This paper proposes a novel technique to enable flow-level multi-path forwarding on IPv6 networks. Generally on such networks, any packet from a node is forwarded toward a destination along the same path, even if some of the packets belong to a different flow with different characteristics. In accordance with packet characteristics and to fulfil demands such as traffic engineering and QoS routing, flow-level multi-path forwarding allows explicit selection of the paths on which to send packets. Multi protocol label switching (MPLS) technology has been used to perform this function so far. However, to apply MPLS on an existing IPv6 network, all non-MPLS-enabled routers in the network must be replaced with MPLS-enabled routers. Therefore, the migration cost is generally expensive. Our previous work has proposed a technique called flow-mapping explicit host routing (FMEHR,), that renders similar results to MPLS using unused address spaces such as IP private addresses. This paper describes the FMEHR concept and its realization on an IPv6 network and discusses its characteristics.

We design a scalable and expressive naming system called SENS, which can retrieve information of computing and content resources distributed widely on the Internet by exact queries and multi-attribute range queries over resource names. Our system utilizes a descriptive naming scheme to name resources and a multi-dimensional resource ID space for message routing through the overlay network of name servers (NSs). The resource ID space is constructed on the overlay network based on CAN routing algorithm. We propose a novel mapping scheme between resource names and resource IDs, which can preserve the locality of resource IDs while still achieving a good degree of load balancing regarding resource information distribution. We also propose a multicast routing algorithm to deliver resource information and a broadcast routing algorithm to route query messages to corresponding NSs at minimum cost. Our simulation results show that our system can achieve good routing performance and load balancing

This paper proposes a MAC protocol for information discovery in ubiquitous networks. The proposed protocol is based on proactive discovery in which wireless devices periodically send advertisement broadcasts. The objective of the protocol is to provide the specified discovery time of the single-hop neighbors in a mobile ad hoc network. Since collisions in wireless network degrade performance on the discovery time, a node selects an adequate broadcast rate considering the network topology. In this paper, we show that using information about the number of neighbors in combination with framed Aloha scheme can provide the specified discovery time. We also consider a simple basic power saving mechanism which allows significantly reduce the power consumption

Application-level multicast (ALM) is a novel technology for multipoint applications, such as large scale file distribution, video and audio streaming, and video conference. Though several ALM systems have been proposed, all the multicast functions have been independently developed and integrated into individual applications. In such a situation, the development includes a lot of redundancy. Our goal is to develop RelayCast, the middleware which provides the common functions of ALM to eliminate the redundancy. RelayCast has some functional units which support fundamental and minimum functions respectively, and realizes one complete ALM system by cooperation of the units. The functional unit contains several components with different algorithms, and RelayCast meets the requirements of various applications by choosing the appropriate component. In this paper, we propose the RelayCast architecture, and present the implementation and experiment of a prototype.

When ad hoc networks are linked to wired networks by access points, the traffic tends to be non-uniformly distributed in the sense that it is more likely to be concentrated on the access points than on other nodes. However, most traditional schemes of ad hoc routing focus on the pure ad hoc network with a uniform traffic pattern. The purpose of this paper is to build multi-hop routes for non-uniform route connectivity with low routing overhead. To achieve efficient route discovery and route maintenance, we develop a new routing scheme of hopcount-based routing, which utilizes hopcount information to localize the route discovery within a limited area in order to reduce routing overhead. The simulation results show that the hopcount-based routing scheme highly reduces routing overhead while preserving high rate of successfully discovering route to the destination.

Tiny networked sensor devices will be disseminated over our physical life space, and take a significant role in realizing a ubiquitous computing environment. As sensor network technologies and its applications are still at its early stages, the architecture of the sensor network heavily relies on the applications. We believe it quite essential to come up with various kinds of applications, and obtain sufficient knowledge of sensor network architecture and its peripheral technologies through demonstrations. In this paper, we introduce our sensor network applications and present the way sensor network is used in them.

