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

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.

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

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

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

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

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.

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.

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

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

Multihop path simulation AP dispersion 2 sender back to back packets wired Internet wireless multihop dispersion 1

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

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

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.