Performance and Robustness Testing of Explicit-Rate ABR Flow Control Schemes

1. Performance and Robustness Testing of Explicit-Rate ABR Flow Control Schemes Milan Zoranovic Carey Williamson October 26, 1999

2. Agenda • Introduction and Motivation • Background Information • Explicit-Rate ABR Traffic Control Schemes (ERICA, ERICA+, DEBRA) • Experimental Methodology • Simulation Results: Performance Testing • Simulation Results: Robustness Testing • Summary and Conclusions MASCOTS 1999

3. 1 Introduction • Problem Definition and Motivation: • Explicit-Rate (ER) ABR flow control schemes • Many (ER) ABR flow control schemes have been proposed • Performance evaluations are author and scheme dependent • Difficult to do direct comparison • Study Objectives: • Propose set of benchmark network configurations • Evaluate and compare ERICA, ERICA+, and DEBRA strategies on this set of benchmark configurations • Use Asynchronous Transfer Mode -Traffic and Network (ATM-TN) simulator for this purpose MASCOTS 1999

4. Background • ABR Flow Control Mechanism • There are five classes of service (CBR, VBR (2), UBR, and ABR) • ABR and UBR use the remaining bandwidth • ABR bandwidth varies between minimum bandwidth and the extra bandwidth freed by the VBR traffic sources • ABR flow control schemes are in charge of managing this bandwidth effectively • Resource Management (RM) Cells • Used as mechanism for ABR flow control • RM-cell contains information about the state of the network (CI, ER, CCR, MCR. DIR,…) • The mechanism is called closed-loop • Behavior of ABR flow control: MASCOTS 1999

5. Data FRM Data FRM Source Switch Destin. BRM BRM Background Continued . . . MASCOTS 1999

6. Explicit-Rate ABR Traffic Control Schemes • The ERICA Algorithm • ERICA (Explicit Rate Indication for Congestion Avoidance) is proposed by Ray Jain et al. • ERICA tries to achieve a fair and efficient allocation of the available bandwidth to competing sources • Each switch monitors the incoming cell rates of each ABR traffic source, the available capacity, and the number of active sources • Aggregate ABR demand vs target load • The ERICA+ algorithm • It uses a target queuing delay rather than a target utilization, and refined parametersfor source rate adjustmentforfaster convergence • The target queuing delay (D), determines the steady state buffer occupancy at the bottleneck link • ERICA+ achieves higher network utilization then ERICA , while only slightly increasing the end-to-end delay MASCOTS 1999

7. Explicit-Rate ABR Traffic Control Schemes Continued ... • The Dynamic Explicit Bid Rate Algorithm (DEBRA) • Based on a rate-based flow control strategy called loss-load curves • Switches compute and provide to traffic sources concise aggregate load information • Sources compute precise transmission rates that provide the best trade off between offered load and the level of packet loss in the network •  = r * (1-p) •  - allocated bandwidth to a current VC • r - requested bandwidth by a current VC • p - loss probability assigned to a current VC • f - a fraction of total capacity requested by current VC • K- controls aggressiveness, responsiveness and convergence MASCOTS 1999

8. Experimental Methodology • ATM-TN Simulator • Provides cell-level simulation of the ATM-TN traffic flows from traffic sources to traffic sinks • ABR persistent sources • Per-port output-buffered switch model • ERICA, ERICA+ and DEBRA are implemented in the simulator • A set of nine network configurations for performance evaluation • A set of four network configuration for robustness tests MASCOTS 1999

9. Experimental Methodology Continued... • Performance Metrics • Allowed Cell Rate (ACR): Mbps • Link Utilisation: Percentage • Queue Length: Number of Cells • Throughput: Number of Cells • Cell Loss Ratio (CLR): Percentage • Experimental Design • Performance Testing: each of the algorithms is evaluated on set of nine benchmark scenarios • Robustness Testing: each of the algorithms is evaluated on a set of four benchmark scenarios for testing the robustness MASCOTS 1999

10. Performance TestingSet of Benchmark Scenarios MASCOTS 1999

11. Performance Testing Continued ... • Simulation results for all the three schemes are shown on One-at-a-Time and Generic Fairness Configuration 1 network scenarios (ACR and Link Utilisation) • One-at-a -Time Network Configuration • LAN network configuration with 30 sources • Start up one at a time, every 10 ms • Test responsiveness, fairness, efficiency, and scalability MASCOTS 1999

12. Performance Testing Continued …One-at-a-Time: ACR and Link Utilisation ERICA ERICA+ DEBRA MASCOTS 1999

13. Performance Testing Continued…Generic Fairness Configuration 1 (GFC1) • Five Switch “Parking-Lot” WAN Network Topology • Used by ATM Forum • There are 23 traffic sources • Purpose: testing for max-min fairness among the sources with different bottlenecks, rates and RTT MASCOTS 1999

14. Performance Testing Continued…GFC1: ACR and Link Utilisation ERICA ERICA+ DEBRA MASCOTS 1999

15. Performance Testing Continued… • Summary of Performance Testing Results • All three algorithms performed well on One-at-a-Time scenario • DEBRA needs more time to converge to a steady-state than ERICA+ on GFC1, but less than ERICA (link utilization) • ERICA+ performs better than its predecessor ERICA • ERICA and ERICA+ did not perform as well as DEBRA during the steady-state on GFC1 (more oscillations for higher rate sources in both ACR and Link Utilization) • ERICA and ERICA+ showed to be very sensitive to parameters configuration( and D) MASCOTS 1999

16. Robustness TestingSet of Benchmark Scenarios • Network scenarios with non-cooperative traffic sources • Intentional overuse of underuse of their fair-share • Dishonest and honest traffic sources • Based on Two Sources network scenario MASCOTS 1999

17. Robustness Testing Continued…Dishonest Sources Scenario: ACR and Throughput ERICA+ DEBRA ERICA MASCOTS 1999

18. Robustness Testing Continued…Honest Sources-One High Scenario: ACR/Throughput ERICA ERICA+ DEBRA MASCOTS 1999

19. Robustness Testing Continued… • Summary of Robustness Testing Results • None of the schemes performs properly when sources are greedy and dishonest • ERICA+ is able to avoid congestion on all the scenarios, but do not achieve fairness • ERICA is not very robust - experience both, unfairness and congestion (CLR) when sources are greedy • DEBRA the only one to perform properly on the scenarios with honest and greedy ABR traffic sources MASCOTS 1999

20. Conclusions and Future Work ... • Conclusions • Set of benchmark network configuration is needed for good comparison • Simulation results show: none of the schemes is perfect • ERICA+ performed better than its predecessor ERICA • DEBRA, a new ER ABR flow control scheme is very competitive • Performed as well as ERICA+ on basic set of network configuration • Performed better than ERICA+ on the robustness tests • Future Work • Study ABR performance with more realistic traffic (bursty traffic sources, self-similar traffic, finite traffic sources) • Interaction between TCP and ATM ABR • Improving the DEBRA algorithm (avoiding the buffer overflow problem at the source start-up time) by adding gradual ramp-up feature (THIS ONE WILL BE REMOVED) MASCOTS 1999