Wireless sensor networks are for sensor data transmission from a wireless sensor node to a sink node with help of intermediate wireless sensor nodes which forwards sensor data messages along a wireless multihop transmission route. For achieving shorter transmission delay in transmissions of high priority sensor data messages, various priority-based transmission methods for 1-hop and multihop wireless transmissions have been proposed. However, most of the methods do not consider longer transmission delay of low-priority sensor data message transmissions. This paper proposes a novel method for reduction of transmission delay of low priority sensor data messages by buffering them into wireless sensor nodes nearer to the sink node even though they are out of their original wireless multihop transmission route under a condition that they never interfere the transmissions of high priority sensor data message transmissions. Simulation experiments show that the proposed method achieves 3.49%-12.2% reduction of transmission delay of low priority sensor data messages. In cases that the sink nodes are on or near the edge of the wireless sensor network, higher performance improvement is achieved. Thus, the proposed method is better to be applied to such sensor network.

For achieving higher end-to-end throughput of data messages in wireless multihop networks, collisions and contentions among wireless nodes in a transmission route are required to be avoided or reduced. Under an assumption that each wireless node communicates by using a single channel, collisions are avoided by RH2SWL since a transmission route consists of a sequence of hop-by-hop shortening wireless links. However, distance between a source and a destination wireless nodes connected by a sequence of hop-by-hop shortening wireless links is limited. Therefore, it is difficult for RH2SWL to be applied in wide-area networks. This paper proposes an extension of RH2SWL by introduction of an extended wireless link into a transmission route in which a subsidiary channel different from a usual channel used in each hop-by-hop shortening link is applied. Here, no collisions occur and connectivity is improved.

In a mobile ad-hoc network, network topology changes dynamically due to mobility of computers, battery consumption and failure of mobile computers. Until now, many ad- hoc routing protocol tolerating such changes of network topology have been proposed. Here, all data messages are forwarded by all mobile computers included in a message transmission route detected by an ad-hoc routing protocol. No intermediate mobile computers are added and removed other than in route repair and switching. This paper proposes a dynamic modification of a message transmission route for achieving shorter end-to- end transmission delay with less control messages in an ad- hoc network. Here, data messages are retransmitted not by a previous hop mobile computer but by another mobile computer which receives them correctly and is the nearest to a next hop mobile computer. This paper shows a routing protocol and a data message transmission protocol for the dynamic route modification according to the surrogate of retransmission. Performance evaluation is simulation shows that own proposal method achieves reduction of numbers of retransmission i.e., shorter end-to-end transmission delay, especially in a dense ad- hoc network.

In wireless multihop transmission of sensor data, in addition to avoidance of contentions and collisions of wireless signals, available capacity of communication buffers in sensor nodes should be considered. If a communication buffer in a next-hop wireless sensor node is filled, it is impossible for a wireless sensor node to forward a message with sensor data to the next-hop one. Here, the sensor node stores the message to its communication buffer and waits for the buffer in the next-hop sensor node to have enough space. The buffered messages are required to be transmitted to a sink node as soon as possible. This paper proposes a method to store the messages not only into communication buffers in wireless sensor nodes along the multihop transmission route but also in wireless sensor nodes neighboring to the multihop transmission route. By applying this method, messages with sensor data are stored into communication buffers of wireless sensor nodes nearer to the sink node and shorter end-to-end transmission delay is required. We design a routing protocol and a message transmission protocol for implementation and evaluate time duration required to transmit all buffered messages to a destination sink node by comparing with the conventional multihop transmission protocol.

For development of ad-hoc networks and sensor networks where wireless multihop message transmission among multiple mobile computers, design and implementation of routing protocols with lower communication overhead are critical. Here, characteristics and performance of a routing protocol primarily depend on the method for transmission of Rreq to a destination mobile computer. Many ad-hoc routing protocols apply flooding of an Rreq message. FACE routing protocol transmits an Rreq message without flooding. Though each mobile computer receiving an Rreq message determines its next hop mobile computer only by location of neighbor mobile computers, it surely detects a message transmission route; i.e. no deadend. However, it is required for each mobile computer to exchange its location repeatedly since up-to-date location of all neighbor mobile computers is used for determination of a next hop mobile computer. This paper proposes a novel ad-hoc routing protocol NB-FACE (No Beacon FACE) routing protocol which determines a next hop mobile computer without location of neighbor mobile computers and achieves the same message transmission route as FACE.

