Leandro Galvao

Towards an efficient header compression scheme to improve VoIP over wireless mesh networks

Header compression techniques can improve the speech quality of VoIP applications. However, its deployment over wireless mesh environments may not offer much improvement, since the wireless and multi-hop characteristics of such a network impose a high packet loss rate. In this work, we propose a new approach for header compression, using packet aggregation to cooperate with the header compression scheme. Simulation results show that the new cooperative approach can decrease significantly the packet loss, impacting positively on the speech quality.

Drop Less Known strategy for buffer management in DTN Nodes

Certain kinds of delay and disruption tolerant networks need the human support to send data between users without a contemporaneous end-to-end path between them. However, humans are socially selfish and tend to cooperate with whom they have a social relationship, fact that affects the overall performance. Memory space is a critical resource on mobile devices, and since the intermediate nodes have to store the messages, buffer management strategy becomes a crucial factor to achieve a satisfactory network performance. Very little attention has been directed towards applying the social characteristics of the users to mitigate the congestion in DTN. This paper presents a buffer management strategy for DTNs that takes into account a value associated with the social relationship strength among the users. We evaluated this policy in conjunction with the Epidemic and PRoPHET routing algorithms. By means of a thoroughly planned set of steady-state simulation experiments, we found that the proposed scheme can increase the delivery rate besides decreasing the average delay.

Impact evaluation of radio propagation models on performance parameters of application layer in Wireless Mesh Backbone simulation

In this paper we propose a VoIP study case to evaluate the impact of different radio propagation models on performance parameters of application layer in simulation studies of Wireless Mesh Backbones. For each presented model, we carried out experiments taking into account the credibility aspects suggested by simulation theory of stochastic processes. Results showed that, for the same scenario, using different propagation models, voice speech quality can switch from acceptable to unacceptable.

FSF: Friendship and selfishness forwarding for Delay Tolerant Networks

This paper presents the friendship and selfishness forwarding (FSF) algorithm for Delay Tolerant Networks. This novel solution is based on two social characteristics of nodes: friendship and selfishness. When a contact opportunity arises, FSF analyzes two aspects to make message forwarding decisions: first, FSF assesses the friendship strength among the pair of nodes, then it determines the individual selfishness of the relay node. Unlike other algorithms proposed in the DTN literature, we use a machine learning algorithm to quantify the friendship strength among pairs of nodes in the network. The individual selfishness of the relay node is determined by using a model based on the current level of its resources. The primary goal is to take into account the case where, despite a strong friendship with the message destination, the relay node does not accept processing the message to save its resources. By using trace-driven simulations we show that the FSF algorithm achieves better results in terms of delivery rate, average cost and efficiency.

Influence of Routing Protocol on VoIP Quality Performance in Wireless Mesh Backbone

In this paper we focus on the following question: how routing protocols, working under different channel conditions, can influence the human perceived quality of VoIP calls in a wireless mesh backbone? In order to respond this question, we propose a study case where we analyze two routing approaches in a 802.11 wireless mesh backbone, namely, reactive AODV and proactive OLSR. We calculated the voice speech quality by making use of a reviewed version of ITU-T E-model proposed in previous work. Results obtained from highly credible stochastic simulation environment, also described in this paper, showed that AODV performs better in very hostile mediums while OLSR presents better results when more friendly mediums take place.

An Empirical Study about the Influence of Project Manager Personality in Software Project Effort

Project effort is a main concern on software organizations. The project budget is derived from project effort which in turn is based on the software engineersâ?? effort cost. Project manager is responsible for planning and controlling this effort estimation. Some researches relate how project manager can influence the project success, specially when considering project manager personality. This research aims to evaluate the influence between project manager personality and teamwork behavior over projectâ??s effort deviation. A case study was performed with 65 real projects collected from a software company dedicated to develop software projects for its local government. Unlike previous researches our results show no statistically significant influence of project manager personality, assesed by MBTI test, over projectâ??s effort deviation. However, our results show the project manager teamwork behavior, assesed by Belbinâ??s BTRSPI, has a statistically significant influence on the projectâ??s effort deviation.