Nodes in a wireless sensor network have nonuniform energy consumption rates. As a result, early death among highly loaded nodes is a common phenomenon which makes it impossible to use the full capacity of the network. In this paper, we propose to deploy sensors either with variable battery capacities or with nonuniform densities in order to counterbalance the nonuniform energy drainage, thus achieving a longer network lifetime. We divide the monitored region into concentric ring areas and deploy nodes in these areas such that the highest battery resources are allocated to the ring where the highest energy drainage takes place. Results show that up to 6 to 7 times longer lifetime values are attained without any increase in costs with this approach.Index Terms-Variable battery capacity, concentric ring deployment, nonuniform density deployment, lifetime optimization, wireless sensor networks

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Environmental factors such as unavoidable physical constraints, intentional destruction of the sensors or asymmetric load distribution will lead to formation of holes in the wireless sensor networks. Holes hinder the operational quality of the network, where earlier formations have higher impact. In this paper, we study the sensing hole problem and propose a redeployment method to mitigate it. Image processing algorithms are used for identifying the sensing holes. A portion of the sensors are kept as spare; after identifying the holes, they are redeployed over the holes. The results indicate that the method leads to a considerable increase on the sustainable sensing quality of the network.Index Terms-Wireless sensor networks, sensing hole, redeployment, deployment quality measure, image processing.

Özetçe -Dagıtık hizmet engelleme saldırıları günümüzde bilişim sistemleri için ciddi bir tehdit oluşturmaktadır. Bu çalışma dagıtık hizmet engelleme saldırılarından birisi olan veri iletim kontrolü protokolü senkronizasyon paketi baskını saldırılarının, ag trafigine ait çeşitli öznitelikler üzerindeki etkisini incelemektedir. Öznitelikler arasındaki ilinti katsayı matrisi ve bu özniteliklerden hesaplanan olagandışılık dizisi kullanılarak, tek boyutlu bir dizi olan saglık fonksiyonu hesaplanmıştır. Bu fonskiyon eşiklenerek saldırının başlangıç ve bitiş noktaları tespit edilmiştir. Bu yöntem DETER test ortamında yapılan benzetimlerden elde edilen verilerle test edilmiştir.Anahtar Kelimeler-DDoS , saldırı tespit, hizmet engelleme saldırıları, sinyal işleme.Abstract-Distributed denial of service attacks pose an immense threat to the internet. In this work the effect of TCP SYN flood attacks on traffic features are examined. Using traffic features and correlation coefficient matrix and anomaly vector obtained from these features; a network health function is calculated. Applying a threshold to network health function gives alarms that are used to detect beginning and end points of TCP SYN flood attacks. This method is tested using data obtained from experiments of DETER testbed.

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