Modern mobile devices (smart phones, wearable devices, and smart vehicles) have greater resources (communication, computation, and sensing) than before, and these resources are not always fully utilized by device users. Therefore, mobile devices, from time to time, encounter other devices that could provide resources to them. Because the amount of such resources has increased with the number of mobile devices, researchers have begun to consider making use of these resources, located at the “edge” of mobile networks, to increase the scalability of future information networks. This has led to a cooperation based architecture of mobile cloud computing (MCC). This paper reports the concept and design of a resource sharing mechanism that utilizes resources in mobile devices through opportunistic contacts between them. Theoretical models and formal definitions of problems are presented. The efficiency of the proposed mechanism is validated through simulation.

Information-Centric Networking (ICN) employs communication based on location independent data identifiers (IDs) that enables efficient data dissemination. However, some important challenges still remains in the conventional ICN schemes when they are applied to a highly mobile and distributed environment, such as growth in amount of route information or increased transaction load of name resolution services. To accommodate this, we propose a new ICN scheme where routes are aggregated at aggregation nodes and optimized routes are established during data registration transactions to mitigate the amount of route information, delay, and transaction load. We evaluate the proposed scheme using a nation-wide test bed of 37 intermediate nodes and 336 mobile terminals. We show that the proposed scheme enables efficient data dissemination where the mobile terminals register and retrieve data in widely distributed manner.

DTN (delay/disruption-tolerant networking) is a network enabling data to be carried end-to-end without continuous connection. DTN uses a store and forward method, in which a node stores the data when no other nodes exist in a communicable range and forwards a copy of the data when they do. Since the buffer has a limited buffering capacity, the data often need to be dropped. When there are data that have different priorities, the high priority data may be pushed out from the buffer by the low priority data. Thus the high priority data arrival rate lowered by pushing data out needs to be increased. In this paper, we propose and evaluate a buffer control system to raise the high priority data arrival rate without decreasing the total arrival rate when the buffer has a limit. The priority control system avoids the high priority data dropping caused by low priority data by choosing the dropped data in reference to the data priority when the new data are sent to the full node. We show that the priority control system increases the high priority data arrival rate and maintains the high priority data drop rate at no more than the desired value.

Bandwidth barter is an effective way of satisfying throughput requirements in wireless networks; we could expect a station (STA) allows another STA to borrow its bandwidth as long as it is also beneficial for the STA. Our previous work proved bandwidth barter between two STAs is optimized based on Nash bargaining solution (NBS), which brings the Pareto efficiency and the proportional fairness in the bartering game. However, it still remains an open issue how to solve the bartering game when the number of STAs is N (N >; 2), which is discussed in this paper.

In this paper, we discuss problems in densely deployed wireless networks. Particularly, we focus on wireless local area networks (WLANs) because they have enabled us to provide seamless and high capacity wireless access easily and inexpensively. However, recently, channel interference between different services has become a serious problem because access points (APs) of WLANs are located too densely. In the carrier sense multiple access with collision avoidance used in WLANs, the hidden terminal (HT) and the exposed terminal (ET) problems occur depending on the distance between stations and the carrier sensing range. In the higher dense deployment mentioned above, the HT and ET problems occur complicatedly. Therefore, we propose an AP cooperation system that detects the HT and ET problems between stations (STAs). In our system, APs are operated with time synchronization and obtain the information of connected STAs from received frames. The HT and ET problems are identified from the integration of the information obtained at different APs. The effectiveness is verified by simulations.

Composite Packet in Multi-Wavelength Optical Packet Switching (MW-OPS) networks is studied to improve network efficiency by reducing non-transmission time. At the same time, long packets suffer higher packet loss rate in Fiber Delay Line (FDL) buffer under variable packet length environment. To further improve optical packet network performances, this paper proposes a composite packet system which tries to adjust packet length constant as well as to reduce the number of packet in optical domain. Improved performances are shown through computer simulations.

