Submitted By:

Harwinder Singh Sohal

A Novel Congestion Control Scheme in

Wireless Sensor Networks

A Novel Congestion Control Scheme in

Wireless Sensor Networks

Wireless Sensor Networks

A wireless sensor network (WSN) consists of spatially distributed autonomous sensors to cooperatively monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants.

Figure 1: Wireless Sensor Networks.

What is the Congestion in Computer Networks

For any time interval, the total sum of demands on a source is more than its available capacity the source is said to be congested for that interval.

Mathematically speaking:

Σ Demand >Available Resources

What is Congestion in WSNs?

WSN congestion occurs when offered traffic load exceeds available capacity at any point in the network.

Equation : Total Sensing Data in Transit

If this value reaches a certain fraction of the channel capacity, congestion will occur. If the Ctotal is the total channel capacity then:

Equation: Upper Bound of Reporting Rate

The lower bound is application specific so application requirements are met.

Equation : Reporting Rate Bounds

Types of Congestion Congestion in WSNs may appear in different types depending on how the packets are lost:

Type H1 Congestion Type H2 Congestion Type W1 Congestion (Source Congestion)Type W2 Congestion (Sink Congestion)Type W3 Congestion (Forwarder Congestion)

Main Causes Of Congestion Problem

Sensor Node Architecture Characteristics :Insufficient memory

SLOW processors

Energy

Sensor Node Architecture Characteristics :Many to One Nature

Event- Driven Traffic

Network Size-Density

Packet Collisions

Reporting Rate

Routing Protocols

Congestion Key Symptoms

Some key symptoms of congestion collapse in wireless sensor networks are:

•Dramatic increase in loss rates.

•Starvation of most of the network due to traffic from nodes one hop

away from the sink.

•Degradation on information fidelity measured on sink.

Various methods to remove congestion:Many research works have been conducted on :

•reliable transmission

•congestion mitigation

•congestion control

Reliable Multi-Segment Transport (RMST)

End-to-end data-packet transfer reliability

Each RMST node caches the packets

When a packet is not received before the so-

called WATCHDOG timer expires, a NAK is sent

backward

The first RMST node that has the required packet

along the path retransmits the packet

In-network caching brings significant overhead in

terms of power and processing

Relies on Directed Diffusion Scheme

SinkSink

RMST Node

Source Node