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 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.

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

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

8. 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

9. Proposed Approach: AsymProbe

10. AsymProbe: Example C1C1 C2C2 P1P1 P2P2 T1T1 T2T2 C' 1 C' 2 1000 kbps 500 kbps 1500 bytes100 bytes12 ms1.6 ms1000.00 kbps66.67 kbps 1500 bytes300 bytes12 ms4.8 ms1000.00 kbps200.00 kbps 1500 bytes500 bytes12 ms8 ms1000.00 kbps333.33 kbps 1500 bytes700 bytes12 ms11.2 ms1000.00 kbps466.67 kbps 1500 bytes900 bytes12 ms14.4 ms833.33 kbps500.00 kbps 1500 bytes1100 bytes12 ms17.6 ms681.82 kbps500.00 kbps 1500 bytes1300 bytes12 ms20.8 ms576.92 kbps500.00 kbps 1500 bytes 12 ms24 ms500.00 kbps 500 kbps 1000 kbps 100 bytes1500 bytes1.6 ms12 ms66.67 kbps1000.00 kbps 300 bytes1500 bytes4.8 ms12 ms200.00 kbps1000.00 kbps 500 bytes1500 bytes8 ms12 ms333.33 kbps1000.00 kbps 700 bytes1500 bytes11.2 ms12 ms466.67 kbps1000.00 kbps 900 bytes1500 bytes14.4 ms12 ms500.00 kbps833.33 kbps 1100 bytes1500 bytes17.6 ms12 ms500.00 kbps681.82 kbps 1300 bytes1500 bytes20.8 ms12 ms500.00 kbps576.92 kbps 1500 bytes 24 ms12 ms500.00 kbps C=P/TC=P/T

11. AsymProbe Algorithm AsymProbe has four phases:  Phase 1: the probing phase (P 1 =P max ; P 2 =P max ) (=> CapProbe)  Phase 2: the probing phase (P 1 =P max ; P 2 =P min )  Phase 3: the probing phase (P 1 =P min ; P 2 =P max )  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 P min /P max and smaller than P max /P min. AsymProbe can not estimate “extremely asymmetric” links. P max is limited by MTU. P min is limited by the supported system time resolution. Packet Size Narrow Link Capacity 100 Mbps10 Mbps1 Mbps 500 bytes0.04 ms0.4 ms4 ms 1000 bytes0.08 ms0.8 ms8 ms 1500 bytes0.12 ms1.2 ms12 ms

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

15. Simulation Results P max =1500 bytes ; P min =100 bytes

16. Emulation P max =1500 bytes ; P min =500 bytes

17. Emulation Results

18. Internet Experiments P 1 =1500 bytes, P 2 =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 T 1 >T 2 TCP Probe estimates the capacity of the forward direction link  If, then T 1 <T 2 TCP Probe estimates the capacity of the reverse direction link

20. TCP Probe DelAck TCP Probe: CapProbe: 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 Unit: bps TCP Probe with “fast rate adaptation” Vertical handoff from 10Mbps to 100Mbps

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: CapProbe: http://nrl.cs.ucla.edu/CapProbe/