Celso Massaki Hirata

A survey on congestion control for delay and disruption tolerant networks

Delay and disruption tolerant networks (DTNs) may experience frequent and long-lived connectivity disruptions. Unlike traditional networks, such as the TCP/IP-based Internet, DTNs are often subject to high latency caused by very long propagation delays (e.g., interplanetary communication) and/or intermittent connectivity. Another feature that sets DTNs apart from conventional networks is that there is no guarantee of end-to-end connectivity between source and destination. Such distinct features pose a number of technical challenges in designing core network functions such as routing and congestion control. In this paper, we survey the state-of-the-art in DTN congestion control. We propose a taxonomy to map the DTN congestion control design space and use it to classify existing DTN congestion control mechanisms.

A Guide to Map Application Components to Support Multi-User Real-Time Collaboration

Building a collaborative application from scratch is a hard task. In the last decade many advances have been made to help the developers to construct collaborative applications, however little effort has been made to extend existing single-user applications to support real-time collaboration. This work presents a mapping from the main components of an existing single-user model-view-controller based application to multiuser real-time components of the collaborative application. The mapping allows reuse of existing single-user components by facilitating the construction of collaborative applications. This paper describes the mapping, the extension of an existing single-user application and discusses an experiment of the prototype application where the mapping was applied

GroupSim: A Collaborative Environment for Discrete Event Simulation Software Development for the World Wide Web

The simulation process involves the collaboration of different participants, such as simulation analysts, programmers, statisticians, and users of the simulation software. Many simulation tasks such as modeling, verification, validation, and design for experimentation require the participants to meet. It is understood that these meetings are time-consuming and expensive. This paper proposes a collaborative environment to help with the tasks of discrete event simulation software development using the World Wide Web platform. The environment, named GroupSim, is based on a collaborative computer system and uses the concepts of distributed modeling with automatic program generation and distributed control of experimentation. The authors show some examples to illustrate the use of the environment and discuss some issues related to collaborative environments such as concurrency control, access control, awareness, and performance.

Integrating functional metrics, COCOMO II and earned value analysis for software projects using PMBoK

Nowadays, Function Point and Use Case Point metrics have been largely adopted in the software industry to measure the size of the development work of the project. Metrics should be used in conjunction with estimating techniques such as COCOMO. There has been an increasing interest in monitoring and controlling project performance. Earned Value Analysis present itself as an easy-to-understand technique that helps to monitor and control projects performance. This article presents a sequence of steps which allows the integration of software functional sizing metrics, COCOMO II and Earned Value Analysis in the processes recommended by the PMBoK for planning and controlling software development projects. The goal of such a sequence of steps is to help project managers to plan, monitor and control software development projects using the PMBoK and software functional metrics. The two metrics were chosen as the basic units due to their large acceptance by industry. COCOMO is a technique largely adopted in the software engineering area. A case study using an actual software project data was undertaken to evaluate our proposal. An add-in for Microsoft Project tool was developed to support that such a sequence of steps can be automated and integrated.

Supporting Cache Coherence in Mobile Cooperative Systems

Efficient cache coherence strategies are critical to maintain data consistency and provide a reasonable performance of wireless applications with mobile devices. However, the majority of the current strategies for cache coherence in mobile environments have not been designed to be used in cooperative applications. In this paper we propose and describe an implementation of a cache coherence scheme for mobile cooperative work. The scheme is based on periodic broadcast of invalidation reports and provides some aspects of awareness information. The implementation is made through the development of a prototype cooperative application.

Extending NCTUns simulator to support mobile networks

NCTUns is a Linux based network simulator/emulator which has a great deal of features such as the possibility to execute real world applications without modifications, and provision to model a wide range of network devices using real TCP/IP network stack. However NCTUns only supports simulation/emulation of mobile hosts instead of mobile networks. Hence, using the conventional NCTUns, it is not possible to model more elaborated scenarios, including C4I2SR systems which have mobile networks, for example, aircrafts with internal embedded networks communicating with external networks (terrestrial control center). Motivated by this restriction, we propose and describe an extension of NCTUns in order to allow the modeling and emulation of systems which require two instances of NCTUns. The extension allows the emulation of C4I2SR systems scenarios with video stream and composed of mobile networks using distributed computers. The approach permits improving the confidence on the modeling.

