Improving the Quality of Mobile Learning Services

Wireless Personal Communications - The quality of services (QoS) has a key role to improve the performances of the collaborative mobile learning. However, many factors can limit it such as the...     

Analytical analysis of applying packet fragmentation mechanism on IEEE 802.11b DCF network in non ideal channel with infinite load conditions

The analytical modeling and performance analysis of the 802.11 network in all its various extensions (802.11b, 802.11a, 802.11g, 802.11e, 802.11n, etc.) have already been widely explored over the past years. However, the packet fragmentation mechanism (PFM), which is proposed by the IEEE work group to reduce the impact of bit error rate (BER) on the packet error rate (PER), has not been considered in the analytical models proposed in the literature. Yet, the PFM constitutes a key parameter to achieve the best performances of 802.11 networks. In this paper, we extend the Bianchi’s Markov chain model with the PFM and the PER. Then, we analyze the performance improvement level achieved with the PFM in an IEEE 802.11 network under the impact of BER and packet length. The proposed analysis has been applied on the basic access method of 802.11b network in saturated traffic conditions. So, we have analyzed the throughput and the mean response time of the 802.11 network. The obtained theoretical results are validated by simulation.     

Dynamic Architecture for Collaborative Distributed Storage of Collected Data in Fog Environments

Wireless Personal Communications - Fog computing needs, particularly in terms of performance, availability and reliability, are increasing every day due to the rapid growth in the number of...     

Modeling and performance evaluation of the IEEE 802.15.4e LLDN mechanism designed for industrial applications in WSNs

The IEEE 802.15.4 standard has been introduced for low latency and low energy consumption in wireless sensor networks. To better support the requirements of industrial applications, where the use of this standard is limited, the low latency deterministic network (LLDN) mechanism of the IEEE 802.15.4e amendment has been proposed. In this paper, we develop a three dimensional Markov chain model for the IEEE 802.15.4e LLDN mechanism. Then, we estimate the stationary probability distribution of this chain in order to derive theoretical expressions of some performance metrics, as the reliability, energy consumption, throughput, delay and jitter. After that, we conduct a comparative study between the IEEE 802.15.4e LLDN and the IEEE 802.15.4 slotted carrier sense multiple access with collision avoidance (CSMA/CA). Numerical results show that the deterministic behavior of the LLDN mechanism significantly reduces the collision probability providing best performances in terms of reliability, energy consumption, throughput and delay compared to the IEEE 802.15.4 slotted CSMA/CA. Finally, the accuracy of our theoretical analysis is validated by Monte Carlo simulations.     

GPM: A generic and scalable P2P model that optimizes tree depth for multicast communications

Group communications (real‐time and non‐real‐time) refer to one‐to‐many or many‐to‐many communications. On the one hand, multicast is considered as an appropriate solution for supporting group communication‐oriented applications (we distinguish IP network multicast from application layer multicast). On the other hand, peer‐to‐peer model tends to be a good candidate for supporting today Internet applications (e.g. P2P IPTV, P2P VoIP, etc.). In this context, P2P has attracted significant interest in the recent years. This is mainly due to its properties that also make P2P well adapted to today social networks. In this paper, we propose GPM (Generic P2P Multicast): a novel generic and scalable approach, that optimizes multicast tree depth in P2P networks (structured and unstructured), and contributes to control the network overlay latency. For multicast tree construction, the approach we propose is based on a distributed algorithm using a specific data structures (adjacency and forwarding matrixes). GPM model inherits from P2P attributes such as scalability, flexibility and fault tolerance, while taking into consideration the respective characteristics of one‐to‐many and many‐to‐many type of applications. We also give a performance evaluation for validation and comparison purposes while considering some main existing application layer multicast protocols. Copyright © 2011 John Wiley & Sons, Ltd.     

Improving the performance for task assignment in distributed server systems by partitioning the large tasks

Task Assignment in distributed server systems focuses on the policy that assigns the tasks reached these systems in order to improve the response time. These tasks, generally, have the property that there is a tiny fraction (about 3%) of the large tasks that makes half (50%) of the total load. However, this property creates additional problems: the large tasks make the load difficult to balance among the servers, and the small tasks will be delayed by the large ones when they are in the same queue. In this paper, we propose a new policy for the Web clusters that we call Partitioning Large Tasks (PLT) and which deals with these problems mostly under a high traffic demand and a high variability of task sizes. PLT partitions each large task into fragments and assigns them to be processed in a parallel way and completing at the same time to improve the mean response time, and separates the small tasks from the large tasks to avoid being delayed. Performance tests show a significantly improvement in performance of PLT over the existing task assignment policies.     

Energy-Aware Link Scheduling Protocol for Wireless Sensor Networks

By reducing interferences drastically, time division multiple access (TDMA) based approaches are considered one of the most efficient solutions to optimize resources’ use. The existing protocols, however, address only the latency minimization without considering the waste of energy, which typically results from idle listening or frequent transitions of the radio module between sleep and active modes. Besides, only saturated systems are considered in these protocols, which may imply resources’ underutilization in some practical use cases. In this paper, we present an energy-aware TDMA-based link scheduling protocol, named deterministic link scheduling protocol (DLSP), designed with the aim of achieving both low energy consumption and low latency in wireless sensor networks. DLSP takes advantage of the spatial reuse of interference-free time slots using conflict graphs. Unlike earlier studies that often considered saturated traffic, we propose to relax the saturation assumption in order to maintain good performance when some of the nodes have no data to send. Thus, we propose to define the following transmission periods: a period to send the own data of the nodes and a period to relay packets. The simulation results clearly show the effectiveness of the proposed protocol, in terms of latency and energy consumption, compared to existing approaches.