Given the limited channel capacity in wireless LANs, it is important to achieve high throughput and good fairness through medium access control (MAC) schemes. Although many schemes have been proposed to enhance throughput or fairness of the original IEEE 802.11 standard, they either fail to consider both throughput and fairness, or to do so with complicated algorithms. In this paper, we propose a new MAC scheme that dynamically optimizes each active node's backoff process. The key idea is to enable each node to adjust its Contention Window (CW) to approach the optimal one that will maximize the throughput. Meanwhile, when the network enters into steady state in saturated case, i.e., under heavy traffic load, all the nodes will maintain approximately identical CWs, which guarantees fair share of the channel among all nodes. A distinguishing feature of this scheme is the use of an index called average channel idle interval for optimizing the backoff process without estimating the number of active nodes in networks. We show through theoretical analysis that the average channel ideal interval can represent current network traffic load and indicate the optimal CW. Moreover, since it can be obtained through direct measurement, our scheme eliminates the need for complicated estimation of the number of active nodes as required in previous schemes, which makes our schemes simpler and more reliable when network traffic changes frequently. Through simulation comparison with previous schemes, we show that our scheme can greatly improve the throughput no matter the network is in saturated or non-saturated case, while maintaining good fairness.

Emerging GMPLS (Generalized Multi-Protocol Label Switching)-based photonic networks are expected to realize the dynamic allocation of network resources for a wide range of applications, such as carriers' backbone networks as well as enterprise core networks and GRID computing. To address diverse reliability requirements corresponding to different application needs, photonic networks have to support various optical path recovery schemes. Thus GMPLS standardization bodies have developed failure recovery protocols for 1+1 protection, 1:N protection and restoration, with support of extra traffic and shared use of back-up resources. Whereas the standardization efforts cover a full spectrum of recovery schemes, there have not been many reports on actual implementations of such functionalities, and none of them included extra traffic. This paper introduces an OXC (Optical Cross Connect) implementation of GMPLS's failure recovery functionalities supporting 1+1 protection, M:N protection and extra path. Here extra path is an extension of GMPLS protection's extra traffic which can partially reuse protected paths' back-up resources. Evaluation of the implementation confirms rapid recovery of protected traffic upon a failure, even when preemption of an extra path is involved. It is also shown that its preemption scheme can resolve the issue of the poor scalability of GMPLS-based preemption when multiple extra paths are preempted upon a failure.

WLANs have become increasingly popular and widely deployed. The MAC protocol is one of the important technology of the WLAN and affects communication efficiency directly. In this paper, focusing on MAC protocol, we propose a novel protocol that network nodes dynamically optimize their backoff process to achieve high throughput while supporting satisfied QoS. A distributed MAC protocol has an advantage that no infrastructure such as access point is necessary. On the other hand, total throughput decreases heavily and cannot guarantee QoS under high traffic load, which needs to be improved. Through theoretical analysis, we find that the average idle interval can represent current network traffic load and can be used together with estimated number of nodes for setting optimal CW. Since necessary indexes can be obtained directly through observing channel, our scheme based on those indexes will not increase any added load to networks, which makes our schemes simpler and more effective. Through simulation comparison with conventional method, we show that our scheme can greatly enhance the throughput and the QoS no matter the network is in saturated or non-saturated case, while maintaining good fairness.

We propose an architecture of a high-speed internetworking device using central control method. Co-operations of hardware and software is required to realize high relay performance. For the hardware, we have designed an original bus arbitration control method to achieve a high throughput of a data bus. For the software, we have devided a normal relay processing from other processing and built it as a basic function of the monitor. By this method, relay perfomance improves dramatically, because of a multiple effect of the reduction of software overheads and the improvement of cache hit ratio. We have developed the prototype device and confirmed the effects of the proposed method.

Today's enterprise information systems are modeled on the client/server paradigm over LANs interconnected by WANs, but it involves problems of network management costs and complicated management jobs. So efficient network management is strongly required for LANs interconnected by WANs. In this paper, we describe a hierarchical enterprise network management system for LANs interconnected by WANs, based upon analysis of LAN management operations. This network management system has a hierarchical model with three levels, i.e., center level, area level, and user-site level. We also describe how this system was implemented as a nation-wide corporate network with many LAN sites, emphasizing on its functional structure. This network's success has confirmed usefulness of the management system.

It has been proposed that the collaborative working environments have been created by the computing assistance for human behaviors with the instructions of related information and items. The purpose of this study is to propose the collaboration mechanism and the environments constrained by the roles. The basic principle at issue in this studies is that all members should behave autonomously, and behave collaboratively with understanding the surrounding environments. We have already presented the Distributed Collaborative Computing architecture called Noah that has the concept of field with tupple space. On this mechanism, we designed the role-based cooperative work environments on the collaboration and coordination mechanism. We applied this mechanism to the typical models in the industrial system's domain.

An Ad Hoc network is a collection of wireless mobile nodes dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration. The choice of medium access is difficult in Ad Hoc networks due to the time-varying network topology and the lack of centralized control. In this paper, we propose a novel multichannel schedule-based Medium Access Control (MAC) protocol for Ad Hoc networks named Multichannel Reservation Protocol for TDMA-based networks (MRPT). MRPT ensures collision free in successfully reserved data links, even when hidden terminals exist. The reservation of MRPT is based a control channel and in order to improve throughput we propose Four-Phase-Two-Division (FPTD) as a media access scheme of the control channel for broadcasting control or reservation messages. In FPTD, the collision can be solved rapidly with an efficient backoff algorithm which results in that system block is avoided in case of high traffic. In this paper, we also present the throughput performance of MRPT, which shows a high value and no system block even in case of high traffic load.