ROUTING IN SENSOR NETWORKSTEAM MEMBERS:

PALLAVI MEHARIAAARTHI RAGHAVENDRAABHYUDAYA UPADHAYAY

OUTLINE

Introduction

Challenges and Design issues

LEACH

Rumor Routing

Conclusion

Introduction

Routing protocols differ in WSN based on the application and network architecture.

Based on the network structure, routing protocols are classified into three: Flat Routing – Same role is assigned to all the nodes Hierarchical Routing – Different roles are assigned to nodes Location based Routing – Position of the nodes are exploited to route

the data. Further classified into multipath-based, query-based, negotiation-based,

QoS-based, and coherent-based depending on the protocol operation. Trade off exists between energy consumption and communication

overhead.

Challenges and design issues

Node deployment Manual Deployment Random Deployment

Data routing methods

Application-specific

Time-driven: Periodic monitoring

Event-driven: Respond to sudden changes

Query-driven: Respond to queries

Hybrid

Challenges and design issues

Node link/ heterogeneity

Homogeneous sensors

Heterogeneous sensors

Fault tolerance

Transmission media

Connectivity

Coverage

Data aggregation

Quality of Service

Leach - Low Energy Adaptive Clustering Hierarchy

It is a hierarchical routing protocol that suggests both hierarchical and centralized schemes.

Self-Organizing, adaptive clustering protocol.

Minimal setup time, even distribution of energy load among the sensors thus enhancing the lifetime of the network.

Dynamic cluster formation. Randomized rotation of cluster heads

after each round. Cluster-heads communicate data with

the base station. Application-specific data processing,

such as data aggregation.

leach Each LEACH round consists of two phases:

Set-up Phase Cluster head selection Cluster formation

Steady-State Phase Cluster head maintenance Data transmission between nodes

Leach – Set up phase

At the beginning of each round, each node advertises it probability to be the Cluster Head, to all other nodes.

Probability for each node i to be the Cluster-head at time t

where Ci(t) = determines whether node i has been a Cluster head in the most recent rounds

Higher the probability better are the chances to be chosen as the Cluster Head.

Leach – Set up phase

Cluster Head broadcasts an advertisement message (ADV) using CSMA MAC protocol.

Based on the received signal strength of the ADV message, each non-cluster head node decides its Cluster Head for that round.

Each node transmits a join-request message (Join-REQ) back to its chosen Cluster Head.

Cluster Head node sets up the TDMA schedule for coordinating data transmission with the cluster.

Using TDMA schedule has two advantages:

Avoid collision of data packets from different nodes within a cluster.

Conserve energy in the non-cluster head nodes.

Leach – steady state phase

Node uses the time slot assigned to it to transfer data to the cluster head.

Cluster head aggregates the data received from all the nodes of the cluster.

Communication is via direct-sequence spread spectrum (DSSS) and each cluster uses a unique spreading code to reduce inter-cluster interference.

Intra-cluster communication uses TDMA and Inter-cluster communication uses CDMA.

Rumor routing

It is a flat routing protocol.

Ensures network longevity, robustness in handling node failures.

Intended to fill the region between query flooding and event flooding.

Transmits data packets through random paths rather than shortest path.

Event – Abstraction of a localized phenomena occurring in a fixed region of space.

Query – Information of interest to be retrieved.

Rumor routing

Each node maintains a list of neighbors and its event table. When a node witnesses an event, it adds it to its event table with

distance zero and generates an agent simultaneously. An agent is a long-lived packet, which travels the network,

propagating information about local events to distant nodes. Any node can generate a query, then forward the query in a

random direction to find the path. The query keep going until its TTL expires or it intersects with the agent path leading it to the destination event.

If the node that originated the query determines the query died, it can retransmit, give up or flood the query.

Rumor routing

Basic scheme Each node maintain

A lists of neighbors An event table

When a node detects an eventGenerate an agent Let it travel on a random path The visited node form a gradient

to the event When a sink needs an event

Transmit a query The query meets some node

which lies on the gradient Route establishment

Agent

• Set up path by random walk.

• Aggregate paths.

• Optimize paths in the network.

Agent

Each agent carries a list of all the events it encountered along with the number of hops to that event.

Each node among the path maintains a table of events, the number of hops to that event and the next node in the path toward the event.

Agent

A straightening algorithm is used when determining the agent’s next hop Agent maintains a list of recently seen nodes. When it decides the

next hop, it tries the nodes not in the list. When it passes a node, the node’s neighbors are added to the list.

A node that witnessed an event would generate an agent at a fixed probability in the simulation The future work can do better by generating agents according to

number of events, event size and node density. For applications where events are temporal, the event table may

have an expiration timestamp associated with each event

Query

A query can be generated at any time by any node.

Before reaching the path, nodes forward queries using the same straightening algorithm – keep a list of recently seen nodes and avoid visiting them.

Each query has a TTL to avoid looping routes. If the query dies, the node originating the query detects the failure and decide to retransmit it or flood the query.

References

1. Rumor Routing Algorithm for Sensor Networks

http://research.cens.ucla.edu/people/estrin/resources/conferences/2002sept-Brainsky-Etrin-Rumor.pdf

2. Energy- Efficient Communication Protocol for Wireless Microsensor Networks

http://pdos.csail.mit.edu/decouto/papers/heinzelman00.pdf

3. Introduction to Wireless and Mobile Systems by Dharma Prakash Agarwal and Qing-An Zeng.

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