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Many researchers have recently studied various applications such as Inter-Vehicle Communications (IVC) and Road-to-Vehicle Communications (RVC) for Intelligent Transport Systems (ITS). RVC is a key technology that can connect vehicles with the internet through Road Side Units (RSUs). Relative positions between vehicles vary within short periods of time. Neighboring vehicles and barriers cause shadowing that blocks communication for extended periods of time between RSUs and vehicles. We propose a fast scheme of Mobile IPv6 handover using dual-band communications in RVC. This scheme uses ISM and UHF dual bands. It switches to the UHF band during handover or in the shadowing period. We demonstrate that the proposed scheme can establish continuous communications through computer simulations.

Various recent intelligent transport system projects are promoting vehicle safety and efficient vehicular traffic control all over the world. One of ITS applications is a system that solves road traffic problems by using vehicular communications technology. Inter-vehicle communication (IVC) is the communications technology for vehicles to exchange moving vehicle information by wireless networks without any base stations. The Vehicular Ad-hoc Network (VANET) is expected to provide new applications for passengers of vehicles by enabling vehicles to communicate with each other via IVC as well as with roadside base stations via roadside-to-vehicle communications. However, when each vehicle transmits its own information to neighboring vehicles, the amount of information being transmitted increases significantly. To solve this problem, we present a novel real-time recognition method for vehicular traffic congestion via VANET with IVC. Vehicles collect the original GPS information of other vehicles by communicating with each other, and they create content that may be useful for drivers by analyzing that original information. The proposed method can reduce the information amount and deliver the analyzed contents to other vehicles efficiently. Computer simulation results show that the proposed method provides real-time information of vehicular accidents and traffic congestion to distant vehicles accurately.

Inter-Vehicle Communication (IVC) is one of the most important technologies to realize advanced Intelligent Transport Systems (ITS). We extensively apply the IVC technology to the communications between pedestrians and vehicles. We call this kind of communications VPEC (Vehicle-PEdestrian Communications). The objective of this paper is to present an effective control scheme for VPEC and to evaluate the performance of proposed scheme by experiments. We deal with direct communications between pedestrians and vehicles. Due to the battery shortage of pedestrians' terminals (p-node), we have presented a reflect-transmission scheme. In this paper, we propose a new access protocol for reflect-transmission scheme, and show its validity by various experiments with several vehicles.

Bluetooth utilizes fast frequency hopping to mitigate interference from other wireless devices and other Bluetooth piconets that share the same frequency range. However, it still cannot avoid the interference between piconets entirely. In our simulation, we observed that the inter-piconet interference can significantly degrade the system throughput by more than 10%. The system throughput within a piconet can be improved by a proper arrangement of the segmentation/reassembling (SAR) policy and a good selection of MAC scheduling protocols. Many SAR policies and MAC scheduling protocols were proposed, but none of them takes the inter-piconet interference into consideration. In this paper, we study the impact of the interference on the performance of TCP traffic over a Bluetooth scatternet with multiple overlapping piconets. To alleviate the impact, we propose interference-aware SAR policies as well as the interference-aware MAC scheduling protocols. The simulation results show that our schemes help reduce the impact of the inter-piconet interference by more than 15%.

In this study, we investigate the problem of accommodating multicast traffic in ATM networks, with emphasis on the virtual path (VP) environment. We propose a network structure called “virtual copy network” that is suitable for multicast communication and connection setup scheme, taking into account the VP environment. With our technique, we can expect statistical multiplexing gain in accommodating multiple multicast traffic streams over a VP. Also, we propose two multicast routing algorithms (the CNR-LH algorithm and the improved CNR-LH algorithm) for an ATM network environment. In these algorithms, in addition to determining an adequate route, the exact corresponding VPs on the route are also obtained. We examine the efficiency of the algorithms by demonstrating their basic characteristics using computer simulations.