Wireless sensor network technologies are expected to be a key technology to support various innovative applications in the future ubiquitous computing environment. So far, the mainstream of sensor network research has been focused on simulation-based development of battery-aware communication protocols. However, when we apply sensor network technologies to practical applications such as environmental monitoring or factory automation, we find a lot of practical problems that are not considered in simulation-based approach. We believe that finding and solving such practical problems are quite important for deploying sensor network technologies beyond laboratory use. From this point of view, we have been trying to find such problems through various implementations of sensor network system for several years. This paper describes our opinions of designing sensor network system and introduces our approaches for developing practical systems.

Ubiquitous computing as the integration of sensors, middleware, and networking technologies to form a "smart space" environment relies on the development of both software and hardware solutions. For over 3 years, our group has been developing a smart-space environment, involving the exploration of core technologies and attractive applications. We introduce the challenges faced and lessons learned in designing and developing a smart-space environment, including device control services, locating systems, wireless sensor nodes, and middleware services.

Application-level multicast (ALM) is being increasingly recognized as a solution to support multipoint applications without the need for a network layer multicast protocol. Though several ALM systems have been proposed, all the multicast functions are independently developed and integrated into individual applications. However, we can find out the common functions of ALM among the existing systems. Our goal is to abstract the common functions and incorporate them in the middleware called RelayCast. RelayCast meets the fundamental requirements of various applications by combining several components of ALM functions. In this paper, we firstly present the architecture and implementation of RelayCast. Then, we present the multipath routing mechanism as a component. The multi-path routing achieves fast tree rebuilding at the time of tree partition caused by end-host's leave or failure.

Decentralized and unstructured peer-to-peer (P2P) networks such as Gnutella are attractive for Internet-scale information retrieval and search systems because they require neither any centralized directory nor any centralized management of overlay network topology and data placement. However, due to this decentralized architecture, current P2P keyword search systems lack useful global knowledge such as popularity of data items and relationships between keywords and data items. As a result, current P2P keyword search systems supports only naive text-match search and can find only data items with a keyword (or meta-data) exactly indicated in a query. In this paper, we show an efficient P2P search system which increases possibility of discovering desired data items. The key mechanism is query expansion, where a received query is expanded based on keyword relationships managed in a distributed fashion by participating nodes. Keyword relationships are improved through search and retrieval processes and each relationships is shared among nodes holding similar data items. We also present implementation of our P2P search system.

High-speed wireless access networks have been studied for future mobile networking. In wireless links, the higher the transmission rate, the smaller its cell size becomes. As a result, a lot of discontinuous spotted areas will exist at many places in cities. In such an environment, a mobile host moving with high-speed like a car will go through cells during a very short time. Therefore, it will repeat discontinuous connection with the network, and will not be able to have enough time for communication. We present a prefetch architecture referred as to proactive data transfer for supporting these networks. In this architecture, a user utilizes a cellular network for file requests while she stays outside the area of the hot-spotted network. The requested files are prefetched at a spool server located in the hot-spotted network. Proactive data transfer enables a user to start high-speed data communication as soon as she enters into the area of high-speed wireless networks. Moreover, throughput deterioration caused by congestion of backbone networks can be alleviated. The experimental results show the effectiveness of proactive data transfer.

Layered multicasting with a layered source coding scheme enables efficient distribution of real-time streaming media over heterogeneous networks such as the Internet. In layered multicast, rate control is required to cope with congestion quickly because packet losses in a layer with higher priority lead greater degradation of the received quality. In addition, rate control for layered multicast is required to assure fair bandwidth allocation among competitive layered multicast sessions at a congested link independent of their start time. We present a novel rate control scheme for layered multicast, called network-supported layered multicast (NLM). In NLM, routers distributed within the network support rate control. NLM avoids packet losses on a layer with high priority and achieves fair bandwidth allocation by filtering and signaling. A router filters a layer with low priority when it detects congestion, or when it is informed that the layer is needless by signaling. Simulation results show NLM offers significant advantages compared with receiver-driven rate control.

