Peer to peer networks have become one of the most popular networking methods because of their flexibility and many use cases such as file sharing and distributed computations. Unstructured overlay peer to peer networks are one of key components of peer to peer systems that are considerable because of their low cost in network construction and maintenance. One of the main challenges in unstructured peer to peer overlay networks is the topology mismatch between overlay network and the underlying physical infrastructure. The root of this challenge is lack of awareness about peers in the network infrastructure during connection to and disconnection from overlay network, in addition to the neighbor selection mechanism in the overlay network. Different types of awareness of network infrastructure includes awareness of the location of internet service providers. Also awareness of proximity, geographical location and resources of peers. In this article we present a middleware which configures overlay network by using public measurements and the estimated delay among peers in order to have the most conformity with the topology of physical infrastructure. To evaluate the performance, our middleware is implemented on the top of Gnutella which is an unstructured overlay peer-to-peer network. Our simulations show that our middleware enhances the conformity of overlay network to the topology of physical network infrastructure. In addition, it improved the average throughput and the average delay.

Cloud computing environments have introduced a new model of computing by shifting the location of computing infrastructure to the Internet network to reduce the cost associated with the management of hardware and software resources. The Cloud model uses virtualization technology to effectively consolidate virtual machines (VMs) into physical machines (PMs) to improve the utilization of PMs. Studies however have shown that the average utilization of PMs in many Cloud data centers is still lower than expected. The Cloud model is expected to improve the existing level of utilization by employing new approaches of consolidation mechanisms. In this paper we propose a new approach for dynamic consolidation of VMs in order to maximize the utilization of PMs. This is achieved by a dynamic programing algorithm that selects the best VMs for migration from an overloaded PM, considering the migration overhead of a VM. Evaluation results demonstrate that our algorithms achieve good performance.

Not very long ago, organizations used to identify their customers by means of one-factor authentication mechanisms. In today's world, however, these mechanisms cannot overcome the new security threats at least when it comes to high risk situations. Hence, identity providers have introduced varieties of two-factor authentication mechanisms. It may be argued that users may experience difficulties at time of authentication in systems that use two-factor authentication mechanisms for example because they may be forced to carry extra devices to be authenticated more accurately. This is however the tradeoff between ease-of-use and having a secure system that may be decided by the users and not the security providers. In this paper we present a new two-factor authentication mechanism that secures systems and at the same time is easier to use. We have used mnemonic features and the cache concept to achieve ease-of-use and security, respectively. Also, we have tested our method with almost 6500 users in real world using The Mechanical Turk Developer Sandbox.

In the recent years, Cloud Computing has been one of the top ten new technologies which provides various services such as software, platform and infrastructure for internet users. The Cloud Computing is a promising IT paradigm which enables the Internet evolution into a global market of collaborating services. In order to provide better services for cloud customers, cloud providers need services that are in cooperation with other services. Therefore, Cloud Computing semantic interoperability plays a key role in Cloud Computing services. In this paper, we address interoperability issues in Cloud Computing environments. After a description of Cloud Computing interoperability from different aspects and references, we describe two architectures of cloud service interoperability. Architecturally, we classify existing interoperability challenges and we describe them. Moreover, we use these aspects to discuss and compare several interoperability approaches.