Mobile sensor networks are attracting a lot of interests. In these networks, nodes not only have sensing capability but mobility as well. Therefore, a few sensor nodes can a cover larger sensing area by moving around. Additionally, dangerous areas where people cannot access, such as disaster sites or radiation-contaminated areas, can be searched by nodes moving around their sensing positions autonomously. A conventional method was proposed to control node movements by using push-based broadcast. However, in the conventional method, nodes cannot move autonomously without broadcast information, and they consume power unequally. We propose a more efficient power reduction scheme that involves relaying data among nodes on rails.

We propose a TCP window-size delegation method for TXOP Exchange applicable to the downlink in wireless access networks. In TXOP Exchange, the compliant stations (STAs) cooperatively use their available bandwidth in accordance with their required QoSs. TXOP Exchange was previously validated for the uplink. The proposed delegation method enables STAs to delegate their bandwidth for the downlink as well without requiring any modifications to the legacy access point or the STAs. Simulation demonstrated that this method works well.

This paper discusses the modeling, the observation, and the analysis of a social experiment, in which we built an online social network to observe interactions between people. We try to model the problem from the micro-economics aspect; we use the concept of utility to model people's behaviors in this experiment. Furthermore, we consider incentive reward as an external factor and observed how people's behavior would change based on how we give incentive reward. We assumed the scenario of content recommendation in an online social network and compared the two reward assignment rules: i) a user gets reward if she or he informs her/his friend of the pointer to the content and ii) a user gets reward if her/his friend she or he informed of the content pointer reacts to the content. We expect that, in the former, the social network is not activated because the information flow is unidirectional, while, in the latter, the social network can be activated because it stimulates people to react to the information they have received.

It can be essential in the new-generation content services to predict the potential demands of people, which they themselves have not recognized or cannot express precisely. Social graphs representing the relationships between people are used for predicting demand in current Internet-based services. However, these graphs cannot represent the relationships of two users residing in common communities or common places. We propose representing not only a person but also things like communities and social events together as a single node in a social graph. This representation allows us to estimate who shares potential interests with a given person. We evaluated the estimation accuracy of our representation using an actual relational dataset from an academic database. Results show that our representation can estimate if two people share common interests that cannot be found with conventional methods that only use human nodes for estimation, and it can estimate the relations without using human nodes.

In recent years there is a rapid increase of traffic to a given web server within a short time as the number of Internet users increases, and such a phenomenon is called a flash crowd. Once flash crowds occur in the web server, a response rate decreases or the web server may crash as the load increases. We propose a load reduction system, which prevents excessive accesses and stably delivers content without enhancing the performance of the web server even when flash crowds occur. In the proposed system, a proxy server detects flash crowds by monitoring the number of requests and changes a content delivery system. To limit accesses to the web server, the proxy server redirects a request to another client that holds the content in the cache when flash crowds occur. We also propose a content delivery system that uses a tree construction to reduce the client load. Moreover, its efficacy is shown through simulations.

The enhancements of the transmission speed in wireless access networks and mobile-device capacity enable us to use data/audio streaming/video streaming multicast service in large scale networks via their personal mobile devices. Peer-to-peer (P2P) architecture ensures scalability and robustness more easily and more economically than server-client architecture; as the number of nodes in a P2P network increases, the amount of workload per node decreases and lessens the impact of node failure. However, mobile users feel much larger psychological cost due to strict limitations on bandwidth, processing power, memory capacity, and battery life, and they want to minimize their contributions to these services. Therefore, the issue of how we can reduce this psychological cost remains. In this paper, we consider how effective a social networking service is as a platform for mobile P2P multicast. We model users' cooperative behaviors in mobile P2P multicast streaming, and propose a social-network based P2P streaming architecture for mobile networks. We also measured the psychological forwarding cost of real users in mobile P2P multicast streaming through an emulation experiment, and verify that our social-network based mobile P2P multicast streaming improves service quality by reducing the psychological forwarding cost using multi-agent simulation.

