Antonio Jose Estepa

Improving VoIP quality through path switching

The current best-effort Internet cannot readily provide the service guarantees that VoIP applications often require. Path switching can potentially address this problem without requiring new network mechanisms, simply by leveraging the robustness to performance variations available from connectivity options such as multi-homing and overlays. In this paper, we evaluate the effectiveness and benefits of path switching in improving the quality of VoIP applications, and demonstrate its feasibility through the design and implementation of a prototype gateway. We argue for an application-driven path switching system that accounts for both network path characteristics and application-specific factors (e.g., codec algorithms, playout buffering schemes). We also develop an application path quality estimator based on the ITU-T E-model for voice quality assessment, and an application-driven path switching algorithm that dynamically adapts the time scales over which path switching decisions are made to maximize voice quality. Through network emulation and experiments over a wide-area multi-homed test bed, we show that, with sufficient path diversity, path switching can yield meaningful improvements in voice quality. Hence by exploiting the inherent path diversity of the Internet, application-driven path switching is a viable option in providing quality-of-service to applications.

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.

Accurate resource estimation for homogeneous VoIP aggregated traffic

Modern VoIP codecs like G.729, G.723.1 or AMR can generate traffic during voice inactivity periods for Comfort Noise Generation (CNG). This feature alters the classical on-off pattern typically used to model the traffic generated by codecs with a Silence Suppression scheme. Therefore, the traffic generated due to CNG leads to severe inaccuracies in the dimensioning analysis done through traditional models based on multiplexing on-off sources like MMPP or fluid model. This paper addresses the VoIP dimensioning issue. First, we extend the traditional MMPP and fluid analytical models to include those traffic sources which perform the CNG feature. Second, we propose a simple but efficient algorithm which can be applied in dimensioning or admission control to find out the bandwidth reservation required to guarantee delay and loss in a packet-switch multiplexer node for VoIP traffic. Results are validated by simulations and VoIP traces and demonstrate a significant improvement in accuracy with respect to current on-off-based approaches.

More Effective Use of Urban Space by Autonomous Double Parking

The new capabilities of autonomous cars can be used to mitigate to a large extent safety concerns and nuisance traditionally associated with double parking. In this paper double parking for autonom ...

Reusing UI elements with Model-Based User Interface Development

This paper introduces the potential for reusing UI elements in the context of Model-Based UI Development (MBUID) and provides guidance for future MBUID systems with enhanced reutilization capabilities. Our study is based upon the development of six inter-related projects with a specific MBUID environment which supports standard techniques for reuse such as parametrization and sub-specification, inclusion or shared repositories.We analyze our experience and discuss the benefits and limitations of each technique supported by our MBUID environment. The system architecture, the structure and composition of UI elements and the models specification languages have a decisive impact on reusability. In our case, more than 40% of the elements defined in the UI specifications were reused, resulting in a reduction of 55% of the specification size. Inclusion, parametrization and sub-specification have facilitated modularity and internal reuse of UI specifications at development time, whereas the reuse of UI elements between applications has greatly benefited from sharing repositories of UI elements at run time. HighlightsReusing UI assets reduces the development effort in software industry.We provide a real case study where reusing UI resulted in significant benefits in productivity.The structure of UI Models and its components has a significant impact on reusability.MBUIDEs with run-time architecture can benefit from sharing repositories between various projects.