Utf-8 Iit Documentation

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A COMPARATIVE

STUDY

OFOPERATING SYSTEMS

FOR

WIRELESS SENSOR NETWORKS


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WIRELESS SENSOR NETWORKS:

A wireless sensor network (WSN) is a wireless network

consisting of distributed autonomous devices (say motes) which contains

sensors to monitor environmental changes and these changes are

communicated to a remote computer at regular intervals.

MOTES:

Mote is a tiny hardware device which consists of Sensors,

Micro controller, Transceiver, Analog to Digital Converter and power

supply. It is capable of gathering information and send/receive data from

nodes in the wireless sensor network.

CHARACTERISTICS OF MOTES:

Smaller in size

Highly memory constrained devices

Low power consumption

Limited processing capacity


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OPERATING SYSTEM FOR MOTES:

Motes are simple hardware devices and they need to

communicate with each other. For this we need an Operating System to

establish communication with other motes.

Operating Systems are used in Motes to achieve the following

features

Efficient multi-tasking

Networking

Memory managementPower management

Process scheduling

Available operating system for motes is as follows:


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TINY

OPERATING

SYSTEM


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TINY OS:

Tiny OS is a free open and open source operating system for

Wireless Sensor Networks. It started as a collaboration between the

University of California and Intel Research. Tiny OS is completely

written using nesC programming language.

FEATURES OF TINY OS:

Component-Based operating system.

Event driven Operating System.Tasks are non-preemptive and run in First In First Out(FIFO) order.

Codes are linked statically.

Application and Libraries are written using nesC, a programming

language .

COMPONENT-BASED OS:

COMPONENTS:

Components can be defined as a functional part of a program that

has a predefined service. The main advantage of using component based

system is its enhanced reusability.

Eg.Linux OS is an example of a component-based operating

system .If you need an OS with only pdf viewer and media player, you can

simply chop off unnecessary components resulting in a simple OS with only

pdf viewer and media player.


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EVENT DRIVEN OS:

In Event driven OS,the flow of a program is determined by the

sequence of events.Whenever an event occours,an interrupt signal is sent to

processor and yhe interrupt is served with the corresponding Interrupt

Service Routine.

The main reason for using event driven model is to minimize

power consumption.Tiny OS sleeps most of the time and only when the

event occours it moves into active state.This ensures that Tiny OS doesn't

consume most of the battery power.

NON PREEMPTIVE SCHEDULING:

Scheduling determines the order of process execution.In

NonPreemptive scheduling,the process which comes first,gets executed

first.The processes are executed in First In First Out(FIFO) order.

The main disadvantage of Non preemptive scheduling is process

starvation.Even high priority processes must weight in queue to be

executed.If a larger process is currently executing,all other smaller process

in queue has to wait until the previous process has executed.

NOTE:

The use of non preemptive scheduling does not affect the

performance of Tiny OS significantly ,since the processes are

Light weight.

Processs starvation doesn't occur.No High priority process.
http://en.wikipedia.org/wiki/Event_(computing)http://en.wikipedia.org/wiki/Event_(computing)http://en.wikipedia.org/wiki/Event_(computing)


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STATIC LINKING:

In Static linking, all the library files are included in compile

time and they are combined to form a single executable file. The main

advantage of static linking is that they require less time for execution and

the target platform need not contain the library files, since the library files

are linked to form a single executable file.

However Static Linking results in waste of memory, since the

entire library is loaded into the memory during execution .Here is a

comparison of dynamic and static linking stating the differences between

them.

STATIC LINKING DYNAMIC LINKING

Same code will be availableboth on Main memory and

system.

Single copy of code is available inthe system.

Memory space gets wasted. Programs use limited memory.Programs are executed much

faster when compared to

Dynamic linking

Program execution is slower whencompared to Static linking.

Program size is larger than adynamically linked program

Program size is smaller whencompared to Static linking.

