Lesson 3: Wireless Networking
This lesson presents an overview of wireless-network technology. You are introduced to the characteristics of the various wireless environments as well as the major wireless transmission and reception components.
After this lesson, you will be able to:
- Identify the three types of wireless networks and the uses of each.
- Describe the four transmission techniques used in local area networking.
- Describe the three types of signal transmission used in mobile computing.
Estimated lesson time: 25 minutes
The Wireless Environment
The wireless environment is an often appropriate, and sometimes necessary, networking option. Today, manufacturers are offering more products at attractive prices that, in turn, will mean increased sales and demand in the future. As demand increases, the wireless environment will grow and improve.
The phrase "wireless environment" is misleading because it implies a network completely free of cabling. In most cases, this is not true. Most wireless networks actually consist of wireless components communicating with a network that uses the cabling discussed earlier in this chapter in a mixed-component network called a hybrid network.
Wireless Network Capabilities
Wireless networks are attracting attention because wireless components can:
- Provide temporary connections to an existing, cabled network.
- Help provide backup to an existing network.
- Provide some degree of portability.
- Extend networks beyond the limits of physical connectivity.
Uses for Wireless-Network Connectivity
The inherent difficulty of setting up cable networks is a factor that will continue to push wireless environments toward greater acceptance. Wireless connectivity can be especially useful for networking:
- Busy locations, such as lobbies and reception areas.
- Users who are constantly on the move, such as doctors and nurses in hospitals.
- Isolated areas and buildings.
- Departments in which the physical setting changes frequently and unpredictably.
- Structures, such as historic buildings, for which cabling presents challenges.
Types of Wireless Networks
Wireless networks can be divided into three categories based on their technology:
- LANs
- Extended LANs
- Mobile computing
The primary difference between these categories lies in the transmission facilities. Wireless LANs and extended LANs use transmitters and receivers owned by the company in which the network operates. Mobile computing uses public carriers, such as long distance telephone companies, along with local telephone companies and their public services, to transmit and receive signals.
LANs
Except for the media used, a typical wireless network operates almost like a cabled network: a wireless network interface card with a transceiver is installed in each computer, and users communicate with the network just as if they were using cabled computers.
Access Points
The transceiver, sometimes called an access point, broadcasts and receives signals to and from the surrounding computers and passes data back and forth between the wireless computers and the cabled network.
These wireless LANs use small wall-mounted transceivers to connect to the wired network. Figure 2.32 shows a wireless connection between a laptop computer and a LAN. The transceivers establish radio contact with portable networked devices. Note that this is not a true wireless LAN, because it uses a wall-mounted transceiver to connect to a standard, cabled LAN.
Figure 2.32 Wireless portable computer connecting to a cabled network access point
Transmission Techniques
Wireless LANs use four techniques for transmitting data:
- Infrared transmission
- Laser transmission
- Narrowband (single-frequency) radio transmission
- Spread-spectrum radio transmission
Infrared Transmission All infrared wireless networks operate by using an infrared light beam to carry the data between devices. These systems need to generate very strong signals because weak transmission signals are susceptible to interference from light sources such as windows. Many of the high-end printers sold today are preconfigured to accept infrared signals. Figure 2.33 shows a laptop computer using an infrared light beam to send data to a printer.
This method can transmit signals at high rates because of infrared light's high bandwidth. An infrared network can normally broadcast at 10 Mbps.
There are four types of infrared networks:
- Line-of-sight networks As the name implies, this version of infrared networking transmits only if the transmitter and receiver have a clear line of sight between them.
- Scatter infrared networks In this technology, broadcast transmissions are bounced off walls and ceilings and eventually hit the receiver. They are effective within an area limited to about 30.5 meters (100 feet).
- Reflective networks Optical transceivers situated near the computers transmit to a common location that redirects the transmissions to the appropriate computer.
- Broadband optical telepoint This infrared wireless LAN provides broadband services and is capable of handling high-quality multimedia requirements that can match those provided by a cabled network.
Figure 2.33 Wireless portable computer using an infrared light beam to send data to a printer
While its speed and convenience are generating interest, infrared has difficulty transmitting for distances greater than 30.5 meters (100 feet). It is also subject to interference from the strong ambient light found in most business environments.
