CS8803ISA Course Reading Summaries

Paper #: 5.2 - 16
Title: Effects of power conversion, wireless coverage and cooperation 
on data dissemination among mobile devices

(1) Problems
The system addresses the problem of providing data sharing among 
mobile, wireless devices.  The idea is to increase data availability 
to mobile users in a metro area, where they have only intermittent 
connectivity to the Internet.  Since mobile devices don't get have 
consistent, cheap access to the Internet, we need ways to share data 
that don't require such access.  The kind of data that people need 
tends to be localized; i.e., folks around a movie theater might all 
need to access a web page to buy tickets.  The system exploits such 
localization and tries to keep up-to-date much-needed information 
available, even without Internet availability.



(2) New Idea and Strengths
The system does what it can, when it can.  It tries to guess what 
users might need, and get it ahead of time (prefetch).  Also of 
course, when a user asks for something, the system makes specific 
demands to get that data (if it hasn't been prefetched).  The system 
is effective because it uses a variety of methods to increase data 
availability.  Nodes share the data they have; forward queries and 
responses to other nodes; and cache popular data objects.  It turns 
out that when the system runs in peer-to-peer mode (like Gnutella, 
where hosts cooperate with each other), data gets distributed faster 
among the hosts in the system.


The system also has good ways to preserve battery power.  When the 
battery is weaker, it can use less ways to get data, for example, 
instead of periodically sending out a data query for something it 
needs (or thinks it will need), it can wait passively for an 
"advertisement" from a host, i.e., a description of information and/or 
applications it has.  Upon receipt of the advertisement, it can send 
the query to that host, knowing that it will be satisfied.

It's neat that the system can be configured to automatically re-fetch 
items that have gotten out-of-date, so when the user needs such an 
item he can access an up-to-date version.

(3) Weaknesses and Extensions


The paper uses simulations and a rudimentary mathematical analysis to 
show that the system works.  To really know it works, we need to see 
an experiment that uses real devices, lots of them, in some realistic 
setting (like an airport or a busy downdown area).  The authors 
propose a neat extension, a mechanism to indicate the appropriate 
interaction (P-P, S-C, etc.) based on parameters such as data 
availability prediction, battery level, and proximity of other 7DS 
devices/applications.  They planned to use the application with a tou 
guide and academic news notification system.  There are significant 
user privacy and security issues to deal with.  Any system like this 
(in its infancy) may not seem very useful and convenient, but this is 
a start and I think it's promising.  However, if we soon get to a 
point where wireless Internet coverage is more available, this 
research may be superceeded by plain Internet access by mobile 
devices.