A computer network comprises computers or network

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					A computer network comprises computers or network-accessible devices —
and sometimes other peripheral devices such as printers — connected in a
way that they transmit data between participants. Computer networks have
been commonplace in offices for nearly 20 years, but with the advent of reasonably
priced wireless networks, computer networks are becoming increasingly
common in homes. Now we mere mortals can share printers, share the
Internet, play multi-player video games, and stream video like the corporate
gods have been doing for years.
A computer network that connects devices in a particular physical location,
such as in a home or in a single office site, is sometimes called a local area
network (LAN). Conversely, the network outside your home that connects
you to the Internet and beyond is called a wide area network (WAN).
In a nutshell, computer networks help people and devices share information
(files and e-mail) and expensive resources (printers and Internet connections)
more efficiently.
Workstations and servers
Each computer in your home that’s attached to a network is a workstation, also
sometimes referred to as a client computer. The Windows operating system
(OS) refers to the computers residing together on the same local area network
as a workgroup. A Windows-based computer network enables the workstations
in a workgroup to share files and printers that are visible through the Network
Neighborhood (or My Network Places). Home networks based on the Apple
Macintosh OS offer the same capability. On a Mac, all the computers on the
network are called a network neighborhood.
26 Part I: Wireless Networking Fundamentals
Some networks also have servers, which are special-purpose computers or
other devices that provide one or more services to other computers and
devices on a network. Examples of typical servers include
   File server: A file server makes storage space on hard disks or some
other type of storage device available to workstations on the network.
Home networks seldom have a file server because each computer typically
has enough storage space to store the files created on that computer.
Common in-home applications of a file server today are consumer
devices such as Yamaha’s MusicCast (www.yamaha.com; $2,000) or
Turtle Beach Systems’ AudioTron (www.turtlebeach.com; $269) MP3
servers that enable you to play your MP3s over your stereo wirelessly.
   Print server: A print server is a computer or other device that makes it
possible for the computers on the network to share one or more printers.
You won’t commonly find a print server in a home network, but
some wireless networking equipment comes with a print server feature
built in, which turns out to be very handy.
   E-mail server: An e-mail server is a computer that provides a system for
sending e-mail to users on the network. You might never see an e-mail
server on a home network. Most often, home users send e-mail through
a third-party service, such as America Online (AOL), EarthLink, MSN
Hotmail, Yahoo!, and so on.
   DHCP server: Every computer on a network, even a home network,
must have its own unique network address in order to communicate
with the other computers on the network. A Dynamic Host Configuration
Protocol (DHCP) server automatically assigns a network address to
every computer on a network. You most often find DHCP servers in
another device like a router or an AP.
There are many types of client computers — network-aware devices — that
you can find on your network, too. Some examples include
 Gaming consoles: Microsoft’s Xbox (www.xbox.com), Sony PlayStation 2
(www.playstation.com), and Nintendo’s GameCube (www.nintendo.
com) have adapters for network connections or multi-player gaming and
talking to other players while gaming. Cool! Read more about online
gaming in Chapter 12.
                                               -
 Wireless network cameras: Panasonic’s KXHCM250 and KX-HCM270
Network Cameras (www.panasonic.com/consumer_electronics/
gate/cameras.asp) enable you to not only view your home from when
away but also pan, tilt, scan, zoom, and so on your way around the
home. Now that’s a nanny-cam.
Chapter 2: From a to g and b-yond 27
                                               t
 MP3 players: Yamaha’s MusicCAST interacive wireless home music network
system (www.yamaha.com) enables you to use wireless technology
to stream music files throughout your home. The system uses a main
server (about $2,000), which stores your CDs in the MP3 (or other) electronic
format, and a series of receivers or clients (about $800) in remote
rooms for playing back music. You can have one in each room — if you
can afford it!
Most consumer manufacturers are trying to network-enable their devices, so
expect to see everything from your washer and dryer to your vacuum cleaner
network-enabled at some point. Why? Because after such appliances are on a
network, they can be monitored for breakdowns, software upgrades, and so
forth without you having to manually monitor them.
Network infrastructure
Workstations must be electronically interconnected in order to communicate.
The equipment over which the network traffic (electronic signals) travels
between computers on the network is the network infrastructure.
Network hubs
In a typical office network, a strand of wiring similar to phone cable is run
from each computer to a central location, such as a phone closet, where each
wire is connected to a network hub. The network hub, similar conceptually to
the hub of a wheel, receives signals transmitted by each computer on the network
and sends the signals out to all other computers on the network.
