Ad-hoc Storage Overlay System (ASOS): A Delay-Tolerant Approach in MANETs
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Ad-hoc Storage Overlay System (ASOS): A Delay-Tolerant
Approach in MANETs
Guang Yang, Ling-Jyh Chen, Tony Sun, Biao Zhou and Mario Gerla
Computer Science Department, UCLA
Mobile Adhoc and Sensor Systems (MASS), 2006 IEEE International Conference on
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Outline
Introduction Application Scenarios and Design
Principles The Ad-hoc Storage Overlay System
(ASOS) Architecture Probabilistic Data Replication Evaluation Conclusion
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INTRODUCTION
MANETs set up rapidly without pre-deployed infras
tructure Military battlefields, disaster recovery
tasks must be fulfilled quickly Nodes may crash, lose power, be blocked,
or move out of the communication range of its neighbors
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Motivation
End-to-end connectivity is highly susceptible to disruption Adjusting the motion of existing
nodes or deploying additional nodes can improve it
For scenarios where connectivity cannot be immediately improved
Proposed solution: Ad-hoc Storage Overlay System (ASOS)
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Assumption A heterogenous MANET environment File transfer are considered as delay toler
ant A number of mobile nodes capture useful
data and send back to the control center Part of the data may not be delivered to t
he control center in time due to connectivity disruptions
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Design Principles
Safe and robust storage Immediate availability Efficient storage and easy delivery Friendly interface
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ASOS architecture
Initialization and Maintenance of ASOS Selecting ASOS peers Peer and file IDs Initialization Maintenance
ASOS Interface Data Management
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ASOS architecture
source ASOS
disconnect
destination
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Selecting ASOS peers
ASOS is a self-organized P2P overlay of existing nodes
It is desirable to designate a set of powerful nodes
Other regular nodes must understand the ASOS interface to access the storage utility
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Peer and file IDs
Every node has a unique ID Files can be uniquely identified by
hashing from source/destination IDs and other information
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Initialization
All ASOS peers form a multicast group Each ASOS peer multicasts periodic HELL
O messages to all ASOS peers Every peer can hear from all other reacha
ble peers and know which files are stored in ASOS and where they are
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Format of a HELLO message
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Maintenance
Each ASOS peer maintains a lookup table of reachable neighbors
Entries in the table contain similar fields as in the HELLO messages
Each entry is also associated with an expiration timer that is reset when the entry is refreshed
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ASOS architecture
Initialization and Maintenance of ASOS ASOS Interface
Advertising of ASOS peers Disruption detection and data submission Data retrieval from ASOS
Data Management
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Advertising of ASOS peers
Regular nodes could look at the HELLO messages to learn about the nearby ASOS peers and stored files Overhead
Introduce a new type of ADVERTISE messages
One node only forwards the first fresh ADVERTISE message it receives
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Decouple the task of advertising
ASOS
A
ADVERTISE message
Entries
lookup table
A1
10unit(5,10)files
F
D
GC
E
B
a A 100k info
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Disruption detection and data submission
ASOS
ASOS ASOS
A
Source
B
C
destination
disconnected
RERRRERR
Switching end-to-end flowto the ASOS mode
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Disruption detection and data submission
ASOS
ASOS ASOS
A
Source
B
C
destination
disconnected
File Start Size
1 200 150
File Start Size
1 150 50
File Start Size
1 0 200
be divided into several chunks
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Data retrieval from ASOS: pull model
ASOS
ASOS ASOS
A
Source
B
C
destinationADVERTISE
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Data retrieval from ASOS: push model
ASOS
ASOS ASOS
A
Source
B
C
destination
hello
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ASOS architecture Initialization and Maintenance of
ASOS ASOS Interface Data Management
Probabilistic selection of storage locations
Other data transfer between ASOS peers
Data deletion and replacement
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Probabilistic selection of storage locations
To increase storage reliability, data is also replicated to other ASOS peers
Storage locations are selected by probabilistic replication: A peer closer to the destination node A peer further away from other ASOS
peers A peer less heavily loaded have a higher
probability to be selected
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Other data transfer between ASOS peers
An ASOS peer may also dynamically transfer stored data to another peer running short of power or storage space
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Data deletion and replacement
When the data is successfully delivered or has lost its usefulness
The original source or destination message its ASOS agent to delete data
The agent disseminates this message to all ASOS peers
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ASOS Peer Deployment and Probabilistic Location selection under the VT Mobility Model
The Virtual Track (VT) mobility model targets the MANET scenario where mobility of the grouped nodes is constrained
Initially, each group contains a certain number of ASOS peers
Due to splitting, a group may temporarily have zero ASOS peers nodes turn to ASOS peers, or to static/individual
peers
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The Virtual Track mobility model
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Evaluation Application module: QualNet Simulation scenario: UCLA campus map 30 Nodes 1600 m×1600 m square area: 5 static,
5 individual (RWP) and 20 grouped (divided into 4 groups)
Each source generates a periodic constant-bit-rate (CBR) flow, at the rate of 80 Kbps, for 10 seconds every minute
Each simulation runs 20 minutes
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Screen snapshot of the simulation topology in QualNet
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Simulation parameters are summarized
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Simulation parameters are summarized
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Instantaneous throughput measured at the destination node
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Cumulative amount of data delivered to the destination as time proceeds
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Delivery ratios of data generated in each minute
static node individual node grouped node
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Cumulative distribution function (CDF) of the size of HELLO messages
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Delivery ratio vs. number of ASOS peers
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Delivery ratio vs. number of replicated data copies
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Conclusion
The Ad-hoc Storage Overlay System (ASOS) that extends end-to-end data transport in MANETs when connectivity is disrupted
Storing undeliverable data reliably in an overlay of storage-abundant
Implemented the ASOS in QualNet
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Future work
ASOS peers can be dynamically elected Data encryption, user authentication and
intrusion detection are needed Soft disruptions
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Thank you!