In the asynchronous transfer mode (ATM) switch, unbalance with respect to the statistical destination port selection among the output ports can exist. There has been some research on output buffer-type ATM switching architecture in the case of the point-to-point cell arrival, assuming such nonuniform load condition of the output ports. However, the multicast traffic arrival condition, very important in future multimedia networks, has not been considered. Therefore, we evaluate the switch performance of the output buffer-type architecture in the case of including multicast cells at various ratios among the arrival cells on condition that the total amount of traffic load through all output ports is constant. As a result, it is clarified that exchanging the multicast cells intentionally in the ATM switch leads to the improvement of cell-loss performance in the output buffers having statistically high selection rate, if the buffers that are offered statistically high load, actually accommodate as many of the multicast cells as possible. From these results, by means of the network control that incorporates the multicast calls at a constant ratio in each ATM switch, it is possible to prevent the excessive load concentration to specific output port having statistically high utilization.

This paper considers a new transmission method (quasisynchronous transfer mode, Q-STM), as a means to eliminate both the cell loss and the network delay fluctuation in an ATM network. the concept of time-switch in circuit switching is introduced into the ATM switching framework. A switching structure and the call establishment procedure are proposed. In the proposed method, the time-switch is introduced, which eliminates in principle the output port contention in the ATM switching fabric. By preparing a buffer with a certain capacity, cell loss due to buffer overflow in the output port of the ATM switch can be completely eliminated.

This paper considers the shared output buffertype switching system as an architecture suited to the large-scale ATM switching system. an architecture is proposed, which can solve the fair throughput assignment problem among the ports belonging to the same shared memory, which is a problem in sharing the output buffer. the proposed architecture realizes fair access to the destination port contained in the specified shared buffer, by sort processing and the address attachment, without using the random access contention unit to the buffer in the knockout switch. For the proposed architecture and the conventional shared output buffer-type knockout switching system, the performances are compared by deriving the cell loss probability due to the output contention for each port. As a result, it is verified that the proposed architecture is better in terms of the realized cell loss probability. The performance of the switching system is evaluated by a computer stimulation when various buffering schemes are applied to the shared output buffer. Then it is shown that the fair throughput assignment among the considered output ports can be realized by combining the proposed architecture with an adequate buffering scheme.

The problem of accommodating multicast traffic in a virtual path (VP) environment under asynchronous transfer mode (ATM) conditions is examined. A network structure scheme suitable for all possible multicast communications is proposed. the expected result, statistical multiplexing effects during the accommodation of multiple multicast traffic over a VP should reduce hardware costs associated with the accommodation of multicast traffic. Multicast routing algorithms (the carrier-to-noise ratio (CNR) algorithm and the improved CNR algorithm) for an ATM network environment are proposed here. the efficiency of these algorithms is tested using their basic characteristics in computer simulations.

Optical Burst Switching (OBS) [1][2][3][4] has been proposed for the next generation Internet based on the Wavelength Division Multiplexing (WDM) [5] network technologies. In the OBS, the serious problem is the burst loss due to the burst contention. There have been a number of traffic control methods [6][7] for solving the burst contention problem. The Internet has two traffic classes, i.e. real-time bursts and reliable bursts. However, most of the conventional traffic controls aren’t suitable for the real-time bursts.

In this paper, we propose network construction methods of sensor nodes for Border Security Systems. A Border Security System watches intruders by using sensor nodes with communication function. The detection of some intruders and the use of a long-term operation system are required in this system. In this paper, we propose two methods to reduce the power consumption of the whole network system by effective control of sensor nodes. By computer simulation, we show that the proposed network construction methods are suitable for Border Security Systems.

This paper discusses the channel assignment problem in the multichannel, high-speed packet network. It is assumed that multiple channels exist between a pair of switches in the network. It is expected that by regarding those channels as a single channel group and executing the packet transmission, a more efficient high-speed and large-capacity transmission will be realized. This paper newly introduces, in contrast to the virtual circuit in the multichannel network, the concept of a channel group-virtual circuit (CG-VC) for the multichannel network, where the packets are assigned to the channels based on the concept of the overflow traffic. To realize the CG-VC system in the high-speed environment, a simple and practical switch structure is proposed. The switch uses optical fibering as the basic module and the system is constructed by superposing the basic modules. Each packet automatically selects an appropriate channel from the set of output channels belonging to the same channel group. It is shown as a result of performance evaluation that, compared to the conventional VC packet switching system, the proposed system greatly improves the transmission delay and utilizes efficiently the channel.

