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Lecture 5
Communications and Networks
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Communications
What is computer communications? A process in which one computer transfers data,
instructions, and information to another computer(s)
a
ad
c
b
e
a
a
f
c
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Uses of Communications Technologies Voice mail
Fax E-mail Chatroom Instant Message FTP
Newsgroup Telephony Videoconference Groupware Global Positioning
System (GPS)
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share software
share hardware
Networks
What is a network? A collection of
computers and devices connected by communications channels
Facilitates communications among users
Allows users to share resources
facilitate communications
share data and information
Networks
What is a local area network (LAN)?
Network that connects computers and devices in a limited geographical area.
Often uses Ethernet protocol
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Networks
What is a node ? Each computer or device on a network
often the nodes are connected to the LAN via cables
a wireless LAN (WLAN) is a LAN
that uses no physical wires
node
node
node
node
node
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Administration
Adding, deleting, and organizing users and performing maintenance tasks
File management
Locating and transferring files
Networks
What is a network operating system? The system
software that organizes and coordinates the activities on LAN
Also called a network OS or NOS Printer management
Prioritizing print jobs and reports sent to specific printers on the network
Security
Monitoring and, when necessary, restricting access to network resources
Networks
What are servers and clients? Server• Controls access to the
hardware and software on the network
• Provides a centralized storage are for programs
• Dedicated servers perform a specific task
Clients• Other computers on the
network• Rely on the server for
resources
database server stores and provides access to a database
network servermanages network traffic
print server manages printers and print jobs
file server stores and manages files
Networks
What is an Internet use of peer-to-peer (P2P)?
An Internet network that enables users with the same networking software to connect to each other’s hard disks and exchange files directly
Napster and Gnutella are two examples of P2P
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Networks
What is a network topology? The configuration, or physical arrangement, of the
devices in a communications network Networks usually use combinations of three topologies
ring
star
bus
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Networks
What is a bus network? Consists of a single
central cable, to which all computers and other devices connect
The bus is the physical cable
The bus is also called the backbone
Inexpensive and easy to install
personal computer
personal computer
personal computer
personal computer
personal computer
Networks
What is a ring network? A cable forms a
closed ring, or loop, with all computers and devices arranged along the ring
Data travels from device to device around the entire ring
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Networks
What is a star network? All of the devices
connect to a central computer/hub
All data that transfers from one computer to another passes through the hub
host computer
printerfile server
personal computer
personal computer
personal computer
personal computer
Networks
uses TCP/IP technologies
has a Web server
supports multimedia Web pages coded in
HTML
accessible via a Web browser
users can post and update information on the intranet by creating and posting a
Web page
An internal network that uses Internet technologies
Generally make company information accessible to employees and facilitate working in groups
Typically also includes a connection to the Internet
What is an intranet?
Networks
What is an extranet? Allows customers
or suppliers to access part of a company’s intranet
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Networks
What is a firewall? Hardware and/or software that restricts access to data
and information on a network
personal computer
personal computer
personal computer
personal computer
personal computer
personal computer
personal computer
printer
firewall
corporate network Internet
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Networks
What is a home network? Multiple computers connected together
in a home or home office All computers in the
house can• connect to the
Internet at the same time
• Access files and programs on the other computers in the home
• Share peripherals
Networks
What is an intelligent home network? Extends the
basic home network to include features such as lighting control, thermostat adjustment, and a security system
Communications Software
What is communications software? Consists of programs that help you establish a
connection to another computer or network Manages the transmission of
data, instructions, and information
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The Telephone Network
What is a dial-up line? A temporary connection that uses one or more analog
telephone lines for communications A modem at the sending end dials the telephone
number of a modem at the receiving end
Advantages
Costs no more than making a regular call
Computers at any two locations can establish a
connection using modems and the
telephone network
Disadvantage
Cannot control the quality of the connection because the
telephone company’s switching office randomly
