Download topology discovery in sensor networks

TOPOLOGY
DISCOVERY IN
SENSOR NETWORKS
Budhaditya Deb, Sudeept Bhatnagar
Badri Nath
Department of Computer Science, Rutgers
University, May 2001.
WHAT ARE SENSOR NETWORKS ?
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Distributed and highly complex network systems
Hundreds of tiny sensor nodes
Behavior is highly unpredictable
Randomness in individual node state and
network structure.
Used for automated information gathering.
CONSTRAINTS FACED BY NODES IN
SENSOR NETWORKS
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Sensor network nodes are resource constrained
Energy is limited by battery power
Form factor limits the amount of resources that
can be put in a node
Protocols designed for sensor networks need to
be highly efficient and optimized in terms of
resources they consume.
The TopDisc Algorithm(Overview)
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Because of the above reasons, regular SNMP
functionalities cannot be used over wireless
sensor networks
Paper describes a TopDisc algorithm which is
a topology discovery algorithm used for
Data dissemination
Data aggregation
Duty cycle assignments
Network State Retrieval
Overview of TopDisc
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A set of distinguished nodes is obtained.
These nodes only reply to the topology
discovery probes.
These nodes form clusters comprised of the
nodes in their neighborhood.
These clusters form a tree structure called TreC,
rooted at the monitoring node.
Models for sensor networks
Models depict the current state of the network.
Some useful models would be :
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Network Topology
Energy Map
Usage Pattern
Non-deterministic Models
Network Management Functions
The models described above could be used for
many network management functions like :
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Deployment of sensors
Setting Network Operating Parameters
Monitor Network States using Network Models
Network Maintenance
Predict Future Network States
Design of Sensor Networks
TopDisc Algorithm
The TopDisc Algorithm can be divided into three
stages of execution :
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A monitoring node requiring the topology of the
network initiates a "topology discovery request".
This request diverges throughout the network reaching
all active nodes.
A response action is set up which converges back to the
initiating node with the topology information.
Topology Discovery
Three methods can be used for topology discovery
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Direct Response
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Aggregated Response
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Clustered Response
TopDisc Algorithm
Two different approaches are used to select
cluster heads :
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Three color approach
Four color approach
The three color approach
The three different colors used and what they mean
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White: Yet undiscovered node
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Black: Cluster head node
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Grey: Node which is covered by black node
The Three Color Approach
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Initiate topology discovery Black
Receiver
White
Sender
Black
Converts to
Grey
Action Taken
Broadcast
White
Grey
Black(With
random del)
Black, Grey
XXXX
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From black,
becomes
grey
Ignore
requests
The Three Color Approach(contd)
The Four Color Approach
The four different colors used and what they
mean :
 White: Yet undiscovered node.
 Black: Cluster head node
 Grey: neighbor of a black node.
 Dark Grey: Discovered node, which currently is
not covered by any neighboring black node.
The Four Color Approach (Contd)
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Initiate topology discovery  Black
Grey or black  IGNORE Requests
Four color approach
Receiver
Sender
Converts to
Action taken
White
Black
Grey
Broadcast
with delay
White
Grey
Dark Grey
Broadcast,
Start timer
White
Dark Grey
Black
With random
delay, if
packet from
black--grey
Four color (Example)
TopDisc Response Mechanism
Each node has the following information at the end of
the topology discovery period:
 Cluster identification  Black node
 Grey node knows its cluster id.
 Each node knows its parent black node.
 Each black node knows the default node to which it
should forward packets to reach the parent black node.
 All nodes have their neighborhood information.
TopDisc Response
Using the above information, the steps for TopDisc
Response are described as follows.
 When a node becomes black  starts timer to receive
information from its children
 Aggregates information forwards to its parent
 All forwarding nodes in between black nodes may also
add their adjacency lists to the list from black nodes.
Applications
1. Retrieving Network State
Connectivity Map
Reachability Map
Energy Model
Usage Model
2. Data Dissemination and Aggregation
3. Duty Cycle Assignment
Applications(contd)
1. Assignment with location
information
2. Assignment without location
information
Conclusion
Further work and research on TopDisc to come
up with sNMP (Sensor Network Management
Protocol).