Estimating Link Capacity in High Speed Networks

1. Estimating Link Capacity in High Speed Networks Ling-Jyh Chen1, Tony Sun2, Li Lao2, Guang Yang2, M.Y. Sanadidi2, Mario Gerla2 1Institute of Information Science, Academia Sinica 2Dept. of Computer Science, University of California at Los Angeles

2. Definition • Capacity: maximum IP-layer throughput that a flow can get, without any cross traffic. • Available Bandwidth: maximum IP-layer throughput that a flow can get, given (stationary) cross traffic.

3. Previous Work on Capacity Estimation • Per-hop based • pathchar: use different packet sizes to probe the per-hop link capacity • clink, pchar: variants of pathchar • Nettimer: use “packet tailgating” technique • End-to-end based • Pathrate, Sprobe, CapProbe • For specialized networks: AsymProbe, ALBP, AdHoc Probe • How about high speed networks?

4. Estimating High Speed Links • High speed links are becoming popular (e.g. GB links, DVB links, and UWB links) • However, capacity estimation on high speed links remains a challenge (e.g., probing pksize and system time resolution are limited) • And, an effective estimation tool for high speed links is still desired

5. Our Contribution • We propose an end-to-end capacity estimation technique for high speed links, called PBProbe. • PBProbe is based on CapProbe • One-way method • UDP based • packet bulk based • simple, fast, and accurate

6. 20Mbps 10Mbps 5Mbps 10Mbps 20Mbps 8Mbps T1 Narrowest Link T2 T3 T3 T3 T3 Packet Pair Dispersion Capacity = (Packet Size) / (Dispersion)

7. Issues: Compression and Expansion • Queueing delay on the first packet => compression • Queueing delay on the second packet => expansion

8. Capacity CapProbe (Rohit et al, SIGCOMM’04) • Key insight: a packet pair that gets through with zero queueing delay yields the exact estimate. • CapProbe uses “Minimum Delay Sum” filter.

9. Proposed Approach: PBProbe • Have two phases for both forward and backward link estimation • Use packet bulk (instead of packet pair) of length k in each probing • Adapt k to enlarge the dispersion between the first and last packet, and thus overcome the timer resolution problem • Tradeoff BW consumption and estimation speed by U parameter

10. Proposed Approach: PBProbe

11. Proposed Approach: PBProbe • k is depended on the estimated link capacity and the supported timer resolution. • n is set to 200. • Dthresh is set to 1ms. • U is set to 0.002.

12. Analysis • Poisson cross traffic (arrival and service rates are λ and μ), service time is τ • Prob. of obtaining a good sample: • Expected number of samples required for obtaining a good sample:

13. Analysis

14. Evaluation • NISTNet emulation • High speed Internet experiments • Comparison of PBProbe and Pathrate

15. Evaluation 1: NISTNet emulation • No cross traffic

16. Evaluation 2: Internet experiments • 5 hosts: NTNU, UCLA, CalTech, GaTech, PSC(n = 200, k = 100, 20 runs)

17. Evaluation 3: PBProbe vs Pathrate

18. Summary • We propose an end-to-end capacity estimation technique, called PBProbe, for high speed links. • We evaluate PBProbe by analysis, emulation and Internet experiments. • We show that PBProbe can correctly and rapidly estimate bottleneck capacity in almost all test cases.

19. Acknowledgements • This work is co-sponsored by the National Science Council and the National Science Foundation under grant numbers NSC-94-2218-E-001-002 and CNS-0435515. • We are grateful to the following people for their help in carrying out PBProbe measurements: Sanjay Hegde (CalTech), Che-Chih Liu (NTNU), Cesar A. C. Marcondes (UCLA), and Anders Persson (UCLA).

20. Thanks! CapProbe: http://nrl.cs.ucla.edu/CapProbe/