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Buffer Sizing for Congested Internet Links

Buffer Sizing for Congested Internet Links. Chi Yin Cheung Cs 395 Advanced Networking. Introduction. Buffers are important for routers Common rule of thumb is to assign buffers based on bandwidth delay product Why is this so? Potential problems?. Related work. Stanford Scheme

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Buffer Sizing for Congested Internet Links

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  1. Buffer Sizing for Congested Internet Links Chi Yin Cheung Cs 395 Advanced Networking

  2. Introduction • Buffers are important for routers • Common rule of thumb is to assign buffers based on bandwidth delay product • Why is this so? • Potential problems?

  3. Related work • Stanford Scheme • Buffer requirement to achieve ~100% util is given by • B = CT(avg) / root(N) N=no. of TCP flows • However, focuses only on utilization, does not consider loss rate

  4. Purpose of BSCL • Focus on Buffer requirement of a Drop-queue design, given • Min utilization • Max loss rate • Max queuing delay • Applicable when 80-90% of traffic of given link belongs to Nb locally bottlenecked flows. Rest can be UDP flows, or short TCP flows

  5. Assumptions • Single queue • Constant Capacity C, buffer space B bytes • Drop-tail Policy • At real routers, typically only one queue is used • Buffer is structured in terms of bytes, rather than units of cells etc.

  6. Goals • Full utilization: avg utilization should be 100% • Max loss rate should not be more than 1-2% for a fully saturated link • Max queuing delay should not exceed a bound d-hat

  7. Traffic types • Locally Bottlenecked Persistent • Remotely Bottlenecked Persistent • Window-limited Persistent TCP flows • Short TCP flows and non-TCP traffic • Paper assumes that most of the traffic is generated by LBP flows – if LBP flows is a large proportion, buffer reqs for other flows can be igonred.

  8. Evaluation • NS-2 simulator used for simulation • Capacity = 50Mbps, loaded with 4 types of traffic, with LBP flows varying from 2 – 400, other two types of flow is minimal (10-20) • Simulate traffic by first setting buffer according to rule of thumb, then stanford, then BSCL • BSCL works better than other two in terms of maintaining utilization and low loss

  9. Results • When Number of flows is small (20-40) BSCL predicts much smaller number of buffers than rule-of-thumb. • Stanford approach requires more buffering than BSCL for small number of flows • When more flows are simulated, stanford buffer requirements drop quickly, but loss rates increase rapidly

  10. Conclusions • BSCL is applicable for traffic where 80-90% of the traffic comes from LBP TCP flows • Considers number of heterogeneous RTTs and partial loss synchornization • It is better than the stanford scheme in that it maintains high utilization whilst keeping loss rate low. • Limitations: work is based solely on simulations

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