A hybrid controlled dynamic routing scheme called State- and Time-dependent Routing (STR), has been proposed for telephone networks. The STR is characterized by two-level control processes: routing domain definition and call-level routing. In the routing domain definition, a set of possible alternate routes for each origin-destination node pair for each time period of the day is determined once a week by a centralized control method. In the call-level routing, each exchange determines a near-optimum alternate route from the set of possible alternate routes, which is determined in the routing domain definition process according to only the network information obtained in the call-connection processes. This paper proposes advanced call-level routing schemes for improving the performance of the basic STR. Call-by-call computer simulation of call-level routing schemes under unbalanced traffic conditions and focused overload conditions shows that the advanced schemes can achieve high performance with minimal changes of existing exchange software and operations systems. The performance of the advanced scheme based on isolated control capabilities built into each exchange is close to that of an ideal state-dependent scheme that is based on centralized control capabilities and uses data on the status of the entire network.

This paper presents novel flooding schemes for wireless mobile ad hoc networks. Clustering of nodes is assumed as a basic ad hoc network structure. GWF (Gateway Forwarding) and SGF (Selected Gateway Forwarding) are presented based on clustering. A new protocol, termed FGS (Flooding Gateway Selection) protocol, between a cluster head and its gateways to realize SGF is presented. It is shown that SGF significantly improves the packet delivery performance in ad hoc networks by reducing flooding traffic.

An architecture is presented for efficient and reliable delivery of multimedia contents from a primary center (PC) to secondary centers (SCs). Requested contents are delivered from the PC to the SCs through a satellite broadcast channel, or from one SC to another SC through a terrestrial channel. Cycling methods are presented that enable sharing of the contents directory of each SC. Several fundamental models and algorithms are introduced for possible consideration during the planning and design of a contents-delivery system. Simulation has shown that using both satellite broadcast and terrestrial channels for contents delivery is superior in terms of cost to the conventional use of only a satellite network.

We propose an efficient IP address assignment protocol in mobile ad hoc networks, which use a proactive routing protocol. In this method, which is termed the Bisected-Range based Assignment (BRA), a node repeatedly broadcasts an Agent Request to ask for address assignment. If there are one or more neighbor MANET nodes, one of them becomes an agent to select and assign an IP address to the requesting node. We use address location in the IP address space so that each agent maintains its own exclusive address range to be used for address selection, resulting to decrease the possibility of address conflict. If the requesting node cannot discover any neighbor MANET node over pre-determined random agent-search time, it selects by itself an IP address at random from the given address block. We evaluate performance of the basic and enhanced BRAs by computer simulation. It is shown that the basic and enhanced BRAs can reduce address conflict compared with random assignment. It is also shown that the enhanced BRA is superior in terms of control traffic overhead as well as address assignment delay over the random assignment with the strong Duplicate Address Detection.

A smart community can be considered an essential component to realize a sustainable, low-carbon, and disaster-tolerant society, thereby providing a base for community inhabitants to lead a simple, healthy, and energy-saving way of life as well as ensuring safety, security, and a high quality-of-life in the community. In particular, a smart community can be essential for senior citizens in an aging society. Smart community enablers such as information and communication technology (ICT) and electric vehicles (EVs) can perform essential roles to realize a smart community. With regard to ICT, the necessity of a dedicated wireless sensor backbone has been identified. With regard to EV, a small-sized EV with one or two seats (Mini-EV) has been identified as an emerging player to support personal daily mobility in an aged society. The Mini-EV may be powered by a solar battery, thereby mitigating vehicular maintenance burden for the elderly. It is essential to realize a dependable ICT network and communication service for a smart community. In the study, we present the concept of trans-locatable design to achieve this goal. The two possible roles of EVs in contributing to a dependable ICT network are highlighted; these include EV charging of the batteries of the base stations in the network, and the creation of a Mini-EV based ad-hoc network that can enable applications such as safe driving assistance and secure neighborhoods.

In a sensor network, a certain area or environment are observed by a lot of distributed sensor nodes and a sink collects data observed by sensor nodes. The observed data sequences that sensor nodes generate may have space- and/or time-dependent correlation. This correlation is regarded as redundant information and can be used for channel error correction by joint decoder using correlation. In this paper, we propose the joint decoding scheme using the time-dependent correlation consisting of the consecutive data sequences generated by a sensor node. We also propose a power control scheme using the time-dependent correlation for reduction in energy consumption. We evaluate the packet error rate and the energy consumption ratio, and clarify the effect of our proposed schemes.

