IEEE 802.11WLANs 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 present continuing evaluation of a method for reducing exposed nodes in 802.11 ad hoc WLANs using asymmetric transmission ranges for RTS and CTS frames.NS-2 simulations show that the proposed method improves overall network throughput in a topology scenario of a 3-D network faced with ceiling/floor obstructions.

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 method achieved higher throughput in some degree.

In tomorrow's automated offices, an important role will be played by voice storage systems which enable telephone communication at any time. This paper discusses the problems and technical consideration in designing a flexible voice storage system featuring a distributed structure whose capacity can be expanded at will. Recent advances in microprocessors and magnetic minidisk devices have made this kind of system economically feasible. An efficient new method for real-time accessing of distributed files is proposed which guarantees continuous storing and forwarding of voice messages. A simple method of estimating the required file capacity is also given on the basis of a voice message traffic analysis.