1. How to Select a Good Alternate Path in Large Peer-to-Peer Systems
Teng Fei, Shu Tao, Lixin Gao and Roch Guerin
Univ. of Massachusetts, Amherst Univ. of Pennsylvania
IEEE Infocom 2006
Barcelona, Spain April,

2. Background Performance degradations occur in Internet
Application path switching is helpful when multiple paths exist
Peer-to-Peer network is an attractive platform
Heterogeneous network
Minimum infrastructure support requirement

3. Selecting Alternate Paths
From thousands of IP addresses
choose one as relay
Better than random
Uncorrelated paths

4. Illustration of Earliest Divergence Rule
Select paths diverge at the earliest AS
Among pre-selected path set, select one
Randomly (basic EDR)
“Farthest” from the source (extended EDR)
Relay1
Relay2
Src
Dst A B C D

5. Evaluation of EDR
Parallel paths diverging early have smaller overall overlapping
Topology based study
AS path data obtained from Oregon/RIPE and Planet lab
Physically less overlapped paths have less correlated performance
Measurement based study
Active UDP probe using Planetlab nodes

6. Effect of Reducing Relay Node Numbers
Reduces the relay number for most src-dst pairs
Extended ED help further
Planetlab

7. Effect of Selecting Disjoint Paths
ED rejects bad paths, retain good ones
Increases the likelihood of selecting good ones
Before applying ED
After applying ED

8. Comparison With Random-4
Perform better than random-4
Improve the candidate set of random-4
Planetlab
Oregon/RIPE

9. Evaluation of EDR
Parallel paths diverging early have smaller overall overlapping
Topology based study
AS path data obtained from Oregon/RIPE and Planet lab
Physically less overlapped paths have less correlated performance
Measurement based study
Active UDP probe using 47 Planetlab nodes

10. Performance Correlation Metrics
Focus on delay and loss variation of paths
Delay and loss degradation
Correlated
Evaluate overlay path “goodness” by percentage of delay degradation on default path may be avoided

11. Extended Earliest Divergence Rule
First apply the earliest divergence rule
Select an acceptable maximum delay constrain
Select the node with largest round-trip delay within the delay constrain
Intuition
A far away node is less likely to merge back

12. Performance Evaluation of EDR
Better than random in most cases
Significantly better in many cases

13. Comparison With Other Schemes

14. Summary
Physical path disjointness indicates less correlated application performance
EDR is effective in selecting disjoint overlay paths
EDR effective selects overlay with uncorrelated performance with the default path using local topological information
Benefit of EDR more significant when source AS degree is small

15. Question?