NOTE :

Eventhough Dynamic linking is preferred to Static linking,in

Tiny OS ,program size is very small and hence using Static linking does

not have any adverse effect on Tiny OS performance.


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nesC PROGRAMMING LANGUAGE :

nesC is a programming language for developing Tiny OSapplications.

Tiny OS libraries are written using nesC programming languagenesC language is considered as an extension of C Programming

language and its syntax are similar to C.

The building blocks of Tiny OS are Components, Configurationsand Interfaces.

Let us discuss about them and how they are implemented using nesC.

COMPONENTS:

Components are discrete units with a specified function. Component can reference variables only from its local namespace. Component must not only declare the function it implements but also

declare the function it calls.

Every component has a specification.COMPONENT SPECIFICATION:

Every component must declare not only the functions it provides

(implements) but also the functions that it uses (calls).

module SmoothingFilterC {

provides command uint8_t topRead(uint8_t* array, uint8_t len);

uses command uint8_t bottomRead(uint8_t* array, uint8_t len);

}


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Here the component SmoothingFilterCdeclares both the functions

topRead(which it implements) and bottomRead(which it calls) from

another component. The components are wired together using

Configurations.

CONFIGURATION:

Configurations are used for wiring (linking) the components toform a complete program.

Configuration must specify the components (to be wired) and has apredefined format.

Configuration can provide and use interfaces.CONFIGURATION SPECIFICATION:

Here the configuration LedsC specifies the components LedsP

and PlatformLedsC, which needs to be wired. The o perator -> is used

for wiring the components. The operator arrow -> points from user to

provider.

configuration LedsC {

provides interface Leds;

}

implementation {

components LedsP, PlatformLedsC;

Init = LedsP;Leds = LedsP;

LedsP.Led0 -> PlatformLedsC.Led0;

LedsP.Led1 -> PlatformLedsC.Led1;

}


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INTERFACE:

Interface provides a set of functions that can be implemented byComponents and Configurations.

Interfaces are bidirectional in nature. They provide a set offunctions to be implemented by the inter-faces provider

(commands) and a set to be implemented by the interfaces user

(events).

Interfaces decide the functionality of the component that itimplements.

INTERFACE SPECIFICATION:

Here the interface Send provides the commands and events

which needs to be specified by the interface-provider and interface-user

respectively.

Thus we have discussed the building blocks of Tiny OS programs

like Components, Configuration and Interfaces.

interface Send {

command error_t send(message_t* msg, uint8_t len);

event void sendDone(message_t* msg, error_t error);

command error_t cancel(message_t* msg);

command void* getPayload(message_t* msg);

}


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CONTIKI

OPERATING

SYSTEM


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CONTIKI OS:

Contiki OS is a open source and highy portable operatingSystem for Wireless Sensor Networks.

Contiki OS was developed by Dr. Adam Dunkels at theSwedish Institute of Computer Science.

Contiki OS is developed for highly memory constrainedsystems.

FEATURES OF CONTIKI OS:

Contiki OS provides a multitasking kernel. Contiki OS comes with a Managed Memory Allocator to

guard against memory fragmentation.

Contiki OS uses a preemptive scheduling technique forscheduling the processes.

Contiki OS processes uses extremely light weight threadscalled Protothreads.

Typical Contiki OS program requires minimum memory of2KB RAM.

MULTITASKING KERNEL:

Multitasking is a method in which several CPU processesshare same processing resources like Central Processing Unit.

Multitasking resolves concurrency problems by scheduling the

processes.

Multitasking enhances the performance of the OS by reducingthe execution time of a process.


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MANAGED MEMORY ALLOCATOR:

Managed Memory Allocator helps to guard against memoryfragmentation.

Fragmentation refers to situation in which storage space getswasted due to improper memory allocation.

Fragmentation can be classified into three types as follows1. Internal fragmentation2. External fragmentation3. Data fragmentation

INTERNAL FRAGMENTATION:

In internal fragmentation, storage space is allocated but it isnever used.