Laser Transmission Laser technology is similar to infrared technology in that it requires a direct line of sight, and any person or thing that breaks the laser beam will block the transmission.
Narrowband (Single-Frequency) Radio Transmission This approach is similar to broadcasting from a radio station. The user tunes both the transmitter and the receiver to a certain frequency. This does not require line-of-sight focusing because the broadcast range is 3000 meters (9842 feet). However, because the signal is high frequency, it is subject to attenuation from steel and load-bearing walls.
Narrowband radio is a subscription service. The service provider handles all the Federal Communications Commission (FCC) licensing requirements. This method is relatively slow; transmission is in the 4.8 Mbps range.
Spread-Spectrum Radio Transmission Spread-spectrum radio broadcasts signals over a range of frequencies. This helps it avoid narrowband communication problems.
The available frequencies are divided into channels, known as hops, which are comparable to one leg of a journey that includes intervening stops between the starting point and the destination. The spread-spectrum adapters tune in to a specific hop for a predetermined length of time, after which they switch to a different hop. A hopping sequence determines the timing. The computers in the network are all synchronized to the hop timing. This type of signaling provides some built-in security in that the frequency-hopping algorithm of the network would have to be known in order to tap into the data stream.
To further enhance security and to keep unauthorized users from listening in to the broadcast, the sender and the receiver can encrypt the transmission.
Spread-spectrum radio technology provides for a truly wireless network. For example, two or more computers equipped with spread-spectrum network adapters and an operating system with built-in networking capability can act as a peer-to-peer network with no connecting cables. In addition, such a wireless network can be tied into an existing network by adding an appropriate interface to one of the computers on that network.
Although some implementations of spread-spectrum radio can offer transmission speeds of 4 Mbps over distances of about 3.22 kilometers (two miles) outdoors and 244 meters (800 feet) indoors, the typical speed of 250 Kbps (kilobits per second) makes this method much slower than the other wireless networking options discussed.
Point-to-Point Transmission
The point-to-point method of data communication does not fall neatly into the present definitions of networking. It uses a point-to-point technology that transfers data from one computer to another instead of communicating among several computers and peripherals. However, additional components such as single and host transceivers are available. These can be implemented in either stand-alone computers or computers already on a network to form a wireless data-transfer network.
This technology involves wireless serial data transfer that:
- Uses a point-to-point radio link for fast, error-free data transmission.
- Penetrates through walls, ceilings, and floors.
- Supports data rates from 1.2 to 38.4 Kbps up to 61 meters (200 feet) indoors or about 0.5 kilometers (0.30 miles) with line-of-sight transmission.
This type of system transfers data between computers, or between computers and other devices such as printers or bar-code readers.
Extended LANs
Other types of wireless components are able to function in the extended LAN environment similarly to their cabled counterparts. A wireless LAN bridge, for example, can connect networks up to 4.8 kilometers (three miles) apart.
Multipoint Wireless Connectivity
A wireless bridge is a component that offers an easy way to link buildings without using cable. In the same way that a footbridge provides a path between two points, a wireless bridge provides a data path between two buildings. Figure 2.34 shows a wireless bridge connecting two LANs. The AIRLAN/Bridge Plus, for example, uses spread-spectrum radio technology to create a wireless backbone to tie locations together over distances beyond the reach of LANs. With variations that depend on atmospheric and geographic conditions, this distance can be up to 4.8 kilometers (three miles).
Though costly, such a component might be justified because it eliminates the expense of leased lines.
Figure 2.34 Wireless bridge connecting two LANs
The Long-Range Wireless Bridge
If the wireless bridge will not reach far enough, another alternative to consider is a long-range wireless bridge. These also use spread-spectrum radio technology to provide both Ethernet and Token Ring bridging, but for a distance of up to 40 kilometers (about 25 miles).
As with the original wireless bridge, the cost of the long-range bridge might be justified because it eliminates the need for T1 line or microwave connections.
NOTE
A T1 line is a high-speed communications line that can handle digital communications and Internet access at the rate of 1.544 Mbps.
Mobile Computing
Wireless mobile networks use telephone carriers and public services to transmit and receive signals using:
- Packet-radio communication.
- Cellular networks.
- Satellite stations.
