2021年lecture1-Overview.ppt

Things that Make Computer Networks Fascinating and Challenging
Most people use it, but few understand it (black box)
Scale
Billions of users, many attackers
Thousands of applications
Hundreds of thousands of routers, millions of switches
Hundreds of millions of end hosts (computer, phone, …)
Complexity
Network has many functions
Network is made of many technologies
Network has complex structure and dynamics
Distributed
Network is shared
Network has no one central coordination point
Network has many dynamic agents (applications, OS, humans)
Routers cannot do too much or will be too slow
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lecture1-Overview
History of Computer Networks
Communication
Telecommunication
Telecommunication network
Computer network
Convergence network
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Early Communication over Long Distance
Between human beings
Letter and messenger
Information carried by physical objects
Speed limited by transportation means: horse, bird, train, car
Hard disks over FedEx?
Bandwidth? distance? security?
Fire
Early optical communication
Speed of light
Bandwidth? distance? security?
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Telegraph: Communication Using Electrons
Between human beings
Major milestones:
1827: Ohm’s Law
1837: “workable” telegraph invented by Samuel Morse
1838: demonstration over 10 miles at 10 .
1844: Capitol Hill to Baltimore
1851: Western Union founded
1868: transatlantic cable laid
1985: last telegraph circuit closed down
Other important dates
1869: transcontinental railway
1876: Alexander Bell invented telephone
word per minute
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Telegraph Engineering
Technical issues
How to encode information?
How to feed/input information to the system?
How to output information?
How to improve the distance?
How to improve the speed?
Common issues faced by all telecommunication systems
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Telephony
Interactive telecommunication between people
Analog voice
Transmitter/receiver