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Network Border Patrol Celio Albuquerque, Brett J. Vickers and Tatsuya Suda. Jaideep Vaidya CS590F Fall 2000. Need. End to End Congestion Control / Avoidance Mechanisms not enough. Unresponsive flows Rogue TCP stacks Network level mechanisms - Necessary Evil
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Network Border PatrolCelio Albuquerque, Brett J. Vickers and Tatsuya Suda Jaideep Vaidya CS590F Fall 2000
Need • End to End Congestion Control / Avoidance Mechanisms not enough. • Unresponsive flows • Rogue TCP stacks • Network level mechanisms - Necessary Evil • Try to push as much to the border of the network as possible
Essential Idea • Core Stateless Congestion Avoidance Mechanism • Exchange of feedback between Edge Routers • Per-flow rate monitoring at Egress Routers • Per-flow rate control at Ingress Routers
Goals • Eliminate congestion collapse resulting from undelivered packets • When combined with fair queueing, achieve approximately max-min fair bandwidth allocations for competing network flows
Feedback Control Algorithm • Decides how and when feedback packets are exchanged between edge routers. • Necessary for discovering source, communicate per-flow bit rates & detect network congestion by estimating RTT • BFFs can be generated asynchronously. (RTT cannot be calculated in this case)
Rate Control Algorithm • Regulates rate at which each flow enters the network. Converge on set of per-flow transmission rates, preventing congestion collapse. Maximize link utilization. • Similar to TCP congestion control (Slow start and Congestion avoidance phases) • Handles synchronous and asynchronous packets differently
Rate Control Algorithm contd. • Activated on receipt of feedback packet. • Synchronous feedback • Update baseRTT • Calculate mrc (minimum rate change) • Change rate based on phase • Aysnchronous feedback • Use old mrc and modify rate based on current phase
Results from Simulation Experiments • Preventing congestion collapse
Results from Simulation Experiments • Max-min fairness
Fairness Results • NBP by itself is not able to provide fairness. • With WFQ or CSFQ, NBP provides approximate fairness, and avoids congestion collapse • Results with WFQ are better than results with CSFQ. • CSFQ’s fairness mechanism engages only when congestion is detected • CSFQ is an approximation of WFQ
Implementation Issues • Scalable Flow Classification • Scalable inter-domain deployment • Scalable fairness • Incremental Deployment • Multicast • Multi-path routing • Integrated or Differentiated service
Conclusion • Pros • Good paper. Limitations noted. • Stop gap solution. Adequate for goals noted. • Cons • Incremental deployment not easy. • Deployment based on whether we expect QoS technology to be available soon. • Overload is directly proportional to number of flows. Would not work well with HTTP 1.0 (more number of flows)