The concept of wireless ad hoc networking has unique features in which neither base stations nor wired backbone networks are required and a mobile node can communicate with a partner beyond the transmission range by multihopping. In this paper, innovations and issues in ad hoc network technologies are reviewed. The concept of a general-purpose ad hoc network is identified as a step toward next-generation ad hoc network development. The concept of an open community network is then presented as a vision for general-purpose ad hoc networks. An open community network is a novel information infrastructure for local communities based on wireless multihopping technologies, which may support an advanced information-oriented society in the twenty-first century. As a case study, an experimental system using PHS (Personal Handy Phone System) is described and some research issues for developing an open community network are identified.

Significant traffic variations occur in telecommunication networks. This paper focuses on hour-to-hour traffic variations during 24 hours and investigates the possibility of using idle periods effectively by introducing non-realtime service at a discount rate. In order to provide non-realtime service, memory is placed at each telecom center. When immediate service is not available, messages of non-realtime calls are stored in the memory and served later when network resources are available. Realtime calls are served with preference. A basic model and a method of dimensioning the memory capacity are presented. The basic model is extended to the network model, and methods of designing a minimum cost network and pricing and profit issues are presented. The results for a basic model are verified by traffic simulation. Numerical examples are given to show the effectiveness of non-realtime service.

In this paper, we propose a novel Hidden-terminal and Exposed-terminal Interference aware routing metric (HEI-ETT) for Multi-Radio and Multi-Rate wireless mesh networks in which each stationary mesh node is equipped with multi-radio interfaces that relays traffic to the extend networks by using multi-hop transmissions. We have two main design goals for HEI-ETT. First, we will characterize interferences as Hidden-terminal Interference and Exposed-terminal Interference regardless of inter- or intra-flow interference and should take into account both interference effects while computing the path metric. Second, an efficient transmission rate adaptation should be employed in HEI-ETT to enhance the network throughput. We incorporated our metric in well known Optimized Link State Routing protocol version 2 (OLSRv2) which is one of the two standard routing protocols for MANETs and evaluated the performance of our metric by simulation. The results show that our metric outperforms existing metrics such as ETX, ETT and WCETT.

The development of ad hoc networking is now being watched with keen interest, because it is a key technology for realizing ubiquitous networks and ubiquitous society. In Japan, on ad hoc network, much R&D and related works have been done and on going in academia, industries and governments. Test-bed based research is an important aspect of research on ad hoc networks. The performance of ad hoc networks in real-world situations typically depends on many complex phenomena. This paper introduces a few topics of test-bed based ad hoc network research activities in Japan.

One of the most promising applications of a mobile ad hoc network is a vehicular ad hoc network (VANET). Each vehicle is aware of its position information by GPS or other methods, so position-based routing is a useful approach in VANET. The position-based routing protocol can be classified roughly into a next-hop forwarding method and a directed flooding method. We evaluate performance of both methods by analytic approach and compare them in this paper. From the evaluation results, we conclude that it is effective for the position-based routing to choose either the next-hop forwarding method or the directed flooding method according to the environment. Then we propose the hybrid transmission method which can select one of them according to the environment, and clarify that the proposed method can keep the packet delivery ratio at a high level and reduce the delay time.

Transient routing loops have been observed to form in Mobile Ad-hoc Networks running the OLSRv2 proactive link-state routing protocol. The packets falling into loops impact the surrounding network thus degrading throughput even though only a small proportion of the traffic may enter these loops and only for a short time. This becomes significantly more evident when Link Layer Notification is used to catch broken links, inadvertently leading to an increase in the number of loops. Two methods of Loop Detection are introduced and are used to trigger either Loop Suppression by selectively and preemptively discarding the looping packets that are unlikely to reach their destination, or Loop Correction by the notification of the routing protocol to cut the link over which the packet is looping. The newly introduced Loop Suppression and Loop Correction techniques used with Link Layer Notification are shown to significantly increase network performance over plain OLSRv2 and OLSRv2 with Link Layer Notification.