Figure 2-1 illustrates a network with a star-shaped topology (the physical
design of a network). Other network topologies include ring and bus. Home
networks typically use a star topology because it’s the simplest to install and
troubleshoot.
Hub
PC
PC
PC PC
PC
Figure 2-1:
It’s all in the
stars: A
typical
network
star-shaped
topology.
28 Part I: Wireless Networking Fundamentals
Bridges
A network bridge provides a pathway for network traffic between networks or
segments of networks. A device that connects a wireless network segment to
a wired network segment is a type of network bridge. In larger networks, network
bridges are sometimes used to connect networks on different floors in
the same building or in different buildings. In a wireless home network, the
device that manages the wireless network, an access point, often acts as a
bridge between a wireless segment of the network and a wired segment.
Hubs and switches
Networks transmit data in bundles called packets. Along with the raw information
that’s being transmitted, each packet also contains the network
address of the computer that sent it and the network address of the recipient
computer. Network hubs send packets indiscriminately to all ports of all computers
connected to the hub.
A special type of hub called a switched hub examines each packet, determines
the addressee and port, and forwards the packet only to the computer and port
to which it is addressed. Most often, switched hubs are just called switches.
A switch reads the addressee information in each packet and sends the packet
directly to the segment of the network to which the addressee is connected.
Packets that aren’t addressed to a particular network segment are never
transmitted over that segment, and the switch acts as a filter to eliminate
unnecessary network traffic. Switches make more efficient use of the available
transmission bandwidth than standard hubs and therefore offer higher
aggregate throughput to the devices on the switched network.
Routers
Over a large network and on the Internet, a router is analogous to a superefficient
postal service — reading the addressee information in each data
packet and communicating with other routers over the network or Internet to
determine the best route for each packet to take. Routers can be a standalone
device, but more often, home networks use a device known as a cable/(digital
subscriber line) DSL router. This type of router — which marries a cable or DSL
modem and a router — uses a capability called Network Address Translation
(NAT) to enable all the computers on a home network to share a single
Internet address on the cable or DSL network. Such routers also exist for
satellite and dialup connections. Generically, these are called WAN routers
because they have access to your wide area network connection, whether it’s
broadband or dialup.
So your local area network, or LAN, in your home connects to your wide area
network, or WAN, which takes signals out of the home.
Chapter 2: From a to g and b-yond 29
Transmission Control Protocol/Internet Protocol (TCP/IP) is the most common
protocol for transmitting packets around a network. Every computer on a
TCP/IP network must have its own IP address, which is a 32-bit numeric
address that’s written as four numbers separated by periods (for example,
192.168.1.100). Each number can have a value from 0 (zero) to 254. The
Internet transmits packets by using the TCP/IP protocol. When you use the
Internet, the Internet service provider (ISP), such as AOL or EarthLink,
assigns a unique TCP/IP number to your computer. For the period of time
that your computer is connected, your computer “leases” this unique
address and uses it like a postal address to send and receive information
over the Internet to and from other computers.
A WAN router with the Network Address Translation (NAT) feature also helps
to protect the data on your computers from intruders. The NAT feature acts
as a protection because it hides the real network addresses of networked
computers from computers outside the network. (For more details on NAT,
see Chapter 9.) Many WAN routers also have additional security features that
more actively prevent intruders from gaining unauthorized access to your
network through the Internet. This type of protection is sometimes described
generically as a firewall. Good firewall software usually offers a suite of tools
that not only block unauthorized access but also help you to detect and monitor
suspicious computer activity. In addition, these tools also provide you
ways to safely permit computers on your network to access the Internet.
Internet gateways
In some cases, you can get a device that really does it all — a wireless Internet
gateway. These devices combine all the features of an access point, a router,
and a broadband modem (typically cable or DSL). Some wireless Internet
gateways even include a print server (that enables you to connect a printer
directly to the gateway and use it from any networked PC), a dialup modem,
and even some Ethernet ports for computers and devices that connect to
your network using wires.
For example, the Cayman Systems 3500 Series Smart Gateways (www.
netopia.com) include a built-in DSL modem, a router, a wireless access
point, and other networking features such as a firewall and an easy-to-use
graphical user interface (GUI) for configuring and setting up the gateway.
There aren’t a lot of these devices on the market; you can’t buy many of them
off-the-shelf, but you can get them directly from your broadband service
provider.

				
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