We propose a light-weight performance analysis of Wi-Fi offload using a simple Markov model. Although the proposed model does not describe the behavior of the contention window of each station in detail, it allows us to analyze the non-saturation throughput while considering interaction among interfering stations and the queueing behavior of each station. In addition to this, the proposed model does not need to use the assumption that frames arrive at relay station according to a Poisson process. In this paper, we show how to apply the mean field approximation to the model to significantly reduce the amount of computation. We show that the proposed model accurately estimates the throughput performance of the Wi-Fi offload, and that the mean-field approximation is still valid in the scenario of the Wi-Fi offload.

IEEE 802.15.4 beacon-enabled mode can use the superframe structure for data transmission. In using the superframe structure, the duty cycle of the wireless personal area network defined by the values of the beacon order (BO) and superframe order (SO) can be adjusted in order to achieve high channel utilization and low power consumption. The optimum values of BO and SO vary according to the network condition. The present paper proposes a novel method that achieves low power consumption and low latency in a multi-hop wireless sensor network. In the proposed method, active periods in the superframe structure are appropriately assigned to routing nodes according to the network topology prior to data transmission, and the values of SO are dynamically adjusted depending on the traffic load. Simulation results demonstrate the effectiveness of the proposed method.

In a smart home, smart taps will be important sensors that constitute a multihop home sensor network. Since a smart tap is connected to household AC power, there is no need to consider batteries. Therefore, if power-supplied nodes like smart taps are selected as relay nodes, network lifetime will be maximized. In this paper, a new route determination scheme is proposed that preferentially selects power-supplied nodes like smart taps as relay nodes in an IPv6-implemented wireless sensor network for a smart home. The performance of the proposed scheme is evaluated using computer simulations. The simulation results show that the proposed scheme prolongs the network lifetime compared to the current schemes.

IEEE 802.11e Enhanced Distributed Channel Access (EDCA) is a MAC protocol for WLAN to realize Quality of Service (QoS) control. EDCA offers the possibility of defining four different classes of service at the MAC layer so that QoS requirements can be supported. Service between classes is differentiated by different sets of channel contention parameters. However, it is difficult to guarantee QoS of the high-priority stations in EDCA where both EDCA stations and Distributed Coordination Function (DCF) stations are connected to an access point (AP), because quality control is not considered in DCF. This paper proposes a novel scheme to guarantee the QoS requirement of the high-priority stations in EDCA in such a mixed environment. In this scheme, Receiving-Opportunity Control in MAC Frame (ROC) proposed by the authors is employed. ROC probabilistically refuses data frames from low-priority stations. This paper analyzes the appropriate probability which satisfies the requirement of high-priority stations in EDCA. The effectiveness of the proposed scheme is validated through simulation.

This paper proposes a MAC protocol for ad hoc networks with directional antennas for mitigating the directional hidden-node problem. In the proposed protocol, it is possible to tell the communication situation to the directional hidden node by using DATA-frame fragmentations and short busy advertisement signals. As a result, the frame collisions induced by the directional hidden nodes can be reduced and the network throughput is enhanced compared with the conventional protocol. Simulation results show the validity and effectiveness of the proposed protocol.

We propose to use a buffer management scheme, called adaptive pushout, in the transmission buffer of the access point (AP) in order to solve unfairness problems between competing TCP flows over wireless LANs. The adaptive pushout comes from the observation that multiple ACK segments in a TCP connection are redundant because of the cumulative acknowledgment mechanism of the TCP. Under the adaptive pushout, an arriving packet encountering the full buffer removes one of redundant ACKs from the transmission buffer of the AP to enter there. When the buffer is full and has no redundant ACK, the arriving packet adaptively chooses one of packets in the buffer for pushing it out from the buffer. The choice of the packet to be pushed out depends on the number of uplink and downlink TCP flows, which are continuously monitored in the proposal. We have conducted simulation experiments to show that the adaptive pushout greatly improves the fairness compared with existing proposals.

The purpose of our study is to guarantee the required throughput of high-priority (UDP) flows and to achieve the stable throughput for each flow in a wireless LAN in which both high-priority and low-priority (TCP) flows exist. The authors previously proposed a QoS control scheme called Receiving Opportunity Control in MAC Frame (ROC), in which an Access Point (AP) intentionally does not return an ACK for low-priority data frames. In this paper, we propose a novel QoS control scheme using Token Bucket Filter (TBF) based ROC, which achieves the above function. The TBF mechanism is known as a basic token based traffic control. The simulation results show the effectiveness of the proposed scheme.

When multicasting through wireless multihop networks, frame losses at the wireless link cause data losses at the application layer because of no ACK (Acknowledgment) at both data link layer and transport layer. The authors propose a novel multicast scheme to reduce data losses at the application layer and to improve reliability. The scheme incorporates a retransmission mechanism into the data link layer and selects the reliable IP-based unicast paths. The verification of the proposed multicast scheme is performed with wireless LAN interface equipped nodes in an actual office environment, where an NTSC-Quality MPEG4 movie was successfully forwarded to a 5-hop destination node.

A control scheme for sharing applications that is based on MERMAID, a distributed multiparty desktop conferencing system, is described. The control scheme design is based on a replicated architecture which runs a copy of the application at every site or workstation. It is shown that the approach is applicable to developing shared applications, with slight application-independent modifications, to sharing existing single-user applications. The shared-application structure and the functions required for shared applications are discussed. A method for sharing applications for cases in which external resources are accessed is discussed.>

A distributed multiparty desktop conferencing system (MERMAID) and the architecture on which it is based are described. This architecture, called group collaboration support architecture, is a framework for assisting geographically separate group members to work together at the same time or at different times, efficiently and effectively, by means of computers and electronic communications equipment. The distributed desktop conferencing system provides distributed participants with an environment for holding conferences. This system is implemented by using ISDN (integrated services digital network), widely connected Ethernet, and UNIX-based engineering workstations with electronic writing pads, image scanners, video cameras, microphone-installed loudspeakers, etc. The system provides participants with a means of sharing information in such multimedia forms as video images, voice, text, graphics, still images, and hand-drawn figures.>

This describes a distributed multiparty desktop conferencing system (MERMAID) and presents its preliminary brief evaluation, obtained as a result of daily use. MERMAID, which is designed based on group collaboration system architecture, provides an environment for widely distributed participants, seated at their desks, to hold real-time conferences by interchanging information through video, voice, and multimedia documents. This system is implemented by using narrow-band ISDN, high-speed data network, and UNIX-based EWSs with electronic writing pads, image scanners, video cameras, microphone-installed loudspeakers, etc. The system provides participants with the means for sharing information in such multimedia forms as video images, voice, text, graphics, still images, and hand drawn figures.

An in-house computer-supported desk-to-desk conference system that allows a group of users to conduct a meeting in real time from their telephone-attached personal computers is described. Participants can jointly view and edit relevant multimedia information, including text, graphics, images, and handwritten information distributed through a local area network. Participants can also simultaneously communicate by voice to discuss the information they are sharing. The system's design principle, i.e. the group communication architecture, and the protocol for conference coordination are discussed. The system configuration, service functions, and related control mechanisms are presented. User experiences and the results of feasibility evaluations are examined. The system has proved to be applicable to a wide variety of cooperative work, such as distributed software development, joint authoring, and group decision support.>