This paper presents a distributed power control scheme for next-generation multiservices CDMA systems. CDMA has inherent capability to control the quality-of-service (QoS) requirements by assigning different power levels to each traffic type. Toward this, optimum power control schemes have been investigated. The main drawback of the previously proposed algorithms is that they would require all users' transmission state necessitating a complicated control process or peak-rate bandwidth allocation. To overcome this, we exploit the Markovian property to obtain the statistics of the traffic. The statistical formulation is presented for allocating power distributedly so as to keep the "collision" probability below a predefined probability. Numerical examples show that the distributed power control scheme allows better utilization of wireless resources through statistical multiplexing than peak-rate bandwidth assignment, and it does not require a complicated control process while keeping total transmitted power at slightly greater than optimum power control.

A credible introduction strategy for B-ISDN is described. The first step is the introduction of asynchronous transfer mode (ATM) techniques into the path layer. The strategy is shown to be effective, since it enables not only the realization of a cost-effective and flexible network infrastructure, but also the provision of high-speed multimedia leased line services. The service advantages possible with virtual paths are also demonstrated. The authors' technical advances, including ATM network resource management techniques and network utilization enhancement techniques, are highlighted.>

The International Telegraph and Telephone Consultative Committee (CCITT) has recommended an algorithm to code wideband speech and music (i.e. 7-kHz audio) with 64 kb/s as an international standard (recommendation G.722). A multimedia multipoint teleconference system using the 7-kHz audio coding standard is discussed. System requirements for teleconferencing are examined, and control procedures for the system are examined. A system using digital leased circuits is presented, and the audio-bridging technique used in this system is discussed.>

The design objectives and test results of a new services integrated system using a packetized speech technique are presented. First, several important design parameters are investigated through theoretical analysis and computer simulation. Second, an experimental system for confirming the choice of design parameters as well as measuring the speech and data communication quality is described, and the test results of this system are discussed.

This paper describes a 32kbit/s adaptive delta modulation (ADM) CODEC which can be applied to digital portable telephones. This ADM CODEC employs a new adaptation algorithm and parameters adjusted for speech signals. The encoding algorithm makes it possible to achieve higher quality with the 32 kbit/s ADM CODEC than with 6 bit µ-law PCM coding. The developed ADM CODEC including a coder, a decoder and switched-capacitor filters on a chip can operate on a single power supply(3.6∼ 5V). The power dissipation is only 30 mW during normal operation and less than 10 mW in the power-down mode. The CMOS chip is an a 16-pin package, 7 × 4.3mm.

This paper describes a complete hardware implementation of a 24 channel transmultiplexer employing a digital signal processor. The algorithm for the TDM-FDM translation adopted here is a modification of the FFT and digital polyphase method. The modification is mainly directed towards the reduction of roundoff noise, so that the wordlength of the processor can be minimized. In this case, 16 bits for multiplication with double precision accumulation is found to be sufficient to meet the noise requirements as recommended by CCITT G.792. The above modification enables the implementation of the translation algorithm by a 16 bit parallel type digital signal processor. This processor is designed to be firmware controllable and, thus, has a wide range of applications. The entire 24 channel transmultiplexer comprises 1) four signal processors, each handling 12 channels one way translation including signaling; 2) digital interface part to connect to 1.544 Mbit/s PCM system; and 3) codec and Nyquist filter to connect to two 12-channel FDM systems.

This paper describes a new integrated service network using packetized voice/data technology which was developed in consideration of the sophisticated service demands for voice, data, and facsimile communication. A major problem in constructing this network is in the local distribution network, i.e., the subscriber interface unit, the local end office, and the subscriber loop which connects them. The concepts, choice of design parameters, and laboratory test results of the packetized service integration network are briefly discussed.

A 120-channel transmultiplexer has been developed which interfaces two FDM basic supergroup signals (2 x 60 channels) directly to the digital time division switch or digital transmission systems. The equiplnent exploits a block processing digital SSB-FDM multiplex/demultiplex scheme, and has been built using newly developed high-speed CMOS pipeline multipliers and variable length shift registers. System design considerations and hardware implementation techniques are described in detail as well as the measured performance.