Data Management in WSN

1
Data-Centric Cooperative Storage in Wireless
Sensor Networks
Abdalkarim Awad, Reinhard German and Falko
Dressler Chair for Computer Networks and
Communication Systems Erlangen-Nuremberg
University November 2009
2
Wireless Sensor Networks (WSNs)
Limited storage capacity!
3
WSNs Algorithms
storage
4
VCP Virtual Cord Protocol

• How to build the cord?
• How to route using the cord?
• How to make use of
• the available storage capacity ?

5
VCP-Join
range 0,1
Requirements
One node must be pre-programmed as initial node,
i.e. it gets position 0
0
Proactive each joined node sends hello messages
periodically
6
VCP-Join
0
0
1
7
VCP-Join
0
1
1
0.50
0
8
VCP-Join
1
0.50
0
1
0.50
0.75
0
9
VCP-Join
1
0.50
0.75
0
1
0.75
0.50
0
0.6
10
VCP-Join
1
0.75
0.50
0
0.6
0.52
1
0.75
0.50
0
0.6
11
VCP-Routing
Routing greedy forwarding based on local
information
Hash(Data)0.781
Given a static network, routing in VCP is loop
free.
12
Cooperative Storage

• If the nodes are supposed to store data for long
  time, the storage capacity of an individual
  sensor node can gets exhausted.
• Use the successors on the cord to store data
• Bloom filters can be used to restrict query
  forwarding

Ring disabled
Ring enabled
13
Bloom Filters

• Compact data structures to represent a set of a
  data items
• Appropriate to answer membership queries

14
Bloom Filters (contd)
0
H1(x)
Belong(y)
check the bits at positions H1(y), H2(y),
H3(y).
Insert(x)
H2(x)
set the bits at positions H1(x), H2(x), H3(x).
H3(x)
m
15
Bloom Filters (contd)

• Appearance of false positives.
• False positive the probability that the filter
  recognizes an element as belonging to the set
  although it does not.
• P (1 - e-kn/m)k
• k number of hash functions
• nnumber of data items
• m size of the filter

16
Performance Evaluation
Simulation using OMNET
INET Framework IEEE802.11b-complete network stack
17
Ability to store Data
Stored data items
Query success rate
18
Path length
Data insertion path length
Query path length
19
Different parameters - insertion path length
Network Size
Partial Storage
Data Distribution
20
Conclusion

• Cooperative storage suits the characteristics of
  WSN
• Our approach has several attractive
  characteristics
• Self-Organizing
• The successors and predecessors are in the
  vicinity
• Lightweight
• Simulation Results shows
• Stability in the Performance, efficient usage of
  resources

21
Questions?