Wireless local area networks (WLANs) have allowed us to deploy seamless and high capacity wireless systems easily and inexpensively. However, recently, channel interference between different services has become a serious problem because access points (APs) of WLANs are located too densely. In the carrier sense multiple access with collision avoidance used in WLANs, the hidden terminal (HT) problems occur depending on the distance between stations and the carrier sensing range. In the higher dense deployment mentioned above, the HT problems occur complicatedly. In this paper, we propose an AP cooperation system that detects the HT problems between stations (STAs). In our system, APs obtain the information of connected STAs from received frames and the HT problems are identified from the integration of the information obtained at different APs. The effectiveness is verified by simulations.

The dominant IP traffic is moving from Web to peer-to-peer (P2P) these days. As a result, elephant flows consume bandwidth and unfairness in resources allocation occurs. The main packet-scheduling mechanism currently employed is first-in first-out (FIFO) where the available bandwidth of short flows is limited by elephant flows. Least attained service (LAS), which decides transfer priority of packets by the total amount of transferred data in all flows, was proposed to solve this problem. However, routers with LAS limit flows with large amount of transferred data even if they are low-rate. Therefore, it is necessary to improve the quality of low-rate flows with long holding times such as voice over Internet protocol (VoIP) applications. This paper proposes rate-based priority control (RBPC), which calculates the flow rate and control the priority by using it. Our proposed method can transfer short flows and low-rate flows in advance. Moreover, its fair performance is shown through simulations

Enhancements of transmission speed and mobile node capability in wireless access networks enable people to watch movies and share large files with friends via their personal mobile devices. Considering the increased demand for such services in the next five to ten years, we will need to introduce P2P architectures to mobile networks to handle the large number of requests from mobile nodes. However, in mobile P2P networks, since negative effects caused by instable links and high leave rates are propagated to down-stream nodes, it is difficult to ensure service quality and long service lifetime. To solve this problem, we describe a novel node-allocation framework using multi-dimensional context parameters of mobile nodes, which includes available bandwidth, disconnection rate, and remaining battery capacity. Taking into account the significance of each parameter, our framework integrates the context parameters into a single parameter called Relay Ability. Each node is allocated to the P2P topology in accordance with its relay ability. To test our method, we applied our architecture to overlay multicast and several of results from comparative evaluations through computer simulation.

Unstructured peer-to-peer (P2P) networks have power-law topology, and the number of content requests also follows power-law distributions. These properties cause two problems: the high-load of high-degree peers and the quick deletion of rarely requested contents. We propose a new caching scheme that replaces the cache on the basis of the number of request messages per unit of time. It significantly reduces the load of high-degree peers and improves the hit rate. Moreover, we use a simulation to show the effectivity of our proposed method.

The growth in broadband access and increases in terminal capability have enabled us to provide large-scale multimedia services. The traditional unicast architecture cannot support such a service because the transportation from a content server to many end hosts causes the overload to a content server. Overlay multicast techniques have been proposed to solve this problem. This high-layer technology allows us to provide largescale multicast services even for mobile networks. Also, the recent rapid growth of mobile broadband brought the large-scale mobile multicast services into reality. However, stream relays by users are indispensable in overlay multicast. Moreover, in mobile environments, users' willingness to relay depends on user states such as remaining battery charge, movement conditions, and the relationship with the relay requestor. In this paper, we investigate user actions and states in mobile overlay networks and model user actions as agents. Then, we discuss how user actions affect the performance of the mobile overlay network and which user states we should pay attention to in order to build effective networks through multiagent simulations.