We present a novel transmission rate control method for Wireless Mesh Networks, termed Semi-Fixed Rate Control (SFRC), which incorporates the advantages of Fixed Rate Control (FRC) and Adaptive Rate Control (ARC). SFRC has two periods, which are alternately repeated: an autorate period and a fixed-rate period. A unit of an autorate period and the successive fixed-rate period is termed “rate-control period”. The duration of the rate-control period is set considerably longer than that of the autorate period. In the autorate period, RTS/CTS is used with the lowest transmission rate, transmission rate adjustment is only applied to data frames, and loss of CTS frames is not reflected in the transmission rate adjustment. In the fixed-rate period, the transmission rate that was used most frequently in the preceding autorate period (optimum rate) is fixed, and RTS/CTS is not used. Implementation of SFRC is straightforward as it uses conventional IEEE 802.11 DCF and only minor modification of the wireless LAN driver is required. SFRC, which uses a modified SampleRate, an ARC implementation in the Madwifi, (SampleRate+) in the autorate period, termed SFRC-SampleRate+, was developed. The results of real-world experiments indicate that SFRC-SampleRate+ is superior to SampleRate and SampleRate+, and is closer to FRC, which uses optimum rate on each link, in terms of throughput in wireless mesh network environments.

Network management technologies based on network-wide real-time control schemes have become significant in ensuring both high throughput and GOS fairness and maintaining high usage of network facilities. The first part discusses the roles of network control schemes in the network resource hierarchy. With respect to the layering concept for network resources, it is clarified as to why each network control scheme should maintain its autonomy in each corresponding network resource layer, as well as cooperate with the other control schemes. Examples of cooperative control are presented to show that both dynamic routing in the circuit layer networks and path assignment control in the path layer networks can mutually compensate each other for any insufficient control. In the second part, an advanced routing scheme called "State- and Time-dependent Routing (STR) " is proposed. The principle of STR is a combination of routing-domain definition on a time-dependent basis and call-level routing on a state-dependent basis. Performance evaluation examples of STR through large-scale call-by-call computer simulations are presented to show its high throughput performance as well as high adaptability to real-time traffic fluctuations. A system configuration example featuring the STR algorithm which is currently under development for use in NTT's transit networks is also shown.

An overview of the evolution of intelligent transport systems (ITS) supported by advances in information and communication technologies is presented. Focusing on a sensing platform as one of the ITS applications, this paper presents a survey on vehicular ad hoc network-based geographic routing. In addition to the minimum requirement of street-awareness based on street maps, traffic and packet-awareness are considered essential to achieve acceptable packet delivery performance. In particular, in addition to statistical information, real-time traffic and packet level information are indispensable for making routing protocols feasible and effective. Considering traffic conditions that are highly space- and time-dependent, static nodes can be used to assist with geographic routing, and a protocol workable under a partial deployment of static nodes is considered.

This study clarifies the effects of network complexity and network map transformation on the ability of network managers to use graphic network displays. Maps of Japan and the United States with outlines of their respective prefectures or states were displayed on a CRT. Each map displayed a fictitious network of nodes and their interconnections. These networks were two-level hierarchical and non-meshed, meaning that each low-level node was connected to a single high-level node, but not all high-level nodes were linked together. The subjects, task was to identify a path between two low-level nodes. In each trial, two low-level nodes were highlighted, and the subject attempted to find the shortest path between these nodes. This was done by using a mouse to select intermediate nodes. Completing a path required a minimum of 4 node traversals. Three variables were manipulated. First, the number of nodes was defined as the total number of low-level nodes in a network (70, 150, or 200). The second variable was the level of transformation. Very densely populated areas of the maps were systematically transformed to reduce congestion. There were three levels of transformation. The final variable was the country map used, that is, the map of Japan and the map of the United States. Several behavioral measures were used. The most informativ. appeared to be the time required to complete a path (the response time), and how often subjects returned to previous portions of a path (back-ups). For both of these measures, the data pattern was essentially the same. Increasing the number of nodes hurts performance. This was particularly pronounced when the map of Japan was tested. However, as the level of transformation increased, this effect was substantially reduced or completely eliminated. The results are discussed in terms of engineering rules and guidelines for designing graphical network representations.