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IEEE 802.11 WLANs use carrier sense multiple access with collision avoidance (CSMA/CA) to initiate the Request to Send / Clear to Send (RTS/CTS) handshaking mechanism that solves the hidden node problem. However RTS/CTS also causes the exposed node problem where a node is unnecessarily prevented from accessing the wireless channel even when such access will not disrupt another nodes ongoing transmission...
In this paper, we evaluate a novel method for reducing exposed nodes in IEEE 802.11 ad hoc WLANs using asymmetric transmission ranges for RTS and CTS frames. The RTS/CTS handshake communication control mechanism used in IEEE 802.11 networks solves the hidden node problem but causes the exposed node problem. Our proposed method uses asymmetric transmission ranges for RTS and CTS control frames to solve...
In this paper, the evaluation result of a task clustering heuristic algorithm proposed for heterogeneous distributed systems is shown. The proposed heuristic algorithm is based on our original concept, known as “Worst Schedule Length (WSL)”. It derives the lower bound of the total execution time of the cluster for each processor using WSL, then the processor which contributes to minimize WSL is chosen...
The W-LAN Ad Hoc network tends to cause problems called “Hidden Node” and “Exposed Node”. RTS/CTS mechanism has been introduced to mitigate Hidden Node and most of existing researches assume that RTS and CTS are sent at the same transmission range. This paper describes a new method to improve the network throughput by adjusting the RTS transmission range. The simulation result showed that the proposed...
A wireless network node with the Omni antenna tends to cause problems called "Hidden Node" and "Exposed Node". RTS/CTS mechanism has been introduced to mitigate Hidden Node and most of existing researches assume that RTS and CTS are sent at the same data rate. In this paper we have intentionally allocate different transmission rate to RTS and CTS in order to mitigate effect of...
This paper proposes a new QoS management method for W-LAN network considering hidden node issue which handles the communication priority in accordance with each node's required bit rate. By the proposed method a W-LAN node requiring the higher bit rates can have more chance to send data to control QoS requirement with propriety.
This paper describes VoIP system for the enterprise network based on Asterisk. First the main ideas and the features of the VoIP system are described that we have developed by using Asterisk in the Intranet environment. Then the new scheme to realize high security by using Open VPN is described when developing the large scale enterprise network.
Mobile networks are being evolved from 3.5G to 3.9G/4G, integrated into IP core network based on IMS (IP Multimedia Sub-system). In this environment, it is essential to provide sufficient QoS(Quality of Service) mechanism which enables different services to provide enhanced user satisfaction. In this paper, we propose a new QoS mechanism providing adaptive resource allocation based on each user's...
The wireless ubiquitous network and various communication services are expected to be realized. The wireless ubiquitous network is defined as the converged network to integrate the mobile network with the fixed IP based network. First, the concept of wireless ubiquitous network architecture is shown which is based on IMS standardized by 3GPP. Next, Parlay is described as the solution of Open API approach...
Field data collection system to be described in this paper is an application example of the wireless sensor network. The purpose of the system is to provide more accurate analyzing method with the researchers in the remote sensing area by matching appropriate field data with the satellite data, which means to realize the ground truth in the area of remote sensing.
Mobile network has been tremendously increased in the number of users, diversity of applications and of interface technologies. Also mobile network need to provide sufficient adaptive End-to-End QoS management mechanism to provide enhanced user satisfaction. In this paper, we propose a new adaptive End-to-End QoS management mechanism based on the concept of utility function which we have borrowed...
This paper addresses to the issues (e.g. firewall, network congestion, access control, voice function) to be solved when the services like second life or OpenSim are accessed from the enterprise network environment and proposes the solutions for these issues. Especially this paper describes the cache server (e.g. design, evaluation result), the white list filtering system (e.g. design, scheme) based...
This paper addresses to the issues to be solved when the services like Second Life or OpenSim are used in the enterprise network environment and proposes the solutions for these issues. Especially this paper describes the Cache Server and the White List Filtering system based on the Information Server for the Second Life and OpenSim.
In this paper, the field data collection system to match the satellite data using location information is proposed based on the wireless sensor network. The purpose of the proposed system is to realize the ground truth in the area of remote sensing.
In recent years, the study of new network architectures has defined a clear trend towards using IP end-to-end. One of the most important issues for these types of all-IP networks is how to provide quality of service guarantees while a user is moving in wireless networks. The quality of service may degrade due to insufficient resources in the air links of any of the calling parties. In 3G cellular...
Multi-hop WLAN is convenient option to deploy tentative network while it doesn't support multi-vendor and it could be an issue to secure Internet connectivity for at tentative location. We propose wireless device which has both WLAN AP and client capabilities simultaneously. WLAN client interface doesn't have interoperability issue, and also it can be used to connect the multi-hop network to Internet...
This paper propose an example of FMC based on IMS. Then the outline of the VoIP system which has been experimentally developed for the university network based on the proposed FMC is described.
In this paper, the wireless ubiquitous network architecture is described based on IMS which has been standardized by 3GPP (3rd generation partnership program). Then the field data collection system to match the satellite data using location information is described based on the wireless ubiquitous network.
In this paper, first, the wireless ubiquitous network architecture is described based on IMS which has been standardized by 3GPP (3rd Generation Partnership Program). Next, Parlay is described as one of the solution of the service creation issue. Then the vehicle dispatcher service is described as an example of service.
In this paper, the concept of the wireless ubiquitous network is described based on IMS (IP multimedia subsystem) which has been standardized by 3GPP (3rd Generation Partnership Program). Next, the outline and field data result of the local network developed for Tokyo University of Information Sciences is described which is based on the proposed concept of the wireless ubiquitous network.
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