Computers and Networks

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Published Research Papers from Vol. 1 (2005) to Vol. 9 (2013) ISSN: 1744-2397

Mediterranean Journal of Computers and Networks covers all technical aspects of  computers and networks. Its scope encompasses cutting-edge research and development, education and applications.
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MediaMac - A NEW PROTOCOL FOR QoS IN WIRELESS HOME NETWORKS

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R. L. Sizeland, A. O. Fapojuwo, R. J. Davies,
This paper proposes and evaluates a new Medium Access Control (MAC) protocol, MediaMac, and network architecture built specifically for the distribution of high quality multimedia over a wireless link in the home. The protocol was evaluated in an event driven simulator and compared with a simulation of an enhanced version of the IEEE 802.11 MAC protocol. It is shown that the proposed protocol outperforms contention based protocols such as 802.11 in terms of throughput and delay performance metrics. A wireless protocol such as MediaMac is required to provide flexible multimedia distribution in a home rivaling the quality provided by a wired solution.

USING MOBILE AGENTS FOR DATA COLLECTION, DATA CORRELATION AND RESPONSE IN AN INTRUSION DETECTION AND RESPONSE SYSTEM

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N. Chatprechakul, P. Nobles
Intrusion detection, the process of identifying and responding to malicious activity targeted at computing and network resources, despite being a subject for research dating back to 1980, is still not as reliable as it should be. The main reasons are the failure to handle new unknown types of intrusion in the case of misuse based detection and the generation of false positives for anomaly based detection. The lack of a better understanding of overall network status has also contributed to a failure to handle intrusion detection effectively. In this paper, we propose a distributed mobile agent based intrusion detection and response system for limited bandwidth networks, such as wireless networks, that has the ability to detect and respond to intrusions by performing data mining and data correlation upon information gathered by mobile agents both in our system and from other proprietary security products. Results are presented that demonstrate the improved performance of the mobile agent IDS over traditional distributed IDS. The agent based IDS we have developed, provides functionality beyond that of the current generation of IDS and is being used to develop more effective security methods for network environments.

A MULTICONSTRAINED QOS AWARE SCHEDULER FOR CLASS-BASED IP NETWORKS

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P. Sousa, P. Carvalho, V. Freitas,
This paper presents a modular scheduler with powerful semantics able to differentiate simultaneously multiple QoS metrics in class-based IP networks. In opposition to traditional scheduling mechanisms, this scheduler encompasses rate, loss and delay differentiation capabilities in a flexible way. This behavior stems from new relative and mixed differentiation models able to bound QoS parameters on high sensitive traffic classes. The results show that using simple and intuitive configuration procedures the proposed architecture is able to provide enhanced QoS differentiation behavior in IP networks according to the users and applications needs. In this way, this proposal may be useful to system designers and network engineers aiming at simple, intuitive, easy to configure and effective mechanisms to enhance QoS in IP networks.

DROP Precedence Mapping on Dynamic Class Assignment Method SYSTEMS UNDER FAST SAMPLING

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K. Yasukawa, K. Baba, K. Yamaoka,
In this paper, we exploit the multimedia streaming application traffics “stream flows” and “non-stream flows”. We propose a dynamic class assignment for stream flows to solve the problems of interaction between stream and non-stream flows. In our proposed method, we use drop precedence mapping to maintain the QoS of non-stream flows where the amount of non-stream flow traffic in a class increases after all of the remaining bandwidth of that class has been assigned to stream flows. For implementing the drop precedences mapping, we utilized Multilevel RED (MRED) schemes. However, the results we obtained showed that the average queue size calculation which based on the moving average, causes undesirable packet drops in flows mapped to higher drop precedences. Considering this, we introduce a simpler scheme for implementing the drop precedences that makes the drop-decision based on the actual queue size. We call this scheme the Multilevel Drop Tail (MDT) scheme. Simulations and experimentations showed that MDT can maintain the QoS of flows mapped to lower drop precedences by dropping fewer packets than MRED, even though the amount of traffic or conditions have been changed.

