CSCI 1200 / ASSC 1000
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Transcript of CSCI 1200 / ASSC 1000
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CSCI 1200 / ASSC 1000
Chapter 8
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Telecommunications
• long distance, electronic communications.
• protocol : rules.
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Network
• two or more computers linked together.
• why?– share hardware, software & data.– connect people, allowing collaboration.
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Keep the Network Running
• network administrator (person).
• network management software.
• Network Operating System - NOS
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Network Operating System
• functions for connecting computers & devices to a LAN.
• must deal with multiple computers & coordinate things throughout the network.
• today many operating systems have networking functions built in.
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Intranet
• open standard protocols instead of a proprietary operating system.
• same technology as the Internet, but owned by an organization or individual.
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Important Terms
• nodes – any point on a network (often a computer).
• servers - the computers & devices that allocate resources for the network.
• backbone - key connection, very high speed, heavy traffic.
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Important Terms
Protocol :
In the case of a network, a set of agreed upon rules & signals defining how the computers and devices on the network will communicate.
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Important Terms
• Bridges & Gateways - connect networks, may translate if the networks use different protocols or operating systems, may also handle security (like firewalls).
• Router - forwards network traffic, sending it to bridges & gateways.
• Switches & Hubs – forwards traffic between network nodes
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Type of Networks
• LAN – Local Area Network– physically close, usually the same building.– may use cables or be wireless.– wireless is slower, but convenient and less
invasive.
• MAN - Metropolitan Area Network– city sized network.– typically links several LANs.
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Type of Networks
WAN – Wide Area Network– geographically large.– each node is a site.– telephone lines, microwave towers,
satellite links make WANs possible.– corporate & government.
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Special Networks
GPS – Global Positioning System – network of 24 satellites.– 4 above horizon at any time.– 3 to calculate position, may use up to 6.– land beacons may augment the network.– radio transmitters & atomic clocks, time for the signal
to travel from the satellite to you.– hand held devices, vehicle navigation, mobile phones,
outdoor enthusiasts.– more accurate for the military.
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Special Networks
Financial Networks :–money represented digitally.– banking & financial industry operate on
a global scale.– access your bank account from almost
any country.
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Building a Network
Connection Technology :
• Direct Connection – dedicated physical link.
• Remote Connection – phone lines, cable lines, satellites.
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Building a Network
Traffic Issues :– devoted connection to each node.– or many computers must share the line.
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Building A Network
Network Interface Card– special hardware.– inserted into a slot.– adds a network port for a direct connection.– controls data flow between network &
computer’s memory.– boosts the signal on it’s way out.– Ethernet port is often built in now.
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Bandwidth
• amount of data that can be transmitted in a fixed amount of time.
• bps, kbps, mbps. • to increase speed:– widen the pipe.– increase the speed of traffic through the
pipe.– better protocols.
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Connections
Modem– longer distances.– connect to a telephone line.– internal / external.– phone network – designed for sound.– convert stream of bits to a continuous sound
wave – digital to analogue.– generally slower than a direct connection.– speed measured in bps – 56k.
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Connections
Broadband Technology – single medium (wire) can carry several
channels at once.• DSL – phone lines• Cable Modems – cable television lines• Wireless – radio or infrared waves• Satellite – satellites & dishes
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Connections
Fiber Optic – use light instead of electricity.– replace 10,000 copper telephone lines.– 500 million bps – half a gigabit per
second.– “last mile”
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Connections
Wireless :–may use a radio or infrared transmitter–mobility over speed
Infrared :– line of sight is needed.– short distances.– sunlight
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Connections
Wi-Fi (wireless fidelity)– radio based LAN protocol.– describes any type of 802.11 network.– base station, devices may be a distance
of about 150 feet.
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Connections
Bluetooth – short-range radio links – up to 30 feet.– lower energy than Wi-Fi - battery
operated devices. –mobile computers, mobile phones,
digital cameras, other portable devices.– not competing with Wi-Fi, replace
cables needed to plug stuff in.
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Connections
3G• next generation of mobile communications
technology. • other countries more fully utilize mobile
phones.• increased bandwidth, up to 384 kbps when a
device is stationary or moving at pedestrian speed, 128 kbps in a car, and 2 mbps stationary.
• video, multimedia support.
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Approaches to Networking
Client Server Model– server fulfils client requests– high speed, high capacity computer is
the server– hierarchical structure, server is
essential
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Approaches to Networking
Peer 2 Peer Model– any computer can be a client or a
server.– often used on smaller networks (but not
necessarily, e.g. music sharing).–Windows & MacOS allow for P2P
networking.
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Internet
• global network of networks.
• TCP / IP communication standard.
• to communicate, networks must speak the same language.
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Internet Motivation
• Researchers : share computing resources, very few computers, expensive.
• Military : cold war, wanted a communication network.
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Military Needs
• assume unreliability.
• decentralized : all connected computers are equal.
• most work when lines are broken, and nodes are down.
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Network Must
• connect important government & research computers.
• resist point-of-failure attacks : continue to operate even if a city on the network was destroyed.
• be fault-tolerant : continue to operate even if something went wrong within the network – e.g., a computer crashed, or a transmission line was broken.
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Solution
• designed to be a decentralized network of computers that could adapt the flow of traffic and to changes in the state of the overall system.
• the way that information travels on the Internet is similar to the way that traffic moves on an interconnected system of roads and highways.