The general method available for comparison between the Distributed Hash Table (DHT) based structured overlay networks are average latency per successful lookup and percentage of successful lookups. For a DHT based lookup service with lookup retries for failed lookups, both average latency per successful lookup as well as percentage of successful lookups are key to evaluate the performance. Although, average latency per successful lookup may be less for a DHT overlay protocol, failure of lookups at high churn rates may degrade the protocol's performance if its routing efficiency is less. On the other hand, just routing efficiency is not sufficient to measure the performance of a DHT since an overlay network having higher routing efficiency may not have a good performance due to high average latency per successful lookup. We have developed a metric for DHT comparison which incorporates both average latency per successful lookup and routing efficiency in scenarios where applications do lookup retries. We have also modeled three different timeout mechanisms while developing the performance metric. The paper also incorporates a model where the probability of failure of a lookup is increasing at every retry of lookups.

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Wireless sensor networks have created new opportunities across the spectrum of human endeavors including engineering design and manufacturing, monitoring and control of systems. Involvement of restrained resources in the deployment of WSNs makes it a subject of concern. So its usage needs to be very efficient in order to maximize operational life of network. In this paper a detailed analysis is made between single-hop and multi-hop approaches which are used in the process of transfer of data and queries from source to sink. Different dimensions are used for the purpose of analysis with their respective applications in order to increase the scope of analysis in real world scenarios. Implementation of single-hop and multi-hop is done with the help of MATLAB simulation tool in order to get accurate results and also the comparison of different design constraint.

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CAPTCHA is a security technique used widely over the Internet to verify whether the end user is a human. Textbased CAPTCHAs are the most commonly used. The security of text-based CAPTCHA depends on the ability to resist the segmentation and recognition attacks. The Reading Oriented Overlapping Text (ROOT) based CAPTCHA, introduced in this article, consists of overlapping alphanumeric letters both hand written and computer generated along with a reading pattern scheme that helps to use the same CAPTCHA multiple number of times. The proposed ROOT based CAPTCHA generation algorithm is discussed along with its resistivity to known attacks.