In a wireless mobile network with wireless multihop transmissions such as a mobile adhoc network and a wireless multihop access network, end-to-end bandwidth from a source mobile computer to a destination one is less than 1/3 of bandwidth of a wireless communication link due to random waiting time for contention avoidance and RTS/CTS control for solving a hidden terminal problem. In this paper, the authors propose an adhoc routing protocol and a message transmission protocol with transmission power control for achieving higher end-to-end bandwidth. The maximum end-to-end bandwidth in the proposed protocols is 1/2 of bandwidth of a wireless communication link. Simulation results show that the proposed protocol provides about 60% higher end-to-end bandwidth than a conventional no power control protocol. In addition, it provides almost the same connectivity with conventional no power control protocols if density of mobile computers is sufficiently high.

In an ad-hoc network, a routing protocol which detects a transmission route from a source mobile computer to a destination one is critical due to mobility and limited battery capacity of mobile computers. Here, a communication link between two mobile computers is not always bidirectional, i.e. unidirectional, since transmission power of mobile computers is not the same. Though some ad-hoc routing protocols, e.g. DSR, support routing with unidirectional links, multiple floodings (successive broadcasting) are used and communication overhead is high. This paper proposes a routing protocol LBSR supporting unidirectional links and based on combination of a single flooding and multiple unicast message transmissions. In LDSR, route cache mechanism works better than DSR in an environment with unidirectional links. Simulation results show the efficiency of route cache in LBSR.

We discuss a routing protocol for supporting communication in a wireless LAN with base stations. Though a base station is critical for transmission of a message through a wired network, high cost and overhead for construction and maintenance of base stations are required to achieve a network in which a mobile computer always communicates with a base station directly. We propose a routing protocol CB-WSCP (Cluster to Base Station Wireless Sporadic Communication Protocol) for supporting sporadic communication and achieving transmission of more messages between a base station and a cluster of mobile computers changing locations with high speed.

For achieving an environment for mission-critical network applications with multimedia message transmission, the authors have proposed a novel global consistency for a set of local checkpoints. It reflects features of multimedia network applications. Based on the consistency, the authors have designed a centralized synchronous checkpoint protocol. In order to reduce communication overhead for checkpointing and recovery, This work proposes a communication-induced checkpoint-recovery protocol.

Summary form only given. Several routing protocols, e.g. DSR(dynamic source routing protocol) and AODV(ad-hoc ondemand distance vector routing protocol), have been proposed for routing data packets in ad hoc networks. These are ondemand routing protocols. Only when a node requires to transmit data packets, it searches a route to a destination node. In addition, these are single-path protocols which detect only one route. However, in an ad hoc network, due to mobility of nodes and instability of communication links, multiple-route protocols are required. Here, we propose a novel multiple-route protocol MRAODV(multiple-route ondemand distance vector routing protocol) where separated reverse path fragments are connected to achieve additional routes. According to simulation results, more additional routes are detected in our protocol than MNH protocol.

Summary form only given. For supporting mission-critical applications in a mobile network system, hybrid checkpointing has been proposed. In a recent mobile network, wireless LAN protocols such as IEEE 802.11 and HIPERLAN are getting popular and communication with mobile computers is realized by using Mobile IP in the Internet. We propose a novel hybrid checkpoint protocol. Here, message logging for mobile computers is achieved based on broadcast property of wireless LAN protocols. In addition, by extending Mobile IP, network overload in recovery is avoided. For both checkpointing and recovery in the proposed protocol, all required information is piggied back to messages. That is, no additional message is required.

Summary form only given. In an ad hoc network, a routing protocol which detects a transmission route from a source mobile computer to a destination one is critical due to mobility and limited battery capacity of mobile computers. Here, a communication link between two mobile computers is not always bidirectional, i.e. uni-directional, since transmission power of mobile computers is not the same. Though some ad hoc routing protocols, e.g. DSR, support routing with unidirectional links, multiple flooding* (successive broadcasting) are used and communication overhead is high. We propose a novel routing protocol LBSR supporting unidirectional links and based on combination of a single flooding and multiple unicast message transmissions. In LBSR, route cache mechanism works better than DSR in an environment with unidirectional links. Simulation results show the efficiency of route cache in LBSR.

