TOPOLOGY TOPOLOGY DISCOVERY IN DISCOVERY IN

SENSOR SENSOR NETWORKSNETWORKSBudhaditya Deb, Sudeept Budhaditya Deb, Sudeept

Bhatnagar Bhatnagar Badri NathBadri Nath

Department of Computer Science, Department of Computer Science, Rutgers University, May 2001. Rutgers University, May 2001.

WHAT ARE SENSOR WHAT ARE SENSOR NETWORKS ?NETWORKS ?

Distributed and highly complex Distributed and highly complex network systemsnetwork systems

Hundreds of tiny sensor nodesHundreds of tiny sensor nodes Behavior is highly unpredictable Behavior is highly unpredictable Randomness in individual node state Randomness in individual node state

and network structure.and network structure. Used for automated information Used for automated information

gathering.gathering.

CONSTRAINTS FACED BY NODES CONSTRAINTS FACED BY NODES IN SENSOR NETWORKSIN SENSOR NETWORKS

Sensor network nodes are resource Sensor network nodes are resource constrainedconstrained

Energy is limited by battery powerEnergy is limited by battery power Form factor limits the amount of Form factor limits the amount of

resources that can be put in a noderesources that can be put in a node Protocols designed for sensor Protocols designed for sensor

networks need to be highly efficient networks need to be highly efficient and optimized in terms of resources and optimized in terms of resources they consume.they consume.

The TopDisc The TopDisc Algorithm(Overview)Algorithm(Overview)

Because of the above reasons, regular Because of the above reasons, regular SNMP functionalities cannot be used SNMP functionalities cannot be used over wireless sensor networksover wireless sensor networks

Paper describes a TopDisc algorithm Paper describes a TopDisc algorithm which is a topology discovery algorithm which is a topology discovery algorithm used forused for

1.1. Data disseminationData dissemination2.2. Data aggregationData aggregation3.3. Duty cycle assignmentsDuty cycle assignments4.4. Network State RetrievalNetwork State Retrieval

Overview of TopDiscOverview of TopDisc

A set of distinguished nodes is A set of distinguished nodes is obtained.obtained.

These nodes only reply to the topology These nodes only reply to the topology discovery probes.discovery probes.

These nodes form clusters comprised These nodes form clusters comprised of the nodes in their neighborhood.of the nodes in their neighborhood.

These clusters form a tree structure These clusters form a tree structure called TreC, rooted at the monitoring called TreC, rooted at the monitoring node.node.

Models for sensor Models for sensor networksnetworks

Models depict the current state of the Models depict the current state of the network. network.

Some useful models would be :Some useful models would be :

Network TopologyNetwork Topology Energy MapEnergy Map Usage PatternUsage Pattern Non-deterministic ModelsNon-deterministic Models

Network Management Network Management FunctionsFunctions

The models described above could be The models described above could be used for many network management used for many network management functions like :functions like :

Deployment of sensorsDeployment of sensors Setting Network Operating ParametersSetting Network Operating Parameters Monitor Network States using Network ModelsMonitor Network States using Network Models Network Maintenance Predict Future Network States Design of Sensor Networks

TopDisc AlgorithmTopDisc Algorithm

The TopDisc Algorithm can be divided The TopDisc Algorithm can be divided into three stages of execution :into three stages of execution :

A monitoring node requiring the topology A monitoring node requiring the topology of the network initiates a "topology of the network initiates a "topology discovery request".discovery request".

This request diverges throughout the This request diverges throughout the network reaching all active nodes.network reaching all active nodes.

A response action is set up which A response action is set up which converges back to the initiating node with converges back to the initiating node with the topology informationthe topology information..

Topology DiscoveryTopology Discovery

Three methods can be used for topology Three methods can be used for topology discoverydiscovery

Direct ResponseDirect Response Aggregated ResponseAggregated Response Clustered ResponseClustered Response

TopDisc AlgorithmTopDisc Algorithm

Two different approaches are used to Two different approaches are used to select cluster heads : select cluster heads :

Three color approachThree color approach Four color approachFour color approach

The three color approachThe three color approach

The three different colors used and what The three different colors used and what they mean they mean

White: White: Yet undiscovered nodeYet undiscovered node

BlackBlack: : Cluster head nodeCluster head node

GreyGrey: : Node which is covered by black Node which is covered by black nodenode

The Three Color The Three Color ApproachApproach

Initiate topology discoveryInitiate topology discovery Black Black

ReceiverReceiver Sender Sender Converts Converts toto

Action Action TakenTaken

WhiteWhite BlackBlack GreyGrey BroadcastBroadcast

WhiteWhite GreyGrey Black(WitBlack(With random h random del)del)

From From black, black, becomes becomes greygrey

Black, Black, GreyGrey

XXXXXXXX ---------------------------- Ignore Ignore requestsrequests

The Three Color The Three Color Approach(contd)Approach(contd)

The Four Color ApproachThe Four Color Approach

The four different colors used and what The four different colors used and what they mean : they mean :

White: White: Yet undiscovered node.Yet undiscovered node. BlackBlack: : Cluster head nodeCluster head node GreyGrey: : neighbor of a black node. neighbor of a black node. Dark GreyDark Grey: : Discovered node, which Discovered node, which

currently is not covered by any currently is not covered by any neighboring black node.neighboring black node.

The Four Color Approach (Contd)The Four Color Approach (Contd)

Initiate topology discovery Initiate topology discovery Black Black Grey or black Grey or black IGNORE Requests IGNORE Requests

Four color approachFour color approach

ReceiverReceiver SenderSender Converts Converts toto

Action Action takentaken

WhiteWhite BlackBlack GreyGrey Broadcast Broadcast with delaywith delay

White White GreyGrey Dark GreyDark Grey BroadcastBroadcast, Start , Start timer timer

White White Dark GreyDark Grey BlackBlack With With random random delay, if delay, if packet packet from from black--black--greygrey

Four color (Example)Four color (Example)

TopDisc Response TopDisc Response MechanismMechanism

Each node has the following information at Each node has the following information at the end of the topology discovery period:the end of the topology discovery period:

Cluster identification Cluster identification Black node Black node Grey node knows its cluster id.Grey node knows its cluster id. Each node knows its Each node knows its parent black node.parent black node. Each black node knows the default node to Each black node knows the default node to

which it should forward packets to reach which it should forward packets to reach the parent black node.the parent black node.

All nodes have their neighborhood All nodes have their neighborhood information.information.

TopDisc ResponseTopDisc Response

Using the above information, the steps for Using the above information, the steps for TopDiscTopDisc

Response Response are described as follows.are described as follows. When a node becomes black When a node becomes black starts timer starts timer

to receive information from its childrento receive information from its children Aggregates informationAggregates information forwards to its forwards to its

parentparent All forwarding nodes in between black All forwarding nodes in between black

nodes may also add their adjacency lists to nodes may also add their adjacency lists to the list from black nodes.the list from black nodes.

ApplicationsApplications

1. 1. Retrieving Network StateRetrieving Network State

Connectivity MapConnectivity Map

Reachability MapReachability Map

Energy ModelEnergy Model

Usage ModelUsage Model

2. 2. Data Dissemination and Data Dissemination and AggregationAggregation

3. 3. Duty Cycle Assignment Duty Cycle Assignment

Applications(contd)Applications(contd)

1. Assignment with location1. Assignment with location

informationinformation

2. Assignment without 2. Assignment without locationlocation

informationinformation

ConclusionConclusion

Further work and research on Further work and research on TopDisc to come up with sNMP TopDisc to come up with sNMP (Sensor Network Management (Sensor Network Management Protocol).Protocol).