End-to-end Asymmetric Link Capacity Estimation

1. End-to-end Asymmetric Link Capacity Estimation Ling-Jyh Chen, Tony Sun, Guang Yang, M.Y. Sanadidi, Mario Gerla Dept. 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 • These approaches are either one-way based or unable to estimate asymmetric link capacities.

4. Estimating Asymmetric Links • Asymmetric links are becoming popular (e.g. DSL, cable modems, and satellite links). • Knowing the capacity of BOTH direction links is important for applications. • Related work: • ALBP [Yu et al, ICC’03] employs a multi-packet delay model to estimate “per-hop” capacity of asymmetric links.

5. Our Contribution • We propose an end-to-end asymmetric link capacity estimation technique, called AsymProbe. • AsymProbe is CapProbe based: • round trip method • packet pair 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: AsymProbe

10. AsymProbe: Example C=P/T

11. AsymProbe Algorithm • AsymProbe has four phases: • Phase 1: the probing phase (P1=Pmax ; P2=Pmax ) (=> CapProbe) • Phase 2: the probing phase (P1=Pmax ; P2=Pmin) • Phase 3: the probing phase (P1=Pmin ; P2=Pmax ) • Phase 4: the decision phase

12. AsymProbe Algorithm • The decision phase:

13. Issues • AsymProbe is able to estimate asymmetric link capacities when the “asymmetric ratio” is larger than Pmin /Pmax and smaller than Pmax /Pmin. • AsymProbe can not estimate “extremely asymmetric” links. • Pmax is limited by MTU. • Pmin is limited by the supported system time resolution.

14. Simulation • AsymProbe: A <-> B; Cross Traffic: C <->B • E->D: 1.5Mbps; D->E: 128kbps

15. Simulation Results • Pmax=1500 bytes ; Pmin=100 bytes

16. Emulation • Pmax=1500 bytes ; Pmin=500 bytes

17. Emulation Results

18. Internet Experiments • P1=1500 bytes, P2=500 bytes • Supported “asymmetric ratio” = 3:1

19. Application – TCP Probe • The concept of AsymProbe can be integrated with other data transmission protocols, e.g. TCP. • TCP packet size: • forward direction: TCP data 1500 bytes • reverse direction: TCP ACK 40 bytes • According to AsymProbe algorithm: • If , then T1>T2TCP Probe estimates the capacity of the forward direction link • If , then T1<T2TCP Probe estimates the capacity of the reverse direction link

20. CapProbe: DelAck TCP Probe: TCP Probe • More details in [Anders et al, GI’05]

21. TCP Probe Application • Vertical handoff usually results in a dramatic change in the path capacity. • Service agility using “Fast Rate Adaptation” (FRA) algorithm • FRA forces TCP to enter Slow Start when detecting a handoff from LOW to HIGH

22. Service Agility – TCP Probe • TCP Probe with “fast rate adaptation” • Vertical handoff from 10Mbps to 100Mbps Unit: bps

23. Summary • We propose an end-to-end asymmetric link capacity estimation technique, called AsymProbe. • We evaluate AsymProbe by simulation and Internet experiments. • The concept of AsymProbe can be integrated with other data transmission protocols. • We present a passive capacity estimation technique, called TCP Probe, which integrates AsymProbe with TCP.

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