Transcript Communications and Networking, Chapter 9

Communications and
Networks
Chapter 9
ITSC 1401, Intro to Computers
Instructor: Glenda H. Easter
Communications
and Networking
Define the components required
for successful communications
Describe uses of communications
Identify the various types of
transmission media
Explain the purpose of
communications software
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Communications
and Networking
Describe commonly used
communications devices
Explain the difference between a local
area network and a wide area network
Understand the various communications
protocols
Identify uses of intranets and extranets
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Connectivity
Connectivity is the ability for two or more
computers to exchange information, share
data and resources.
Connectivity can be achieved in two ways:
Telecommunications (computers and
telephones)
Direct Access (computers and networks)
A communication channel is
another word for telecommunications.
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Connectivity
In order for connectivity to occur, you
need either
a modem (Modulator/Demodulator) or
a network card
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Communications
What is needed for communications?
Sending device
Conversion from data into signals
Communications channel
Conversion from signals to data
Receiving device
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Uses of Communications
 E-mail
 Voice mail
 Fax
 Telecommuting
 Videoconferencing
 Groupware
 Instant Messaging
 Smartphones
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How Computer Communications
Work (Continued)
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Uses of Communications
Global Positioning System
Bulletin Board System
The Internet
The Web
E-commerce
Telephony
Structure of the Internet Animation
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Hardware
Channels-Wired Transmission
Media
Twisted-Pair Cable
Coaxial Cable
Fiber-optic Cable
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Communications
Channels
 Twisted pair - telephone wire
 Coaxial cable - used by cable television
companies
 Fiber optic cable - thin wires of glass fiber
 Infrared transmission - a beam of infrared
light
 Microwave transmission - Radio signals
beamed between earth stations
 Satellite transmission - Radio signals beamed
between satellites and earth stations
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Physical Transmission Media
Twisted-pair cable
Hundreds of wires connected together like those used
for telephone lines.
Can often use a building’s existing unused telephone
wiring.
This usage avoids having wiring strung over ceiling
tiles (which may violate fire code and result in
interference from fluorescent light fixtures).
Most buildings are wired with two (2) or three (3) pairs
of wire to each wall outlet.
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Twisted Pair Cable
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Physical Transmission Media
Coaxial cable (coax)
High-frequency line that has a solid cooper
core
Cable TV
Not as susceptible to noise
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Physical Transmission Media
(Continued)
Coaxial cable has the disadvantage that to
add or remove a node, cables may have to
be disconnected and reattached.
Special “T” connectors have to be placed
along the cable for stations to connect to, and
the ends of the cable need to have end-cap
connectors called terminators.
Coaxial cable is used for Ethernet networks.
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Coaxial Cable (Coax)
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Physical Transmission Media
Fiber-optic cable
Transfers data as pulses of light through tubes of
glass. This is what is used for cellular telephones and
microwave transmissions.
Carries many signals
High speed
Less susceptible to noise
Better security
Smaller size
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Physical Transmission Media
Fiber Optic Cable (Continued):
Installation requires special training because
the cable cannot be simply cut or soldered as
electrical wiring can.
Network interface cards are specific to the
computer in which they are installed and to the
type of network to which they are connecting.
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Fiber-Optic Cable
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Hardware
Channels-Wireless Transmission
Modes
Cellular Telephone
Microwave Transmission
Satellite Transmission
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Communication Links
(Continued)
Microwave
Microwaves are high-frequency radio waves that travel
in straight lines through the air.
These can only be transmitted over short distances.
Satellites
Used as microwave relay stations.
Orbit about 22,000 miles above the earth.
Can be used to send large volumes of data.
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Wireless Transmission Media
Broadcast Radio
Long distance
Station frequencies assigned by FCC
• AM
• FM
Slow
Susceptible to noise
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Wireless Transmission Media
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Wireless Transmission Media
Cellular Radio
Cellular telephone
Cells
Mobile telephone switching office (MTSO)
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Wireless Transmission Media
Microwaves
High-speed
Microwave stations
Line-of-sight transmission
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Wireless Transmission Media
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Wireless Transmission Media
Communications Satellite
Space station receives signals and re-transmits
the signals
• Uplink
• Downlink
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Wireless Transmission Media
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Communications Satellite
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Transmissions Characteristics
Signal Type: Analog or Digital
Analog signals are continuous wave
Digital signals are electrical pulses
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Transmissions Modes
Transmission Modes: Asynchronous and
Synchronous
Asynchronous - irregular intervals
Synchronous - regular intervals
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Transmission Modes
Asynchronous is the most common and is
the transmission mode used by personal
computers.
It is slower because data is sent and
received one byte at a time.
With Asynchronous transmission the
following example would be applicable:
Computer A -- Start Bit -- Stop Bit -- Computer B
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Transmission Modes
(Continued)
Synchronous allows several bytes or
blocks of information to be sent within
timed intervals. Data is flowing in both
directions at the same time.
Computer A Computer B
Computer A     Computer B
This is usually the transmission mode used
by mainframes.
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Transmissions Directions
There are three directions or modes of data
flow in a data communications system:
Transmission Direction: Simplex, HalfDuplex, and Full-Duplex
Simplex - one direction only
Half-duplex - either direction, but only one
direction at a time
Full-duplex - both directions at the same time
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Transmission Direction: Simplex,
Half-Duplex, and Full-Duplex
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Simplex Data Flow
Data travels in only one direction.
It is not frequently used in data
communication systems today.

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Half Duplex
Data travels in both directions, but not
simultaneously.
It is frequently used for linking
microcomputers by telephone lines to
other microcomputers, minicomputers,
and mainframes.


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Full-Duplex
Data is transmitted back and forth at the
same time.
It is the fastest and most efficient form of
two-way communication.
It requires special equipment and is used
primarily for mainframe communications.


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Transmission rates
Bandwidth
 The capacity of a
particular medium to
carry information
 Twisted-pair has the
lowest bandwidth
 Aside from microwave and
satellite, fiber optic has the
highest
Bandwidth
Bandwidth is the bits per second transmission
capability of a channel.
It is written as bps (Bits per Second)
There are three types of bandwidth:
Voiceband - Used for microcomputer transmission.
Medium Band used mainly with minicomputers and
mainframes.
Broadband used for very high speed computers
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The Telephone Network
Public switched telephone network (PSTN)
Plain old telephone service (POTS)
Uses variety of media
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The PSTN in Perspective
Sender of call
receiver of call
As a caller moves from one area to another, a new cell site steps in to keep
the signal strong. The sites are connected to a Mobile Telephone Switching
Office (MTSO), which is connected to the standard PSTN telephone system.
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The Telephone Network
Dial-Up Lines
Temporary connection
Same cost as regular phone call
Quality cannot be controlled by the user
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Speeds and Costs of Various
Telephone Connections
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The Telephone Network
Dedicated Lines
ISDN lines
Digital subscriber lines
T-carrier lines
Asynchronous transfer mode (ATM)
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Digital Subscriber Line
Super fast speed
Always on access
Simultaneous voice call and Internet access
Dedicated connection
Bandwidth doesn’t have to be shared; thereby, speeding
up the process.
Hook up DSL to TV or run full-length movies
over computer. Will be able to download video to
hard drive.
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Example of Communications’
Channel
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Software
Communications Software
0
1
0
1
1
1
0
0
0
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Communications Software
Dialing
File transfer
Terminal emulation
Internet access
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Communications Software
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Communication
Devices
Modems Internal/External/Fax/
Modems
Analog Signals
Digital Signals
Demodulation
•
from analog to digital
Modulation
•
from digital to analog
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Modem Types and General
Information
Modems were developed to share and process
data.
External Modems connect with a serial port.
Internal Modems consists of a plug-in circuit
board inside the system unit.
Wireless Modems are similar to the external
modem that connects to the computer’s serial
port. These receive data through the air.
Modems allow dial-up access.
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Wide Area Networks (WAN)
Wide Area Networks (WAN)
Network covers a large geographical area
Usually consists of two or more LANs
connected by a router
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Wide Area Networks (WAN)
A type of private
network
Uses all types of
media to connect
Can cross great
distances
Wide Area Networks (WANs)
WANs connect computers over long
distances.
They have the widest scope of connectivity.
WANs use microwave relays and satellites as a
medium of transmission.
The most widely used WAN is the
Internet.
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Wide Area Network (WAN)
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Metropolitan Area Network
(MAN)
Metropolitan Area Network (MAN)
A backbone network that connects local area
networks in a metropolitan area
Typically includes one or more LANs, but in a
smaller area than a WAN
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Network Architecture
A computer network is a communications
system connecting two or more computers that
work together
to exchange information
to share resources
Communications channels can be connected in
different arrangements, or networks. The way
networks are arranged and how their
resources are shared is referred to as a
network architecture.