Traveling employees can use this technology with portable computers or personal digital assistants (PDAs) to exchange e-mail messages, files, or other information.
While this form of communication offers convenience, it is slow. Transmission rates range from 8 Kbps to 19.2 Kbps. The rates slow further when error correction is included.
Mobile computing incorporates wireless adapters that use cellular-telephone technology to connect portable computers with the cabled network. Portable computers use small antennas to communicate with radio towers in the surrounding area. Satellites in near-earth orbit pick up low-powered signals from portable and mobile networked devices.
Packet-Radio Communication
This system breaks a transmission into packets.
NOTE
A packet is a unit of information transmitted as a whole from one device to another on a network. Packets are discussed in greater detail in Chapter 3, "Understanding Network Architecture."
These radio packets are similar to other network packets. They include:
- The source address.
- The destination address.
- Error-correction information.
The packets are linked up to a satellite that broadcasts them. Only devices with the correct address can receive the broadcast packets.
Cellular Networks
Cellular Digital Packet Data (CDPD) uses the same technology and some of the same systems that cellular telephones use. It offers computer data transmissions over existing analog voice networks between voice calls when the system is not busy. This is very fast technology that suffers only subsecond delays, making it reliable enough for real-time transmission.
As in other wireless networks, there must be a way to tie the cellular network in to the existing cabled network. An Ethernet interface unit (EIU) can provide this connection.
Satellite Stations
Microwave systems are a good choice for interconnecting buildings in small, short-distance systems such as those on a campus or in an industrial park.
Microwave transmission is currently the most widely used long-distance transmission method in the United States. It is excellent for communicating between two line-of-sight points such as:
- Satellite-to-ground links.
- Between two buildings.
- Across large, flat, open areas, such as bodies of water or deserts.
A microwave system consists of the following:
- Two radio transceivers: one to generate (transmitting station) and one to receive (receiving station) the broadcast.
- Two directional antennas pointed at each other to implement communication of the signals broadcast by the transceivers. These antennas are often installed on towers to give them more range and to raise them above anything that might block their signals.
Lesson Summary
The following points summarize the main elements of this lesson:
- The wireless environment is an often appropriate, and sometimes necessary, networking option.
- Computers operating on a wireless network function like their wire-bound counterparts, except that the network interface card is connected to a transceiver instead of a cable.
- A wireless segment can be either point-to-point (separated by short distances or in view of each other) or long-range.
- Wireless networks use infrared, laser, narrowband radio, or spread-spectrum radio signals for transmitting data.
- A wireless bridge can connect buildings that are situated as much as 40 kilometers (about 25 miles) apart.
- Cellular communication, satellite stations, and packet-radio communications are adding mobility to networks.
Exercise 2.3: Network Planning Problem
This exercise provides you with the experience of planning for two aspects of a network (selecting the right media and selecting the right NIC).
Part 1: Choosing Your Networking Media
Research has shown that about 90 percent of all new network installations are using UTP cable in a star-bus topology. Because most of the cost of cable installation is applied to labor, there is often little cost difference between using Category 3 UTP cable and Category 5 UTP cable. Most new installations use Category 5 because it supports transmission speeds of up to 100 Mbps. Category 5 allows you to install a 10 Mbps solution now and upgrade it to a 100 Mbps solution later. However, UTP cable might not be suitable for all networking situations.
The following questions prompt you to think about your network cable needs. Place a check mark next to the choice that applies to your site. To determine which type of cabling would be most appropriate for your site, simply total the check marks next to each type of cable indicator (UTP, coaxial, STP, fiber-optic). The indicator with the highest number of check marks is the candidate unless there is a specific requirement for a particular cable type such as fiber-optic (distance and security). In cases in which more than one type of cable is indicated, choose UTP where possible.
NOTE
UTP is currently the most popular cabling option. Unless there is a compelling reason to use another type, UTP should be the first choice you consider.
For the purpose of answering the questions that follow, "Any" means that UTP can be a choice, depending on your other site considerations. "Depends on other factors" means that you will need to factor in other considerations apart from those presented in the question you're currently answering.
- Are ease of troubleshooting and the cost of long-term maintenance important?
- Are most of your computers located within 100 meters (328 feet) of your wiring closet?
