Transcript CSCI 1200 / ASSC 1000

CSCI 1200 / ASSC 1000
Chapter 8
Telecommunications
• long distance, electronic
communications.
• protocol : rules.
Network
• two or more computers linked
together.
• why?
– share hardware, software & data.
– connect people, allowing collaboration.
Keep the Network Running
• network administrator (person).
• network management software.
• Network Operating System - NOS
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.
Intranet
• open standard protocols instead of a
proprietary operating system.
• same technology as the Internet, but
owned by an organization or
individual.
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.
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.
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
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.
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.
Special Networks
GPS – Global Positioning System
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–
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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.
Special Networks
Financial Networks :
– money represented digitally.
– banking & financial industry operate on
a global scale.
– access your bank account from almost
any country.
Building a Network
Connection Technology :
• Direct Connection – dedicated
physical link.
• Remote Connection – phone lines,
cable lines, satellites.
Building a Network
Traffic Issues :
– devoted connection to each node.
– or many computers must share the line.
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.
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.
Connections
Modem
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–
–
–
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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.
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
Connections
Fiber Optic
– use light instead of electricity.
– replace 10,000 copper telephone lines.
– 500 million bps – half a gigabit per
second.
– “last mile”
Connections
Wireless :
– may use a radio or infrared transmitter
– mobility over speed
Infrared :
– line of sight is needed.
– short distances.
– sunlight
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.
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.
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.
Approaches to Networking
Client Server Model
– server fulfils client requests
– high speed, high capacity computer is
the server
– hierarchical structure, server is
essential
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.
Internet
• global network of networks.
• TCP / IP communication standard.
• to communicate, networks must
speak the same language.
Internet Motivation
• Researchers : share computing
resources, very few computers,
expensive.
• Military : cold war, wanted a
communication network.
Military Needs
• assume unreliability.
• decentralized : all connected
computers are equal.
• most work when lines are broken,
and nodes are down.
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.
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.