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The Red Police

Controlling High-Bandwidth Flows at the Congested Router. The Red Police. By Ratul Mahajan Sally Floyd and David Wetherall. Networking 101. Modern routers use a simple FIFO queue When a router runs out of room to store packets new packets are dropped from the end of the queue. Destination.

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The Red Police

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  1. By Sam Rossoff

  2. Controlling High-Bandwidth Flows at the Congested Router The Red Police By Ratul MahajanSally Floyd andDavid Wetherall By Sam Rossoff

  3. Networking 101 • Modern routers use a simple FIFO queue • When a router runs out of room to store packets new packets are dropped from the end of the queue Destination Internet Router | | | | | | | | | | | | | By Sam Rossoff

  4. Pushy Flows • Because a router's bandwidth is fixed, if a single flow is very large it will hog up all the room on the queue • Solution: Restrict the bandwidth of large flows By Sam Rossoff

  5. Try Try Again • Previous approaches break up into two categories • Continuum: (SFQ, FIFO, etc) • Scheduling: (CSFQ, FRED, RED, etc) By Sam Rossoff

  6. By Sam Rossoff Schedules and You • CHOKe • Find a packet at random, compare to incoming packet and nuke both if same flow. • Limited performance: • When there are too many high • With high UDP flows • CSFQ: Core Stateless Fair Queuing • Estimates packets fair share and drops based on rate estimate and fair share • Requires: • Core “island” of routers • Extra field in packet header

  7. By Sam Rossoff The Design • We really only need to worry about the big flows

  8. On Beyond Zebra • This works because: • A Fraction of the flows make up most of the bandwidth • Predictable effect on the traffic going through the router By Sam Rossoff

  9. By Sam Rossoff The SEC Algorithm • Use the RED drop history • To identify flows that are sending more than ƒ(r,p) , the reference TCP flow’s rate( RTT r and packet drop rate p). And thus dropping more than once in CL(r,p) seconds.

  10. By Sam Rossoff Epoch's are Fun • Congestion epoch length • Maintaining the packet drop history over K x CL(R,p) seconds • Partitioning the history into M lists • RED-PD identifies flows with losses in at least K of M lists • K = 3, M = 5, r = 40ms and p = 1%

  11. By Sam Rossoff But, Does it work? Identifying: g x f(R, p) Flow 1: .1mbps Flow 2: .5 mbps Flow i: Rate(i-1) + .5mbps

  12. By Sam Rossoff I'm Going to Go with Yes • RED-FD responds based on the drop rate. • Few drops and flows run wild 1 CBR flow and 9 TCP flows The CBR flow starts with a rate of 0.25 Mbps, increases it to 4 Mbps at t=50s, and decreases it back to 0.25 Mbps at t=250s. The RTT of the TCP flows ranged from 30 to 70 ms.

  13. By Sam Rossoff And Other Fun Facts on Cereal Boxes • For flows identified as unresponsive, RED-PD increases the drop probability more quickly. • Memory Required is only: • RED-PD targets flows dropped from either itself, RED, or overflow • Nets of these routers have faster response times and are more effecient.

  14. By Sam Rossoff RED-PD Protects the Innocent • Even works when there are a few flows of enormous bandwidth coming in. • Flow 10: 5mbps • Flow 11: 3mbps • Flow 12: 1mbps

  15. Now for my opponent who is a poopoo head Which is Why I Think I Would Make a Good President By Sam Rossoff

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