Optical Burst Switching (OBS) has been proposed to realize the next generation Internet on the Wavelength Division Multiplexing (WDM) network technology. Optical Burst Switching is an ultra high speed switching technology for optical fiber networks but has the data burst contention problem. In this paper, we introduce Virtual Path (VP) concept addressing burst contention resolutions in OBS networks. We propose two novel flow control schemes, named Static Inter Arrival Time Flow Control (S-IAT) and Dynamic Inter Arrival Time Flow Control (D-IAT). S-IAT keeps the data burst contention rat e in an acceptable level on OBS networks. Based on S-IAT, D-IAT achieves almost the same data burst contention rate and higher throughput than S-IAT by using the data burst loss rate threshold. We will show the availability of proposed schemes by computer simulations.

An asynchronous transfer mode (ATM) switch architecture that uses the broadcasting transmission medium for transmission of cells from input ports to output ports is introduced. Cell transmission and its control are separated completely, and cell transmission control, i.e. header operation, is executed before cell transmission (control ahead). With this operation, cell transmission and its control can be executed in a pipeline style, allowing high-speed cell exchange and making transmission control easier. One of the essential problems for ATM switches which use the broadcasting transmission medium is high-speed operation of the transmission medium. The switch fabric performance is analyzed according to its switching speed. Numerical results show that the ATM switch proposed shows good cell loss performance even when its switching speed is restricted, provided that switch utilization is below 1. Extensions to the switch that lead to robustness against bursty traffic are shown. >

The objective of this paper is to exchange the position information between pedestrians and their nearby vehicles effectively, in order to protect the pedestrians from serious traffic accidents. We deal with direct communications between pedestrians and vehicles. We call this kind of communications as VPEC (vehicule-pedestrian communications). In this paper, we propose a cooperative reflect transmission scheme which is transmission control protocol using road infrastructure information. This scheme provides real-time communications between vehicles and pedestrian terminals, and enables to save both the transmission capacity and the power consumption of pedestrian terminals. We also show the validity of this scheme in VPEC by experiments with real vehicles.

The connected dominating set (CDS) has been extensively used for routing and broadcast in mobile ad hoc networks. While existing CDS protocols are successful in constructing CDS of competitive size with localized information, they either lack the mechanism to properly handle nodal mobility or require lengthy period of time to recover when CDS becomes corrupted. In this paper, a novel protocol, namely Multi-Initiator Connected Dominating Set protocol (MI-CDS), is proposed that constructs and maintains CDS of competitive size efficiently without introducing much communication overhead. The simulation results demonstrate that MI-CDS permits CDS to be available for the highest percentage of time in the mobile network scenario compared with the other CDS protocols.

The connected dominating set (CDS) has been generally used for routing and broadcasting in mobile ad hoc networks (MANETs). To reduce the cost of routing table maintenance, it is preferred that the size of CDS to be as small as possible. A number of protocols have been proposed to construct CDS with competitive size, however only few are capable of maintaining CDS under topology changes. In this research, we propose a novel extended mobility handling algorithm which will not only shorten the recovery time of CDS mobility handling but also keep a competitive size of CDS. Our simulation results validate that the algorithm successfully achieves its design goals. In addition, we will introduce an analytical model for the convergence time and the number of messages required by the CDS construction.

Recently, we need high bit rate transmissions of the wireless LAN to access the internet at offices and houses. Multi-Poll access scheme has been proposed as an efficient access control scheme for these necessities. The scheme is a central control scheme using Polling system. In order to establish a high speed multimedia transmission, we need to integrate the required quality of services effectively. In this paper, we propose QoS (Quality of Service) guaranteed Multi-Poll access scheme for multimedia services in wireless LAN. We evaluate the transmission performances of the proposed scheme for effectiveness by computer simulations. We have clarified that the proposed scheme has the outstanding performances on the throughput, delay time, and frame drop rate comparing to the conventional scheme.

