This document discusses using distributed hash tables (DHTs) for data sharing on mobile ad-hoc networks. It notes the increasing number of internet-enabled mobile devices and interest in ad-hoc networks that self-configure without infrastructure. The POSIT application currently uses random walk gossip to share data between devices in ad-hoc mode, but this is inefficient due to high power usage, inability to handle nodes leaving and rejoining, and potential for incomplete data transmission. The document proposes studying the use of DHTs, which could improve efficiency by reducing communication and intelligently routing data even when nodes disconnect and reconnect.

1. Sharing data using Distributed HashTables on MobileAd-hoc Networks
ProjectThor
PrasannaGautam ‘11
Advisor: Dr.Timothy Richards
Computer Science Department

2.  Number of Internet enabled mobile devices is
increasing
(Source: ITU, Mark Lipacis, Morgan Stanley Research)

3.  Mobile Ad-hoc Networks (MANET)
 Self configuring wireless network

4.  Great interest in research and defense industry
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Research Papers trend (1995-2009)
Adhoc Network MANET "Adhoc Network" and MANET
(Source: mendeley.com)

5.  Pros
 Can be used in
▪ Disaster Scenarios
▪ When Infrastructure is unavailable
▪ Deploying infrastructure is too expensive
 Existing implementations in major OSes (802.11
ad hoc mode)
▪ Heterogeneous setup possible
 Quick setup
 Cheap to deploy

6.  Cons
 Power hungry
 Limited network access
 Churn
▪ Nodes coming in and out of network
 Difficult network management

7.  POSIT – search and catalog application
running on Android
 Started in 2008
 RWG Adhoc protocol implemented in
collaboration with Linköping University, Sweden
 RandomWalk Gossip
 Phones send messages randomly
 until a specified number of phones have received
it

8.  POSIT is deployed in a location without
network access
 RWG is used
 After a few hours, they start draining out
 Some phones will never see some data

9.  Power Usage
 Churn
 Nodes coming in and out of the network/range

10.  Without using network (ADP1)
 Phone lasted for ~132 hours = 5.5 days
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0:00:00 24:00:00 48:00:00 72:00:00 96:00:00 120:00:00 144:00:00
Battery Level (no network usage) on HTC ADP1
Battery

11.  Sending ~50 bytes every second
 Phone lasted for 12.8 hours
▪ 14999 messages = 14999*50 bytes = 732.37 KB
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0:00:00 2:24:00 4:48:00 7:12:00 9:36:00 12:00:00 14:24:00
battery performance when sending 50 bytes
per second
level

12.  Sending 1K file every 5 seconds
 Phone lasted for 13.5 hours
▪ 6998 messages = 6998 KB = 6.83 MB
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60
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100
120
0:00:00 2:24:00 4:48:00 7:12:00 9:36:00 12:00:00 14:24:00
battery performance when sending 1K of data
every 5 seconds
level

13.  Sending 1K file every second
 Phone lasted for 8 hours
▪ 14696 messages = 14696 KB = 14.35MB
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40
60
80
100
120
0:00:00 1:12:00 2:24:00 3:36:00 4:48:00 6:00:00 7:12:00 8:24:00 9:36:00
battery performance when sending 1K of data
every second
level

14.  Talk less
 When you do talk, say more

15.  Nodes can come in an out of the network
 Could have multiple sub-networks
 Not necessarily defined structure/topology

16.  Distributed HashTables (DHTs)
 Distributed system provides lookup similar to
hash table
 Information is distributed and replicated among
nodes

17.  Used extensively by peer-to-peer applications
like Bittorrent

18.  A Churn and Mobility ResistantApproach for DHTs (Landsiedel et. al.)
 r being the communication range
 Data can be stored within r/2 distance to be reachable by a node n

19.  Study algorithms based on DHT on Mobile
Ad-hoc Networks
 Design and implement a specialized DHT
simulator program
 Test various conditions
▪ Power usage
▪ Topologies
▪ Effects of churning
▪ Network Partition

20.  RWG
 constantly communicating/sending data
 Random routing
 Can’t handle incomplete downloads
 DHT
 Minimal communication
 Intelligent routing
 Even incomplete data is useful

21.  DHTs have shown to
 Deal with churn effectively
 Reduce overall communication
 Using DHTs for communication on Adhoc
Networks should
 Improve power usage
 Handle churn better