6,052 research outputs found
Optimal configuration of active and backup servers for augmented reality cooperative games
Interactive applications as online games and mobile devices have become more and more popular in recent years. From their combination, new and interesting cooperative services could be generated. For instance, gamers endowed with Augmented Reality (AR) visors connected as wireless nodes in an ad-hoc network, can interact with each other while immersed in the game. To enable this vision, we discuss here a hybrid architecture enabling game play in ad-hoc mode instead of the traditional client-server setting. In our architecture, one of the player nodes also acts as the server of the game, whereas other backup server nodes are ready to become active servers in case of disconnection of the network i.e. due to low energy level of the currently active server. This allows to have a longer gaming session before incurring in disconnections or energy exhaustion. In this context, the server election strategy with the aim of maximizing network lifetime is not so straightforward. To this end, we have hence analyzed this issue through a Mixed Integer Linear Programming (MILP) model and both numerical and simulation-based analysis shows that the backup servers solution fulfills its design objective
The ISIS Project: Real Experience with a Fault Tolerant Programming System
The ISIS project has developed a distributed programming toolkit and a collection of higher level applications based on these tools. ISIS is now in use at more than 300 locations world-wise. The lessons (and surprises) gained from this experience with the real world are discussed
Research issues in real-time database systems
Cataloged from PDF version of article.Today's real-time systems are characterized by managing large volumes of data.
Efficient database management algorithms for accessing and manipulating data are
required to satisfy timing constraints of supported applications. Real-time database
systems involve a new research area investigating possible ways of applying database
systems technology to real-time systems. Management of real-time information through
a database system requires the integration of concepts from both real-time systems and
database systems. Some new criteria need to be developed to involve timing constraints
of real-time applications in many database systems design issues, such as
transaction/query processing, data buffering, CPU, and IO scheduling. In this paper, a
basic understanding of the issues in real-time database systems is provided and the
research efforts in this area are introduced. Different approaches to various problems of
real-time database systems are briefly described, and possible future research directions
are discussed
RAFDA: A Policy-Aware Middleware Supporting the Flexible Separation of Application Logic from Distribution
Middleware technologies often limit the way in which object classes may be
used in distributed applications due to the fixed distribution policies that
they impose. These policies permeate applications developed using existing
middleware systems and force an unnatural encoding of application level
semantics. For example, the application programmer has no direct control over
inter-address-space parameter passing semantics. Semantics are fixed by the
distribution topology of the application, which is dictated early in the design
cycle. This creates applications that are brittle with respect to changes in
distribution. This paper explores technology that provides control over the
extent to which inter-address-space communication is exposed to programmers, in
order to aid the creation, maintenance and evolution of distributed
applications. The described system permits arbitrary objects in an application
to be dynamically exposed for remote access, allowing applications to be
written without concern for distribution. Programmers can conceal or expose the
distributed nature of applications as required, permitting object placement and
distribution boundaries to be decided late in the design cycle and even
dynamically. Inter-address-space parameter passing semantics may also be
decided independently of object implementation and at varying times in the
design cycle, again possibly as late as run-time. Furthermore, transmission
policy may be defined on a per-class, per-method or per-parameter basis,
maximizing plasticity. This flexibility is of utility in the development of new
distributed applications, and the creation of management and monitoring
infrastructures for existing applications.Comment: Submitted to EuroSys 200
Theory and Practice of Transactional Method Caching
Nowadays, tiered architectures are widely accepted for constructing large
scale information systems. In this context application servers often form the
bottleneck for a system's efficiency. An application server exposes an object
oriented interface consisting of set of methods which are accessed by
potentially remote clients. The idea of method caching is to store results of
read-only method invocations with respect to the application server's interface
on the client side. If the client invokes the same method with the same
arguments again, the corresponding result can be taken from the cache without
contacting the server. It has been shown that this approach can considerably
improve a real world system's efficiency.
This paper extends the concept of method caching by addressing the case where
clients wrap related method invocations in ACID transactions. Demarcating
sequences of method calls in this way is supported by many important
application server standards. In this context the paper presents an
architecture, a theory and an efficient protocol for maintaining full
transactional consistency and in particular serializability when using a method
cache on the client side. In order to create a protocol for scheduling cached
method results, the paper extends a classical transaction formalism. Based on
this extension, a recovery protocol and an optimistic serializability protocol
are derived. The latter one differs from traditional transactional cache
protocols in many essential ways. An efficiency experiment validates the
approach: Using the cache a system's performance and scalability are
considerably improved
Analysis domain model for shared virtual environments
The field of shared virtual environments, which also
encompasses online games and social 3D environments, has a
system landscape consisting of multiple solutions that share great functional overlap. However, there is little system interoperability between the different solutions. A shared virtual environment has an associated problem domain that is highly complex raising difficult challenges to the development process, starting with the architectural design of the underlying system. This paper has two main contributions. The first contribution is a broad domain analysis of shared virtual environments, which enables developers to have a better understanding of the whole rather than the part(s). The second contribution is a reference domain model for discussing and describing solutions - the Analysis Domain Model
Analytical considerations for transactional cache protocols
Since the early nineties transactional cache protocols have been
intensively studied in the context of client-server database
systems.
Research has developed a variety of
protocols and compared different aspects of their quality using
simulation systems and applying semi-standardized benchmarks.
Unfortunately none of the related publications substantiated
their experimental findings by thorough analytical considerations.
We try to close this gap at least partially by presenting
comprensive and highly accurate analytical formulas for quality
aspects of two important transactional cache protocols.
We consider the non-adaptive variants of the "Callback
Read Protocol" (CBR) and the "Optimistic Concurrency Control
Protocol"
(OCC).
The paper studies their cache filling size and the number of
messages they
produce
for the so-called UNIFORM workload. In many cases
the cache filling size may considerably differ from a given
maximum cache size - a phenomenon which has been overlooked by
former
publications.
Moreover for OCC, we also give a highly accurate formula which
forecasts
the transaction abortion rate. All formulas are
compared against corresponding simulation results in order to
validate
their correctness
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