الفهرس 
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Abstract
Wireless Sensor Networks (WSNs) was presented for the first time in 1994, aiming at the military application. Today WSNs are used in many civil applications, many academic and industrial researches.
WSNs, as it is well known, suffer from power limitation, small memory capacity, and limited processing capabilities. Therefore, every node may disappear temporarily or permanently from the network due to many different reasons as battery failure or physical damage. Since every node collects significant data aboutits region, fmding a methodto recover these data in case of failure of the source node is very important. Using the centralized storage approach has many problems. For example, the central storage node is exposed to damage.Bythat, the centralized approach will not be efficient in many applications.
The solution for the mentioned problem is by using distributed data collection approach that is used to collect the network data. It is applied two strategies: (I)disseminate the source node data to its neighboring nodes. (II)Recoverthe network data by minimizes the number of queried nodes.Data dissemination increases the existence of the sensed data in the network and protects the sensed data from being lost when the source node fails. This thesis enhances a distributed storage algorithm for Wireless Sensor Networks, which named as Modified Distributed Storage Algorithm (MDSA). MDSAis usingflooding and unicasting to disseminate the data from the source nodes to the distributed storage nodes. This algorithm is applicable for manyapplications anditdoes not depend on geographical information or routing tables. Through the algorithm analysis and simulationcompared with the result of the earlier algorithm Distributed Storage Algorithm (DSA-I). The new algorithm’s success ratio of data recovering is greater than the earlieralgorithm (DSA-I) underthe same conditions. Results have been ensured by repeated experimentations for each step to make sure that our results are closer to the actual implementation of the algorithm. Actually, theaim of this thesis is investigating and proofmg the possibility of recovering the network data from unreliable networks in critical environments. Itis done by querying a smallnumber of live nodes.