1. What Is the Purpose of the Components Required for
Successful Communications, and What Are Various Sending and Receiving Devices?
Computer communications describes a process in which two or
more computers or devices transfer data, instructions, and information. Today,
even the smallest computers and devices can communicate directly with one
another, with hundreds of computers on a company network, or with millions of
other computers around the globe — often via the Internet.
Some communications involve cables and wires; others are
sent wirelessly through the air.
For successful communications, you need the following:
• A sending device that initiates an instruction to transmit
data, instructions, or information.
• A communications device that connects the sending device
to a communications channel.
• A communications channel, or transmission media on which
the data, instructions, or information travel.
• A communications device that connects the communications
channel to a receiving device.
• A receiving device that accepts the transmission of data,
instructions, or information.
All types of computers and mobile devices serve as sending
and receiving devices in a communications system. This includes mainframe
computers, servers, desktop computers, notebook computers, smart phones,
portable media players, handheld game consoles, and GPS receivers. One type of
communications device that connects a communications channel to a sending or
receiving device such as a computer is a modem. Two examples of communications
channels are cable television lines and telephone lines.
2. How Are Computer Communications Used?
Communications technologies include blogs, chat rooms,
e-mail, fax, FTP, instant messaging, newsgroups, RSS, video conferencing, VoIP,
Web, Web folders, and wikis. Users can send and receive wireless messages to
and from smart phones, cell phones, handheld game consoles, and other mobile
devices using text messaging, picture messaging and video messaging, and
wireless instant messaging. People connect wirelessly to the Internet through a
wireless Internet access point. A hot spot is a wireless net- work that provides
Internet connections to mobile computers and devices. A cybercafé is a
coffeehouse, restaurant, or other location that provides computers with
Internet access. A global positioning system (GPS) analyzes signals sent by
satellites to determine an earth-based receiver’s geo- graphic location. Many
software products provide a means to collaborate, or work online with other
users connected to a server. Groupware is software that helps groups of people
work on projects or share information over a net- work. Voice mail allows
someone to leave a voice message for one or more people. Web services describe
standardized software that enables programmers to create applications that
communicate with other remote computers.
3. What Are the Advantages of Using a Network, and How Are
LANs, MANs, and WANs Different?
A network is a collection of computers and devices connected
together via communications devices and transmission media. Advantages of using
a network :
• Facilitating
communications — Using a network, people
communicate efficiently and easily via e-mail, instant messaging, chat rooms,
blogs, wikis, online social networks, video telephone calls, online meetings,
video conferencing, VoIP, wireless
messaging ser- vices, and groupware. Some of these communications, such as
e-mail, occur within a business’s internal network. Other times, they occur
globally over the Internet.
• Sharing hardware — In a networked environment, each
computer on the network can have access to hardware on the network. Business
and home users network their hardware to save money. That is, it may be too
costly to provide each user with the same piece of hardware such as a printer.
If the computers and a laser printer are connected to a network, the computer
users each access the laser printer on the network, as they need it.
• Sharing data and information — In a networked environment,
any authorized computer user can access data and information stored on other
computers on the network. A large company, for example, might have a database
of customer information. Any authorized person, including a mobile user with a
smart phone or other device connected to the network, has access to the
database. Most businesses use a
standard, such as EDI (electronic data interchange), that defines how data
transmits across telephone lines or other means. For example, companies use EDI
to handle product catalog distribution, bids, requests for quotations,
proposals, order placement, shipping notifications, invoicing, and payment
processing. EDI enables businesses to operate with a minimum amount of
paperwork. Another popular data sharing
standard is XML, briefly described earlier in this chapter. Using XML, Web
programmers can create one version of a Web page that then can be displayed in
a form appropriate for a variety of display devices. XML also is used in RSS,
which is used to distribute content, such as news, to subscribers.
