Wireless Networks Defined

Wireless Networks Defined

A wireless network enables people to communicate and access applications and information without wires. This provides freedom of movement and the ability to extend applications to different parts of a building, city, or nearly anywhere in the world. For example, people at home researching on the Internet can do so in a quiet area away from noisy children or in front of the television with the entire family nearby. Wireless networks allow people to interact with e-mail or browse the Internet from a location that they prefer.

Wireless networks have been around for many years. In fact, early forms of wireless communications include Native Americans waving buffalo skins over a fire to send smoke signals to others over great distances. Also, the use of pulsing lights carrying information through Morse code between ships has been and still is an important form of communications. Of course, cell phones are also a type of wireless communication and are popular today for people talking to each other worldwide.

As with networks based on wire, or optical fiber, wireless networks convey information between computer devices. The information can take the form of e-mail messages, web pages, database records, streaming video or voice. In most cases, wireless networks transfer data, such as e-mail messages and files, but advancements in the performance of wireless networks is enabling support for video and voice communications as well.

As discussed in Chapter 3, "Radio Frequency and Light Signal Fundamentals: The Invisible Medium," wireless networks use either radio waves or infrared light as a medium for communication between users, servers, and databases. This type of communication is invisible to the human eye. In addition, the actual medium (air) is transparent to the user. Most manufacturers are now integrating the wireless network interface card (NIC; also referred to as an adapter) and antenna into computing devices and out of view from the user. This makes wireless computing devices mobile and easy to use.

Wireless networks fall into several categories, depending on the size of the physical area that they are capable of covering. The following types of wireless networks satisfy diverse user requirements:

Table 1-1 shows a brief comparison of these forms of wireless networks. Each type of wireless network has complementary attributes that satisfy different requirements. The subsequent sections briefly explore each wireless network.

As Figure 1-1 illustrates, wireless PANs have relatively short range (up to 50 feet) and are most effective for fulfilling requirements within a small room or personal area. The performance of wireless PANs is moderate, with data rates up to 2 Mbps. These attributes satisfy needs for replacing cables in many situations.

The low power consumption and small footprint of most wireless PAN transceivers make it possible to effectively support small user devices equipped with computer processors. The lower power consumption allows the computer device to operate over long periods of time without draining its battery. This, of course, avoids the need for the user to charge batteries often.

Most wireless PANs use radio waves for carrying information through air. For example, the Bluetooth specification defines the operation of a wireless PAN operating in the 2.4-GHz frequency band with a range of 50 feet and data rates up to 2 Mbps. Furthermore, the Institute of Electrical and Electronic Engineers (IEEE) 802.15 standard incorporates the Bluetooth specification for wireless PANs. These technologies offer a reliable, long-term solution for connecting computer devices within a small area.

Some wireless PANs employ infrared light to carry information from one point to another. The Infrared Data Association (IrDA) specification defines the use of direct infrared beams to provide ranges of up to three feet and data rates as high as 4 Mbps. The advantage of infrared light is freedom from radio frequency interference, but the line-of-sight requirement between computer devices limits the placement of wireless components. An office partition, for example, blocks the path of the infrared light signal, which reduces the usability of the wireless device to a small area.

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Refer to Chapter 4, "Wireless PANs: Networks for Small Places," for details on wireless PAN technologies and products.

Wireless LANs supply high performance within and around office buildings, factories, and homes. (See Figure 1-2.) Users in these areas typically have laptops, PCs, and PDAs with large screens and processors that support higher-end applications. Wireless LANs efficiently satisfy connectivity requirements for these types of computer devices.

Wireless LANs are similar to traditional wired Ethernet LANs in their performance, components, costs, and operation.

IEEE 802.11 is the most prevalent standard for wireless LANs, with versions operating in the 2.4-GHz and 5-GHz frequency bands. A problem with 802.11 is that there is limited interoperability among various versions of the standard. For example, a wireless LAN computer device using 802.11a adapters will not connect with another computer device that implements 802.11b. In addition, there are other issues with the 802.11 standard, such as limited security, which is discussed in later chapters of this book.

In order to solve issues with the 802.11 standard, the Wi-Fi Alliance incorporates assorted functions of 802.11 into a standard they refer to as Wireless Fidelity (Wi-Fi). If a wireless LAN product complies with Wi-Fi, there are assurances that the product is interoperable with other Wi-Fi products. The additional openness of Wi-Fi ensures that diverse users can operate on the same wireless LAN. This is extremely important with public wireless LANs.