With the rapid growth of the wireless network and the function of mobile terminal, the services which need the wide bandwidth like video streaming are expected to be used extensively over wireless networks. Overlay multicast in which a terminal relays the content to other terminals is able to deliver it to enormous terminals. However, due to instantaneous disconnection and rapid bandwidth decrease in wireless channels, we need a different architecture from the ones used for fixed environments. In this paper, we propose a new overlay-topology design, where we use the instability information of mobile terminals such as the disconnection rate and the changing range of physical transmission rate determined by the physical conditions including radio signal strength and handover. Moreover, to reduce the performance degradation caused by instantaneous disconnection and rapid bandwidth decrease and to obtain the route-diversity gain, the proposed method assigns more logical links to the terminals that likely suffer from the impact, which results in the improvement of the received stream qualities of the terminals. This paper also shows its superiority to the conventional methods in terms of service quality and robustness from the simulation results using a wireless channel-quality model we newly propose.

In wireless local area networks (WLANs), the demand of the multimedia applications such as voice telephony and peer-to-peer content distribution has followed the necessity of quality-of-service (QoS) control for uplink flows. However, in uplink WLANs, the hidden-station problem causes difficulties in the QoS control because of unfair collision probability. In this paper, we point out this hidden-station problem and clarify the following unfairness between user datagram protocol (UDP) and transmission control protocol (TCP) uplink flows: 1) the effect of collision caused by hidden-station relationship on throughput and 2) the instability of the throughput depending on the number of hidden stations. To solve these problems, we propose a mechanism that first groups stations according to the hidden-station relationship and type of transport protocol they use then assigns a transmission permitted period to each group. Our proposed mechanism eliminates the collisions between hidden stations and provides a flexible control over bandwidth allocation to UDP and TCP. Its performance is shown through simulation.

In P2P content distribution systems, there are many cases in which the content can be classified into hierarchically organized categories. In this paper, we propose a hybrid overlay network design suitable for such content called Pastry/NSHCC (Pastry for non- strictly hierarchically categorized content). The semantic information of classification hierarchies of the content can be utilized regardless of whether they are in a strict tree structure or not. By doing so, the search scope can be restrained to any granularity, and the number of query messages also decreases while maintaining keyword searching available. Through simulation, we showed that the proposed method provides better performance and lower overhead than unstructured overlays exploiting the same semantic information.

In conventional road-vehicle communication systems, user terminals in the vehicles have to directly connect with wireless access points (APs). However, the speed of vehicles is so fast that the channel condition between the terminals and the APs constantly changes because of changing path-loss and time-varying fading. In this paper, to compensate for such deterioration, we propose to reduce relative speed between user terminals and APs by using an inter-vehicle packet relay technique. If a terminal can send or receive data via other vehicles running at lower speeds, the relative speed will decrease, which suppresses the dynamic range of path loss and deterioration by fading. We evaluate our method by computer simulations using a geometric propagation model. In the simulations, phase difference between multiple paths and path-loss fluctuation within one frame duration affect the performance. From the results of the simulations, we validate our method. Moreover, we evaluate interference in the overlapped zone between two AP areas. From the evaluation, we show that our packet relays do not cause a problem in interference between areas.

Users in peer-to-peer (P2P) content sharing can share their content by contributing their own resources to one another. However, since there is no incentive for contributing contents or resources to others, users may attempt to obtain content without any contribution. To motivate users to contribute their resources to the service, incentive-rewarding mechanisms have been proposed. On the other hand, emerging wireless technologies, such as IEEE 802.11 wireless local area networks, beyond third generation (B3G) cellular networks and mobile WiMAX, provide high-speed Internet access for wireless users. Using these high-speed wireless access, wireless users can use P2P services and share their content with other wireless users and with fixed users. However, this diversification of access networks makes it difficult to appropriately assign rewards to each user according to their contributions. This is because the cost necessary for contribution is different in different access networks. In this paper, we propose a novel incentive-rewarding mechanism called EMOTIVER that can assign rewards to users appropriately. The proposed mechanism uses an external evaluator and interactive learning agents. We also investigate a way of appropriately controlling rewards based on the system service's quality and managing policy.