Today, ITS (intelligent transport systems) is paid attention by people all over the world. ITS is the system that solves the road traffic problems by using communications technology of vehicles. IVC ( inter vehicle communications ) is the communications technology that vehicles exchange the information by using wireless LAN without any base stations. VANET ( vehicular ad-hoc network ) have been expected to provide new applications for passengers of vehicles, by enabling vehicles to communicate with each other via IVC as well as with roadside base stations via RVC ( roadside-to-vehicle communications ). We propose the COC ( contents oriented communications ) system on VANET via IVC. With COC, each vehicle collects original information that each vehicle has by communicating each other, and creates contents which may be useful for drivers, by analyzing original information. COC deliver the analyzed contents to other vehicles. The simulation results show that COC provide timely information of vehicular accidents and congestion to drivers.

Optical Burst Switching (OBS) has been proposed to realize the next generation Internet on the Wavelength Division Multiplexing (WDM) network technology. In OBS, the burst contention is the major problem. The deflection routing has been designed for resolving this problem. However the deflection routing cannot prevent the burst contention as the network load becomes high. In this paper, we show that a flow-rate control is essential for OBS. We propose Leaky Bucket Deflection method (LB Deflection method). In LB Deflection method, edge nodes which generate data bursts carry out a flow-rate control based on Leaky Bucket method. In order to verify the effectiveness of a flow-rate control in OBS, we show that LB Deflection method improves the network utilization and reduces the burst loss probability through computer simulation

Optical burst switching (OBS) has been proposed for an effective optical switching technology of WDM networks in broadband Internets. OBS has the advantages, i.e. 1) the high usage rate of the bandwidth and 2) no necessity of optical buffer. However, OBS has the burst-contention problem in control packet phase, and faces to the reduction of the network performance. Recently, slotted OBS has been proposed. The basic performance of slotted OBS is superior to the original OBS. However, slotted OBS itself cannot overcome the burst-contention problem, either. In this paper, we will adapt BECN/CRN typed deflection routing to slotted OBS to obtain the large improvement of the optical network performance. We also present two new schemes for slotted OBS to improve the burst contention problem, i.e. a) enforced waiting control and b) scheduling.

Wireless mesh networks have emerged to be one of the promising applications of ad hoc networks. The idea of installing multiple radio interfaces at each mesh router allows a mesh network to better utilize the available wireless bandwidth, but at the same time complicates the issue of route selection. In this paper, we propose a novel metric that measures the bandwidth and cost ratio of each route. Based on this metric, a Cost-Aware Route Selection (CARS) scheme is proposed to improve the overall throughput of a mesh network. The simulation results confirm that our scheme is able to better utilize the limited wireless resource and improves the overall network throughput by more than 95% with different types of traffic and communication patterns when it is compared against the past route selection schemes.

An optical burst switching (OBS) network provides preferable broadband infrastructure, and is a promising strong candidate for the future optical Internet. However, there is a major deficiency of the OBS, which occurs when multiple bursts contend for the same link and leads to bursts loss. As an effective method to resolve the above important issue of OBS networks, deflection routing has been proposed. A simple deflection routing without proper routing control cannot sufficiently distribute the traffic of bursts and guarantee ideal performance of OBS particularly for heavy traffic condition. In this paper, we propose a new approach for deflection routing in order to reduce the burst loss and minimize end-to-end delay. The simulation results show that the proposed scheme improves the network utilization and minimize both the burst loss probability and end-to-end delay

In the conventional WWW search or P2P file sharing systems, users search for some information by using the explicit information such as keywords, addresses or content names. However, it is very difficult to obtain real-time information immediately just after serious accident (i.e. fires, earthquake, explosion by terrorism, traffic accidents and so on) happens suddenly. The conventional information systems, whether it is centralized nor distributed, cannot support user accesses, since they cannot provide any contents with the Explicit Information, in such short time. In this paper, we propose a new communication scheme named COC - content oriented communications. In COC, distributed information systems don't observe the explicit information (keywords, addresses, content names, etc.) but the implicit information (locations, time, speed, etc.). This is why we call our system content oriented. In this paper, we introduce COC, which enables us to decrease the personal damage of a disaster in a local area where the disaster occurs by searching and getting some information for the evacuation.

