Naohisa Takahashi

Focus+Glue+Context: an improved fisheye approach for web map services

This paper proposes a method for generating a Focus+Glue+Context map for Web map services by improving existing fisheye views methods for cartographic data. While many studies have focused on fisheye views, the problems of the excessively large distortions that maps have over their entire area and/or the high density of roads in the borders of the maps have yet to be resolved. To completely remove the distortions in both the Focus and the Context areas, we propose the inclusion of a Glue area between the two areas. Moreover, we propose the following features. (1) We propose the Dynamic Displacement function to generate a Focus and a Glue having an arbitrary convex or star-shaped polygon. (2) Since the Glue area absorbs all distortion from the Focus and the Context areas, the density of roads along the angular direction of the Glue will be excessively high. To reduce the density of roads, we propose the Following Paths algorithm to display only those roads that are along the radial direction and that are reached from the Focus area to the Context area. This method enables users to understand a map easily with high visibility of the Glue area. (3) To realize Web map services, we have to generate a map quickly. Therefore, the Glue area is generated dynamically, while the Focus and the Context areas display previously generated static maps. These maps are composited in a client Web browser by the Dynamic Map Composition method. We developed a prototype of our system that implements these features and evaluated the advantages of the proposed method. The new system can contribute to novel Web map services with fisheye views.

A topological approach to detect conflicts in firewall policies

Packet filtering provides initial layer of security based upon set of ordered filters called firewall policies. It examines the network packets and decides whether to accept or deny them. But when a packet matches two or more filters conflicts arise. Due to the conflicts, some filters are never executed and some filters are occasionally executed. It may results into unintended traffic and it is a tedious job for administrator to detect conflicts. Detection of conflicts through geometrical approach provides a systematic and powerful error classification, but as the filters and key fields of header increase, it demands high memory and computation time. To solve this problem, we propose a topological approach called BISCAL (Bit-vector based spatial calculus) to detect the conflicts in the firewall policies. As because of our approach preserves only the topology of the filters, it can reduce memory usage and computation time to a great extend

A data flow processor array system: Design and analysis

This paper presents the architecture of a highly parallel processor array system which executes programs by means of a data driven control mechanism. The data driven control mechanism makes it easy to construct an MIMD (multiple instruction stream and multiple data stream) system, since it unifies inter-processor data transfer and intra-processor execution control. The design philosophy of the data flow processor array system presented in this paper is to achieve high performance by adapting a system structure to operational characteristics of application programs, and also to attain flexibility through executing instructions based on a data driven mechanism. The operational characteristics of the proposed system are analyzed using a probability model of the system behavior. Comparing the analytical results with the simulation results through an experimental hardware system, the results of the analysis clarify the principal effectiveness of the proposed system. This system can achieve high operation rates and is neither sensitive to inter-processor communication delay nor sensitive to system load imbalance.

Dynamic Co-allocation Scheme for Parallel Data Transfer in Grid Environment

The large sized data sets are replicated in more than one site for the better availability to the nodes in a grid. Downloading the dataset from these replicated locations have practical difficulties, due to network traffic, congestion, frequent change-in performance of the servers, etc. In order to speed up the download, complex server selection techniques, network and server loads are used. However, consistent performance is not guaranteed due to the shared nature of network links of the load on them, which can vary unpredictably. Hence, we find interest in a co-allocated download model, which enables parallel download of replicated data from multiple servers. In this paper, we proposed a dynamic co-allocation scheme for parallel data transfer in grid environment, which copes up with highly inconsistent network performances of the servers. We have developed an algorithm using circular queue, with which, the data transfer tasks are allocated onto the servers in duplication. Our scheme is highly fault tolerant one, in other words, the process of data transfer will neither be interrupted nor paralyzed, even when the link to servers under consideration is broken or idleness of the servers, whereas, none of the existing mechanisms consider the situation. We used Globus toolkit for our framework and utilized the partial copy feature of GridFTP. We compared our scheme with the existing schemes and the preliminary results show notable improvement in overall completion time of data transfer.

An Elastic Map System with Cognitive Map-based Operations

An elastic map system is presented that enables users to stretch a digital map as if it were an elastic sheet or a tangible device. The system enhances focus+context maps, which displays both local detailed data and global context data in the same view. The system enables users to treat elements of cognitive maps (or mental images of maps), such as paths, landmarks, districts, and others, which were classified by Lynch, as elements of a city’s image. Users are able to collect map objects into a context area and enlarge them in a focus area based on previous geographical knowledge. The system provides uniform scaling of focus and context areas by introducing a glue area between the two areas. This scaling is controlled by using a displacement function and ensures angles, proportionality in distances, and parallelism between lines in focus and context areas are preserved. Furthermore, the system enables users to treat any shaped focus area with an arrangement function to arrange the displacement function so as to be suitable for a focus area of any shape, e.g. a user-specified district or both sides of a user-specified road.

