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A Measurement Study of Path Capacity in 802.11b based Wireless Networks

A Measurement Study of Path Capacity in 802.11b based Wireless Networks. Tony Sun, Guang Yang, Ling-Jyh Chen, M. Y. Sanadidi, Mario Gerla. Outline. Motivation Background What are we trying to measure? Effective Capacity Previous Method AdHoc Probe Experiment Results Conclusion.

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A Measurement Study of Path Capacity in 802.11b based Wireless Networks

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  1. A Measurement Study of Path Capacity in 802.11b based Wireless Networks Tony Sun, Guang Yang, Ling-Jyh Chen, M. Y. Sanadidi, Mario Gerla

  2. Outline • Motivation • Background • What are we trying to measure? • Effective Capacity • Previous Method • AdHoc Probe • Experiment Results • Conclusion WiTMeMo05

  3. Motivation • Capacity estimation extensively studied in wired network but not wireless • Evaluation and measurement of of wireless path capacity is of realistic interest • (i.e. Capacity planning, protocol design, performance analysis, system deployment) • Need a new tool that can monitor and measure wireless path capacity well WiTMeMo05

  4. What do we want to 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. WiTMeMo05

  5. 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 WiTMeMo05

  6. The solid-line circle: effective transmission range (Dr) The dotted-line circle: interference range (Di) Distance between nodes: 200m Effective capacity of a multihop link • If N nodes are within the same interference domain, C’=C/N • Dr=Di=250m =>C’=C/3 • Dr=250m, Di=500m =>C’=C/4 WiTMeMo05

  7. Previous Work (Morris et al) • Dr=250m, Di=500m • Use UDP flows to probe the maximum achievable throughput (brute force method) WiTMeMo05

  8. Outline • Motivation • Background • What are we trying to measure? • Effective Capacity • Previous Method • AdHoc Probe • Experiment Results • Conclusion WiTMeMo05

  9. AdHoc Probe • A recently proposed path capacity estimation tool specially designed for the multi-hop ad hoc wireless environment. • One-way estimation technique, based on CapProbe concepts • Aimed to simplify the path capacity estimation process • AdHoc Probe measures end-to-end effective capacity in wireless ad hoc networks. • AdHoc Probe is simple, fast and less intrusive compared to other schemes. WiTMeMo05

  10. 20Mbps 10Mbps 5Mbps 10Mbps 20Mbps 8Mbps T1 Narrowest Link T2 T3 T3 T3 T3 Packet Pair Dispersion Capacity = (Packet Size) / (Dispersion) WiTMeMo05

  11. Issues: Compression and Expansion • Queueing delay on the first packet => compression • Queueing delay on the second packet => expansion WiTMeMo05

  12. Capacity CapProbe concept • Key insight: a packet pair that gets through with zero queueing delay yields the exact estimate WiTMeMo05

  13. Estimating Capacity in Ad Hoc Network • Path capacity in wireless ad hoc net depends on bottleneck capacity, topology, interference, and other environment parameters. • Data rate can be fixed or auto. WiTMeMo05

  14. Auto Rate Schemes • Rate adaptation • Sender based: ARF, AARF • Receiver based: RBAR • Opportunistic scheduling • OAR, PAC (MAD) WiTMeMo05

  15. Implementation issues • System time synchronization If for , then , and vice versa. • Clock skew WiTMeMo05

  16. Outline • Motivation • Background • What are we trying to measure? • Effective Capacity • Previous Method • AdHoc Probe • Experiment Results • Conclusion WiTMeMo05

  17. 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 WiTMeMo05

  18. Experiment Results (1) • Fixed rate, multihops WiTMeMo05

  19. Experiment Results (2) • Auto Rate, w/ different distance WiTMeMo05

  20. Experiment Results (3) • Auto Rate, w/ Bluetooth interference WiTMeMo05

  21. Experiment Results (4) • Probing from the Internet WiTMeMo05

  22. Summary of AdHoc Probe • AdHoc Probe estimates e2e path capacity in ad hoc net. • AdHoc Probe estimates correctly with multihop, interference, and auto rate. • AdHoc Probe can be performed from Internet to the “opportunistic” ad hoc net. WiTMeMo05

  23. Thanks! CapProbe: http://nrl.cs.ucla.edu/CapProbe/ WiTMeMo05

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