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

2. Outline Motivation Background AdHoc Probe Experiment Results
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
But complexity and convergence time of these schemes not suitable for wireless environment
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.
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5. Effective Capacity of 802.11b
In b, 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
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6. Effective capacity of a multihop link
If N nodes are within the same interference domain, C’=C/N
The solid-line circle: effective transmission range (Dr)
The dotted-line circle: interference range (Di)
Distance between nodes: 200m
Dr=Di=250m => C’=C/3
Dr=250m, Di=500m => C’=C/4
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7. Previous Work (Morris et al)
Dr=250m, Di=500m
Use UDP flows to probe the maximum achievable throughput (brute force method)
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8. Outline Motivation Background AdHoc Probe Experiment Results
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.
End-to-end path capacity is different to bottleneck link capacity in wireless net.
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10. Packet Pair Dispersion
Narrowest Link T2 T3 T3 T3
20Mbps
10Mbps
5Mbps
8Mbps
Capacity = (Packet Size) / (Dispersion)
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11. Issues: Compression and Expansion
Queueing delay on the first packet => compression
Queueing delay on the second packet => expansion
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12. CapProbe concept Capacity
Key insight: a packet pair that gets through with zero queueing delay yields the exact estimate
Capacity
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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.
Previous method (Morris et al) is brute force.
Capacity estimation in wireless net is still challenging.
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14. Auto Rate Schemes Rate adaptation Opportunistic scheduling
Sender based: ARF, AARF
Receiver based: RBAR
Opportunistic scheduling
OAR, PAC (MAD)
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15. Implementation issues
System time synchronization
If for , then , and vice versa.
Clock skew
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16. Outline Motivation Background AdHoc Probe Experiment Results
What are we trying to measure?
Effective Capacity
Previous Method
AdHoc Probe
Experiment Results
Conclusion
WiTMeMo05

17. Multihop path simulationAP
dispersion 2
sender
back to back packets
wired Internet
wireless multihop
dispersion 1
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18. Experiment Results (1)
Fixed rate, multihops
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19. Experiment Results (2)
Auto Rate, w/ different distance
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20. Experiment Results (3)
Auto Rate, w/ Bluetooth interference
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21. Experiment Results (4)
Probing from the Internet
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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.
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23. Thanks!
CapProbe:
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