BGP + Medium Sharing
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BGP + Medium Sharing
![Page 2: BGP + Medium Sharing](https://reader035.fdocuments.in/reader035/viewer/2022062422/568138a8550346895da0695a/html5/thumbnails/2.jpg)
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!
![Page 3: BGP + Medium Sharing](https://reader035.fdocuments.in/reader035/viewer/2022062422/568138a8550346895da0695a/html5/thumbnails/3.jpg)
Business Relationships
peer peerprovider customer
Relations between ASes Customers pay provider Peers don’t pay each other
Business Implications
![Page 4: BGP + Medium Sharing](https://reader035.fdocuments.in/reader035/viewer/2022062422/568138a8550346895da0695a/html5/thumbnails/4.jpg)
Routing Follows the Money!
• Peers provide transit between their customers• Peers do not provide transit to each other
traffic allowed traffic not allowed
![Page 5: BGP + Medium Sharing](https://reader035.fdocuments.in/reader035/viewer/2022062422/568138a8550346895da0695a/html5/thumbnails/5.jpg)
Selection vs Export• Selection policies– determines which paths I want my traffic to take
• Export policies– determines whose traffic I am willing to carry
![Page 6: BGP + Medium Sharing](https://reader035.fdocuments.in/reader035/viewer/2022062422/568138a8550346895da0695a/html5/thumbnails/6.jpg)
Sharing the Medium
• How do multiple hosts share a medium?
Channel Partitioning
TDMA, FDMA
Taking Turns
Polling, Token Passing
Random Access
ALOHA, CSMA
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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?
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Implications of CD
• How long does it take to detect collision?
Dictates minimum frame size, and maximum distance!
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CSMA/CD
• E = Time spent transmitting / (Time spent transmitting + time wasted due to collision)
• = (P/B) / ((P/B) + KD)• P: packet length• B: bandwidth• D: Distance
High for large transmission time, or low propagation time