selects the line
The Telephone Network
What is a dedicated line? A connection that always is
established between two communications devices
The quality and consistency of the connection is better because dedicated lines provide a consistent connection
Can be analog or digital
Digital lines transfer data and information at faster rates than
analog lineswww.shahidrasul.com
bits per second (bps)
The Telephone Network
What is transfer rate? The speed with which a line carries data and information The faster the transfer rate the faster you can send and
receive data and information Usually are expressed as bits per second (bps)
kilobits per second (Kbps)
megabits per second (Mbps)
gigabits per second (Gbps)www.shahidrasul.com
The Telephone Network
What are popular types of digital dedicated lines? ISDN DSL T-carrier CATV ATM
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Communications Devices
What is a communications device? Any type of hardware capable of transmitting data,
instructions, and information between a sending device and a receiving device
Sometimes the device must convert the data, instructions, and information from analog to digital signals or vice versa
dial-up modems
ISDN and DSL modems
cable modems
network interface cards
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Communications Devices
What is a modem? A communications device that converts a computer's
digital signals to analog signals before they are transmitted over standard telephone lines
Sometimes called a dial-up modem
modulateTo change into
an analog signal
demodulateTo convert an
analog signal into a digital signal
mo + dem
DSL modem
Sends and receives digital data to a DSL line
Communications Devices
What is a digital modem? One that sends and receives data and information to
and from a digital telephone line such as ISDN or DSL
ISDN modem
Also called an ISDN adapter
Sends and receives digital data to an ISDN line
Communications Devices
What is a cable modem? A modem that sends and receives data over the cable
television (CATV) network Currently much
faster than a dial-up modem or ISDN
Usually attaches to a USB port or a port on a network interface card
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Communications Devices
What is a network interface card (NIC)? A card you insert into
an expansion slot of a personal computer or other device, enabling the device to connect to a network
NIC for desktop computer
NIC for notebook computer
Communications Channel
What is a BUS? The communications path between two devices
twisted pair cable
twisted pair cable twisted pair wire
Physical Transmission Media
What is twisted-pair cable? Consists of one or more twisted pair wires bundled together Each twisted pair
wire consists of two separate insulated copper wires
Twisted together to reduce noise
Noise is an electrical disturbance that can degrade communications
coaxial cable
plastic outer coating
woven or braided wire
insulating material
copper wire
Physical Transmission Media
What is coaxial cable? Consists of a single copper wire surrounded by at least
three layers Often called
coax Often used
for cable television wiring
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fiber-optic cable between floors of a building
cable contains many optical fibers
outer covering jacket
Physical Transmission Media
What is fiber-optic cable? Contains a core of dozens or hundreds of thin strands of
glass or plastic Uses light to transmit signals Each strand
is called an optical fiber
• Thin as a human hair
protective coating
glass cladding
optical fiber core
transmitter
sends the broadcast radio
signal
Wireless Transmission Media
What is broadcast radio? A wireless transmission medium that distributes
radio signals through the air over long distances such as between cities, regions, and countries and short distances such as within an office or home
Slower and more susceptible to noise than physical transmission media
receiver
accepts the broadcast radio signal
must have an antenna that is located in the range of
the signal
transceiver
both sends and receives signals from wireless
deviceswww.shahidrasul.com
Wireless Transmission Media
What is cellular radio? A form of broadcast radio that is used widely for mobile
communications, specifically wireless modems and cellular telephones
A cellular telephoneis a telephone device that uses radio signals to transmit voice and digital data messages
mobile telephone switching office
(MTSO)
cell
cell
cell
cell
calling party in auto
called party
public switched telephone network
base station (microwave
station)www.shahidrasul.com
Wireless Transmission Media
What is a microwave station? An earth-based
reflective dish that contains the equipment necessary for microwave communications
Microwaves are extremely high-speed signals
Line-of-sight towers• Must transmit in a
straight line
Wireless Transmission Media
What is a communications satellite? A space station that receives
microwave signals from an earth-based station, amplifies the signals, and broadcasts the signals back over a wide area to any number of earth-based stations
Transmission to a satellite is an uplink
Transmission from a satellite to an earth-based station is a downlink
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Wireless Transmission Media
What is infrared (IR)? A wireless transmission
media that sends signals using infrared light waves
Requires a line-of-sight transmission
Many computers and devices have an IrDA port that enables the transfer of data using infrared light rays
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