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Refer to Chapter 5, "Wireless LANs: Networks for Buildings and Campuses," for details on wireless LAN technologies and products.

Wireless MANs encompass areas the size of cities. In most cases, applications involve fixed connectivity, but some implementations enable mobility. For example, a hospital can deploy a wireless MAN to provide data communications between the main hospital facility and a remote clinic. Or, a power utility company can install a wireless MAN throughout a city to supply access to work orders from various sites. As a result, wireless MANs can connect existing network infrastructures together or allow mobile users to communicate with an existing network infrastructure.

Wireless Internet Service Providers (WISPs) provide wireless MANs in cities and rural areas, as Figure 1-3 illustrates, to provide fixed wireless connections for homes and companies. A wireless MAN offers significant advantages when traditional wired connections (such as Digital Subscriber Line [DSL] and cable modem) are not feasible to install. Wireless MANs are effective when right-of-way restrictions make wired systems impossible or too expensive.

A greater number of companies are now beginning to deploy IEEE 802.16 systems, a relatively new standard with products just becoming available. 802.16 offers a standardized solution for deploying effective wireless MANs with performance in the megabits-per-second range over appreciable ranges. As a result, 802.16 will likely become a common standard for wireless MANs.

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Refer to Chapter 6, "Wireless MANs: Networks for Connecting Buildings and Remote Areas," for details on wireless MAN technologies and products.

Wireless WANs offer mobile applications covering a large area, such as a country or continent. Because of economies of scale, a telecommunications operator can feasibly deploy the relatively expensive wireless WAN infrastructure to provide long-range connectivity for a large customer base. The costs such as deployment can be spread across many users, resulting in low subscriber fees.

Wireless WANs, as Figure 1-4 indicates, have nearly worldwide coverage through the cooperation of multiple telecommunications companies. Well-established roaming agreements among telecommunications operators enable continuous connections for instant mobile data communications. By paying one telecommunications service provider, a user can access limited Internet services over a wireless WAN from almost anywhere in the world.

Figure 1-4. A Wireless WAN Is Capable of Supporting Mobile Applications over a Wide Area

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Performance of wireless WANs is relatively low, with data rates of up to 170 kbps and typical rates of 56 kbps. This level of performance is similar to dial-up telephone modems. Special web portals, however, made to streamline information content work efficiently with smaller devices and lower performance networks. This makes the most from the limited bandwidth of wireless WANs.

The per-user data rates of wireless WANs are relatively low, but that is generally acceptable because of the small devices (for example, cell phones and PDAs) that people carry with them in situations where they need wireless WAN connectivity. The smaller screen sizes and limited processing power of cell phones do not require high performance. The transmission of video to a small cell phone or PDA screen can be done with lower data rates.

Wireless WAN applications involve users accessing the Internet, sending and receiving e-mails, and accessing corporate applications while away from the home and office. Subscribers to wireless WAN services, for example, can stay connected while traveling in taxis or walking throughout a city. A wireless WAN can reach more places than other types of wireless networks, enabling users to carry on business and leisure activities from many different locations.

Wireless WANs include several competing standards that are slowly evolving. For example, Cellular Digital Packet Data (CDPD) is an older technology that enables the transmission of data over analog cell phone systems with data rates of 19.2 kbps. Some companies still offer CDPD in the U.S., but it is becoming obsolete as telecommunication operators move toward Third Generation (3G) telecommunications systems, with data rates possible in the megabit-per-second range.

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Refer to Chapter 7, "Wireless WANs: Networks for Worldwide Connections," for details on wireless WAN technologies and products.

Wireless PANs, LANs, MANs, and WANs are complementary and satisfy different types of requirements. Sometimes, however, it is difficult to distinguish one type from the other. For example, a wireless LAN within a building can provide connectivity between a person's PDA and PC, similar to that provided by a wireless PAN.

In terms of the user perspective, wireless networks are blending together. NICs for computer devices that support multiple wireless networks are becoming available. A traveler, for example, might have an advanced cell phone that interfaces with both wireless LANs and wireless WANs. This enables a seamless, wireless connection as the person interfaces with e-mail while roaming inside an airport using a public wireless LAN or travels in a taxi to a hotel while interfacing with one of the cellular-based data services.