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07-May-15
Introduction to Internet
What is Internet?
Internet is a worldwide collection of networks that
connects businesses, government agencies, educational
institutions and more than one billion people who use
the network every day.
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“Online” what is it?
When a computer is connected to a network such as a
LAN, MAN, WAN or to the Internet then it is said to be
“ONLINE”.
Note: A computer can be online without being connected
to the Internet
Server (Host)
- A computer that provides services and connections to
other computers on a network
Web
Function of Web
To create information and make it available for others to
see on the Internet.
Webpage
Webpage is a document on the World Wide Web that can
contain text, graphics, animation, audio and video.
Website
Website is a collection of related Web pages.
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How can Internet use enhance daily life???
Distributed Data Processing
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Network
A NETWORK uses communication equipment to
connect two or more computers and their
resources
Types:
– PC based
– LAN – shares data and resources among users in
close proximity
– WAN – shares data among users who are
geographically distant
Basic Components
• Sending device
• Communications link
• Receiving device
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Data Transmission
• Digital lines
– Sends data as distinct pulses
– Need digital line
• Analog lines
– Sends a continuous electrical signal in the form of
a wave
– Conversion from digital to analog needed
– Telephone lines, coaxial cables, microwave
circuits
Analog Transmission
Alter the carrier wave
• Amplitude – height of the wave is
increased to represent 1
• Frequency – number of times wave
repeats during a specific time
interval can be increased to
represent a 1
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Modem
• MOdulator + DEModulator
• Modulate
– Convert from digital to analog
• Demodulate
– Convert from analog to digital
Modem
Transmission process
• Modulation – Computer
digital signals converted to
analog
• Sent over analog phone line
• Demodulation – Analog signal
converted back to digital
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Types of Modems
• Direct-connect
– External
– Internal
• PCMCIA
– Personal Computer Memory Card International
Association
– Notebook and laptop computers
DSL
Digital Subscriber Line
• Uses conventional telephone lines
• Uses multiple frequencies to simulate many
modems transmitting at once
• No industry standard
– Cost
– Speed
• Phone line shared between computer and voice
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Cable Modem
• Coaxial cables
• Does not interfere with cable TV reception
• Up to 10 million bps
• Always on
• Shared capacity
• Security problem
Bandwidth
Data rate measured in bits (not bytes) per
seconds
– Kbps (Kilobits per seconds)
• 125 chars/sec
– Mbps (Megabits per seconds)
• 1,250 chars/sec
– Gbps (Gigabits per seconds)
• 12,500 chars/sec
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Connecting to the Internet
• Requirement
– A computer or PDA or cell phone
– An account with an ISP (Internet Service Provider)
– A modem (modulator/demodulator) for dial-up
services or a NIC (Network Interface Card) for
DSL/Cable services
Home Network (Single Machine)
Wall Jack
DSL/Cable
Modem
USB/Ethernet
Cable
Laptop
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Home Network (Multiple Machines)
Wall Jack
Hub/Switch/Router
DSL/Cable
Modem
USB/Ethernet
Cable
Laptop
Home Network (Multiple machines)
Wall Jack
Ethernet Cable
DSL/Cable
Modem
Hub/Switch/Router
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Home Wireless Network
Wall Jack
Ethernet Cable
DSL/Cable
Modem
Hub/Switch/Router
Connection Types
•
•
•
•
•
LAN
WLAN
Dial-up Services
Broadband Services
WAN
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LAN (Local Area Network)
• A network of computers that are in the same
physical location, such as home or building
• Usually connected using Ethernet
– A standard on how computers communicate over
a shared media (cable)
Old: BNC connector for coaxial cable
http://en.wikipedia.org/wiki/Image:BNC_connector.jpg
New: RJ45 for twisted pair cable
http://en.wikipedia.org/wiki/Image:Ethernet_RJ45_connector_p1160054.jpg
LAN (Local Area Network)
• Ethernet Standard
– 10BaseT
• 10Mbps (Mega bits per second)
– 100BaseT
• 100Mbps
– 1000BaseT
• 1000Mbps or 1Gbps
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LAN (Local Area Network)
• Question: Can 2 computers communicate by
connecting each other using an Ethernet cable
back-to-back?
WLAN (Wireless LAN)
• Wi-Fi (Wireless Fidelity)
– A wireless technology that connects computers without
cables
• Access Point (AP)
– A device (base station) that connects wireless devices
together
– Usually connected to a wired-network
• ESSID (Extended Service Set ID)
– A “name” for the AP, eg. Mobilenet
• Hotspot
– The area covered by wireless access points
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WLAN (Wireless LAN)
• Standard
– 802.11b - 11Mbps
– 802.11g - 54Mbps
– 802.11a - 54Mbps
2.4G
5G
• Security
– WEP (Wired Equivalen Privacy)
– WPA (Wi-Fi Protected Access)
– To prevent wardriving
Broadband Services
• xDSL (Digital Subscriber Line)
– A technology that provides digital data transmission over
unused frequencies on traditional telephone lines
– For example, ADSL (Asymmetric DSL): DL > UL
– Speed
• Downlink
– 128Kbps - 4Mbps
• Uplink
– 64Kbps - 800Kbps
– Need a DSL modem
– Splitters are needed to separate the voice and data signal
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Broadband Services
• Cable
– A technology that provides digital data
transmission over cable TV infrastructure
– Speed
• Downlink
–128Kbps - 3~5Mbps
• Uplink
–64Kbps - 128Kbps~1Mbps
– Need a cable modem
Broadband Services
• Satellite
– A technology that provide digital data
transmission over satellites
– Speed
• Downlink
–500Kbps - 1Mbps
• Uplink
–50Kbps - 100Kbps
– Need a satellite dish
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WAN (Wide Area Network)
• A LAN spans a large geographic area, such as
connections between cities
• Usually connected using leased line
– T1 (1.5Mbps)
Telecommunication lines
– T3 (45Mbps)
– OC3 (155Mbps)
Fiber optic lines
– OC12 (622Mbps)
– OC48 (2.4Gbps)
Hub/Switch/Router
• To connect multiple segments of networks
into a larger one
• Hub
– A multiport repeater to enhance signal within the
same LAN
• Switch
– Like hub but with intelligent
– Better performance
• Router
– Forward packets from one LAN to another
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Intranet vs. Internet
• Intranet
– A private network that is contained within an
enterprise
– Could be LANs and WANs
• Internet
– A public network of networks
• Both use TCP/IP
TCP/IP (cont)
Application Layer
Eg. WWW, FTP, IRC, Email, telnet, …
Data
Transport Layer
Eg. TCP, UDP
Segments
Network Layer
Eg. IP
Packets
Link Layer
Eg. Ethernet, WiFi
Frames
Physical Layer
Eg. Ethernet Cable, fiber-optics
Bits
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Packets
• A small chunk of data transmitted over the
Internet
Jack
Jill
The
Internet
Thank You
This PPT is downloaded from
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