Recently, mobile computers have become to communicate with each other by using a wireless LAN protocol, for supporting various Internet services. In case that a mobile computer changes a location with high speed, less messages are exchanged between the mobile computer and the Internet. This work proposes a novel routing protocol CB-WSCP for a mobile clustered networks in which mobile computers with almost the same velocity and communication with each other by multihop transmission form a cluster. Here, communication between a cluster and a base station is available while at least one mobile computer in the cluster is within a transmission range of the base station. Hence, it is required to support sporadic communication. For achieving wider bandwidth even though the cluster moves with a high speed, a proposed protocol achieves switching of gateways and updating of routing tables.

For supporting mission-critical applications in a mobile network system, hybrid checkpointing has been proposed. In a recent mobile network, wireless LAN protocols such as IEEE 802.11 and HlPERLAN are getting popular and communication with mobile computers is realized by using mobile IP in the Internet. This paper proposes a novel hybrid checkpoint protocol. Here, message logging for mobile computers is achieved based on broadcast property of wireless LAN protocols. In addition, by extending mobile IP, network overload in recovery is avoided. For both check- pointing and recovery in the proposed protocol, all required information is piggied back to messages. That is, no additional message is required.

Recently, mobile computers have become able to communicate with each other by using a wireless LAN protocol, e.g. IEEE 802.11 and HIPERLAN, for supporting various Internet services. In the case when a mobile computer changes location with high speed, less messages are exchanged between the mobile computer and the Internet. This paper proposes a novel routing protocol CB-WSCP for mobile clustered networks in which mobile computers with almost the same velocity and communication with each other by multi-hop transmission form a cluster. Here, communication between a cluster and a base station is available only if a mobile computer in the cluster is within transmission range of the base station. Hence, it is required to support sporadic communication. For achieving wider bandwidth even though the cluster moves with high speed, the proposed protocol achieves switching of gateways and updating of routing tables.

For supporting mission-critical applications in a mobile network system, hybrid checkpointing has been proposed. In a recent mobile network, wireless LAN protocols such as IEEE 802.11 and HIPERLAN are getting popular and communication with mobile computers is realized by using Mobile IP in the Internet. This paper proposes a novel hybrid checkpoint protocol. Here, message logging for mobile computers is achieved based on the broadcast property of wireless LAN protocols. In addition, by extending Mobile IP, network overload in recovery is avoided. For both checkpointing and recovery in the proposed protocol, all required information is piggied back to messages. That is, no additional message is required.

In order to achieve fault-tolerant distributed systems, checkpoint-recovery has been researched and many protocols have been designed. A global checkpoint taken by the protocols have to be consistent. In conventional network applications, a global checkpoint is consistent if there is no inconsistent message in any communication channel. However, in multimedia network applications, there are different requirements for time-constrained failure-free execution and large-size message transmissions where lost of a part of the message is acceptable by applications. This paper proposes novel criteria, consistency and duplexity for global checkpoints in multimedia network applications.

In an ad-hoc network, a routing protocol which detects a transmission route from a source mobile computer to a destination one is critical due to mobility and limited battery capacity of computers. A communication link between two mobile computers is not always bi-directional, i.e. unidirectional, since the transmission power of mobile computers is not the same. Some ad-hoc routing protocols, e.g. DSR, support routing with uni-directional links, multiple floodings (successive broadcasting) are used and communication overhead is high. The paper proposes a novel routing protocol LBSR, supporting uni-directional links which requires only a single flooding and unicast message transmissions.

Distributed applications are realized by cooperation of multiple objects. A state of an object depends on in what order the objects exchange request and response messages. In this paper, we newly define an object-based precedent relation of messages based on conflicting relation among requests. Here, only the messages to be ordered in the object-based system are ordered and the others are not ordered. We discuss a protocol which supports the object-based ordered delivery of request and response messages. Here, an object vector is newly proposed to order messages.

