Estimating Link Capacity in High Speed Networks Ling-Jyh Chen 1, Tony Sun 2, Li Lao 2, Guang Yang 2, M.Y. Sanadidi 2, Mario Gerla 2 1 Institute of Information Science, Academia Sinica 2 Dept. of Computer Science, University of California at Los Angeles

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

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 high speed How about high speed networks?

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

Our Contribution PBProbe 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  packet bulk based  simple, fast, and accurate

Packet Pair Dispersion T3T3 T2T2 T3T3 T3T3 T1T1 T3T3 Narrowest Link 20Mbps10Mbps5Mbps10Mbps20Mbps8Mbps Capacity = (Packet Size) / (Dispersion)

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

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. Capacity Capacity

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

Proposed Approach: PBProbe

k is depended on the estimated link capacity and the supported timer resolution. n is set to 200. D thresh is set to 1ms. U is set to

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:

Analysis

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

Evaluation 1: NISTNet emulation No cross traffic

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

Evaluation 3: PBProbe vs Pathrate

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.

Acknowledgements This work is co-sponsored by the National Science Council and the National Science Foundation under grant numbers NSC E and CNS 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).

Thanks! CapProbe: CapProbe: