Ubiquitous computing and communication are the key technology for achieving economic growth, sustainable development, safe and secure community towards a ubiquitous network society. Although the technology alone cannot solve the emerging problems, it is important to deploy services everywhere and reach real people with sensor enabled smart phones or devices. Using these devices and wireless sensor networks, we have been creating various types of ubiquitous services which support our everyday life. In this paper, we describe ubiquitous services based on a HOT-SPA model and discuss challenges in creating new ubiquitous services with smart enablers such as smart phones, wireless sensor nodes, social media, and cloud services. We first classify various types of ubiquitous service and introduce the HOT-SPA model which is aimed at modeling ubiquitous services. Several ubiquitous services, such as DIY smart object services, Twitthings, Airy Notes, and SensingCloud, are described. We then address the challenges in creating advanced ubiquitous services by enhancing coupling between a cyber and a physical space.

This paper presents a path compression protocol for on-demand ad hoc network routing protocols, which is called dynamic path shortening (DPS). In DPS, active route paths adapt dynamically to node mobility based on the "local" link quality estimation at each own node, without exchanging periodic control packets such as Hello messages. Each node monitors its own local link quality only when receiving packets and estimates whether to enter the "proximity" of the neighbor node to shorten active paths in a distributed manner. Simulation results of DPS in several scenarios of various node mobility and traffic flows reveal that adding DPS to DSR which is the conventional prominent on-demand ad hoc routing protocol significantly reduces the end-to-end packet latency up to 50-percent and also the number of routing packets up to 70-percent over the pure DSR, in heavy traffic cases. We also demonstrate the other simulation results obtained by using our two novel mobility models which generate more realistic node mobility than the standard random waypoint mobility model: Random Orientation Mobility and Random Escape Mobility models. Finally, simple performance experiments using DPS implementation on FreeBSD OS demonstrate that DPS shortens active routes in the order of milliseconds (about 5 ms).

We have been investigating a new class of ubiquitous services, called Activity Logging, which takes advantage for private and public sensors and the RFID tags on real-world objects. The purpose of Activity Logging is to digitally record users' interests with real-world objects and users' context to describe the users' activity. Such digital information acquired from a range of sensors and tags, if being accumulated, forms a great data source for users to recall their activities later or to share the activities with others. This paper explores the design space to realize Activity Logging, and proposes a simple mobile device called Activity Recorder that marries public and private sensors to provide a powerful Activity Logging service. An Activity Recorder contains a range of private sensors, and has communication capability to work with public sensors around the user.

In this paper, we present a novel forwarding scheme to enhance communication stability based on geographic routing in mobile ad hoc networks, which is called "Position-based Heuristic Forwarding" (PHF). For alternative solutions to traditional ad hoc routings, many geographic routing algorithms have been proposed. Most of the existing routings impose a certain restriction, planarity, on the graph structure of network for delivering messages to destination definitely. PHF achieves the guaranteed packet delivery over Unit Disk Graph, which is more widely employed graph model for the study of ad hoc networks. Accordingly, to eliminate the restriction of the routing algorithms enhances the probability to deliver messages successfully in networks with high nodes' mobility rate. In the simulation of PHF, we have evaluated the performance comparisons between PHF and its related work, Greedy Perimeter Stateless Routing (GPSR) and Dynamic Source Routing (DSR), which are the prominent geographic and conventional topology-based routing protocols, respectively. The results show that PHF provides higher packet delivery success rate indicating better communication stability and equal or less overhead than these work.

