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class24-HowTheInternetWorks

class24-HowTheInternetWorks - The InterWebs and how they...

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The InterWebs and how they work
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What is the Internet? "The Internet is not something that you just dump something on. It's not a big truck. It's, it's a series of tubes." --Sen. Ted Stevens (R-Alaska)
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Network Hardware
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Acronyms IP FTP HTTP TCP DHCP UDP ASAP SMTP
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Protocol a set of rules used to communicate Might include rules for: detecting start and end of messages formatting messages detecting and handling errors
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Our first protocol: Ethernet Local area networks (like the one in your home, dorm, classroom) often use Ethernet . An Ethernet network is like a room full of people trying to talk. The Ethernet protocol is a set of rules for governing that communication.
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People talking in a room buy cows face book email rofl
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Speaking in bits, of course 11011 00001 10111 00101
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Hopefully, one at a time 00101
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Hopefully, one at a time 00001
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Collision: 2 people talking at once 00001 00101
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What everyone might hear 0010001
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Solution: Redundancy Transmit message with redundant information. Instead of 00101, maybe send 0000110011. If we receive 0000111011, what do we know? How might that have happened?
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Using fewer bits Count 1s Find remainder when divided by 4. If 0, append 00 If 1, append 01 If 2, append 10 If 3, append 11
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Checksum How many 1s in 00101? Remainder when 2 is divided by 4? If 2, append what? send 0010110 This is called a checksum .
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Checking Sums Is this message valid? 1111101 five 1s -> 01 valid 0000110 one 1 -> 01 invalid
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Sending to specific addresses Every network card in the world has a unique number. What is it called? MAC Address: 00-2C-48-6E-67-B3
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Ethernet Packets To D5-05-6F- 39-03-4F From C5-9D-A2- EF-8C-21 Teh n00b got pwned, lol. 00110011 11110101 10011000 11110100 Destination MAC Address Source MAC Address Payload Checksum 48 bits 48 bits up to 12,000 bits 32 bits
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The Honor System In an Ethernet network, each user receives everyone's packets.
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