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

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

6. Measurements- Internet, Internet2 (Abilene)
CapProbe implemented using PING packets, sent in pairs To
UCLA-2
UCLA-3 UA
NTNU
Time
Capacity
Cap
Probe
0’03
5.5
0’01 96
0’02 98
0’07 97
5.6
0’04 79
0’17 83
0’22
Pathrate
6’10
0’16
5’19 86
0’29
6’14
5.4
5’20 88
0’25
6’5
5.7
5’18
133
Pathchar
21’12
4.0
22’49 18
3 hr 34
20’43
3.9
27’41 35
21.18
29’47 30

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 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

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

11. Multihop path simulationAP
dispersion 2
sender
back to back packets
wired Internet
wireless multihop
dispersion 1

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

13. 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
600
1200
1800
2200
2600
2800
3000

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.