We consider the uplink case of a cellular system where <svg style="vertical-align:-0.10033pt;width:11.225px;" id="M1" height="7.1374998" version="1.1" viewBox="0 0 11.225 7.1374998" width="11.225" xmlns="http://www.w3.org/2000/svg">
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</svg> bufferless mobiles transmit over a common channel to a base station, using the slotted aloha medium access protocol. We study the performance of this system under several power differentiation schemes. Indeed, we consider a random set of selectable transmission powers and further study the impact of priorities given either to new arrival packets or to the backlogged ones. Later, we address a general capture model where a mobile transmits successfully a packet if its instantaneous SINR (signal to interferences plus noise ratio) is lager than some fixed threshold. Under this capture model, we analyze both the cooperative team in which a common goal is jointly optimized as well as the noncooperative game problem where mobiles reach to optimize their own objectives. Furthermore, we derive the throughput and the expected delay and use them as the objectives to optimize and provide a stability analysis as alternative study. Exhaustive performance evaluations were carried out, we show that schemes with power differentiation improve significantly the individual as well as global performances, and could eliminate in some cases the bi-stable nature of slotted aloha.

Rachid El-Azouzi

Essaid Sabir

Tania Jim&#233;nez

El-Houssine Bouyakhf

Modeling Slotted Aloha as a Stochastic Game with Random Discrete Power Selection Algorithms

The role of Internet Protocol (IP) is becoming more and more problematic especially with the new requirements of mobility and multihoming.  Host Identity protocol (HIP) defines a new protocol between the network and transport layers in order to provide a better management to those requirements. The protocol defines a new namespace based on cryptographic identifiers which enable the IP address roles dissociation. Those new identifiers identify hosts rather than IP addresses. Because HIP is a quite recent protocol, we propose to present an experimental evaluation of its basic characteristics.

Maher Ben Jemaa

Nahla Abid

Maryline Laurent-Maknavicius

Hakima Chaouchi

Experimental Measurements of Host Identity Protocol for Mobile Nodes' Networks

This article proposes a novel approach to synchronize a posteriori the detailed execution traces from several networked computers. It can be used to debug and investigate complex performance problems in systems where several computers exchange information. When the distributed system is under study, detailed execution traces are generated locally on each system using an efficient and accurate system level tracer, LTTng. When the tracing is finished, the individual traces are collected and analysed together. The messaging events in all the traces are then identified and correlated in order to estimate the time offset over time between each node. The time offset computation imprecision, associated with asymmetric network delays and operating system latency in message sending and receiving, is amortized over a large time interval through a linear least square fit over several messages covering a large time span. The resulting accuracy is such that it is possible to estimate the clock offsets in a distributed system, even with a relatively low volume of messages exchanged, to within the order of a microsecond while having a very low impact on the system execution, which is sufficient to properly order the events traced on the individual computers in the distributed system.

Eric Cl&#233;ment

Michel Dagenais

Traces Synchronization in Distributed Networks

This paper presents a framework for reliable and efficient streaming of H.264 video over an IEEE 802.11-based wireless network. The framework relies on a cross-layer mechanism that jointly adapts the video transcoding parameters at the application layer and the video transmission parameters at the data-link layer to the network conditions defined by buffer length and wireless propagation channel. The effectiveness of the proposed framework is demonstrated through the transmission of three test video sequences (Akiyo, Container, and Foreman) having different degrees of motion over an IEEE802.11 wireless network. Simulation results show that the proposed cross-layer-based framework provides an enhancement of up to 3 dB in the video quality with a negligible increase (&lt;5%) in the packet processing time. Hence, the proposed framework achieves a good balance in the tradeoff between video quality and packet processing time. The proposed framework, along with its performance results, provides valuable insights on the selection of network parameter values for efficient and reliable transmission of video applications in wireless networks.

Azfar Moid

Abraham O. Fapojuwo

A Cross-Layer Framework for Efficient Streaming of H.264 Video over IEEE 802.11 Networks

We have addressed the complex problem of recovery for concurrent failures in distributed computing environment. We have proposed a new approach in which we have effectively dealt with both orphan and lost messages. The proposed checkpointing and recovery approaches enable each process to restart from its recent checkpoint and hence guarantee the least amount of recomputation after recovery. It also means that a process needs to save only its recent local checkpoint. In this regard, we have introduced two new ideas. First, the proposed value of the common checkpointing interval is such that it enables an initiator process to log the minimum number of messages sent by each application process. Second, the determination of the lost messages is always done a priori by an initiator process; besides it is done while the normal distributed application is running. This is quite meaningful because it does not delay the recovery approach in any way.

B. Gupta

S. Rahimi

A Novel Low-Overhead Recovery Approach for Distributed Systems

In order to enhance the precision of network simulations, the paper proposes an approach to adaptively decide the maximum of random variables that create the discrete probabilities to generate nodal traffic on simulated networks. In this paper, a statistical model is first suggested to manifest the bound of statistical errors. Then, according to the minimum probability that generates nodal traffic, a formula is proposed to decide the maximum. In the formula, a precision parameter is used to present the degree of simulative accuracy. Meanwhile, the maximum adaptively varies with the traffic distribution among nodes because the decision depends on the minimum probability generating nodal traffic. In order to verify the effect of the adaptive maximum on simulative precision, an optical network is introduced. After simulating the optical network, the theoretic average waiting time of nodes on the optical network is exploited to validate the exactness of the simulation. The proposed formula deciding the adaptive maximum can be generally exploited in the simulations of various networks. Based on the precision parameter K, a recursive procedure will be developed to automatically produce the adaptive maximum for network simulations in the future.

Rong Nan Chiou

Chia-Nian Shyi

Adaptive Maximums of Random Variables for Network Simulations

Standard protocols for reliable data transmission over unreliable channels are based on various Automatic Repeat reQuest (ARQ) schemes, whereby the sending node receives feedback from the receiver and retransmits the missing data. We discuss this issue in the context of one-way data transmission over simple wireless channels characteristic of many sensing and monitoring applications. Using a specific project as an example, we demonstrate how the constraints of a low-cost embedded wireless system get in the way of a workable solution precluding the use of popular schemes based on windows and periodic acknowledgments. We also propose an efficient solution to the problem and demonstrate its advantage over the traditional protocols.

Pawel Gburzynski

Bozena Kaminska

Ashikur Rahman

On Reliable Transmission of Data over Simple Wireless Channels

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Journal of Computer Networks and Communications publishes original research and review articles that investigate both the theoretical and practical aspects of computer networks and communications.

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Journal of Computer Networks and Communications - Table of contents 2009

Journal of Computer Networks and Communications | Hindawi

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Journal of Computer Networks and Communications publishes original research and review articles that investigate both the theoretical and practical aspects of computer networks and communications.

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Journal of Computer Networks and Communications

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Journal of Computer Networks and Communications