Juan M. Vozmediano

A new approach for VoIP traffic characterization

The letter proposes a new frame generation model for those audio codecs which handle SID frames and deduces an analytical expression for the mean bit rate at the input of the IP network as a function of the number of frames per packet. The new model is experimentally validated for the G.729B, G.723.1, and GSM AMR codecs. Results show that the error of the estimation of the mean bit rate can be reduced significantly compared to the traditional on-off model.

Dynamic VoIP codec selection on smartphones

Voice over IP (VoIP) applications can choose a plethora of different speech codecs, which differ in bandwidth, listening speech quality, and resilience to quality degradation under packet loss. However, VoIP Codecs also exhibit differences in facets such as computational complexity or traffic generated that impact on the energy consumption of smartphones due to the use of processor. In this work deals with the study of energy consumption differences among VoIP codecs. We compare the execution time required to encode/decode reference conversations. Our results show that computational complexity has a significant impact on battery consumption (a factor of up to 10 was found between different codecs). Based on our results, we provide a ranking of energy efficiency. We also propose a simple algorithm for codec dynamic selection considering the dimensions of quality, energy and bandwidth. Our algorithm reacts to network conditions choosing the codec that provides less battery consumption constrained to user-defined targets for minimum quality and maximum codec bitrate.

Packetization and Silence Influence on VoIP Traffic Profiles

This article presents an experimental study that extends the current knowledge of the VAD/DTX codec influence in the transmission rate. It considers the new GSM AMR codec as well as G.723.1 and G.729B. The type of the encoded frames have been studied in order to determine the real bit rate and the SID frames effect. The influence of the number of frames per packet have also been addressed, showing that there are optimal values that minimize packet bandwidth consumption.

Background Noise Influence on VoIP Traffic Profile

Modern audio codecs used in VoIP can improve the listening quality by transmitting the main characteristics of the background noise signal during the silence periods. This traffic has been traditionally neglected in the codec mean bit-rate estimation. Nevertheless, when considering an IP environment, the packet overhead increases significantly the required mean transmission bit-rate. Hence, the transmission of the background noise signal can result into either a poor network resource dimensioning in network planning or in the violation of the SLA traffic specifications in a DiffServ scenario.

On the suitability of the E-model to VoIP networks

The increase in IP telephony demands an efficient tool for QoS prediction and measurement in order to allow the planning and design of the underlying networks to meet quality requirements. Among the several tools available for the traditional circuit switched telephony networks, the E-model can be adapted to modern VoIP networks. This paper discusses this adaptation in a corporate WAN scenario in which PC users can communicate with each other. Impairments related to delay and terminals are analysed to derive the proper formulae to be included in the E-model. Impact of other features of the IP networks and terminals in existing factors of the E-model have also been addressed.

Impact of VoIP codecs on the energy consumption of portable devices

In this paper we investigate the influence of the codecs into the energy consumption of VoIP applications. These applications are increasingly extended among users of battery- dependent devices such as laptops, smartphones and tablets. We provide a methodology to compare the energy efficiency of different VoIP codecs for a given device. This allows users and developers to minimize the energy consumption by codec selection, and introduces a new variable into the QoS-bandwidth balance that has traditionally lead the codec selection in VoIP applications. Our results show that the codec can have a significant impact on the energy consumption attributable to the VoIP software of the portable device.

Use of TDM pseudo-wires for an efficient NGN emulation of ISDN multi-channel circuit-mode bearer services

This paper proposes a novel top-down visual saliency detection method for optical satellite images using local adaptive regression kernels. This method provides a saliency map by measuring the likeness of image patches to a given single template image. The local adaptive regression kernel (LARK) is used as a descriptor to extract feature and compare against analogous feature from the target image. A multi-scale pyramid of the target image is constructed to cope with large-scale variations. In addition, accounting for rotation variations, the histogram of kernel orientation is employed to estimate the rotation angle of image patch, and then comparison is performed after rotating the patch by the estimated angle. Moreover, we use the bounded partial correlation (BPC) to compare features between image patches and the template so as to rapidly generate the saliency map. Experiments were performed in optical satellite images to find airplanes, and experimental results demonstrate that the proposed method is effective and robust in complex scenes.

Computing Labs on Virtual Environments: A Flexible, Portable, and Multidisciplinary Model

Computer-aided teaching of practical subjects in engineering education poses new challenges. Computers have to be configured to support the particular requirements of each subject. Virtual environments allow the building of a virtual machine (VM) tailored to the requirements of each subject, allowing flexible, versatile, and low-cost laboratory configurations. However, the use of multiple VM at a shared computing facility poses new problems on the lab sessions, both technical and performance related. To solve these challenges, we have developed the VM on-demand tool. This tool automates the adaptation of each VM to the environment in which it is deployed. As a result, the creation of computer-aided engineering laboratories on a shared computing facility using VM is possible and profitable.

Virtualization environment in telematics labs

The aim of this paper is to show the common scenario for practical content of subjects in the Department of Telematics Engineering by means of virtualization. This Department is responsible for a high number of laboratory groups, requiring many teachers and a high workload. A common environment for all practice groups is desired. A virtual machine was built with the same environment of the Computing Centre at School of Engineering at University of Seville. Then, this virtual machine was provided to students and is used to do practices. This article describes this experience and shows the improvements obtained.

A Productivity-Based Approach to LAN Topology Design

Over the useful life of a LAN, network downtimes will have a negative impact on organizational productivity not included in current Network Topological Design (NTD) problems. We propose a new approach to LAN topological design that includes the impact of these productivity losses into the network design, minimizing not only the CAPEX but also the expected cost of unproductiveness attributable to network downtimes over a certain period of network operation.