• Sharing software — Users connected to a network have
access to software on the net- work. To support multiple users’ access of
software, most vendors sell network versions or site licenses of their
software, which usually cost less than buying individual copies of the software
for each computer. A network license is a legal agreement that allows multiple
users to access the software on a server simultaneously. The network license
fee usually is based on the number of users or the number of computers attached
to the network. A site license is a legal agreement that permits users to
install the software on multiple computers — usually at a volume discount.
• Transferring funds — Called electronic funds transfer (EFT),
it allows users connected to a network to transfer money from one bank account
to another via transmission media. Both businesses and consumers use EFT.
Consumers use an ATM to access their bank account. Businesses deposit payroll
checks directly in employees’ bank accounts. Consumers use credit cards to make
purchases from a retail Web site. Businesses use EFT to purchase and pay for
goods purchased from vendors. Both businesses and consumers pay bills online,
with which they instruct a bank to use EFT to pay creditors.
LANs, MANs, and WANs
Networks usually are classified as a local area network,
metropolitan area network, or wide area network.
LAN
A local area network (LAN) is a network that connects
computers and devices in a limited geographical area such as a home, school
computer laboratory, office building, or closely positioned group of buildings.
Each computer or device on the network, called a node, often shares resources
such as printers, large hard disks, and programs. Often, the nodes are
connected via cables.
A wireless LAN (WLAN) is a LAN that uses no physical wires.
Computers and devices that access a wireless LAN must have built-in wireless
capability or the appropriate wire- less network card, USB network adapter,
ExpressCard module, PC Card, or flash card. Very often, a WLAN communicates
with a wired LAN for access to its resources, such as software, hardware, and
the Internet
MAN
A metropolitan area network (MAN) is a high-speed network
that connects local area networks in a metropolitan area such as a city or town
and handles the bulk of communications activity across that region. A MAN typically
includes one or more LANs, but covers a smaller geographic area than a WAN. A
MAN usually is managed by a consortium of users or by a single network provider
that sells the service to the users. Local and state governments, for example,
regulate some MANs. Telephone companies, cable television operators, and other
organizations provide users with connections to the MAN.
WAN
A wide area network (WAN) is a network that covers a large
geographic area (such as a city, country, or the world) using a communications
channel that combines many types of media such as telephone lines, cables, and
radio waves. A WAN can be one large network or can consist of two or more LANs
connected together. The Internet is the world’s largest WAN.
4. How Are a Client/Server and Peer-to-Peer Networks
Different, and How Does a P2P Network Work?
Client/Server
On a client/server network, one or more computers act as a
server, and the other computers on the network request services from the
server. A server, sometimes called a host computer, controls access to the
hardware, software, and other resources on the network and provides a
centralized storage area for programs, data, and information. The clients are
other computers and mobile devices on the network that rely on the server for
its resources.
Some servers, called dedicated servers, per- form a specific
task and can be placed with other dedicated servers to perform multiple task. For
example, a file server stores and manages files. A print server manages printers
and documents being printed. A database server stores and provides access to a database.
A network server manages network traffic (activity). A Web server is a computer
that delivers requested Web pages to your computer. Although it can connect a
smaller number of computers, a client/server network typically pro- vides an
efficient means to connect 10 or more computers. Most client/server networks
require a person to serve as a network administrator because of the large size
of the network.
Peer-to-Peer
One type of peer-to-peer network is a simple, inexpensive
network that typically connects fewer than 10 computers. Each computer, called
a peer, has equal responsibilities and capabilities, sharing hardware (such as
a printer), data, or information with other computers on the peer-to-peer
network. Each computer stores files on its own storage devices. Thus, each
computer on the network contains both the server operating system and
application software. All computers on the network share any peripheral
device(s) attached to any computer.