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Local Area
Networks
Star Topology
 Bus Topology
 Ring Topology
Topology
• The physical layout of the cables
that connect the nodes of the
network.
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Star Topology
• Places a hub in the center of the network
nodes. Groups of data are routed through
the central hub to their destinations.
• Star: the hub is in the center of the network nodes.
• The entire network goes down
only if the hub is lost.
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Star Topology
(Client/Server Architecture)
In a Star Topology, each point could
represent a computer terminal, and it is
connected at the center by a
A
host computer.
Star provides for time
E
sharing where users
Host
share time on a
central computer.
D
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C
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Star Topology
(Client/Server Architecture)
Uses the polling method of control.
With polling, each device
on the system is
E
given a turn to
Host
send its message.
A
B
D
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Star Topology (Continued)
Each machine is called a client or node.
Your central host connects to the nodes
or machines.
A node is any device that shares
resources on a network.
If the host or server dies, everything
goes down.
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Star Topology
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Ring Topology
• Connects the nodes of the network in a
circular chain in which each node is
connected to the next.
•
If a connection is lost, the entire
network goes down.
•
Ring: each node is chained to
the next.
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Ring Topology
This is the oldest type of
networking system.
Each arrow represents
a computer terminal.
If Computer A tries to
send information to
Computer B, and Computer
B is busy, it will send
the information back to A
until B is no longer busy.
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H
B
G
C
F
D
E
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Ring Topology
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Bus Topology
• A single conduit to which all the network
nodes and peripheral devices are attached.
Bus: a single path connects all devices.
BUS
A broken path can bring down all connected devices.
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Bus Topology
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Bus Topology
This is the type of set-up that exists in the
Computer Lab.
This the most popular type of network.
Each device in the network handles its own
communications control.
There is no host; each node manages part of the
network.
The terminals are connected to a communications
channel.
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Bus Topology
F
D
B
F
P
Printer
A
C
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Protocols
Protocols are sets of communication rules
or standards for the exchange of
information between computer systems.
A communications software package helps
define the protocol, such as speed and
modes for connecting with another
microcomputer.
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Communications Protocols
Ethernet
Developed by Xerox in 1976
Most popular LAN protocol
Carrier Sense Multiple Access/Collision
Detection (CSMA/CD)
Fast Ethernet
Gigabit Ethernet
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Communications Protocols
Token ring
Second most popular protocol for LANs
Based on ring topology
4 Mbps or 16 Mbps
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Communications Protocols
TCP/IP
Transmission control protocol/Internet protocol
Data divided into small pieces called packets
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Transmission Control
Protocol/Internet Protocol (TCP/IP)
TCP/IP is the software of networks.
It sets up a common set of rules for computers
to exchange information.
IP (Internet Protocol) is the numerical address
each machine gets when it logs into a network.
The Internet is the largest packet switching
network on earth. This started to occur when
telephones became widespread.
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Enterprise Intranet
An Internet within the
enterprise
Secure server
For employee use or
by permission only
Corporate gateway to
the Internet
Intranets
Internal networks in an organization that use
Internet and Web technologies
Enterprise network
Uses TCP/IP
Supports Web pages
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Intranets
This is the newest type of network used
within an organization to connect
computers and networks within an
organization by using hardware and
software that is used on the Internet.
There may be times that a company wishes
to share data with clients and to share in
research partnering.
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Network Security
www.mcp.com
Firewalls
Virus
protection
Pretty Good
Privacy (PGP)
for encryption
Firewalls
A firewall looks at updated tables to see
who is authorized to use the information.
A firewall keeps people from intruding on
you network, if they do not have
authorization to do so.
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Firewalls (Continued)
The system may use a multiplexor or a
host, to look at structured information,
such as the IP packet to confirm who you
are.
A firewall looks at updated tables to see
who’s authorized to use the information.
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Intranets and Access Rights
Perhaps, a company will want to share or
transfer certain documents which could be
confidential. Many times, these are files or
documents made available only through
Intranet.
To ensure the safety of those documents, a
company may put up a firewall.
A firewall maintains a list of all the domains
who can access certain resources.
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Firewalls
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Home Networks
Connect multiple computers in a home
Shared Web access
Shared peripherals
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Home Networks
Home Networks
Connect multiple computers in a home
Shared Web access
Shared peripherals
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