The Power of Indirect Ties in Friend-to-Friend Storage Systems

Xiang Zuo1, Jeremy Blackburn2, Nicolas Kourtellis3, John Skvoretz1 and Adriana Iamnitchi1

IEEE International Conference on Peer-to-Peer Computing 2014

1University of South Florida – Florida, USA 2Telefonica Research – Barcelona, Spain 3Yahoo Labs – Barcelona, Spain

Friend-to-Friend (F2F) Storage Systems

Users share storage resources only with friends and expect their friends behave cooperatively.

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Limitations:

Low available storage

Low data availabilitySmall number of friends

Poor Service

Solution: Use Socially Close Indirect Relationships to Expand a User’s Friendsets

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Question: How do we select FoFs with incentives for cooperative storage in F2F storage systems?

Answer: • Social Strength (SS) metric to measure the

strength of indirect ties.• Friendset expansion algorithm to select FoFs

with incentives.

Intuition: In real life, people rely on friends of friends (FoFs) for recommendations.

Observations from Sociology

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The strength of a direct tie is related to the amount

of interactions.

Multiple types of interactions result in a stronger

relationship than only with one type.

The strength of an indirect tie decreases with the

length of the shortest path between the two users.

SSn(A, B) ≠SSn(B, A).

Social Strength Metric

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Example

Friendset Expansion Algorithm

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Our Friendsets Expansion Algorithm:

NOT all indirect ties of a user have incentives for cooperative storage.

i’s friendset: j, k

Social Strength

SS2(i,m)=0.39>0.33, then i’s friendset: j, k and m

i

j

k

m0.67

0.55

0.33 0.8

SS2(i,m)=0.39

n

SS2 (i,n)=0.05

2 8j

k

m

4 6

n

1

i

Each user uses a user-specific, local information of the graph that is needed in the distributed computing of F2F systems.

Improved Data AvailabilityDataset: TF2 and Friends expansion on 2 and 3 hops

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TF2 players’ real-world average

Online/Offline traces of a week.

Timestamps are represented in

PST.

6.5 times

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Imbalanced Workload Distribution

High-degree users are allocated higher workload than

low-degree users.

Solution: Low Degree then Low Workload (LDLW)

Improved Workload Distribution

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Summary

Proposed an indirect tie measurement—Social Strength

metric—and a friendset expansion algorithm.

Expanded friendsets improve the performance of F2F

storage systems.

Social Strength metric and the expansion algorithm can

also be used for more general socially aware systems.

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