Another type of peer-to-peer, called P2P, describes an
Internet network on which users access each other’s hard disks and exchange files
directly over the Internet. This type of peer-to- peer network sometimes is
called a file sharing network because users with compatible software and an
Internet connection copy files from someone else’s hard disk to their hard
disks. As more users connect to the network, each user has access to shared
files on other users’ hard disks. When users log off the network, others no
longer have access to their hard disks. To maintain an acceptable speed for
communications, some implementations of P2P limit the number of users.
5. How Are a Star Network, Bus Network, and Ring Network
Different?
A network topology refers to the layout of the computers and
devices in a communications network. Three commonly used network topologies are
star, bus, and ring.
Star Network
On a star network, all of the computers and devices (nodes)
on the network connect to a central device, thus forming a star. Two types of
devices that provide a common central connection point for nodes on the network
are a hub and a switch. All data that transfers from one node to another passes
through the hub or switch. Star networks are fairly easy to install and
maintain. Nodes can be added to and removed from the network with little or no
disruption to the network. On a star network, if one node fails, only that node
is affected. The other nodes continue to operate normally. If the hub or switch
fails, however, the entire network is inoperable until the device is repaired.
Most large star networks, therefore, keep backup hubs or switches available in
case the primary one fails.
Bus Network
A bus network consists of a single central cable, to which
all computers and other devices connect. The bus is the physical cable that
connects the computers and other devices. The bus in a bus network transmits
data, instructions, and information in both directions. When a sending device transmits
data, the address of the receiving device is included with the transmission so
that the data is routed to the appropriate receiving device. Bus networks are
popular on LANs because they are inexpensive and easy to install. One advantage
of the bus network is that computers and other devices can be attached and
detached at any point on the bus without disturbing the rest of the network.
Another advantage is that failure of one device usually does not affect the
rest of the bus network. The greatest risk to a bus network is that the bus
itself might become inoperable. If that happens, the net- work remains
inoperative until the bus is back in working order.
Ring Network
On a ring network, a cable forms a closed loop (ring) with
all computers and devices arranged along the ring. Data transmitted on a ring network
travels from device to device around the entire ring, in one direction. When a
computer or device sends data, the data travels to each computer on the ring
until it reaches its destination. If a computer or device on a ring network fails,
the entire network potentially could stop functioning. A ring network can span
a larger distance than a bus network, but it is more difficult to install. The
ring topology primarily is used for LANs, but also is used in WANs.
6. What Are Various Network Communications Standards?
A network standard defines guidelines that specify the way
computers access a medium, the type(s) of medium, the speeds on different types
of networks, and the type of physical cable or wireless technology used.
Network communications standards include the following. Ethernet specifies that
no central computer or device on the network should control when data can be
transmitted. Token ring requires devices to share or pass a special signal,
called a token. TCP/IP divides data into packets. Wi-Fi identifies any network
based on the 802.11 standards for wireless communications. Bluetooth uses short-range radio waves to
transmit data. UWB specifies how two UWB devices use short-range radio waves to
communicate at high speeds. IrDA transmits data wirelessly via infrared light
waves. RFID uses radio signals for communications. WiMAX is a network standard
developed by IEEE that specifies how wireless devices communicate over the air
in a wide area. The Wireless Application Protocol (WAP) specifies how some
mobile devices can display Internet content.
7. What Is the Purpose of Communications Software?
Communications software consists of programs that :
(1) help users establish a connection to another computer or
network;
(2) manage the transmission of data, instructions, and
information;
and (3) provide an interface for users to communicate with
one another.
8. What Are Various Types of Lines for Communications over
the Telephone Network?
The public switched telephone network (PSTN) is the
worldwide telephone system that handles voice-oriented telephone calls.
Dial-Up Lines
A dial-up line is a temporary connection that uses one or
more analog telephone lines for communications. A dial-up connection is not
permanent. Using a dial-up line to connect computers costs no more than making
a regular telephone call.
