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Lesson 7 – Introduction to PC
Networking & Types of Networks
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Introduction to PC Networking
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Defining a Computer Network
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A computer network is defined as having two
or more devices (such as workstations,
printers, or servers) that are linked together
for the purpose of sharing information,
resources, or both.
A computer network allows users to
communicate with other users on the same
network by transmitting data on the cables
used to connect them.
Network links are made using copper cables,
fiber-optic cables or wireless connections.
Wireless connections use radio signals,
infrared technology, or satellite
transmissions.
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Defining a Computer Network
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A network consists of many
overlapping systems, such as cabling,
addressing schemes, or applications.
The layers work together to transmit
and receive data.
The Open Systems Interconnection
(OSI) model divides the functions of
the network into seven layers.
Viewing the layers from top to
bottom, it presents a service model.
At each layer, the function provided
depends on the services of the layer
below it.
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File, Print, and Application Services
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Computer networks offer file and print
services.
In networks, different computers take on
specialized roles or functions.
Once connected, one or more computers
in the network can function as network
file servers.
The server is a repository for files that
can be accessed and shared across the
network by many users.
Network file services enable
collaboration in the development of
documents and projects
Network print services can make a highspeed printer accessible to many users.
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File, Print, and Application Services
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All network operating systems offer file
and print services.
Sharing information, collaborating on
projects, and providing access to input
and output devices are common services
of computer networks.
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Mail Services
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E-mail services work like the postal system,
with one computer taking on the function of
post office.
The user e-mail account operates like a post
office box, where mail is held for the user
until it is picked up over the network by an email client program running in the user
system.
The e-mail is sent from the client computer to
the server, which acts as the post office. The
server holds the e-mail until the destination
client retrieves it.
An e-mail address consists of two parts. The
first part is the recipient name and the second
part is the domain name.
In addition to e-mail, instant messaging
services allow network users to chat without
delay (ICQ, AOL Instant Messaging)
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Directory and Name Services
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To enable users and systems on the
network to find the services they require,
computer networks make use of
directories and name services.
The network assigns a name to users,
services, and devices so that they can be
identified and accessed.
Knowing the name of a service on the
network enables users to contact that
service without having to know its
physical location.
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Directory and Name Services
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Directory and name services make a
network easier to use.
After the initial setup of the directory or
name service, this translation takes place
transparently.
In addition to their ease of use, they also
make the network more flexible.
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The Internet
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The Internet is a worldwide public
network of networks, interconnecting
thousands of smaller networks to form
one large “web” of communication.
The Internet functions like a highway
to facilitate exchange between
geographically separated users,
organizations, and branches of
companies.
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The Internet
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The phrase “information superhighway”
describes the benefit of the Internet to
business and private communication.
The Internet breaks down barriers of
time and space, enabling the sharing of
information around the globe almost
instantaneously.
Many private networks, some with
thousands of users of their own, connect
to the Internet by using the services of
Internet Service Providers (ISPs).
These linkages enable long distance
access to network services for
information and device sharing.
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Network Administration
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The ongoing task of network administration is to maintain and adapt the
network to changing conditions.
Network administrator responsibilities include:
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Setting up new user accounts and services
Monitoring network performance
Repairing network failures
Enforcing Security
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Simplex, Half-Duplex,
and Full-Duplex Transmission
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Simplex transmission is a single oneway baseband transmission.
It is also called unidirectional because
the signal travels in only one
direction.
An example of simplex transmission
is the signal sent from the cable TV
station to the home television.
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Simplex, Half-Duplex,
and Full-Duplex Transmission
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This means that only one side can
transmit at a time.
Two-way radios, such as Citizens Band
(CB) and police/emergency
communications mobile radios, work
with half-duplex transmissions.
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Simplex, Half-Duplex,
and Full-Duplex Transmission
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Traffic can travel in both directions at the
same time.
A regular telephone conversation is an
example of full-duplex communication.
Both parties can talk at the same time,
and the person talking on the other end
can still be heard by the other party while
they are talking.
Digital subscriber line (DSL), two-way
cable modem, and other broadband
technologies operate in full-duplex mode.
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Types of Networks
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Overview
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By using local-area network (LAN) and wide-area network (WAN)
technologies, many computers are interconnected to provide services to
their users.
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In providing services, networked computers take on different roles or
functions in relation to each other.
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Some types of applications require computers to function as equal partners.
Other types of applications distribute work so that one computer functions
to serve a number of others in an unequal relationship.
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Peer-to-Peer Networks
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In a peer-to-peer network, the networked
computers act as equal partners, or peers,
to each other.
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As peers, each computer can take on the
client function or the server function
alternately.
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There is no central point of control or
administration in the network. Individual
users must back up their own systems to
be able to recover from data loss in case
of failures.
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Client/Server Networks
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In a client/server network arrangement,
network services are located in a dedicated
computer whose only function is to respond
to the requests of clients.
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The server contains the file, print,
application, security, and other services in a
central computer that is continuously
available to respond to client requests.
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For better control, the client must identify
itself and be authorized (username and
password) to use the server resources.
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Local-Area Networks (LANs)
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A local-area network (LAN) can connect
many computers in a relatively small
geographical area such as a home, an
office, or a campus.
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It allows users to access high bandwidth
media like the Internet and allows users
to share devices such as printers.
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Local-Area Networks (LANs)
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The general shape or layout of a LAN is called
its topology.
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Topology defines the structure of the network.
This includes the physical topology which is
the actual layout of the wire or media, and the
logical topology which is how the media is
accessed by the hosts.
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The communications channel that they all
share is called the medium, and it is typically
a cable that carries electrical signals through
copper or fiber.
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On a LAN, the rules for coordinating the use
of the medium are called Media Access
Control (MAC).
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Wide-Area Networks (WANs)
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A WAN, as the name implies, is designed to work
over a larger area than a LAN.
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A WAN uses point-to-point or point to multipoint,
serial communications lines.
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Point-to-point lines connect only two locations, one
on each side of the line. Point-to-multipoint lines
connect one location on one side of the line to
multiple locations on the other side.
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They are called serial lines because the bits of
information are transmitted one after another in a
series.
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Connections across WAN lines may be temporary or
permanent.
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Wide-Area Networks (WANs)
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Modems
Integrated Services Digital Network (ISDN)
Digital subscriber line (DSL)
Frame Relay
Asynchronous Transfer Mode (ATM)
The T (US) and E (Europe) Carrier series (T1, E1, T3, E3, and so on)
Synchronous Optical Network (SONET)
• Wide-area connections make use of the communication facilities
that are put in place by utility companies, called common carriers,
such as the telephone company.
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Wide-Area Networks (WANs)
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Connections across WAN lines may be
temporary or permanent.
Telephone or dialup lines, might make a
temporary connection to a remote network
from a computer in a home or small office.
In both temporary and permanent cases,
computers that connect over wide area
circuits must use a modem or channel
service unit/data service unit (CSU/DSU) at
each end of the connection.
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Wide-Area Networks (WANs)
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The public telephone system, sometimes
referred to as plain old telephone service
(POTS), is a circuit-switched
communications network.
When a telephone call is placed in this type
of network, only one physical path is used
between the telephones for the duration of
that call.
This pathway is maintained for the
exclusive use of the call, until the
connection is ended and the telephone is
hung up.
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Wide-Area Networks (WANs)
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In a packet-switched network, each
individual packet of data can take a
different route and no dedicated pathway
or circuit is established.
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