1. 1 Aggregate Traffic Performance with Active Queue Management and Drop from Tail Christophe Diot, Gianluca Iannaccone, Martin May Sprint ATL, Università di Pisa, Activia www.sprintlabs.com

2. 2 Active Queue Management queue drop size function averageinstantaneous sharpREDDrop from Tail smoothGentle RED Gentle RED Instantaneous

3. 3 Original RED min-treshmax-tresh max-p buffer size 1

4. 4 Revised RED min-treshmax-tresh max-p buffer size 1

5. 5 Gentle RED min-treshmax-tresh max-p buffer size2 max-tresh 1

6. 6 Experiments Testbed –with CISCO routers (7500) –with Dummynet We use “recommended” RED and GRED parameters Heterogeneous delays (120 to 180 ms)

7. 7 Traffic characteristics 16 to 256 TCP connections sharing the bottleneck. Experimental traffic generated by Chariot –long-lived TCP connections. –more “realistic” traffic mix: 90% short lived TCP connections (up to 20 packets) 10 % long lived TCP connections –1Mbps UDP in both cases

8. 8 Testbed (CISCO routers) 10 Megs 7500

9. 9 Testbed (Dummynet) 7500 10 Megs 100 Megs Dummy net 7500

10. 10 What is Dummynet? application network dummynet

11. 11 Metrics observed Aggregate goodput through a router TCP and UDP loss rate Consecutive losses Queuing behavior

12. 12 Aggregate goodput (long-lived TCP)

13. 13 256 short and long lived TCP connections

14. 14 Consecutive packet losses (long lived)

15. 15 …if we use “optimal” RED parameters

16. 16 Consecutive packet losses (realistic traffic mix)

17. 17 Queuing behavior (256 long lived connections)

18. 18 Queuing behavior (256 connections, realistic mix)

19. 19 In summary... No significant difference on goodput, TCP losses and UDP losses. On consecutive losses, clear advantage to GRED and GRED-I. “gentle” modification solves many RED problems. Oscillations: no clear winner. Traffic seems to be the determining factor.

20. 20 From the ISP standpoint... Not clear there is an advantage in deploying RED, GRED, or GRED-I. Maybe GRED-I is an option if one can find a “universal” exponential dropping function. ECN will work with any scheme. Not clear the solution is in the AQM space.

21. 21 GRED-I with exponential dropping function buffer size 1

22. 22 About Fair Queuing... Not only feasible … easy at the edges! –www.agere.com (an example) –vendors support from 64k to 200k flows Really fair –everybody gets what he/she paid for local signaling (end host to CPE)

23. 23 Number of flows on an OC-3 link