When the number of users of mobile services increases past a certain point in a service area, all of users cannot consistently obtain satisfactory radio resources such as bandwidth and signal power because the resources are limited and shared. A solution for such a problem is user-position control. In the user-position control, the operator informs users of better communication areas (or spots) and navigates them to these positions. However, because of subjective costs caused by subjects moving from their original to a new position, they do not always attempt to move. To motivate users to contribute their resources in network services that require resource contributions for users, incentive-rewarding mechanisms have been proposed. However, there are no mechanisms that distribute rewards appropriately according to subjective factors involving users. Furthermore, since the conventional mechanisms limit how rewards are paid, they are applicable only for the network service they targeted. In this paper, we propose a novel incentive-rewarding mechanism to solve these problems, using an external evaluator and interactive learning agents. We also investigated ways of distributing rewards based on user states and user contributions. We applied the proposed mechanism and reward control to the user-position control, and demonstrated its validity.

The increase in users of wireless local area networks (WLAN) has raised the need for bandwidth management that prevents bandwidth monopolization and that meets users' requirements. In this paper, we propose and design a distributed channel access mechanism for bandwidth management in WLANs. Our mechanism can flexibly assign bandwidth based on a theoretical estimation, even in poor network conditions, where hidden stations exist and the physical transmission rates vary. The usefulness of our mechanism is validated through evaluations using computer simulations.

The demand for Internet access in vehicles has been growing. To access the Internet from vehicles, a wireless road- vehicle communication system is necessary. In conventional road-vehicle communication systems, user terminals in the vehicles have to directly connect to wireless access points (APs). However, the speed of vehicles is so fast that the channel condition between the terminals and the APs constantly changes due to changing path-loss and time-varying fading. In this paper, we used an inter-vehicle packet relay technique to improve channel quality in road-vehicle communication systems. If a terminal can send data via other vehicles moving at lower speed, the relative speed will decrease, which suppresses the dynamic range of path loss and deterioration by fading. We evaluated this method using numerical analysis to verify the availability of the method.

To satisfy the recent increase in demand for uplink data in code division multiple access systems, opportunistic scheduling methods for uplinks have been investigated. In this paper, we discuss an optimum scheduling for voice/data packet systems. When it is implemented in practical systems, limitations such as selectable SF, computation and control costs will reduce the performance. We evaluated three approaches to apply the optimum scheduling to practical systems and compared them to our proposed heuristic scheduling, where minimum computation and control costs are required. The computer simulation results showed that our proposed method is reasonable and the optimum scheduling provides high throughput by expanding the computation and control interval while reducing the costs

Cooperation between different mobile networks linked by multiple-interface mobile stations (MMSs) can yield many benefits, including coverage expansion, load balancing, and throughput improvement. We developed a network control mechanism, cooperative networking, which controls the cooperative benefits in heterogeneous infra-multihop networks. The proposed mechanism assigns a cooperation rule to MSs. By following the rule, every MS chooses a path to a base station, such as direct connection to 3G networks or infra-multihop connection to wireless local area networks. Cooperation rules are designed according to the cooperative benefits. In our proposed cooperative networking mechanism, network operators can adaptively select a networking policy appropriate for network conditions and the needs of users. Computer simulation results validated our proposed mechanism

Optical packet switching network is expected to be the most hopeful candidate for future high-speed internetworking since it is characteristic of large capacity and fine granularity. However, due to lack of effective memory in optical domain for buffering, packet loss event happens even when the load of network is relatively low. This phenomenon overthrows the prerequisite assumption of TCP, which regards packet loss event as the sign of network congestion and decreases the sending rate accordingly. As a result, unnecessary slow down will adversely affect the throughput of optical packet switching network if TCP is adopted. In this paper, we propose a novel flow control algorithm which adaptively controls packet size together with window size in order to improve throughput for optical packet switching network. We evaluate it by simulation on throughput improvement and other properties including convergence and fairness

