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BGP + Medium Sharing

BGP + Medium Sharing. Border Gateway Protocol (BGP). Inter-domain routing Why not distance-vector? Shortest path may not necessarily follow policies Why not link state? Everyone knows everything – privacy goes for a toss! How else can we avoid loops and dead-ends? Path vector!.

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BGP + Medium Sharing

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  1. BGP + Medium Sharing

  2. Border Gateway Protocol (BGP) • Inter-domain routing • Why not distance-vector? • Shortest path may not necessarily follow policies • Why not link state? • Everyone knows everything – privacy goes for a toss! • How else can we avoid loops and dead-ends? • Path vector!

  3. Business Relationships Relations between ASes Business Implications  Customers pay provider  Peers don’t pay each other customer provider peer peer

  4. Routing Follows the Money! • Peers provide transit between their customers • Peers do not provide transit to each other traffic not allowed traffic allowed

  5. Selection vs Export • Selection policies • determines which paths I want my traffic to take • Export policies • determines whose traffic I am willing to carry

  6. Sharing the Medium • How do multiple hosts share a medium? Channel Partitioning TDMA, FDMA Taking Turns Polling, Token Passing Random Access ALOHA, CSMA

  7. Random Access • No “sensing” of medium • ALOHA • Sense the medium (CSMA/CD) • Listen to the channel • Transmit if free, else wait • Upon collision • Stop sending, inform others • Wait for a random time Why would collisions occur if you listen before transmission?

  8. Implications of CD • How long does it take to detect collision? Dictates minimum frame size, and maximum distance!

  9. CSMA/CD • E = Time spent transmitting / (Time spent transmitting + time wasted due to collision) • = (P/B) / ((P/B) + KD) • P: packetlength • B: bandwidth • D: Distance High for large transmission time, or low propagation time

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