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CapProbe

CapProbe is a packet-pair technique to estimate bottleneck capacity in wired networks. AdHoc Probe, based on CapProbe, accurately measures wireless path capacity. It is fast, accurate, and less intrusive.

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CapProbe

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  1. CapProbe Ling-Jyh Chen, M. Y. Sanadidi, Mario Gerla Computer Science Department, UCLA

  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. Potential Applications • Adaptive multimedia streaming • Congestion control • P2P peer selection • Overlay network structuring • Wireless link monitoring • Mobility tracing and detection

  4. 20Mbps 10Mbps 5Mbps 10Mbps 20Mbps 8Mbps T1 Narrowest Link T2 T3 T3 T3 T3 Packet Pair Dispersion

  5. Capacity CapProbe • Key insight: a packet pair that gets through with zero queueing delay yields the exact estimate

  6. Measurements- Internet, Internet2 (Abilene) • CapProbe implemented using PING packets, sent in pairs

  7. CapProbe in Ad Hoc Net • Capacity estimation in wireless net is still challenging. • Previous method (Morris et al) is brute force. • Path capacity in wireless ad hoc net depends on bottleneck capacity, topology, interference, and other environment parameters.

  8. What do we wanna measure? • The effective end-to-end rate is defined as the maximum achievable data rate in the absence of any cross traffic connection. • It is smaller than the raw data rate at the physical layer due to packet O/H and channel access coordination to handle multiple, pipelined packets on the path.

  9. Effective Capacity of 802.11b • In 802.11b, a RTS packet is 40 bytes, CTS and ACK packets are 39 bytes, and the MAC header of a data packet is 47 bytes, the effective capacity of a one-hop link is: • For instance, when the data packet size is 1500 bytes and the data rate of the wireless link is 2Mbps, the effective capacity is at most

  10. One-way/Round-trip estimation Immediate ACK of first probing packet will conflict with the second probing packet!

  11. back to back packets dispersion 1 dispersion 2 wired Internet wireless multihop AP 1 hop 2 hop 3 hop 4 hop 5 hop 6 hop 7 hop sender Multihop path simulation

  12. Simulation of mobile hosts • Probing the capacity of path (1 -> 6) • N2~5 move clockwise • 200 samples/run, 20 runs

  13. 1800 0 2200 3000 2800 2600 1200 600 Simulation of mobile end hosts • Probing the capacity of path (0 ->25) • Mobility: 1 m/sec; Cross Traffic: 1kbps/flow • 200 samples/estimation; 4 samples/second

  14. Summary • CapProbe is a packet-pair based technique to estimate bottleneck capacity in wired networks. • AdHoc Probe is based on CapProbe, and it is able to correctly measure path capacity of a wireless path. • AdHoc Probe is simple, fast, accurate, and much less intrusive.

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