RUP Extension For the Software Performance

Software quality can be described by maintainability, usability, security and performance properties. Performance is generally considered a critical requirement in systems such as distributed systems based on the Web and real time embedded systems. However, the software development processes do not provide suitable support for the construction of a software system that needs to meet performance requirements. RUP (rational unified process) is a well known software engineering process that provides a disciplined approach to assigning tasks and responsibilities within an organized development; however, it has little support for meeting performance requirements. The objective of this work is to propose a more disciplined approach for the extension to RUP for the development of systems to address performance. The performance is embodied in RUP as a knowledge area (discipline) with activities and roles defined through SPE (software performance engineering) and according to the architecture of process engineering UMA (unified method architecture).

Exploring a Brain Controlled Interface for Emotional Awareness

Emotions play an important role in human interaction, communication, coordination, and cooperation. The perception of emotional and affective state in present and past groups activities is a relevant issue since emotional awareness influence the outcome of cooperative work. While there is a growing interest in providing computational support for recognition and representation of emotions, few research efforts explore the potential of Brain Controlled Interfaces (BCI) to collect and present emotional awareness in synchronous collaborative systems. In this paper, we present an initial step in exploring how a low-cost off-the-shelf electroencephalograph (EEG) system can be used to provide emotional awareness information in synchronous collaborative editing systems.

Multidimensional cyclic graph approach: Representing a data cube without common sub-graphs

We present a new full cube computation technique and a cube storage representation approach, called the multidimensional cyclic graph (MCG) approach. The data cube relational operator has exponential complexity and therefore its materialization involves both a huge amount of memory and a substantial amount of time. Reducing the size of data cubes, without a loss of generality, thus becomes a fundamental problem. Previous approaches, such as Dwarf, Star and MDAG, have substantially reduced the cube size using graph representations. In general, they eliminate prefix redundancy and some suffix redundancy from a data cube. The MCG differs significantly from previous approaches as it completely eliminates prefix and suffix redundancies from a data cube. A data cube can be viewed as a set of sub-graphs. In general, redundant sub-graphs are quite common in a data cube, but eliminating them is a hard problem. Dwarf, Star and MDAG approaches only eliminate some specific common sub-graphs. The MCG approach efficiently eliminates all common sub-graphs from the entire cube, based on an exact sub-graph matching solution. We propose a matching function to guarantee one-to-one mapping between sub-graphs. The function is computed incrementally, in a top-down fashion, and its computation uses a minimal amount of information to generate unique results. In addition, it is computed for any measurement type: distributive, algebraic or holistic. MCG performance analysis demonstrates that MCG is 20-40% faster than Dwarf, Star and MDAG approaches when computing sparse data cubes. Dense data cubes have a small number of aggregations, so there is not enough room for runtime and memory consumption optimization, therefore the MCG approach is not useful in computing such dense cubes. The compact representation of sparse data cubes enables the MCG approach to reduce memory consumption by 70-90% when compared to the original Star approach, proposed in [33]. In the same scenarios, the improved Star approach, proposed in [34], reduces memory consumption by only 10-30%, Dwarf by 30-50% and MDAG by 40-60%, when compared to the original Star approach. The MCG is the first approach that uses an exact sub-graph matching function to reduce cube size, avoiding unnecessary aggregation, i.e. improving cube computation runtime.

A technical comparison of the existing approaches to support collaboration in non-collaborative applications

Many approaches can be used to facilitate the implementation of collaborative requirements in noncollaborative applications. In general, each approach uses different design techniques and has specific objectives and pre-conditions. During the implementation of collaborative requirements, it is not always easy to decide which approach is recommended i.e. which criteria should be used to compare the approaches. Based on the literature, this paper presents a set of criteria to technically compare the existing approaches to support collaborative requirements in non-collaborative applications. The criterion help developers in the task of choosing the most suitable approach to develop collaborative applications based on non-collaborative applications.