Performance evaluation of 10Base-T and 100Base-T Ethernets carryingmultimedia traffic

The performance of 10Base-T and 100Base-T Ethernet segments carrying audio/video traffic is presented. End-to-end delay requirements suitable for a wide range of multimedia applications are considered (ranging from 20-500 ms). Given the specific nature of the network considered and the maximum latency requirement, some data is lost. Data loss at the receiver causes quality degradations in the displayed video in the form of discontinuities, referred to as glitches. We define various quantities characterizing the glitches, namely, the total amount of information lost in glitches, their duration, and the rate at which glitches occur. We study these quantities for various network and traffic scenarios, using a computer simulation model driven by real video traffic generated by encoding video sequences. We also determine the maximum number of video streams that can be supported for given maximum delay requirement and glitch rate. We consider various types of video contents (video conferencing, motion pictures, commercials), two encoding schemes (H.261 and MPEG-1), and two encoder control schemes [constant bit rate (CBR) and constant-quality variable bit rate (CQ-VBR)] and compare their results. Furthermore, we consider scenarios with mixtures of video and data traffic (with various degrees of burstiness), and determine the effect of one traffic type over the other     

Voice service interworking for PSTN and IP networks

This article presents an overview of the main technical problems to be addressed for the provision of interoperable services between IP telephony and the PSTN. The pivotal element of the solution resides in an interworking function. This function is typically implemented in a gateway whose requirements and behavior are here analyzed in terms of signaling and control protocols (control plane) as well as user data transfer (user plane). The presentation is structured around these two planes. The control plane defines the set of signaling protocols to be used in each networking context and the translation between them. Detailed scenarios illustrate the signal translation in the gateway allowing for the establishment of a hybrid phone call. The user plane is responsible for adapting the user data to the properties of each network channel and determines the quality of service of the voice call in terms of delay and speech quality     

The influence of the temperature on the stress‐strain curves of a bearing steel and a case hardening steel

In the present paper the influence of the temperature and strain rate on the stress strain behaviour of two different steels were investigated. Two microstructures were considered: pearlitic and austenitic. Tensile tests with the bearing steel 100Cr6 and the case hardening steel 20MnCr5 were accomplished at various temperatures. For this purpose the Ludwik equation was used to describe the stress‐strain curve. The parameter of the constitutive equation was determined for each steel and microstructure. Especially for the austenitic state the parameters of the used material law were described as a function of the temperature.     

User Roles in Online Communities and Their Moderating Effect on Online Community Usage Intention: An Integrated Approach

Recently, it has been evident that the analysis of user data and content in online environments allows practitioners to understand how to motivate online community members and keep them frequently involved in the community, and so to manage these communities successfully. In this sense, practitioners should comprehend community members’ usage intentions to give a better service and to motivate them. However, different user types engage in such communities, so understanding their diverse needs is also essential for practitioners. In parallel, this article addresses the problem of the different user types existing in online communities, and each of them requires different strategies to be motivated and involved in the community. Thus, unlike previous studies, this study firstly identifies user roles in an online community based on the structural role theory, social network analysis, and community members’ contribution behavior. After that, it investigates members’ usage intentions based on the technology acceptance model and examines the moderating effect of identified user roles on their usage intentions. The study also guides practitioners to develop motivational strategies to keep each type of member continually satisfied.     

TRIP and phase evolution for the pearlitic transformation of the steel 100Cr6 under. step‐wise loads

The investigation of complex material behaviour of steel like transformation‐induced plasticity (TRIP) and stress‐dependent phase transformation (SDPT) is a large field of current research. The simulation of the material behaviour of work‐pieces in complex situations requires a knowledge as deep as possible about such phenomena. In addition, there are effects in the case of non‐constant stress which cannot be explained by the widely used Leblond model for TRIP. Therefore, we consider a TRIP model taking into account back stress due to TRIP itself. Based on experimental data for the isothermal pearlitic transformation of the steel 100Cr6 (SAE52100) under step‐wise loads we calculate material parameters for the extended TRIP model. Regardless of the preliminary character of the performed tests, all experiments show a back‐stress effect with a decrease of the TRIP strain after unloading.