enhances performance.

The 802.11a specification utilises a different range of frequencies. Each channel in this case is 20 MHz wide, and similar rules regarding channel separation apply.

When connecting to a Wi-Fi network, your computer or network adapter will automatically detect available Wi-Fi signals and allow you to choose the desired one.

Most Wi-Fi adapters and network interfaces can recognise multiple Wi-Fi protocols and configure the connection accordingly, eliminating the need for manual adjustments.

Wi-Fi devices are subject to limits on transmitter power and antenna gain set by 802.11 specifications and regulatory agencies like the FCC in the United States. These restrictions ensure limited operating distances for Wi-Fi links, allowing multiple networks to utilise the same channels without causing interference.

Wireless Network Devices

Wireless network devices consist of two main categories: network adapters and access points. Network adapters are devices connected to computers or other devices that exchange data with a wireless network.

They can take various physical forms, including plug-in PC cards for laptops, internal network adapters on PCI cards for desktop computers, external USB adapters, built-in adapters in laptops, plug-in adapters for PDAs and handheld devices, and internal network interfaces in other devices like printers and digital cameras.

Access points, on the other hand, serve as the base stations for wireless networks. They act as bridges between the wireless network and a traditional wired network.

Access points are often combined with other network functions and can come in different configurations, such as simple base stations, base stations with additional wired Ethernet ports, broadband routers, software access points using computer network adapters, and residential gateways.

When setting up a Wi-Fi network, two modes can be used: ad hoc networks and infrastructure networks. Ad hoc networks are temporary and self-contained, consisting of wireless stations without access to a larger LAN or the Internet.

Infrastructure networks, on the other hand, have one or more access points that are connected to a wired network. In infrastructure networks, wireless stations communicate with the access point, which relays messages and data to other nodes on the wireless network or the wired LAN.

Infrastructure networks can be basic service sets (BSS) with a single base station or extended service sets (ESS) with multiple access points.

In ESS networks, the system handles the association of a station with a specific access point and manages the handoff of the connection from one access point to another when necessary, similar to how cellular phone systems handle roaming.

Wi-Fi networks can be public or private. Public networks, also known as hotspots, allow any nearby computer to establish a connection, and some may require paid accounts or login credentials.

Private networks, on the other hand, are restricted to specific users and often have security features such as encryption or MAC address restriction to prevent unauthorised access.

It is important to note that while private networks should ideally have security measures in place, some may remain unprotected if the owner fails to enable security tools.

Whats next?

Wireless Network Security