1. pathChirp Efficient Available Bandwidth Estimation
Vinay Ribeiro
Rice University
Rolf Riedi Jiri Navratil
Rich Baraniuk Les Cottrell
(Rice) (SLAC)

2. Network Model End-to-end paths Router queues Multi-hop
No packet reordering
Router queues
FIFO
Constant service rate
Packet delay = constant term
(propagation,
service time) +
variable term
(queuing delay)

3. Available Bandwidth Available bandwidth:
Unused capacity along path
Available bandwidth:
Goal: use end-to-end probing to estimate available bandwidth

4. Applications Server selection Route selection (e.g. BGP)
Network monitoring
SLA verification
Congestion control

5. Available Bandwidth Probing Tool Requirements
Fast estimate within few RTTs
Unobtrusive introduce light probing load
Accurate
No topology information (e.g. link speeds)
Robust to multiple congested links
No topology information (e.g. link speeds)
Robust to multiple congested links

6. Principle of Self-Induced Congestion
Probing rate < available bw  no delay increase
Probing rate > available bw  delay increases
Advantages
No topology information required
Robust to multiple bottlenecks
TCP-Vegas uses self-induced congestion principle

7. Trains of Packet-Pairs (TOPP) [Melander et al]
Shortcoming: packet-pairs
do not capture temporal
queuing behavior useful for
available bandwidth
estimation
Vary sender packet-pair spacing
Compute avg. receiver packet-pair spacing
Constrained regression based estimate
Packet train
Packet-pairs

8. Pathload [Jain & Dovrolis]
CBR packet trains
Vary rate of successive trains
Converge to available bandwidth
Shortcoming
Efficiency: only one data rate per train

9. Chirp Packet Trains
Exponentially decrease packet spacing within packet train
Wide range of probing rates
Efficient: few packets

10. Chirps vs. Packet-Pairs
Each chirp train of N packets contains N-1 packet pairs at different spacings
Reduces load by 50%
Chirps: N-1 packet spacings, N packets
Packet-pairs: N-1 packet spacings, 2N-2 packets
Captures temporal queuing behavior

11. Chirps vs. CBR Trains Multiple rates in each chirping train
Allows one estimate per-chirp
Potentially more efficient estimation

12. CBR Cross-Traffic Scenario
Point of onset of increase in queuing delay gives available bandwidth

13. Bursty Cross-Traffic Scenario
Goal: exploit information in queuing delay signature

14. PathChirp Methodology
Per-packet pair available bandwidth, (k=packet number)
Per-chirp available bandwidth
Smooth per-chirp estimate over sliding time window of size

15. Self-Induced Congestion Heuristic
Definitions: delay of packet k
inst rate at packet k

16. Excursions
Must take care while using self-induced congestion principle
Segment signature into excursions from x-axis
Valid excursions are those consisting of at least “L” packets
Apply only to valid excursions

17. Setting Per-Packet Pair Available Bandwidth
Valid excursion increasing queuing delay
Last excursion
Valid excursion decreasing queuing delay
Invalid excursions

18. pathChirp Tool UDP probe packets
No clock synchronization required, only uses relative queuing delay within a chirp duration
Computation at receiver
Context switching detection
User specified average probing rate
open source distribution at spin.rice.edu

19. Performance with Varying Parameters
Vary probe size, spread factor
Probing load const.
Mean squared error (MSE) of estimates
Result: MSE decreases with increasing probe size, decreasing spread factor

20. Multi-hop Experiments
First queue is bottleneck
Compare
No cross-traffic at queue 2
With cross-traffic at queue 2
Result: MSE close in both scenarios

21. Internet Experiments
3 common hops between SLACRice and ChicagoRice paths
Estimates fall in proportion to introduced Poisson traffic

22. Comparison with TOPP Equal avg. probing rates for pathChirp and TOPP
Result: pathChirp outperforms TOPP
30% utilization
70% utilization

23. Comparison with Pathload
100Mbps links
pathChirp uses 10 times fewer bytes for comparable accuracy
Available bandwidth
Efficiency
Accuracy
pathchirp
pathload
pathChirp
10-90%
Avg.min-max
30Mbps
0.35MB
3.9MB
19-29Mbps
16-31Mbps
50Mbps
0.75MB
5.6MB
39-48Mbps
39-52Mbps
70Mbps
0.6MB
8.6MB
54-63Mbps
63-74Mbps

24. Conclusions Chirp trains pathChirp Experiments
Probe at multiple rates simultaneously
Efficient estimates
pathChirp
Self-induced congestion
Excursion detection
Experiments
Internet experiments promising
Large probe packet size, small spread factor better
Outperforms existing tools
open-source code is available at
spin.rice.edu
Demo during 10:30a.m. break