Akihito Nakamura

Causally ordering broadcast protocol

The distributed applications require group communications among multiple entities. In the group communication, it is important to discuss in what order each entity in the group can receive data units. In order to realize fault-tolerant systems, the same events have to occur in the same order in each entity. The ordering among the events is known as a causal order. This paper presents a reliable causally ordering broadcast (CO) protocol which provides the same causal ordering of data units for all the entities in the group. In the CO protocol, the data units received are causally ordered by using the sequence numbers of the data units. The CO protocol is based on the fully distributed control scheme, i.e. no master controller, and uses high-speed networks where each entity may fail to receive data units due to the buffer overrun. Furthermore, the CO protocol provides asynchronous data transmission for multiple entities in the group.<<ETX>>

Priority-based total and semi-total ordering broadcast protocols

Broadcast protocols that provide priority-based receipt ordering of protocol data units (PDUs) for entities in a cluster are discussed. Three distributed broadcast protocols that provide the priority-based receipt ordering of PDUs by using a single channel system like Ethernet and radio systems are presented. The protocols are priority-based total ordering (PriTO), priority-based semitotal ordering (PriSO) and fast PriO (FPriO).<<ETX>>

Reliable broadcast protocol for selectively partially ordering PDUs (SPO protocol)

Methods to provide reliable broadcast communication for multiple entities in distributed systems by using unreliable broadcast communication services are discussed. In real distributed applications, each entity sends every PDU (protocol data unit) to only the subset, rather than all the entities, and each entity receives only PDUs destined to it from some entity in the same order as they were sent. Such a broadcast service is named an SPO service (service for selectively partially ordering PDUs). How to design a protocol which provides the SPO service for entities by using unreliable broadcast networks in the presence of lost PDUs is discussed. The SPO service can be a useful facility in designing and implementing distributed systems like distributed database systems.<<ETX>>

Group communication protocol for large group

The authors discuss how to provide reliable group communication for a large number of entities interconnected by a high-speed one-channel network. A group of entities is partitioned into disjoint subgroups, named component clusters, interconnected by gateways, in order to reduce the processing time and data unit length. The communication protocol is executed in each component cluster, and the gateways forward data units to other component clusters. There exists only one gateway between every two different component clusters in order to prevent the proliferation of data units.

Partially ordering broadcast (PO) protocol

A design of a reliable broadcast communication system for unreliable broadcast networks like Ethernet and radio networks is presented. The authors try to provide a partially ordering broadcast (PO) service in which every entity receives all messages from one entity in the same order. The PO protocol does not require the total ordering of received protocol data units (PDUs). In order to provide a reliable broadcast communication among multiple entities on an unreliable broadcast service, a data transmission procedure, the execution of which is controlled by all entities in a distributed scheme, is proposed. The correctness of the protocol is shown. The protocol can be very useful in designing and implementing distributed systems, such as distributed database systems and distributed operating systems.<<ETX>>

Totally ordering broadcast (TO) protocol on the Ethernet

The design of reliable broadcast communication systems is presented. These systems provide, on an unreliable broadcast service such as the Ethernet, a totally ordering broadcast service where every entity receives all messages in the same order. In order to provide such a reliable broadcast communication among multiple entities on the unreliable broadcast service, a data transmission procedure is proposed whose execution is controlled by all entities in a distributed scheme. Also, the correctness of the protocol is shown. The protocols can be useful in designing and implementing distributed systems such as distributed database systems and distributed operating systems.<<ETX>>

Starvation-prevented priority-based total ordering broadcast protocol on high-speed single channel network

The authors discuss a distributed broadcast protocol which provides priority-based receipt ordering of protocol data units (PDUs) for the application entities by using the high-speed single-channel network in the presence of the loss of PDUs. There is a starvation problem, i.e. lower-priority PDUs can be left waiting indefinitely in the receipt queue since higher-priority PDUs jump over lower-priority ones. They present a method by which even lower-priority PDUs are delivered to the application entities in some pre-defined time by partitioning the receipt sequence of PDUs into runs, where each runs is priority-based ordered.<<ETX>>

Sophy: a morphological framework for structuring geo-referenced social media

Social networks have played a crucial role of information channels for understanding our daily lives beyond communication tools. In particular, their coupling with geographic location has boosted the worth of social media to detect, track, and predicate dynamic events and situations in the real world. While the amounts of geo-tagged social media are apparently increasing at every moment, we have few framework to handle spatiotemporal changes and analyze their relationships. In this paper, we propose a framework to understand dynamic social phenomena from the mountains of fragmented, noisy data flooding social media. First, we design a data model to describe morphological features of the populations of geo-location of social media and define a set of relationships by using differential measurements in spatial, temporal, and semantic dimensions. Then, we describe our real-time framework to extract morphometric features from streaming tweets, create the topological relationships, and store all features into a graph-based database. In the experiments, we show case studies related to two typhoons (Neoguri and Halong) and a landslide disaster (Hiroshima) with real tweet-sets in a visualization way.

Causally ordering group communication protocol

Distributed application systems require group communications among multiple processes. In the group communication, it is important to discuss in what order each process in the group can receive messages. The paper presents a causally ordering group communication (CO) protocol which provides the same causal ordering of messages for all the processes in the group. In the CO protocol, the messages received are causally ordered by using the sequence numbers of the messages. The CO protocol is based on the fully distributed control scheme, i.e. no master controller, and uses high-speed networks where each process may fail to receive messages due to the buffer overrun. Furthermore, the CO protocol provides asynchronous data transmission for multiple processes in the group.

Towards Unified Vulnerability Assessment with Open Data

Continuous and comprehensive vulnerability management is a difficult task for administrators. The difficulties are not because of a lack of tools, but because they are designed without service-oriented architecture viewpoint and there is insufficient trustworthy machine-readable input data. This paper presents a service-oriented architecture for vulnerability assessment systems based on the open security standards and related contents. If the functions are provided as a service, various kinds of security applications can be interoperated and integrated in loosely-coupled way. We also studied the effectiveness of the available public data for automated vulnerability assessment. Despite the large amount of efforts that goes toward describing machine-readable assessment test in conformity to the OVAL standard, the evaluation result proves inadequate for comprehensive vulnerability assessment. Only about 12% of all the known vulnerabilities are covered by existing OVAL tests, while some popular client applications in the Top 30 with most unique vulnerabilities are covered more than 90%.