Current Issue : October - December Volume : 2015 Issue Number : 4 Articles : 5 Articles
IEEE 802.15.4 is an important standard for Low Rate Wireless Personal Area Network (LRWPAN). The IEEE 802.15.4 presents a\nflexible MAC protocol that provides good efficiency for data transmission by adapting its parameters according to characteristics\nof different applications. In this research work, some restrictions of this standard are explained and an improvement of traffic\nefficiency by optimizing MAC layer is proposed. Implementation details for several blocks of communication system are carefully\nmodeled.The protocol implementation is done usingVHDL language.Theanalysis gives a full understanding of the behavior of the\nMAC protocol with regard to backoff delay, data loss probability, congestion probability, slot effectiveness, and traffic distribution\nfor terminals. Two ideas are proposed and tested to improve efficiency of CSMA/CA mechanism for IEEE 802.15.4 MAC Layer.\nPrimarily, we dynamically adjust the backoff exponent (BE) according to queue level of each node. Secondly, we vary the number of\nconsecutive clear channel assessment (CCA) for packet transmission.We demonstrate also that slot compensation provided by the\nenhanced MAC protocol can greatly avoid unused slots. The results show the significant improvements expected by our approach\namong the IEEE 802.15.4 MAC standards. Synthesis results show also hardware performances of our proposed architecture....
In the Internet,Autonomous Systems (ASes) exchange traffic through interconnected links.As traffic demand increases,more traffic\nbecomes concentrated on such links. The traffic concentrations depend heavily on the global structure of the Internet topology.\nTherefore, a topological evolution considering the global structure is necessary to continually accommodate future traffic amount.\nIn this paper, we first develop a method to identify the hierarchical nature of traffic aggregation on the Internet topology and\nuse this method to discuss the long-term changes in traffic flow. Our basic approach is to extract the ââ?¬Å?flow hierarchy,ââ?¬Â which is a\nhierarchical structure associated with traffic aggregation. Our results show that the current connection policy will lead to a severe\ntraffic concentration in the future.We then examine a new evolution process that attempts to reduce this traffic concentration. Our\nproposed evolution process increases the number of links in the deeper level in the hierarchy, thus relaxing the traffic concentration.\nWe apply our evolution process to the Internet topology in 2000 and evolve this scenario over 13 years. The results show that our\nevolution process could reduce the traffic concentration by more than half compared with that without our evolution process....
802.11-based wireless mesh networks (WMNs) as last mile solutions frequently become bottlenecks in the overall Internet\ncommunication structure. The lack of end-to-end capacity on routes also affects vertical traffic coming from or flowing towards\nexternal networks, such as the Internet. The presented approach aims to increase the overall network performance by exploiting\nchannel diversity and to additionally favor vertical traffic. To achieve this, first we propose a general system that modifies an existing\nmesh node architecture, in order to prepare a more efficient resource management and to enhance the restricted transmission\ncapacity in standard WMNs. The parallel use of nonoverlapping channels, based on a multiradio node, marks the starting point.\nThe system treats aspects of channel assignment, traffic analysis, and fast layer 2 forwarding. Then, the impact of a novel Multihop\nRadio Resource Management process is discussed as a relevant component of this new system architecture.The process combines\nper-hop priority queuing and load balancing in a novel way. It was designed, developed, and evaluated in the presented paper,\nresulting in the fact that capacity in WMNs was significantly increased, Quality-of-Service parameters were improved, and more\nefficient use of multiple radios could be reached.The proposed process was validated using a simulation approach....
The vehicular ad hoc network (VANET) for intelligent transportation systems is an emerging concept to improve transportation\nsecurity, reliability, and management. The network behavior can be totally different in topological aspects because of the mobility\nof vehicular nodes. The topology can be fully connected when the flow of vehicles is high and may have low connectivity or be\ninvalid when the flow of vehicles is low or unbalanced. In big cities, the metropolitan buses that travel on exclusive lanes may\nbe used to set up a metropolitan vehicular data network (backbone), raising the connectivity among the vehicles. Therefore, this\npaper proposes the implementation of a living mobile backbone, totally ad hoc (MOB-NET), which will provide infrastructure and\nraise the network connectivity. In order to show the viability of MOB-NET, statistical analyses were made with real data of express\nbuses that travel through exclusive lanes, besides evaluations through simulations and analytic models. The statistic, analytic, and\nsimulation results prove that the buses that travel through exclusive lanes can be used to build a communication network totally ad\nhoc and provide connectivity in more than 99% of the time, besides raising the delivery rate up to 95%....
Since certificateless public key cryptosystem can solve the complex certificate management problem in the traditional public\nkey cryptosystem and the key escrow problem in identity-based cryptosystem and the pairing computation is slower than scalar\nmultiplication over the elliptic curve, how to design certificateless signature (CLS) scheme without bilinear pairings is a challenge.\nIn this paper, we first propose a new pairing-free CLS scheme, and then the security proof is presented in the random oracle model\n(ROM) under the discrete logarithm assumption. The proposed scheme is more efficient than the previous CLS schemes in terms\nof computation and communication costs and is more suitable for the applications of low-bandwidth environments....
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