From: The History of the Telephone Herbert N. Casson 1910

Transcription

1 As for Bell's first telephone lines, they were as simple as clothes-lines. Each short little wire stood by itself, with one instrument at each end.... There were no switchboards of any account, no cables of any value, no wires that were in any sense adequate, no theory of tests or signals, no exchanges, no telephone system of any sort whatever. But there had now come a time when more than two persons wanted to be in the same conversational group.... Here was the new problem, and a most stupendous one -- how to link together three telephones, or three hundred, or three thousand, or three million, so that any two of them could be joined at a moment's notice. From: The History of the Telephone Herbert N. Casson 1910

2 Announcements Homework 4 due today (Hw 5 available soon Away on Thursday and Friday Lab 4/Getting ready for Lab 5 help this afternoon (1:45-3:15) Midterm: Evening of March 15th At 6 p.m. or 7:30 p.m. in Biology minute exam Sample midterm will be available online

3 Today s Plan Broadcast Networks -- Ethernet (and WiFi)

4 As for Bell's first telephone lines, they were as simple as clothes-lines. Each short little wire stood by itself, with one instrument at each end.... There were no switchboards of any account, no cables of any value, no wires that were in any sense adequate, no theory of tests or signals, no exchanges, no telephone system of any sort whatever. But there had now come a time when more than two persons wanted to be in the same conversational group.... Here was the new problem, and a most stupendous one -- how to link together three telephones, or three hundred, or three thousand, or three million, so that any two of them could be joined at a moment's notice. From: The History of the Telephone Herbert N. Casson 1910

5 ...

6 ~ 1974

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9 ~ 1974

10 Bronfman 119 ~ 2015

11 Bronfman 119 ~ 1974 Prof. Steve Lewis 60 Economics Larry Wright 58 Computer Center Director Shane Riorden College Business Manager Xerox 530 Computer with 64KB of memory

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13 Alto with 512KB of memory + 2.5MB disk

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15 David Boggs

16 Robert Metcalfe

17 Robert Metcalfe

18 Aloha Network Norm Abramson

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21 Broadcasting on a Cable

22 Ethernet Frame Format PREAMBLE TO FROM LENGTH/ TYPE DATA ERROR CHECK between 46 and bytes

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24 Carrier Sense Multiple Access with Collision Detection a.k.a. SHARING CSMA/CD NICELY

25 Ethernet-etiquette Don t interrupt Be persistent Know when to back off Know how to back off CARRIER SENSE MULTIPLE ACCESS WITH COLLISION DETECTION

26 Ethernet-etiquette Don t interrupt (Carrier Sense) Be persistent Know when to back off Know how to back off CARRIER SENSE MULTIPLE ACCESS WITH COLLISION DETECTION

27 Ethernet-etiquette Don t interrupt (Carrier Sense) Be persistent (1 Persistence) Know when to back off Know how to back off CARRIER SENSE MULTIPLE ACCESS WITH COLLISION DETECTION

28 Ethernet-etiquette Don t interrupt (Carrier Sense) Be persistent (1 Persistence) Know when to back off (Collision Detection) Know how to back off CARRIER SENSE MULTIPLE ACCESS WITH COLLISION DETECTION

29 Ethernet-etiquette Don t interrupt (Carrier Sense) Be persistent (1 Persistence) Know when to back off (Collision Detection) Know how to back off (Exponential Backoff) CARRIER SENSE MULTIPLE ACCESS WITH COLLISION DETECTION

30 Binary Exponential Backoff After detecting a collision: Pick a random number between 0 and 2 attempts - 1 slots Wait that many time units and then try again.

31 ETHERNET TRANSMISSION ALGORITHM Preamble complete receiver idle Packet becomes ready receiver not idle receiver idle Eager to send a packet Receiver becomes idle Transmitting packet preamble backoff complete receiver not idle backoff complete receiver idle Waiting for backoff slots Jamming complete Transmitting packet contents Preamble complete receiver not idle Receiver becomes busy Transmitting jamming signal DONE CARRIER SENSE MULTIPLE ACCESS WITH COLLISION DETECTION