In order to achieve a safe automotive society, it is necessary to develop an on-board intelligent system with inter-vehicle communications (IVC). We want to avoid vehicle collisions under most situations, such as intersections, highways, and blind corners, by using IVC technology through wireless ad hoc networks. The paper describes a vehicular collision avoidance support system (VCASS), and shows its performance by various experiments with two real vehicles. We have installed personal computers, telecommunication equipment, and GPS in the vehicles. A vehicle exchanges location information and velocity vectors with the other by a UDP broadcast, and calculates the relative position/speed. Vehicles warn the drivers of the possibility of collision. We verify the validity and effectiveness of VCASS by experiments.

Inter-vehicle communications (IVC) is one of the most important technologies for realizing advanced intelligent transport systems (ITS). We deal with Vehicle-PEdestrian Communications (VPEC) as communication between vehicles and pedestrians. The objective of VPEC is to protect pedestrians from traffic accidents. In VPEC without any controls, pedestrians (p-nodes) transmit many packets to vehicles (v-nodes) to provide the position information of p-nodes. But, the battery capacity of p-nodes is small. It is necessary to suppress the transmission of p-nodes to obtain proper information exchanges. We present effective reflect-transmission schemes which can reduce needless transmissions from p-nodes on VPEC. In addition, we present silent control protocol, mask control protocol and distance-based priority control protocol as more effective protocols for the reflect-transmission scheme. The proposed protocols can operate the reflect-transmission scheme more efficiently. Further, we have carried out a VPEC experiment to verify the control behavior of VPEC. We outline the experiments and show some results obtained.

The anycast communication protocol is to select the best server and the best route for a particular client from a group of replicated servers with the same contents. As users have come to demand contents with high QoS, the necessity to support the anycast communications in QoS networks has grown. In this paper, we propose a server and route selection method with application-level QoS-based anycast protocol. The protocol we propose has the following advantages: 1) the latest server and route information can be constantly acquired through distributed resource management by E-BB; 2) the server and route selection algorithm enable us to consider both the server load and network load simultaneously; and 3) high reliability can be guaranteed by decentralized control.

In recent years, WDM networks have received much attention as the Internet backbone networks because of the explosive growth of the Internet IP-based traffic. The optical burst switching (OBS) has been proposed as an effective optical switching technology in the WDM networks (C. Qiao and M. Yoo, 1999). OBS has the advantages in 1) the high usage rate of the bandwidth, and 2) no necessity of optical buffer. However OBS has the burst-contention problem in the networks. The deflection routing is proposed as one of means to solve this problem. In this paper, we propose a new routing method of using deflection routing. In addition, we propose a QoS/CoS control method using a new routing algorithm. Finally, we show the variety of the proposed methods by computer simulations.

Bluetooth utilizes fast frequency hopping to mitigate interference from other wireless devices and other Bluetooth piconets that share the same frequency range. However, it still can not avoid the interference between piconets entirely. In our simulation, we observed that the inter-piconet interference can significantly degrade the system throughput by more than 30%. The system throughput within a piconet can be improved by a proper arrangement of the segmentation/reassembling (SAR) policy and a good selection of MAC scheduling protocols. Many SAR policies and MAC scheduling protocols were proposed, but none of them takes the inter-piconet interference into consideration. In this paper, we study the impact of the interference on the performance of TCP traffic over a Bluetooth scatternet with multiple overlapping piconets. To alleviate the impact, we propose interference-aware SAR policies as well as the interference-aware MAC scheduling protocols. The simulation results show that our schemes help reduce the impact of the inter-piconet interference by more than 50%.

