1. Network Border Patrol Celio Albuquerque, Brett J. Vickers and Tatsuya Suda Jaideep Vaidya CS590F Fall 2000

2. 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

3. 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

4. Goals Eliminate congestion collapse resulting from undelivered packets When combined with fair queueing, achieve approximately max-min fair bandwidth allocations for competing network flows

5. NBP Egress Router

6. NBP Ingress Router

7. 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)

8. FeedBack Packets

9. 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

10. 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

11. Results from Simulation Experiments Preventing congestion collapse

12. Results from Simulation Experiments Max-min fairness

13. 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

14. Implementation Issues Scalable Flow Classification Scalable inter-domain deployment Scalable fairness Incremental Deployment Multicast Multi-path routing Integrated or Differentiated service

15. 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)

16. Questions?