Realizing short-interval-traffic behaviors is important for network performance management. However, it is difficult to measure short-interval-traffic volumes because there are complications in collecting short-interval-traffic data from routers, for example, a heavy load on routers or inaccurate measurement by the short-polling interval. It even demands expensive measurement tools. To resolve these disadvantages, an estimating method of short-interval-traffic distribution (EMSIT) has been proposed. This method estimates short-interval-traffic distributions using MIB (management information base) data, which collects traffic volumes in cycles of several minutes. We propose a new estimating method (EMSIT-LD) based on EMSIT, which applies to the case of long-term-traffic dynamics. We evaluate it by computer simulations and actual traffic data.

Hierarchical mobile IPv6 (HMIPv6) has been proposed to improve the performance capability of mobile IPv6 at handover. In HMIPv6, local entities named mobility anchor points (MAPs) are distributed throughout a network to localize the management of intra-domain mobility. In this paper, we propose a location management method for hierarchical mobile IPv6 using the mobile node's (MN) mobile history. In this method, when a MN performs a handover, the access router calculates the area-covered rate of each upper MAP from the MN's mobile history and selects the MAP that best manages the MN in accordance with its rate. Thus, the proposed method reduces both the number of binding updates to the home agent and the signaling traffic. We evaluate the performance of the proposed method by simulation.

In an asynchronous transfer mode (ATM) network multimedia environment, the bandwidth efficiency can be improved by defining multiple quality of service (QOS) classes and using a traffic control which manages required QOS of each class individually (QOS control). Priority assignment control is presented as a QOS control method in an ATM switching node. To quantitatively evaluate the control performance, the region determined by the offered load of each class where the QOS requirements of all the classes are satisfied is analytically obtained and various combinations of two classes and related control effects are discussed. When required values of cell loss rate and delay time are both different between the classes, the control effect is large; however, when only either of them is different, the effect is relatively small. The control scheme to enlarge the actual admissible offer load region by adaptively changing the priority assignment ratio is presented and its feasibility is confirmed by the simulation.>

Fundamental issues arising in the design and implementation of architectures and protocols for integrated local area networks (ILAN's) supporting video, voice, graphics, data, and facsimile, are addressed, and open questions are identified. To characterize the performance of ILAN's, a set of performance evaluation guidelines is established. A class of conceptual solutions for ILAN's is proposed, and its expected performance is obtained by means of simulation. The class includes priority assignment schemes, parametrized sequential and simultaneous scheduling algorithms, and centralized and decentralized access control mechanisms. Our analysis, based upon simulations, shows that the bandwidth freed up by the video and voice calls during periods of little movement in the images and silence periods in the speech signals can be efficiently utilized for graphics and data transmission. The optimal priority mechanism among the different user classes depends on the traffic mix. Finally, it is argued that additional experimentation providing empirical data is imperative for understanding the real-time behavior of ILAN's. Consequently, a network testbed (NTB) called MAGNET is proposed for evaluating the performance of the proposed theoretical systems. It consists of an adaptive ILAN whose mediaaccess protocol is controlled by an Expert System.

MAGNET is a Network Testbed (NTB) designed to evaluate the performance of local area network architectures and protocols supporting integrated services such as televideo, video conferencing, telephone, computer communication, and facsimile. The integrated local area network (ILAN) presented in this paper has been designed to support the research activities intended for MAGNET. An active slotted ring topology was chosen to implement adaptive sequential-type access mechanisms that are a function of the network loading. The ILAN is based on fiber optic technology with wavelength-division multiplexing of two 100 Mbit/s channels. The media-access protocol provides higher levels with the capability of implementing two modes of operation referred to as circuit-switching, and packet-switching modes, respectively. Provisions have also been made for implementing simultaneous scheduling as well as centralized and decentralized access control schemes. Finally, the reconfigurable structure of the network testbed enables the study of the reliability and availability of ILAN's.

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.