1. FTDCS 2003 Network Tomography based Unresponsive Flow Detection and Control Authors Ahsan Habib, Bharat Bhragava habib,bb@cs.purdue.edu Presenter Mohamed M. Hefeeda Department of Computer Sciences Purdue University Support: NSF, CERIAS, IBM

2. Motivation Efficient resource management by utilizing wasted resources Adaptive flows do not starve due to unresponsive flows Coordinated congestion control by propagating congestion information to upstream domains

3. Example Unresponsive flows waste resources by taking their share of the upstream links and dropping packets at downstream links are congested

4. Related Work Congestion collapse from undelivered packets [Flyod et al., TON ’99] Network Border Patrol [Albuquerque et al., INFOCOM ’00] Edge routers periodically poll cores [Chow et al., Internet draft ’00] Direct Congestion Control Scheme [Wu et al., Internet draft ’00] Loss of high class packet means congestion Core-assisted Congestion Control [Habib, Bhargava PDCS ’01]

5. Network Tomography Network tomography uses correlations among end-to-end measurements to infer per-link characteristics. Back-to-back packets experience similar congestion in a queue with a high probability [Duffield et al., INFOCOM ’01] Receiver observes the probes and correlates them for loss inference For general tree? Send stripe from root to every order-pair of leaves

6. Tomography-based Congestion Control (TCC) Only edge to edge measurements are used to detect and control unresponsive flows

7. TCC- Detection 1. Measure Delay Ingress routers sample user traffic The user packet headers are copied to probe edge-to-edge path for delay Exponential moving weighting average is computed with more weight to the recent history and less weight to the current sample If probed delay is higher than a specified threshold, a path is suspected to be congested

8. TCC- Detection (Cont’d) 2. Measure Loss A loss probing tree is generated with a set of paths that have high delay. The tree is probed to infer loss ratio of each individual link of the suspected paths Need to know Topology Senders Receivers

9. TCC- Detection (Cont’d) 3. Identify egress routers Through which suspected flows are leaving the domain. The links with high losses are feeding flows to these routers 4. Identify misbehaving flows These are determined with the rate at which suspected flows are entering into and leaving from a domain

10. TCC- Control We know the misbehaving flows from detection The rate of suspected flows are adjusted based on Loss ratio and Change of loss ratio with time

11. Experiments: Evaluation methodology Simulation using ns-2 Use parameter settings (queue, traffic, …) from reference work Input Parameters We vary RTT, number of flows, and life time of flows Output Parameters Measure delay, loss ratio, throughput Topology

12. Delay Measurements End-to-end delay is high due to excessive flows With control the delay goes down Time (Sec) End –to-End Delay (Sec)

13. Loss inference Validation Three different experiments Actual loss is close to infer loss Converges within 10-15 sec Actual Loss Inferred Loss

14. Flow Control Time (Sec) Bandwidth (Mbps) Flow control mechanism increases the bandwidth of adaptive flows by consuming bandwidth wasted by unresponsive flows Time (Sec) TCP congestion window

15. Flow Control Loss ratio of an unresponsive flows with and without flow control Goes down sharply with time Converges to a low specified value Time (Sec) Loss Ratio

16. Flow Aggregation… 6-10 aggregate flows of each type 10-100 micro flows per aggregate Works fine even more and more flows misbehave Number of flows Bandwidth (Mbps)

17. Conclusion A new way to detect and control unresponsive flows No involvement of core routers Scalable Easy to deploy Low overhead. Probe traffic less than 0.015% of the link capacity (OC3)