This paper deals with an effective method to share various kinds of vehicular information among a great number of vehicles for advanced inter-vehicle communications (IVC). We present a simple and effective communication scheme named two-way approached information spreading system (TWAIS) in order to provide high quality communications service in ITS. It makes smooth communications and high availability suitable for IVC.

The inter-vehicle communications (IVC) is one of the most important technologies to realize advanced intelligent transport systems (ITS). Conventional IVC is vehicle-to-vehicle communication through line of sight communication by millimeter wave in a narrow area. Here, we deal with more progressive IVC in a wide area. In this paper, we propose Dynamic Integrated Transmission Control (DITRAC) for IVC. DITRAC optimizes transmission power and transmission interval of vehicles according to the fluctuation of the communications circumstance of the ad-hoc vehicular communications network. In order to estimate the fluctuation of the neighboring communications, we present an effective and simple method, the road-weight with receiving history (WH) method. The simulations are conducted to show the validity of DITRAC for IVC.

A control scheme to significantly reduce the packet collision in multiple-access networks with random-access protocols is proposed. The scheme intensively enforces the capture effect by controlling packet transmission power increasingly as time. As a result of this power control, if the first packet in collision arrives earlier than the others by a certain amount of time, the difference in power necessary for the capture effect is retained during the whole colliding period, and the first packet can capture the channel. The essential point of the scheme is that the difference in the packets' arrival times causes the difference in power between packets. The scheme is thus named the power control during transmission (PCT) scheme. >

A traffic control scheme for FDDI (fiber distributed data interface) interconnection through an ATM (asynchronous transfer mode) network is presented. The scheme consists of two parts, a VP (virtual path) bandwidth allocation algorithm and a feedback type buffer protection flow control. Both use the acknowledge for the frame of FDDI as a control unit. Simulation results show that VP bandwidth allocated by the scheme increases according to arrival traffic when the destination FDDI has enough capacity and allocated bandwidth is not increased when its capacity is less than arrival traffic. Thus, the scheme has desirable VP bandwidth allocation characteristics. Simulation results also show that the scheme prevents cell loss at a destination gateway completely. >

The authors present a new access scheme for packet radio networks with variable length packets, called S-ALOHA/IT (slotted ALOHA with immediate transmission) in which a packet can be sent immediately unless it overrides the slot boundary. In the s-ALOHA/IT, the PCT (power control during transmission) method is added for improving efficiency. The basic idea of the PCT method is to control the packet transmission power increasingly as a time function and to lead the capture effect. By the PCT method, some packets are successfully transmitted even when packet collisions occur. In addition, the initial power is also varied to introduce the capture effect among collided packet. A performance comparison of the s-ALOHA/IT is carried out with the conventional s-ALOHA by using computer simulation. In all cases, the throughput of s-ALOHA/IT is about twice that of the conventional s-ALOHA. >

Presents a new access control scheme for the wireless communication packet networks of variable packet length environment, s-ALOHA/PAIT (slotted ALOHA with power assigning and immediate transmission controls). The scheme improves channel throughput in two aspects, capture effect and reuse of vacant period of a slot. For reuse of vacant period of a slot, a packet can be transmitted immediately unless it overrides the slot boundary even though the timing is not at the beginning of the slot. It enables more than one packet to be transmitted successfully in a slot. Transmission power is varied to lead capture effect among packets transmitted at the beginning of a slot and also between a packet at the beginning of a slot and one transmitted in the middle of the same slot. The authors evaluate the performance of s-ALOHA/PAIT compared with the conventional s-ALOHA and show that s-ALOHA/PAIT obtains considerable improvement of the throughput performance. >

