Here are a few additional things to consider about bridges: ⻬ As I mentioned, some bridges also have the capability to translate the
messages from one format to another. For example, if the Marketing folks build their network with Ethernet and the accountants use Token
Ring, a bridge can tie the two together. ⻬ You can get a basic bridge to partition two Ethernet networks for about
500 from mail-order suppliers. More sophisticated bridges can cost as much as 5,000 or more.
Routers
A router is like a bridge, but with a key difference. Bridges use actual hard- ware addresses known as MAC addresses to tell which network node each
message is sent to so it can forward the message to the appropriate segment. However, a bridge doesn’t have the ability to actually look inside the message
to see what type of information is being sent. A router can. As a result, routers work at a higher level than bridges. Thus, routers can perform additional tasks
such as filtering packets based on their content. Note that many routers also have built-in bridging functions, so routers are often used as bridges.
You can configure a network with several routers that can work cooperatively together. For example, some routers are able to monitor the network to deter-
mine the most efficient path for sending a message to its ultimate destination. If a part of the network is extremely busy, a router can automatically route
messages along a less-busy route. In this respect, the router is kind of like a traffic reporter up in a helicopter. The router knows that the 101 is bumper-
to-bumper all the way through Sunnyvale, so it sends the message on the 280 instead.
Here is some additional information about routers: ⻬ Routers used to be expensive and used only on large networks. However,
the price of small routers has dropped substantially in recent years, so they’re now becoming common even on small networks.
⻬ The functional distinctions between bridges and routers — and switches and hubs, for that matter — get blurrier all the time. Multifunction routers,
which combine the functions of routers, bridges, hubs, and switches are often used to handle some of the chores that used to require separate
devices.
⻬ Some routers are nothing more than computers with delusions of grandeur — along with several network interface cards and special
software to perform the router functions.
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⻬ Routers can also connect networks that are geographically distant from each other via a phone line using modems or ISDN.
⻬ One of the main reasons for using routers is to connect a LAN to the Internet. Figure 9-8 shows a router used for this purpose.
Hub
Router The
Internet
Figure 9-8:
Using a router to
connect a LAN to the
Internet.
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Part II: Building Your Own Network
Chapter 10
Setting Up a Wireless Network
In This Chapter
䊳
Looking at wireless network standards
䊳
Reviewing some basic radio terms
䊳
Considering infrastructure and ad-hoc networks
䊳
Working with a wireless access point
䊳
Worrying about wireless security
S
ince the beginning of Ethernet networking, cable has been getting smaller and easier to work with. The original Ethernet cable was about as thick
as your thumb, weighed a ton, and was difficult to bend around tight corners. Then came Thinnet cable, which was lighter and easier to work with. Thinnet
cable was supplanted by unshielded twisted-pair UTP cable, which is lighter yet. UTP cable is still cable, though — which means you have to drill holes
and pull cable through walls and ceilings in order to wire your entire home or office.
That’s why wireless networking has become so popular. With wireless network- ing, you don’t need cables to connect your computers. Instead, wireless net-
works use radio waves to send and receive network signals. As a result, a computer can connect to a wireless network at any location in your home
or office.
Wireless networks are especially useful for notebook computers. After all, the main benefit of a notebook computer is that you can carry it around with you
wherever you go. At work, you can use your notebook computer at your desk, in the conference room, in the break room, or even out in the parking lot. At
home, you can use it in the bedroom, kitchen, den, game room, or out by the pool. With wireless networking, your notebook computer can be connected
to the network, no matter where you take it.
This chapter introduces you to the ins and outs of setting up a wireless net- work. I tell you what you need to know about wireless networking standards,
how to plan a wireless network, how to install and configure wireless network components, and how to create a network that mixes both wireless and cabled
components.
Diving into Wireless Networking
A wireless network is a network that uses radio signals rather than direct cable connections to exchange information. A computer with a wireless network
connection is like a cell phone. Just as you don’t have to be connected to a phone line to use a cell phone, you don’t have to be connected to a network
cable to use a wireless networked computer.
The following paragraphs summarize some of the key concepts and terms that you need to understand in order to set up and use a basic wireless network:
⻬ The most common type of wireless technology is called Wi-Fi. Technically, Wi-Fi refers to wireless Ethernet implemented according to a standard
called 802.11b. Wi-Fi networking is now becoming so commonplace that you can buy wireless devices at home improvement stores like
Home Depot. For more information about wireless standards includ- ing Wi-Fi, see the section “Eight-Oh-Two-Dot-Eleventy Something?
Or, Understanding Wireless Standards,” later in this chapter, for more information.
⻬ A wireless network is also sometimes referred to as a WLAN, for wireless local-area network. Some people prefer to switch the acronym around to
local-area wireless network, or LAWN. ⻬ A wireless network has a name, known as a SSID. SSID stands for service
set identifier — wouldn’t that make a great Jeopardy question? I’ll take obscure four-letter acronyms for 400, please All computers that belong
to a single wireless network must have the same SSID. ⻬ Wireless networks can transmit over any of several channels. In order
for computers to talk to each other, they must be configured to transmit on the same channel.
⻬ The simplest type of wireless network consists of two or more computers with wireless network adapters. This type of network is called an ad-hoc
mode network. ⻬ A more complex type of network is an infrastructure mode network. All
this really means is that a group of wireless computers can be connected not only to each other, but also to an existing cabled network via a device
called a wireless access point, or WAP. I tell you more about ad-hoc and infrastructure networks later in this chapter.
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Part II: Building Your Own Network
A Little High-School Electronics
I was a real nerd in high school: I took three years of electronics. The elec- tronics class at my school was right next door to the auto shop. Of course,
all the cool kids took auto shop and only nerds like me took electronics. We hung in there, though, and learned all about capacitors and diodes while the
cool kids were learning how to raise their cars and install 2-Gigawatt stereo systems.
It turns out that a little of that high-school electronics information proves useful when it comes to wireless networking. Not much, mind you. But you’ll
understand wireless networking much better if you know the meanings of some basic radio terms.
Waves and frequencies
For starters, radio consists of electromagnetic waves that are sent through the atmosphere. You can’t see or hear them, but radio receivers can pick
them up and convert them into sounds, images, or — in the case of wireless networks — data.
Radio waves are actually cyclical waves of electromagnetic energy that repeat at a particular rate, called the frequency. Figure 10-1 shows two frequencies of
radio waves: the first is one cycle per second; the second is two cycles per second. Real radio doesn’t operate at that low of a frequency, but I figured
one and two cycles per second would be easier to draw than 680,000 cycles per second or 2.4 million cycles per second.
The measure of a frequency is cycles per second, which indicates how many complete cycles the wave makes in one second duh. In honor of Heinrich
Hertz, the first person to successfully send and receive radio waves it hap- pened in the 1880s, cycles per second is usually referred to as Hertz, abbre-
viated Hz. Thus, 1 Hz is one cycle per second. Incidentally, when the prefix K for Kilo, or 1,000, M for Mega, 1 million, or G for Giga, 1 billion is
added to the front of Hz, the H is still capitalized. Thus, 2.4GHz is correct not 2.4Ghz.
The beauty of radio frequencies is that transmitters can be tuned to broad- cast radio waves at a precise frequency. Likewise, receivers can be tuned to
receive radio waves at a precise frequency, ignoring waves at other frequen- cies. That’s why you can tune the radio in your car to listen to dozens of dif-
ferent radio stations: Each station broadcasts at its own frequency.
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