Space remains unused inside the allocated region leading toinefficient memory management.

EXTERNAL FRAGMENTATION:

In external fragmentation, memory space becomes unusablesince its get divided into several small pieces over a period of

time.

Reasons for external fragmentation can be attributed to poormemory management algorithms.

For example, in dynamic memory allocation, a block of 1000bytes might be requested, but the largest contiguous block of

free space has only 300 bytes. The memory allocation fails in

this case.


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DATA FRAGMENTATION:

In data fragmentation, the piece of data in the memory isscattered into different pieces.

Data gets fragmented into many pieces in case of datafragmentation.

PREEMPTIVE SCHEDULING:

In preemptive scheduling, the processes are scheduled on thebasis of priority.

Whenever a high priority process comes in,the low priorityprocess is temporarily preempted(interrupted) and the high

priority process get executed.

The main advantage of preemptive scheduling is that highpriority processes gets maximum attention and they need not

wait.

However preemptive scheduling also leads to processstarvation,since the low priority process needs to wait

indefinitely until the high priority processes are executed.

PROTOTHREADS:

Protothreads are lightweight, stackless threads used by ContikiOS processes.

Protothreads don't require their own stack rather allprotothreads run on the same stack.

Protothreads are lightweight because they use very limitedmemory ( 2KB/protothread).

Protothreads do not make operating system call. Protothreads provides a linear code of execution.


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NOTE:

Sharing a stack between the processes is impossible in order toavoid concurrency problems.

In general, every thread requires it's own stack for execution. Protothreads provides linear execution and hence it becomes

difficult to use conditional statements like if() and while()

statements.

Thus we have discussed the features of Contiki OS like Managed

Memory Allocator, Preemptive Scheduling and Protothreads.


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SIMPLE

OPERARTING

SYSTEM (SOS)


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APPLICATIONS OF DYNAMIC RECONFIGURABILITY:

Applying patches and updates while OS is running. Alter the software module, whenever it is needed. Any 3rd party modules can be installed and reconfigured

remotely.

COMPACT KERNEL INTERFACE:

SOS provides a multitasking kernel that provides1. Dynamic Memory Management2. Garbage collection3. Priority Scheduling

DYNAMIC MEMORY MANAGEMENT:

Dynamic memory management refers to allocating anddeallocating memory during run-time.

Garbage collection is a part of Dynamic memory management. Garbage collection refers to removing the objects, which are no

longer needed in a program and reclaim the memory.

Dynamic memory management increases the efficiency ofprograms and uses the memory efficiently.


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PRIORITY SCHEDULING:

Priority scheduling is a technique in which the processes arescheduled on the basis of priority.

Whenever a high priority process comes for execution, lowpriority process is preempted (interrupted).

A context switch is said to have occurred (ie) current state of thelow priority process is saved in a Process Control Block (PCB).

Once the high priority process has finished executing, the state ofthe low priority process is restored from the Process Control

Block (PCB) and the process starts executing from the state

where it was originally preempted.

The main advantage of Priority scheduling is that high priorityprocess doesn't starve and executed immediately.

CONCLUSION:

Thus Simple Operating System(SOS) provides the following

features

Dynamic Reconfiguration Multitasking kernel Dynamic Memory Management Garbage collection Priority schedulingFrom this we can infer that SOS offers exciting features for

programming memory constrained, mote class Wireless Sensor Networks.


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NANO-RK

OPERATING

SYSTEM


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NANO-RK:

Nano-RK is an operating system for mote class Wireless Sensor

Networks developed by Carnegie Mellon University. Nano-RK currently

runs on the FireFly Sensor Networking Platform as well as the MicaZ

motes.

FEATURES OF NANO-RK:

Nano-RK is a reservation based operating system. Nano-RK has a multitasking kernel. Nano-RK supports priority based preemptive scheduling. Nano-RK enforces resource usage limitations.

