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Wireless sensor networks are widely used in many application domains. One of the well-known applications of such networks is tracking of moving objects. In this paper we propose a novel algorithm in which head and members of next clusters are chosen and woken up dynamically by the current active cluster head in a grid network of wireless sensors. This dynamic algorithm is designed for target tracking applications. The proposed solution is a distributed clustering scheme, in which, head and cluster members of the next cluster are selected cooperatively. Based on the distributed solution, a semi-localized clustering scheme is also presented. Moreover, a distributed target movement history recording algorithm is proposed to reduce target misses. Simulation results show that by using the proposed method, there are significant reductions in the average number of received messages, averaged number of sent messages, and average number of samplings of the sensing subsystem. In addition, a meaningful reduction in target miss rate is achieved by using distributed target movement recording algorithm. [ABSTRACT FROM AUTHOR]

With respect to the increasing growth in the subscribers of wireless cellular networks and the necessity of providing network services with reasonable quality in any location, the importance of enhancement in the wireless network services is deeply felt. This means that network users expect to receive voice, data, and multimedia services with reasonable QoS, regardless of their locations and mobility patterns. Therefore, failures which may occur in mobile wireless network and may inhibit communication or result in loss of critical data will be not tolerated. Hence, providing wireless networks services in the presence of network failures has a great importance and can cause the networks to avoid from reducing their subscribers. In this paper, two main schemes are proposed, in order to reduce bad effects, which can be generated for the case of network failures. These schemes try to reduce dropping probabilities and cause mobile hosts in the failed cell to continue their calls with high probability for the case of failure. One of the proposed schemes uses ad hoc relaying and the other uses bandwidth degradation, in order to improve network performance in the case of failure. Simulation results show that these two schemes have great impacts in improving network performance for the case of failure. [ABSTRACT FROM AUTHOR]

The expansion of Internet, increases the number of users and applications. Having higher speed and better quality are the main chalanges of computer network development. Using MPLS and proper traffic design, it is possible to improve the quality of service and reduce the possibility of congestion. It is possible to use MPLS in a BGP/MPLS VPN network for data transmition. In this paper we explain BGP/MPLS VPN and we implement an MPLS network based on Diffserv over VPN services. Using OPNET various senarios are simpulated. In most of the previous proposed systems, with incressing the number of low traffic priority sources like BE and AF, higher priority traffic like EF faces difficulty. Our simulation shows with using traffic engineering, congestion control for low priority sourses and management methods, it is possible to have better quality of services for those traffics which are sensitive to delay. [ABSTRACT FROM AUTHOR]