A multipath on-demand routing with path selection probabilities for mobile ad hoc networks

This paper proposes a novel on-demand multipath routing protocol (AODVM-PSP) for a mobile ad hoc network. We devised a new multipath utilization method with probability selection, with which each node deliberately selects one of the multipath routes to utilize. We examined our protocol under various network loads. We evaluated our protocol with Omnet simulator and the performance is compared with conventional methods. When the network load is high, the number of the routing control packets is prodigious. The simulation results show that our proposed protocol has significant improvement over others in high load.

Parallelization of IP-packet filter rules

A compiler for parallelizing IP-packet filter rules is presented which will improve network security and reduce packet-forwarding performance degradation. It analyzes the interdependence of packet-filtering rules specified by a network administrator and translates them into an intermediate program whose instructions can be executed in parallel. Three types of compiler operations are introduced: division is used to divide the rules into parallel expressions, simplification is used to simplify redundant rules, deletion is used to delete infeasible rules.

Simultaneous Analysis of Time and Space for Conflict Detection in Time-Based Firewall Policies

Firewalls are one of the most deployed mechanisms to protect the network from unauthorized access and security threats. However, maintenance of firewall policy is an error-prone and complicated task for a dynamic network environment. Conflict is a misconfiguration that happens when a packet matches two or more filters resulting in shadowing and redundancy of the filters. Network administrators reconfigure the filters to minimize the effect of conflicts, as the filters do not reflect for what it was intended. Nowadays, time-based filters are used in CISCO firewalls and LINUX Iptables to control network traffic in time. Conflict occurs when a packet matches two or more time-based filters active in the same timing. Detection of conflicts in time-based filters is necessary, because the existing conflict detection techniques turns ineffective, as analysis of filters in time is not considered. This problem is not been addressed in research regardless of its significance. To resolve it, in this paper, we propose an n+1 dimensional approach (n refers the number of key fields in a packet header) to detect conflicts by analyzing time and space simultaneously. We compute characterization vectors to detect the conflicting filters which discards the non-conflicting filters in the initial stage of computation and remove the unnecessary steps. Further, we implemented a prototype system and conducted experiments on time-based filters with and without considering time. We found that approximately 50% of conflicting filters becomes non-conflicting when time is considered. Hence, our conflict detection system for time-based filters reduces the workload of the administrator as the filters for reconfiguration is considerably reduced.

Wired Fisheye Lens: A Motion-Based Improved Fisheye Interface for Mobile Web Map Services

We propose a mobile Web map interface that is based on a metaphor of the Wired Fisheye Lens. The interface was developed by using improved fisheye views (Focus+Glue+Context map). When a user wants to obtain information on both the details of the target area and the geographical relation between the present location and the target area by using existing Web map services, he/she has to scroll maps and change the scale of the maps many times. These operations result in a large cognitive cost for users. The Wired Fisheye Lens enables users to easily search an area surrounding the present location since it has the following features: 1) The Focus+Glue+Context map enables users to view both a large-scale map (Focus) and a small-scale map (Context) without changing the scales of the maps; 2) The posture sensor enables users to search for details of the surrounding area by tilting, shaking, and looking through the fisheye lens; 3) The Focus is moved by considering it to be a fisheye lens connected with the present location by a rubber wire on the map. Even if the lens approaches the edge of the screen, it can be kept within the screen by scaling down the Context as if the lens were pulled in by its rubber wire and as if the map were a rubber sheet and pulled in by the lens. As a result, the user can easily navigate through the area surrounding the present location while keeping the Focus within the map. These features enable users to find the target quickly. We developed the Web-based mobile map system that uses commercial maps that are utilized by Yahoo Japan. We confirmed the advantages of the proposed system by evaluation experiments. The new system will be able to contribute to the novel mobile Web map services with fisheye views for mobile terminals such as cellular phones.

Detection of Conflicts Caused by a Combination of Filters Based on Spatial Relationships

Packet filtering in firewalls is one of the useful techniques for network security. This technique examines network packets and determines whether to accept or deny them based on an ordered set of filters. If conflicts exist in filters of a firewall, for example, one filter is never executed because of the prevention of a preceding filter, the behavior of the firewall might be different from the administrators intention. For this reason, it is necessary to detect conflicts in a set of filters. Previous researches that focused on detecting conflicts in filters paid considerable attention to conflicts caused by one filter affecting another, but they did not consider conflicts caused by a combination of multiple filters. We developed a method of detecting conflicts caused by a combination of filters affecting another individual filter based on their spatial relationships. We also developed two methods of finding all requisite filter combinations from a given combination of filters that intrinsically cause errors to another filter based on top-down and bottom-up algorithms. We implemented prototype systems to determine how effective the methods we developed were. The experimental results revealed that the detecting conflicts method and the method of finding all requisite filter combinations based on the bottom-up algorithm can be used for practical firewall policies.