RESERVATION BASED OS:

Nano-RK enforces strict reservation policy. In order to ensure that the process starvation doesn't happen,

all the process must inform the Nano-RK Resource Kernel, in

advance, regarding their memory and resource

requirements.

Nano-RK kernel carefully monitors the resource usage foreach process.

Only the process that haven't depleted their resource limits areeligible for scheduling.


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PRIORITY BASED PREEMPTIVE SCHEDULING:

In Preemptive scheduling, the process in a running state can

be preempted by a process having a higher priority than the

current process.

In Nano-RK we use priority based preemptive scheduling

where the higher priority process, can preempt (interrupt) the

lower priority process and obtain access to the CPU.

The main advantage of using priority based preemptive

scheduling is to ensure that critical (high priority) processesdoesnt wait in a queue for execution.

POWER CONSUMPTION:

Nano-RK enforces power savings in order to maximize

battery life.

Nano-RK ensures that all the sensors are turned off (by

default) to reduce power consumption.

The power consumption of a typical FireFly Sensor node in

active state is around 24mW.

Thus Nano-RK is a reservation-based, energy-efficient

operating system for highly resource-constrained sensor network

environments. Nano-RK also supports multitasking and provides API for

enhancing the ease of application development.


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MANTIS

OPERATING

SYSTEM


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MANTIS OS:

Mantis is the acronym of MultimodAl system for

NeTworks of In-Situ wireless Sensors.

Mantis OS originated as a WSN project at the University of

Colarado.

Mantis OS is purely written using C Programming

language.

It is energy efficient OS for mote class Wireless Sensor

Networks.

FEATURES OF MANTIS OS:

Mantis OS supports Dynamic Reprogramming.

Mantis OS uses priority based round robin scheduling.

Mantis OS consists of a multithreaded kernel.

Mantis OS has a very small memory footprint. A simple

Mantis OS program requires only about 500 Bytes ofRAM.

Mantis OS is a highly energy efficient OS and consumes

about 20 mA current in active state.

MULTITHREADED KERNEL:

Multithreading ensures that several threads of processes can

share the same CPU resource.

Multithreading does not mean that several threads run at

the same time because CPU executes only one thread at a

time.

Since the processor can execute multiple threads within a

given time period, is referred to as Multithreading.


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Consider a process having a clock speed of3.33GHz, then

the time of execution of a thread is approximately 300s.

Multithreading implies that a processor can execute several

processes within a given time slice.

PRIORITY BASED ROUND ROBIN SCHEDULING:

Round Robin Scheduling algorithm specifies a time

quantum for each process.

All the processes are expected to complete their execution

within the given time quantum.

If the process doesnt complete its execution within the

specified time quantum, the process gets preempted and it

is sent to the tail of the queue.

Each process must repeat this, until it is completely

executed.

However, in Mantis OS we use a prioritybased round robin

scheduling.

Round Robin Scheduling is considered as one of the best

scheduling algorithms, since it ensures fairness in process

scheduling and all the process gets access to their resources.

However, there is a memory overhead in Round Robin

Scheduling Algorithm is considered as undesirable.

Memory overhead occurs in Round Robin Scheduling

Algorithm due to the following reasons


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Once the time quantum of a process is over,the process is preempted (interrupted) and

sent to the tail of the queue.

As a result, the current state of the runningprocess (context) must be saved in a Process

ControlBlock (PCB), in order to restore the

state of the process after some period of time.

As a result of frequent context switching,the states of the preempted process must be

saved frequently in the Process Control

Block.

This results in a memory overhead involvingsaving and restoring the context of the

threads.

The only difference in priority based Round Robin

scheduling than that ofnormal Round Robin scheduling is

that the processes are served on the basisoftheir priority.

ILLUSTRATION:

Consider the following table stating the processes, their

priority along with their Service Time.