Many handover techniques in the Internet have been introduced with the development of mobile computing technologies. Although many proposed handover schemes utilize multiple wireless interfaces, having multiple wireless interfaces in a mobile device increases its power consumption, device installation space, and hardware costs. We have been studying handover schemes for mobile nodes with a single wireless interface. To achieve seamless and efficient handover, we focus on Stream Control Transmission Protocol (SCTP) that offers a message-oriented, reliable and connection-oriented delivery transport service. Unlike other transport protocols like TCP, SCTP can provide an end-to-end handover mechanism with multi-homing feature. However, the handover mechanism in the current SCTP causes large handover latency particularly when a mobile node has only one single wireless interface. This paper investigates the current issues of the SCTP handover mechanism, and proposes a new efficient handover scheme based on SCTP, which identifies a communication path as a pair of source and destination address. Additionally, we modified SCTP behavior when an SCTP endpoint received a SET PRIMARY message to change primary destination of peer endpoint. This paper shows that our scheme can reduce the handover latency by two to thirty seconds.

In forthcoming home network environment, computation capability will be embedded invisibly in home appliances, sensors, walls, ceilings, and floors. People will conduct various tasks using multiple devices simultaneously without consciousness of using computers. In this paper, first, we propose an application model named Virtual Network Appliance (VNA) model which simplify and expand device utilization. In the model, each device has VNA runtime system and function objects, called VNA components, running on it. A user task is defined in an application called VNA which is a logical appliance consisting of abstract function requirements and a message graph among them. Second, we propose Virtual Plug&Play mechanism which is a dynamic service integration mechanism in VNA model implementation. When a user conducts a task, he/she makes a VNA runtime system on a user-side terminal load a VNA definition appropriate for the task. Virtual Plug&Play dynamically discovers required VNA components and establishes the message graph as defined. Since XML documents are used to describe a VNA, users can share and customize it easily. We call the device integration done by Virtual Plug&Play top-down integration, which existing middleware do not aim at. Finally, we show that Virtual Plug&Play affords practical performance for top-down integration by performance evaluation.

In forthcoming multimedia environments, continuous-media data, such as video and audio data, will be used by a variety of multimedia applications. Multimedia applications require efficient and flexible support from real-time operating systems. This is because the changes in system and network loads require dynamic management of real-time thread behavior. If threads are implemented at the user level, operations on threads can be processed at the user level, and the efficient management of threads becomes possible by avoiding kernel interventions. Thus, we can provide an effective platform for multimedia applications. The goal of our work is to realize high-performance user-level real-time threads which satisfy the above requirements of multimedia systems. In this paper we describe the design and implementation of a user-level real-time threads package, called RTC-Threads, which is being developed on the RT-Mach microkernel. The results of performance evaluations show that our user-level real-time threads outperform real-time kernel-provided threads, which are implemented in the microkernel, in terms of efficiency and accuracy.

When multiple flows including continuous media streams are simultaneously sent from a computer, allocation and management of both processor capacity and network bandwidth need to be considered. We propose a framework of Quality of Service (QoS) management inside a sending host that controls execution of sending threads in consideration of utilization of processor capacity and network bandwidth. To distinguish from flows which require only best-effort service, we call a flow which requires a specific rate of service "reserved flow. " To guarantee QoS of such reserved flow both in processor- and network-intensive cases in a sending host, processor capacity reserve is allocated such that the rate of each reserved flow is attained and non-conforming data are policed before they are transmitted. Processor Capacity Manager and the network device driver exchange information in a cooperative manner to support the rate adaptive allocation of processor capacity reserve. In this paper, we describe design and implementation of our framework on RT-Mach. The results of performance evaluations demonstrate that our scheme performs well for full-duplex Ethernet.

In this paper, we propose an efficient route discovery scheme for mobile ad hoc networks called Hop-Wise Limited broadcast (HoWL). Since nodes do not identify the location of other nodes, some of the routing protocols proposed for mobile ad hoc networks use network-wide broadcasts to discover a route. In contrast, HoWL limits the area of a route discovery by predicting the current location of the destination node using history of hop counts of previously used routes. We also introduce Characterized Environmental Indicators (CEI) which characterize environments for networks of mobile nodes. Specifically, environments can be characterized by three indicators: node density, average hop count of utilized routes, and frequency of link failure. We have implemented HoWL as an extension to DSR on GloMoSim network simulator. Quantitative and qualitative performance comparisons were evaluated between HoWL and its related work, Expanding Ring Search (RING) and LAR. The simulations show that HoWL performs best when low communication overhead is desired where up to 20% decrease over RING and three-fold decrease over LAR in the overhead were demonstrated. Thus, HoWL is most effective in overhead sensitive environments such as battery-limited sensor networks.

