“Effects of power conservation, wireless
coverage and cooperation on data
dissemination among mobile devices”
2001
Authors: Maria Papadopouli and
Henning Schulzrinne
Presented by:
Taylor Perkins
About Me

Taylor Perkins
– 5th Year Co-op Computer Science Major
– Specializations: UI & Databases
– From Roswell, GA
– Interests:
 Anything new and interesting
 More high-level, less low-level
Problem

Increase in non-voice data
– News, traffic, weather, sports, etc.

Sparse coverage or high cost
 Requires connectivity to the Internet
 Lots of Power Usage
 How to increase data access, but not
increase power usage?
Solution

Share data between roaming users
 Motivation:
– High spatial locality of info
– Different information providers
 Not necessarily cooperating with each other

Imagine: A Train or Airport
– High spatial locality: News, sports, schedules
– Popular info: Music & Video games
7DS – P2P sharing system
“7DS is an architecture, a set of protocols,
and an implementation enabling the
exchange of data among peers that are not
necessarily connected to the Internet.”
 Application
 Mobile & Stationary Devices
 Anticipate information needs, searches
among peers for this information.

How it Works

Two modes
– Prefetch
 Anticipate information needs
– On-demand
 Search among peers after fetch from Internet fails

Two interaction types
– Peer-to-peer (P-P) – 7DS’s main focus
 Data sharing
 Message forwarding
 Caching popular information
– Server-Client (S-C) – Servers also connected to other servers
 Data sharing
 Message forwarding
 Caching popular information
More Details

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Device forms queries based on URL of request
Also predicts future URLs
Multicasts these queries to other devices
Host can select subset of requests to listen to
(Saves power)
7DS-enabled servers can broadcast that they have
data (advertisement)
7DS organizes and manages device cache
– User can view, browse and manage cache through GUI
How it Saves Power

Trades power for data only when battery is above
threshold.
 Reduce energy consumption
–
–
–
–

Idle periods
Low expectation of data
Battery life below threshold
Periodically turn off network interface
Reduce collaboration (Thresholds):
– Above 75% Battery: Active querying
– 50%-75%: Passive querying (only responds)
– Below 50%: Stops participation in 7DS
Some Results
Experiment Setup:
1km x 1km test space.
One node has data, which all
other nodes are interested in
getting.
Some More Results
And More Results
Criticism

7 Years old
– More power, more bandwidth

Requires other 7DS users
– Software install
– Cooperation

Hard to Perform Experiments
– Requires simulation