Objects support abstract methods in object-based systems. We discuss a novel object-based locking (OBL) protocol to lock replicated objects by extending the quorum-based protocol handling read and write requests to abstract methods. Unless two methods op/sub 1/ and op/sub 2/ conflict, the quorum sets of the methods may not intersect even if op/sub 1/ and op/sub 2/ update the replicas. Here, a pair of replicas A and B compute op/sub 1/ and opt, respectively. If op/sub 1/ and op/sub 2/ do not conflict, A and B can later compute op/sub 2/ and op/sub 1/, respectively. We newly propose a version vector to identify what methods are computed on a replica. We discuss the OBL protocol where the replicas exchange the compatible methods by using the version vector.

A multimedia object supports methods to manipulate the multimedia data in the object. A method changes not only the state of the object but also the QoS (quality of service) of the state. We discuss new equivalent and compatible relations among methods with respect to QoS. By using the relations, we discuss a QoS-based compensation method to undo the computation. We also discuss a locking scheme for objects.

In distributed applications, a group of multiple processes cooperate by exchanging messages. It is critical to support the group of application processes with enough quality of service (QoS) including the ordered delivery of messages. The delay time and the message loss ratio are significant QoS parameters. In Internet applications, the delay time and the loss ratio are significantly different in different communication channels. The authors define a novel causality named /spl Delta/*-causality among the messages to hold in the world-wide environment. They discuss how to transmit messages to the destination processes and how to resolve message loss and delay supporting the /spl Delta/*-causality given the requirements of delay time and message loss ratio.

Distributed applications are realized by cooperation of objects. A state of the object depends on in what order the object exchanges request and response messages and computes requests. In this paper, we newly define a significantly precedent order of messages based on a conflicting relation among requests. The objects can be mutually consistent if the objects take messages in the significantly precedent order. We discuss a protocol which supports the significantly ordered delivery of request and response messages. Here, an object vector is newly proposed to significantly order messages.

In object-based systems, objects supporting abstract methods are replicated to increase the performance, reliability and availability. We discuss a novel object-based locking (OBL) protocol to lock replicas of objects by extending the quorum-based protocol for read and write to abstract methods. Unless two methods conflict, subsets of the replicas locked by the methods do not intersect even if the methods change the replicas. Methods not computed on a replica A but computed on another replica are computed on A when a method conflicting with the methods are issued to A in the OBL protocol. We newly propose a version vector to identify what methods are computed on a replica.

This paper discusses how to make a distributed object system flexible so as to satisfy applications' requirements when changing the system environment. The system change is modeled to be the change of not only types of service but also quality of service (QoS) supported by the objects. There are two types of methods changing the objects, one for manipulating the states of the objects and another for changing QoS of the objects. We discuss new relations among methods with respect to QoS. By using the QoS-based relations, we newly discuss a QoS-based compensating way to recover the object from the less qualified state.

In group protocols, larger computation and communication are consumed to causally order all messages transmitted in the network. Transactions in clients manipulate objects in servers by sending read and write requests to the servers. In this paper we define significant messages, which are to be ordered at the application level, by using a conflicting relation among the transactions. We newly propose an object vector to causally order only the significant messages. The scheme of the object vector is invariant in the change of the group membership. We also show a TBCO (transaction-based causally ordered) protocol adopting the object vector; by which the number of messages to be causally ordered are reduced.

Information systems consist of mobile stations and fixed stations. Mission critical applications are required to be executed fault-tolerantly in these systems. However, mobile stations support neither enough volume of storage and processing power nor enough capacity of battery to do reliable, long-term communications. Moreover, wireless channels are less reliable. Hence, the channels with the mobile stations are often disconnected. Therefore, it is difficult for multiple mobile stations to synchronously take checkpoints since the communication channels with the mobile stations may be disconnected even during taking the checkpoints. In this paper, we propose a novel hybrid checkpointing protocol where the mobile stations take asynchronously and the fixed ones take synchronously checkpoints. Reliable information systems including mobile stations can be realized by the hybrid checkpointing protocol.