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TIME QUANTUM=2s

The process of Round Robin scheduling can be illustrated

with the help of Gantt chart.

P1 P1 P2 P2 P2 P3 P4 P4

0 2 4 6 8 10 12 14 16

Here the process is P1 preempted after the given time

quantum and sent to the tail of the queue.

But how process P1immediately comes to the execution?

It should have been actually executed only after P4!

The answer for the abovequestion is priority (because

process P1 has highest priority).

Similarly other processes namely P2, P3 and P4 are

executed on the basis of priority.

PROCESSES PRIORITY SERVICE TIME

P1 1 4

P2 2 6

P3 3 2

P4 4 4

P1 P1 P2 P2 P2 P3 P4 P4


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DYNAMIC REPROGRAMMING:

Mantis OS provides remote management feature through

dynamic reprogramming.

Dynamic Reprogramming is an feature for Wireless Sensor

Network OS for the following reasons

Mote devices used in Wireless Sensor Network aredeployed in remote areas, which may remain

inaccessible to humans.

Whenever we need to modify a software module, itbecomes impossible to locate the mote and thenmodifying its software components.

There we need dynamic reprogramming, inorder toensure remote management of Wireless Sensor

Network nodes.

Mantis OS offers two modes of programming for the purpose of

dynamic reprogramming.

SIMPLER PROGRAMMINGIn simpler programming, the user simply

connects the PC directly to the Mantis node

used in the Wireless Sensor Network.

The user simply connects the node to a PC

and opens the MANTIS shell.

MOS enters a boot loader that checks for

communication from the shell.

The OS gets directly downloaded to the

MOS mode and the node is updated.


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ADVANCED PROGRAMMING:In this mode, the node doesnt require a

direct connection with the computer.

Dynamic Reconfigurability capability is

actually implemented as a system call

library, which is built into the MOS

kernel

After the call, the code is downloaded and

stored in a flash memory.

The software is completely reset and the

reprogramming is done.

Dynamic Reconfigurability is usually

performed by establishing a remote

connection with the node in the Wireless

Sensor Network.

The support for Dynamic Reconfiguration is in progress and yet to

attain a stable state.

Thus Mantis OS provides a support for Dynamic Reconfiguration

providing a remote management facility to the user and uses an

efficient Round Robin Scheduling algorithm.


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SUN SMALL

PROGRAMMABLE

OBJECT

TECHNOLOGY


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SUN SPOT:

SUN Small Programmable Object Technology is an Operating

System for Wireless Sensor Network developed by Sun

Microsystems.

SUN Small Programmable Object Technology is deployed in a

device called as Sun SPOT device.

Sun SPOT device is a small and wireless device developed by

Sun labs.

Sun SPOT device is Java platform wireless device and they are

programmed purely in Java.


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SUN SPOT DEVICE:

Sun SPOT devices are the target platform for Sun SPOT

Technology.

Sun SPOT devices are programmed in Java and any java program

needs a virtual machine for execution.

Squawk Virtual Machine is an open source Java virtual machine

for highly resource constrained Wireless Sensor Networks.

The main advantage that Sun SPOT is that, it is programmer

friendly. The programmer can use the native Java tools for

developing applications for Sun SPOT device.Sun SPOT provides a Software Development Kit, providing the

API and hence programming the Sun SPOT device becomes easy.


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SUN SPOT FEATURES:

Sun SPOT uses a compact Squawk Virtual Machine.

Sun SPOT is the only operating system for Wireless Sensor

Networks that comes with inbuilt security feature.

Sun SPOT uses Elliptic Curve Cryptography(ECC) for ensuring

the security of the data packets shared across the nodes in the

Wireless Sensor Network

Sun SPOT has a Garbage Collector and it ensures automatic

memory management.

Sun SPOT is easy to program, since it is facilitates the user to code

the programs using the familiar Java Programming Language.

SQUAWK VIRTUAL MACHINE:

Squawk Virtual Machine is an open source Java Virtual Machine

developed by Sun Microsystems.