In the ATM network, various kinds of traffic will be supported. This includes traffic which requires high quality of service. For example, coded HDTV requires no cell loss because of high compression and no possibility of retransmission. CBR (constant bit rate) services require no delay jitter. Thus, it will be required to support some class of services with no cell loss and no delay jitter. This paper proposes a new transmission method Q-STM, with which no cell loss and no delay jitter can be supported in the ATM network. The Q-STM introduces two new concepts into the ATM networks; frame structure and time slot reservation. A frame structure itself is similar to the framed ATM. However, in the Q-STM, a frame is divided into some subframes and each subframe is a unit of time switching in intermediate switching nodes. This leads to smaller end-to-end delay than that of the framed ATM. Time slots in a frame are reserved for each Q-STM call in a call setup phase and this leads to no delay jitter and no cell loss. Ordinary ATM service class is also supported and this kind of cell uses an empty slot which is not reserved or is not used because of fluctuation of Q-STM call transmission rate.

We study allocation problems of multimedia files in distributed network systems. In these systems, the files are shared by users connected with different servers through high-speed communication networks. One of the most important problems in distributed systems is how to assign the files to servers in view of costs and delays. In these systems, it is obvious that there is a trading-off relationship between costs and delays. Our objective is to find the optimal file allocation such that the total cost is minimized subject to the total delay. In order to evaluate the optimization, we present a system model that can cover a wide range of multimedia network applications such as VoD (video on demand), corporation information networks, and so on. We introduce a 0-1 integer programming formulation for the optimization problem. We find the optimal file allocation by solving these formulae, and quantify the general tendency in distributed systems. Moreover, we make a comparison between the exhaustive search and the approximate method that we use for optimization.

Optical switching networks to transport vast amounts of information are important for B-ISDN services. Wavelength division multiplexing (WDM) is emerging as the dominant technology for future optical networks. A large capacity photonic ATM switch architecture using WDM technology is proposed in this paper. The proposed switch is suitable for WDM optical ATM networks, that is, the input and an output of the switch are wavelength division multiplexed. The switch can provide very large ATM cell switching capacity, for instance, 10 Tbit/s, with reasonable complexity. The basic switch module of the proposed switch has a simple architecture, and reduces the amount of a buffer hardware by introducing the WDM concept.

We present a novel access scheme called CDMA/CS-CF (code division multiple access/code sense for collision free access), which can transmit two kind of traffic i.e. voice and data efficiently. This scheme avoids the collision of packets that occur in CSMA (code sense multiple access), and can assign codes fairly to terminals. This assignment of codes to terminals is operated autonomously by terminals themselves. This scheme can improve the characteristics of throughput, access delay and packet loss rate. We evaluate the performances of CDMA/CS-CF compared with CDMA/PRMA, and show the validity, numerically. Moreover, we consider enhanced CDMA/CS-CF and show the effectiveness in the environment with hidden terminals.

We present a novel access scheme called CDMA/CS-CF (code division multiple access/code sense for collision free access), which can transmit two kind of traffic i.e. voice and date efficiently. This scheme avoids the collision of packets that occur in CSMA (code sense multiple access), and can assign codes fairly to terminals. This assignment of codes to terminals is operated autonomously by terminals themselves. This scheme can improve the characteristics of throughput and access delay. We evaluate the performance of CDMA/CS-CF compared with CDMA/PRMA, and show the validity, numerically.

Intelligent Transportation Systems (ITS) have become a focus for many countries. To achieve ITS, Inter Vehicle Communication (IVC) is required for the exchange and distribution of data such as congestion or emergency information. If this communication can be done without fixed infrastructure, the systems can be deployed quickly and on a larger scale. Ad hoc networking technologies are one such technology to achieve IVC. However, if generic ad hoc network solutions are applied directly to IVC, performance can degrade quickly as the system scales particularly for broadcast type messages. In this paper we propose two new broadcast protocols that reduce bandwidth required for broadcast communication by taking advantage of a vehicle's highly directional movement and Global Positioning Information. To show the performance of our new protocols, we compare our approach with generic ad hoc broadcasting techniques. Our results show that it is possible to achieve several hundred percent improvement of bandwidth utilization with very slight sacrifice of reachability.