- Is ease of reconfiguration important?
- Does any of your staff have experience with UTP cable?
Yes ____ UTP cable
No ____ Any of the discussed cable types
Yes ____ UTP cable
No ____ Coaxial or fiber-optic cable
Yes ____ UTP cable
No ____ Any of the discussed cable types
Yes ____ UTP cable
No ____ UTP cable, depending on other factors (See the following Note.)
NOTE
Even if no one on your staff has experience with UTP, someone may have transferable experience with another type of cable such as coaxial, STP, or even fiber-optic cable.
- Does your network have any existing STP cabling?
- Does the topology or NIC you want to use require the use of STP cable?
- Do you have a need for cable that is more resistant than UTP to EMI (electromagnetic interference)?
- Do you have existing coaxial cabling in your network?
- Is your network very small (10 or fewer computers)?
- Will your network be installed in an open area using cubicles to separate work areas?
Yes ____ STP cable
No ____ Any of the discussed cable types
Yes ____ STP
No ____ Depends on other factors
Yes ____ STP, coaxial, or fiber-optic cable
No ____ UTP cable, depending on other factors
Yes ____ Coaxial cable
No ____ Any of the discussed cable types
Yes ____ Coaxial cable (bus), UTP cable
No ____ Any of the discussed cable types, depending on other factors
Yes ____ Coaxial, or UTP cable
No ____ Depends on other factors
NOTE
Some situations require fiber-optic cable. This is especially true where other types of cable will not meet specific distance or security requirements. In such cases, fiber-optic cable is the only cable type that can be considered, regardless of what the questions in the other areas indicate.
- Do you have a need for network cabling that is completely immune to electromagnetic interference (EMI)?
- Do you have a need for network cabling that is relatively secure from most eavesdropping or corporate intelligence-gathering equipment?
- Do you have a need for network transmission speeds that are higher than those supported by copper media?
- Do you have a need for longer cabling distances than those supported by copper media?
- Do you have a budget that can absorb the costs of implementing fiber-optic cable?
Yes ____ Fiber-optic cable
No ____ Any of the discussed cable types, depending on other factors
Yes ____ Fiber-optic cable
No ____ Any of the discussed cable types, depending on other factors
Yes ____ Fiber-optic cable
No ____ Any of the discussed cable types, depending on other factors
Yes ____ Fiber-optic cable
No ____ Any of the discussed cable types, depending on other factors
Yes ____ Fiber-optic cable or any of the discussed cable types, depending on other factors
No ____ Any of the discussed cable types, depending on other factors
NOTE
In the questions that follow, wireless, like fiber-optic cable, may be the only option in some cases, regardless of what the questions in the other areas indicate. Keep in mind that wireless networking can also be used in combination with a cabled network.
- Do users on your network need to physically move their computers in the course of their workday?
- Are there limitations that make it very difficult or impossible to cable computers to the network?
- Does your network have unique needs that are best fulfilled by one or more of the features of current wireless technology, such as computer mobility, or the ability to have a network in a building in which it is very difficult or impossible to install cable?
Yes ____ Wireless network, depends on other factors
No ____ Any of the discussed cable types, depending on other factors
Yes ____ Wireless network
No ____ Any of the discussed cable types, depending on other factors
Yes ____ Wireless network
No ____ Any of the discussed cable types, depending on other factors
Part 2: Choosing Your Network Interface Card
There are dozens of manufacturers making each type of NIC, and each card has slightly different features. Setup is sometimes accomplished with jumpers or switches, sometimes using a software setup program, sometimes by means of a Plug and Play (PnP) bus type, and so on. You should do some research to determine which card is best for you because the industry is constantly changing. The best card this month might be updated or superseded by another manufacturer's card next month.
If you answer yes to each of the following questions, then the card you have chosen will probably work in your environment.
NOTE
These questions are not designed to promote a particular card but, rather, to ensure that the card you choose is compatible with the rest of your network.
- Are drivers available for the card that can work with the operating system you are using?
- Is the card compatible with the cable type and topology you have chosen?
- Is the card compatible with the bus type of the computer into which it will be installed?
Yes ____
No ____
Yes ____
No ____
Yes ____
No ____
EAN: 2147483647
Pages: 106