AN EXPERIMENTAL APPROACH FOR OPTIMISING MOBILE AGENT MIGRATIONS

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D. Gavalas
The field of mobile agent (MA) technology has been intensively researched during the past few years, resulting in the phenomenal proliferation of available MA platforms, all sharing several common design characteristics. Research projects have mainly focused on identifying applications where the employment of MAs is preferable compared to centralized or alternative distributed computing models. Very little work has been made on examining how MA platforms design can be optimized so as the network traffic and latency associated with MA transfers are minimized. The work presented in this paper addresses these issues by investigating the effect of several optimization ideas applied on our MA platform prototype. Furthermore, we discuss the results of a set of timing experiments that offers a better understanding of the agent migration process and recommend new techniques for reducing MA transfers delay

COOPERATIVE PROBLEM SOLVING PROGRAMMING ENVIRONEMENT - A REVIEW

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N. Al-Darwish,
COPS (Cooperative Problem Solving) is a programming environment that supports coding and execution of a parallel algorithm by a number of networked computers running Microsoft Windows. The original implementation of COPS relied on Microsoft® DCOM for cross-process (and cross-machine) calls. This has now been replaced by Microsoft® .NET Remoting. The new implementation boosts a Web-based interface and makes use of several key features of the Microsoft® .NET Framework such as asynchronous calls and serialization. This paper is meant to document the current state of COPS, the rational behind some of the enhancements and the role played by the .NET Framework, and introducing a fault-tolerance scheme that relies on state checkpointing and algorithm restructuring to minimize state data. The scheme enables clients to join or leave a problem solving session at will, and also enables the system to schedule automatic start and stop of a problem-solving session.

IMPROVED ANTNET ROUTING ALGORITHM FOR PACKET SWITCHING

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F. Tekiner, Z. Ghassemlooy,
Antnet is a software agent based routing algorithm that is influenced by the unsophisticated and individual ant’s emergent behaviour. In this paper a modified antnet algorithm for packet switched network has been proposed that offer improvement in the throughput and the average delay by means of detecting and dropping packets routed through the non-optimal routes. By applying boundaries to the reinforcement parameter it also limits the effect of traffic fluctuations. The round trip feedback information, supplied by the software agents, is reinforced by the updated probability entries in the distance vector table. In addition link usage information is also used to prevent stagnation problems. Also discussed is antnet with multiple ant colonies applied to packet switched networks. Simulation results show that the average delay experienced by data packets is reduced for evaporation for all cases when non-uniform traffic model traffic is used. However, there was no performance gain on the uniform traffic models. In addition, multiple ant colonies was applied to the packet switched networks and results were compared with the other approaches. Results showed that the throughput could be increased when compared with other schemes, but with no gain in average packet delay.

Gbit/s DATA RATE IRDA PROTOCOL PERFORMANCE EVALUATION

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A. C. Boucouvalas, Pi Huang
Indoor infrared links are anticipated to reach Gbit/s or even higher data rates in the near future. The aim of this paper is to examine how the existing IrDA IrLAP protocol performs at very high data rates. The contribution of this work is to assess backwards compatibility of future development with existing products and give design guidelines for performance at very high speed. This contribution is achieved by modelling the link layer protocol and including in the model the effects of link minimum turnaround time and propagation delay. A comprehensive analytic model for throughput is derived by using the concept of "window transmission time". We present equations to optimize the link layer parameters for maximum throughput for any line BER. Furthermore, based on the analytically derived equations, we produce numerical results offering guideline parameter values for optimum throughput for any BER.

REAL-TIME CALCULATION OF THE R-FACTOR OF VOIP CONNECTIONS USING RTP/RTCP TRAFFIC

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T. Dagiuklas, S. Xarhoulacos, P. Dallas,
This paper presents a fast method to calculate in real-time the R-factor of the ITU-T E-model in order to evaluate the perceived QoS of VoIP Connections. In the proposed method, the parameters of the E-model (codec, one way delay and packet loss) are determined in real-time from the header fields of the RTP/RTCP traffic at the receiver at fixed time intervals. The calculated R-factor gives similar results with those obtained from the estimated R-factor, through MOS. The predicted error (absolute difference between the mean calculated and the mean estimated R-factor value) is relative low under diverse network conditions (packet loss and average one way delay).

AUGMENTED REALITY TECHNIQUES FOR MUSEUM ENVIRONMENTS

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F. Liarokapis, M. White,
Research into indoor exhibition systems associated with the use of augmented reality technologies is very limited. In this paper, we propose an architecture that is capable of generating accurate 3D models using as input only a few photographs and then merging real and virtual information in a seamless way. We have experimentally applied two simple but effective ways of visualising incomplete or broken real objects as they were in their original state by superimposing their missing parts. To enhance the immersion and realism of the simulated environment, the system allows augmented exhibition of other modes of multimedia content such as textual and pictorial information within the 3D world space. Finally, human-computer interaction techniques are implemented to allow users to naturally manipulate the augmented scenarios.