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CS 101 – Nov. 23

CS 101 – Nov. 23. Communication, continued LANs Bus (ethernet) communication Token ring communication How the Internet works: TCP/IP. Bus topology. All machines share the same channel All continuously listening “Ethernet” protocol (dinner table) don’t talk when someone else is talking

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CS 101 – Nov. 23

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  1. CS 101 – Nov. 23 Communication, continued • LANs • Bus (ethernet) communication • Token ring communication • How the Internet works: TCP/IP

  2. Bus topology • All machines share the same channel • All continuously listening • “Ethernet” protocol (dinner table) • don’t talk when someone else is talking • collisions • Amplify signal with repeaters

  3. Token ring • Fast messaging over larger distances • Logically arranged in loop • Messaging: Token passed around the ring. • Am I busy? • From • To • message

  4. Token action • When you receive token: • Is the message for me? • If so, read and change to ack. • If not, just pass token. • Do I need token? • Wait until it comes back as not “busy”

  5. Example • 4 machines: A, B, C, D. • A has message for C. • When A gets token, writes message for C. • B passes token. • C receives msg, sends ack message to A. • D passes token. • A receives ack, clears token. …

  6. Example #2 • We have 4 machines A, B, C, D. • What happens when… • Token starts at D. • A has a message for C. • C has a message for A. • B has a message for D. …………………………………………

  7. TCP Transfer Control Protocol • Break up message into packets • Sequence number on each packet • Receiver detects lost packets • How big should a packet be?

  8. IP Internet Protocol • Every machine has IP address • 156.143.128.20 • Packets are individually addressed • Routers • Not all packets go the same way! • Just like 2 people driving to Seattle might not take the exact path.

  9. Behind the scenes • “ping” program • Send empty packets, check for ack • 75 ms to San Diego… 840 ms to Pretoria • “traceroute” program • Lists all routers between here and another machine

  10. Snooping The “dark side” of TCP/IP • Web site can track you by IP address • Localized marketing • Privacy concerns • Anonymous IP servers • Ex. “Anonymouse”

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