Dedicated Lines
A dedicated line is a type of always-on connection that is
established between two communications devices (unlike a dial-up line where the
connection is reestablished each time it is used). The quality and consistency
of the connection on a dedicated line are better than a dial-up line because
dedicated lines provide a constant connection. Businesses often use dedicated
lines to connect geographically distant offices. Dedicated lines can be either
analog or digital. Digital lines increasingly are connecting home and business
users to networks around the globe because they transmit data and information
at faster rates than analog lines. Five types of digital dedicated lines are
ISDN lines, DSL, FTTP, T-carrier lines, and ATM. Although cable television
(CATV) lines and fixed wireless are not a type of telephone line, they are very
popular ways for the home user to connect to the Internet. Fixed wireless
Internet connections use an antenna on your house or business to communicate
with a tower location via radio signals. Later sections in this chapter discuss
the use of CATV lines and radio signals to connect to the Internet.
ISDN Lines
For the small business and home user, an ISDN line provides
faster transfer rates than dial-up telephone lines. Not as widely used today as
in the past, ISDN (Integrated Services Digital Network) is a set of standards for
digital transmission of data over standard copper telephone lines. With ISDN,
the same telephone line that could carry only one computer signal now can carry
three or more signals at once through the same line, using a technique called
multiplexing.
DSL
DSL is a popular digital line alternative for the small
business or home user. DSL (Digital Subscriber Line) transmits at fast speeds
on existing standard copper telephone wiring. Some DSL installations include a
dial tone, providing users with both voice and data communications. These DSL
installations often require that filters be installed to reduce noise
interference when voice communications share the same line. ADSL is one of the
more popular types of DSLs. As shown in Figure 9-25, ADSL (asymmetric digital
subscriber line) is a type of DSL that supports faster transfer rates when
receiving data (the downstream rate) than when sending data (the upstream
rate). ADSL is ideal for Internet access because most users download more information
from the Internet than they upload.
FTTP
FTTP, which stands for Fiber to the Premises, uses
fiber-optic cable to provide extremely high-speed Internet access to a user’s
physical permanent location. Two specific types of FTTP are FTTH and FTTB. FTTH
(Fiber to the Home) provides home users with Internet access via fiber-optic
cable. Similarly, FTTB (Fiber to the Building) refers to small businesses that
use fiber-optic cables to access the Internet. With FTTP service, an optical
terminal at your location receives the signals and transfers them to a router
connected to your computer. As the cost of installing fiber decreases, more
homes and businesses will opt for this
high-speed Internet access.
T-Carrier Lines
A T-carrier line is any of several types of long-distance
digital telephone lines that carry multiple signals over a single communications
line. Whereas a standard dial-up telephone line carries only one signal,
digital T-carrier lines use multiplexing so that multiple signals share the
line. T-carrier lines provide very fast data transfer rates. Only medium to
large companies usually can afford the investment in T-carrier lines because
these lines are so expensive.
ATM
ATM (Asynchronous Transfer Mode) is a service that carries
voice, data, video, and multimedia at very high speeds. Telephone net- works,
the Internet, and other networks with large amounts of traffic use ATM. Some
experts predict that ATM eventually will become the Internet standard for data
transmission, replacing T3 lines.
9. What Are Commonly Used Communications Devices?
A communications device is hardware capable of transmitting
data between a sending device and a receiving device. A dial-up modem converts
digital signals to analog signals and analog signals to digital signals so that
data can travel along analog telephone lines. A digital modem sends and
receives data and information to and from a digital line. An ISDN modem
transmits digital data to and from an ISDN line, while a DSL modem transmits
digital data to and from a DSL line. A cable modem, sometimes called a
broadband modem, is a digital modem that sends and receives digital data over
the cable television network. A wireless modem uses the cell phone network to
connect to the Internet wirelessly from mobile computers and devices. A network
card enables a computer or device that does not have built-in networking
capability to access a network. A wireless access point allows computers and
devices to transfer data wirelessly. A router connects multiple computers or
other routers together and transmits data to its correct destination on the
network. A hub or switch is a device that provides a central point for cables
in a network.
