class24-HowTheInternetWorks

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

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Unformatted text preview: The InterWebs and how they work 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) Network Hardware Acronyms IP FTP HTTP TCP DHCP UDP ASAP SMTP Protocol a set of rules used to communicate Might include rules for: detecting start and end of messages formatting messages detecting and handling errors 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. People talking in a room buy cows face book email rofl Speaking in bits, of course 11011 00001 10111 00101 Hopefully, one at a time 00101 Hopefully, one at a time 00001 Collision: 2 people talking at once 00001 00101 What everyone might hear 0010001 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? 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 Checksum How many 1s in 00101? Remainder when 2 is divided by 4? If 2, append what? send 0010110 This is called a checksum . Checking Sums Is this message valid? 1111101 five 1s -> 01 valid 0000110 one 1 -> 01 invalid 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 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 The Honor System In an Ethernet network, each user receives everyone's packets. You should only look at packets addressed to you. Network Layers Hardware Ethernet To D5-05-6F- 39-03-4F From C5-9D-A2- EF-8C-21 Teh n00b got pwned, lol....
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This note was uploaded on 09/14/2010 for the course CS 15-100 taught by Professor Dave during the Spring '08 term at Carnegie Mellon.

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

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