The specialty about the Squawk Virtual Machine is that it is

majorly (not fully) written using Java Programming Language.

Squawk Virtual Machine outputs a very compact byte code. The

original output byte code is only about 35-40% ofstandard J2ME

class file.

Squawk Virtual Machine uses a Garbage Collector for managing

memory.

Squawk Virtual Machine uses a green threading model, in which

the processes are scheduled purely by the Virtual Machine and

not by the Operating System.


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GREEN THREADING MODULE:

In green threading module, the green threads (threads) are

scheduled by the Virtual Machine and not by the underlying

Operating System.

Generally the virtual memory can be differentiated into User

Space and Kernel Space.

Green threads are managed in the User Space and they do not rely

on the underlying OS.

In fact, Operating System does not know about the Green

threads.

Green Threading model uses priority scheduling to schedule the

green threads.

The main advantage of using green threaded model is due to the

following reason

Reduces the overhead on OS, since the Virtual Machinetakes care ofscheduling the green threads.

Enhances the portability of a program ,since the greenthreads doesnt depend on the Operating System and they

purely rely on Virtual Machine


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GARBAGE COLLECTOR:

Garbage collection is a memory management feature present in

Squawk Java Virtual Machine.

The term garbage refers to the unused objects (or they are no

longer needed) in the Java program.

Whenever the object is no longer referenced by the program, then

the heap space it occupies must be freed.

Garbage Collector must determine the unusedobject and reclaim

the free space.

Hence the Garbage Collector is not only responsible for automatic

memory management but also guard against memory

fragmentation (inefficient usage of memory space).

Thus we have discussed the features of Sun SPOT like

Green Threaded Model, Squawk Virtual Machine, Garbage Collection

and Preemptive Scheduling.


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COMPARATIVE STUDY OF

OPERATING SYSTEMS

FOR

WIRELESS

SENSOR NETWORKS


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POINTS OF COMPARISON:

Supported Hardware Platforms

Nature of Operating System

Nature of Scheduling

Nature of Programming Language

Dynamic Reconfigurability

Garbage collection


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SUPPORTED HARWARE PLATFORMS:

TelOS Mica2

Mote

ESB TMote

Sky

Atmel-

Atmeg

a

Oki

Arm

Fire

Fly

Sun

Spots

TINY

OS

CONTIKI

OS

SOS

NANO-RK

MANTIS

SUN

SPOT


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NATURE OF OPERATING SYSTEM:

EVENT-

DRIVEN

OS

MULTITASKING

OS

TINY OS

CONTIKI OS

SOS

NANO-RK

MANTIS

SUN SPOTS


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NATURE OF SCHEDULING:

NON

PREEMPTIVE

SCHEDULING

PRIORITY

SCHEDULING

ROUND

ROBIN

SCHEDULING

TINY OS

CONTIKI

OS

SOS

NANO-

RK

MANTIS

SUNSPOTS


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PROGRAMMING LANGUAGE:

nesC C JAVA

TINY OS

CONTIKI OS

SOS

NANO-RK

MANTIS

SUN SPOTS


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DYNAMIC RECONFIGURABILITY:

DYNAMIC

RECONGIGURANILITY

TINY OS

CONTIKI OS

SOS

NANO-RK

MANTIS

SUN SPOTS


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GARBAGE COLLECTION:

GARBAGE COLLECTION

TINY OS

CONTIKI OS

SOS

NANO-RK

MANTIS

SUN SPOTS


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CONCLUSION:

Thus we have discussed following operating systems for Wireless

Sensor Networks

We have also discussed the salient features of these operating

systems like

Nature of operating System

Nature of Linking

Nature of Process Scheduling

Nature of Programming language.

Each Operating System has its unique feature and they have their

own merits and demerits.

However the operating systems for Wireless Sensor Networks are

gradually evolving to attain stability and security.

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