The intelligent transportation systems (ITS) use advanced communications and control technologies to improve current transportation systems. To achieve many ITS applications, the ability to exchange messages between vehicles is necessary. This is generally required as inter vehicle communication (IVC). IVC can be considered as a special case of ad hoc networks, where nodes only move along predefined road paths. We propose new broadcast protocols that make use of global positioning system (GPS) information to enhance the performance of broadcast service in IVC. The ability to efficiently broadcast messages is necessary for any communications in IVC (e.g, updating routing tables, etc). We propose two algorithms that effectively reduce the number of re-broadcast messages without affecting the number of hosts (vehicles) that receive the broadcast. The simulation results show up to several hundred percentage of bandwidth utilization improvement can be achieved by our proposed broadcast protocols.

In order to realize the intelligent transport system (ITS) without any road facilities, inter-vehicle communications (IVC) is considered as preferable. IVC makes it possible to exchange real-time information among vehicles. This paper focuses on the packet-based IVC, and presents the vehicular information broadcasting relay (VIBROR) protocol to realize an effective multi-hop transmission scheme for broadcasting information without any complex negotiation among the vehicles.

The authors propose two multicast routing algorithms which distribute copy operation of packets over all nodes along the multicast path: a link-added type algorithm and a loop-constructed type algorithm. Both algorithms, at first, derive an approximate solution for minimum cast path, and then improve the solution to prevent concentration of packet copy operation at one switching node at a little sacrifice of total cost along the path. Computer simulation results show that too much copy operation per node can be avoided by these algorithms. Compared to the minimum cost solution of the tree-shaped multicast path, the solution of the proposed algorithms makes the average distance connecting a source-destination pair longer, but the sacrifice of total cost is verb small. These algorithms can be applied not only to packet networks but also asynchronous transfer mode (ATM) networks. >

A novel packet switch architecture is proposed based on a channel grouped virtual circuit (CG-VC) scheme for high-speed communication networks. The case is considered in which there are several parallel channels between two switching nodes. The CG-VC scheme allows a packet to select an available channel in such a way as to avoid congested channels using a simple, hardware-based, self-routing mechanism. As a result, the architecture provides efficient channel use and low switching delay. The performance of the proposed switch is evaluated by simulation. The results show the proposed switch significantly improves channel utilization and switching delay compared with conventional single-channel allocation transmission policies. >

A new configuration for packet radio networks, called local/global (LG) network configuration, is proposed, aiming at total throughput improvement. By using two kinds of channels (local channel and global channel) and geographically partitioning the total area, the spatial reuse of channel capacity is realized. The performance of this LG configuration is analyzed for a fixed radio network by introducing the delay ratio γ between local and global channels. s-ALOHA protocol is used under heavy overload. By the performance analysis and numerical results, it is concluded that the improvement of the total throughput is attained for a typical network configuration without greatly increasing the mean delay. Also, various schemes for determining the allocation ratio of channel capacity to the local and global channels are presented and studied to apply this LG configuration effectively.

The CSMA/CD method, one of the communication schemes for bus-type LANs, has problems with respect to transmission capability and its function. This paper presents an access control method named multichannel CSMA/CD for local area networks. In this method, CSMA/CD combined with a new load distribution mechanism and channel selection function is extended to multichannel organization. This method aims at LANs having high performance and multiple functions. As a result of performance evaluation, multichannel CSMA/CD is shown to be superior to the original CSMA/CD with respect to (1) total transmission capacity, (2) throughput-delay characteristic performance, (3) channel stability and (4) adaptability to various kinds of user demands in networks.

The objectives of this study are: (1) to show numerically the performance advantages of the resolvable-contention-ring (ReC-ring) in comparison with typical ring control methods like IEEE 802.5 token-ring, ANSI FDDI I token-ring, slotted-ring and contention-ring, and (2) to consider the possibility of using the priority mechanism of the ReC-ring for multimedia high-speed communications networks. The authors present a simple priority control mechanism based on the time-token scheme for multimedia communications of ReC-rings. The performance of the prioritized and nonprioritized ReC-rings is compared by computer simulation, and the priority mechanism presented is proved to have sufficient validity for multimedia communications networks. >