1. Bandwidth Measurement of Pakistan’s Internet Topology

2. Motivation Available Bandwidth impacts application performance, VoIP, Video Conferencing Load balancing, Multi-Homing To choose alternate paths in overlay networks

3. Definitions Available Bandwidth: The spare or unused capacity of a link during a certain time period. Dispersion The time difference between the last bit of the first and last packet in train of packets. Transmission Rate The total number of bits sent in a time unit

4. Measurement Techniques

5. Packet Pair Algorithm Two packets of known length (L) are sent with fixed inter-packet interval. The receiver measures dispersal (ΔD) of received pair Bandwidth (B) is calculated by: B = L / ΔD Assumption Link does not carry other traffic because it could effect dispersion

6. Packet Train Dispersion Probing Similar to Packet Pair Algorithm but uses many packets instead just one pair Dispersal calculated between first and last packet in train Cross traffic delays are amortized

7. Self-Loading Periodic Streams Send a stream of packets at constant rate and measure one way delay of each If successive packets have same delay (See Fig a) then transmission rate < bandwidth If successive packets have increasing delay then they themselves causing congestion (See Fig b) Fig 1a Fig 1b

8. SLoPS (Continued) This implies transmission rate > bandwidth If transmission rate > bandwidth then receive rate = bandwidth We find the transmission rate that just causes congestion A binary search mechanism is used to vary transmission rate

9. Tailgating Send a train of very small packets and measure end-to-end latency Send a very large packet with TTL 1 followed by a small packet of high TTL. The large packet will slow the small tailgate packet behind it (for one hop). Size of large packet divided by change in latency can be used to estimate link bandwidth Repeat experiment many times, increasing TTL every time to calculate bandwidth of successive links

10. Tools TechniqueTools Packet Pairs & Trains B-Probe, C-Probe, Nettimer, Pathrate, Spruce SLoPSPathload, PathChirp TailgatingSTAB

11. References “Locating Available Bandwidth Bottlenecks” Vinay J. Ribeiro, Rudolf H. Riedi, and Richard G. Baraniuk. IEEE Internet Computing Sept 2004 Lecture Slides, EEC274, UC Davis Chen-Nee Chuah “A measurement Study of Available Bandwidth Estimation tools” Jacob Strauss, Dina Katabi, Frans Kaashoek