This paper proposes a novel algorithm for taking checkpoints and rolling back the processes for recovery in asynchronous distributed systems. The algorithm has the following properties: (1) multiple processes can simultaneously initiate the checkpointing; (2) no additional message is transmitted for taking checkpoints; (3) a set of local checkpoints taken by multiple processes denotes a consistent global state; (4) multiple processes can initiate simultaneously the rollback recovery; (5) the minimum number of processes are rolled back; and (6) each process is rolled back asynchronously. The number of messages for rolling back the processes is O(l) where l is the number of channels. Therefore, the system is kept highly available by the algorithm presented.

Recently, large-scale distributed systems are being developed. Since it is expensive to newly develop the system, it is required to adopt the system in use to the changes of the user requirements and the environments. Therefore, it is essential to discuss how to upgrade the distributed programs. The system cannot be kept highly available by the conventional upgrading methods because multiple processes have to be suspended simultaneously. This paper discusses a new method which allows each process to invoke the upgrading procedure independently of the other processes. The key idea is that multiple versions of processes are allowed to co-exist temporarily. If the multiple versions of processes co-exist, such protocol errors as the unspecified receptions and the communication deadlocks can occur. Each pair of an old-version process and a new-version one is named a process group. The group communication protocol proposed in this paper supports message transmissions among the process groups. Moreover, the protocol errors can be detected and resolved by using checkpointing, timeout and rollback recovery.

In large-scale distributed systems, the processes have to be upgraded to absorb the changes of user requirements and system environments. The system cannot be kept available by the conventional upgrading methods because multiple processes have to be suspended simultaneously. This paper discusses a new method where each process can invoke asynchronously the upgrading procedure. The key idea is that multiple versions of processes can be operated temporarily. Each pair of an old-version process and a new-version one are managed as one process group. The group communication protocol proposed supports the message transmission among the process groups. Moreover, the protocol detects protocol errors caused by the co-existence of multiple versions of processes. A checkpoint-rollback algorithm for resolving the protocol errors is proposed. By using the algorithm, the minimum number of processes are rolled back asynchronously. Hence, the system is highly available even if protocol error occurs.

Large-scale distributed systems are not always stable because the environments and the user requirements are changeable. The author has discussed the receptive platform to make distributed systems flexible and reliable. In order to achieve the receptive platform, it is essential to discuss how to update the distributed programs. Since conventional updating methods require that multiple processes be suspended simultaneously, the availability of the system becomes lower. A new method called the dynamic updating has been proposed. The key idea is that multiple versions of processes are allowed to co-exist temporarily while the old-version processes are not used anymore. If such protocol errors as the unspecified receptions and the dead-locks caused by the co-existence occurs, the suspended old-version processes are restarted from the consistent state. An algorithm, has been designed for treating the unspecified receptions. This paper proposes an extended group communication algorithm that can detect and resolve the deadlocks. By using the algorithm, the dynamic updating can be applied to more general distributed application programs.

In distributed systems, a group of processes are cooperated to execute an application program. A group is established among multiple processes and only processes in the group communicate with each other. This type of group communication is named intra-group communication. The communication system has to support the reliable intra-group communication in the presence of the process fault. In order to tolerate the process fault, each process in the group is replicated into a collection of multiple replicas named a cluster. In this paper, we would like to propose a new intra-group communication protocol which supports the causally ordered delivery of messages for the processes within the group. In addition, the protocol supports the reliable delivery of messages in the presence of the Byzantine faults of the processes.

The paper proposes a novel updating technique, dynamically updating to achieve extension or modification of functions in a distributed system. Usual updating techniques require multiple processes to suspend simultaneously in order to avoid an unspecified reception caused by the conflict of different versions of processes. By using the proposed dynamically updating technique, the updating operation can be invoked asynchronously by each process with the assurance of correct execution of the system, i.e., the system can cope with the effect of an unspecified reception caused by a mixture of multiple version processes. This is implemented by using a novel distributed algorithm that consists of group communication, checkpoint setting, and rollback recovery. This algorithm achieves rollback recovery with the lowest overhead, i.e., a set of checkpoints determines the last global state for consistent rollback recovery and a set of processes that need to rollback simultaneously is the smallest.