Traffic management schemes such as Connection Admission Control (CAC), policing, and traffic shaping are important to provide multimedia communications with better Quality of Service (QoS). In the conventional model, admission control and policing are done at intermediate nodes, and traffic shaping is done at the edge of a network. However, QoS of communications should be defined between tasks or threads rather than between hosts. Therefore traffic management inside a host is as important as that in networks. We propose software-based traffic management architecture over a real-time microkernel. The architecture focuses on the interface between a network driver and user threads calling the driver. We categorized services of communication threads into three classes: Real-Time at Guaranteed Rate (RT-GR), Real-Time at Available Rate (RT-AR), and Best-Effort (BE). Our architecture is designed for an environment containing a mixture of these services. In the architecture, a sender periodic thread of RT-GR or RT-AR is executed such that the sending rate matches a user-specified rate. The network driver monitors the per-flow rate of injected data and discards the data if the injected rate exceeds the user-specified rate. To avoid the continuous discarding of data, the sending thread can adjust its sending rate by periodically looking at logged data concerning the rate. RT-AR service can achieve more than the specified rate when bandwidth is available. The scheme of software traffic management is effective in attaining higher throughput not only for full-duplex Ethernet but also for ATM because the difference of rate between hardware and software is reduced. In this paper, we describe the design and implementation of the software-based traffic management architecture on Real-Time Mach. The results of performance evaluations demonstrate that our traffic management scheme performs well for full-duplex Ethernet.

We propose a mechanism to facilitate the development of component-based mobile applications with adaptive behaviors. The design principles and communication patterns of legacy software systems will greatly change in a forthcoming environment, where a variety of computing devices become embedded in home and office environments, users move around with/without portable computing devices, and all the devices are interconnected through wired/wireless networks. In the proposed mechanism, Improvised Assembly Mechanism (IAM), we realize functionality to compose an application in an ad hoc manner and to achieve the adaptation of applications by adding, replacing, supplementing, and relocating components at system runtime according to various environmental changes such as the locational changes of computing devices and users. The mechanism is implemented as a built-in functionality of the Soul component, which is one of the fundamental elements in the Possession model.

TCP Redirection (TCP-R) is an extension of TCP, which maintains active TCP connections when the disconnection occurs due to IP address changes. In mobile computing environments, IP addresses may be changed frequently as the host moves across subnets or changes network devices. However, it is difficult for most stateful network applications to work continuously in that situation. There is much research to support such dynamics in the network layer, but these attempts in the IP layer tend to incur some complexity. This paper intends to investigate the end-to-end mobility support in the transport layer. We developed a simple redirection mechanism for TCP, which enables us to keep our working activities continuous without any intermediate agents for IP packet forwarding. We also show that TCP-R enables the intentional replacement of IP addresses, which is useful for certain network services. We implemented and evaluated a prototype of TCP-R. The measured performance indicates that TCP-R can realize continuous operation with minimal overhead and complexity.

In ubiquitous computing, or ubiquitous network environment, many sensors and devices are embedded in the environment. Moreover, information appliances and smart space technologies allow users to enjoy high computational power, which also gives freedom and extrication from traditional computing style that often caused users' inconvenience and restriction of their demands and needs. However, due to the characteristics of ubiquitous computing, application's high adaptability to the changes of environments is required. To achieve this high adaptability of applications, we introduce a design approach of "snapshot-based application." The snapshot-based application can store its status as a snapshot. By utilizing the snapshot, an application can be recreated as it is in the status of the snapshot. In this paper, we propose an application framework named "u-Snap," which realizes snapshot-based applications. We have exemplified the effectiveness of this framework with implementation of "u-Photo," which utilize a snapshot of an application as contextual information that is embedded in a photo image.