10. How Can a Home Network Be Set Up?
Many home users are connecting multiple computers and
devices together in a home network. Home
networking saves the home user money and provides many conveniences. Each
networked computer in the house has the following capabilities:
• Connect to the Internet at the same time
• Share a single high-speed Internet connection
• Access files and programs on the other computers in the
house
• Share peripherals
such as a printer, scanner, external hard disk, or optical disc drive
• Play multiplayer games with players on other computers in
the house
• Connect game consoles to the Internet
• Subscribe to and use VoIP
Many vendors offer home networking packages that include all
the necessary hardware and software to network your home using wired or
wireless techniques. Some of these packages also offer intelligent networking
capabilities. An intelligent home network extends the basic home network to
include features such as lighting control, thermostat adjustment, and a
security system. You no longer need extensive knowledge of networks to set up a
home network. For example, the latest version of Windows allows you to connect
all computers in your house to a home network easily.
Wired Home Networks
As with other networks, a home network can use wires, be
wireless, or use a combination of wired and wireless. Three types of wired home
networks are Ethernet, powerline cable, and phoneline.
Ethernet Network
As discussed earlier in this chapter, traditional Ethernet
networks require that each computer have built-in network capabilities or
contain a network card, which connects to a central network hub or similar
device with a physical cable. This may involve running cable through walls,
ceilings, and floors in the house. For the average home user, the hardware and
software of an Ethernet network can be difficult to configure.
Powerline Cable
Network
A home powerline cable network is a network that uses the
same lines that bring electricity into the house. This network requires no
additional wiring. One end of a cable plugs in the computer’s USB port and the
other end of the cable plugs in a wall outlet. The data transmits through the
existing power lines in the house.
Phoneline Network
A phoneline network is an easy-to-install and inexpensive
network that uses existing telephone lines in the home. With this network, one
end of a cable connects to an adapter card or PC Card in the computer and the
other end plugs in a wall telephone jack. The phoneline network does not
interfere with voice and data transmissions on the telephone lines. That is,
you can talk on the telephone and use the same line to connect to the Internet.
Wireless Home
Networks
To network computers and devices that span multiple rooms or
floors in a home, it may be more convenient to use a wireless strategy. One
advantage of wireless networks is that you can take a mobile computer outside,
for example in the backyard, and connect to the Internet through the home
network, as long as you are in the network’s range. Most home networks use a
Wi-Fi network, which sends signals through the air at distances of up to 1,500
feet in some configurations. Wi-Fi networks are fairly easy to configure. Each
computer accessing the network must have the appropriate built-in wireless networking
capabilities (such as Intel’s Centrino technology) or a wireless network card,
which communicates either with a wireless access point or a combination
router/wireless access point. Even in a wireless home network, one desktop
computer usually connects to the router/wireless access point using a cable.
Wireless networks do have the disadvantage of interference. Walls, ceilings,
and electrical devices such as cordless telephones and microwave ovens can
disrupt wireless network communications.
11. What Are Various Physical and Wireless Transmission
Media?
Transmission media consist of materials or substances
capable of carrying one or more signals. Physical transmission media use
tangible materials to send communications signals. Twisted-pair cable consists
of one or more twisted-pair wires bundled together. Coaxial cable consists of a
single copper wire surrounded by at least three layers: an insulating material,
a woven or braided metal, and a plastic outer coating. Fiber-optic cable consists
of thin strands of glass or plastic that use light to transmit signals.
Wireless transmission media send communications signals through the air or
space. Infrared (IR) sends signals using infrared light waves. Broadcast radio
distributes radio signals through the air over long and short distances.
Cellular radio is a form of broadcast radio that is used widely for mobile communications.
Microwaves are radio waves that provide a high-speed signal transmission. A
communications satellite is a space station that receives microwave signals
from an earth-based station, amplifies the signals, and broadcasts the signals
back over a wide area.
