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Understanding BGP and Medium Sharing: Protocols, Policies, and Collision Management

This article delves into the Border Gateway Protocol (BGP), exploring inter-domain routing, why distance-vector and link-state protocols fall short, and the significance of path vector mechanisms. It highlights the business relationships between Autonomous Systems (ASes) and how routing decisions impact traffic management. Additionally, it discusses how multiple hosts share a medium through various techniques such as TDMA and CSMA/CD, addressing concerns of collisions and retransmission strategies. Gain insights into BGP’s operational framework and medium sharing strategies.

heidi-dixon
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Understanding BGP and Medium Sharing: Protocols, Policies, and Collision Management

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Presentation Transcript

  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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