Stefaan Vanhastel

On the influence of best-effort network conditions on the perceived speech quality of VoIP connections

When voice traffic is transported over a packet-based network, a number of conditions different from the ones in the traditional circuit-switched network will have an influence on the quality of the speech signal as perceived by the users. In particular, distortion of the voice signal due to delay jitter and partial loss of signal caused by packet loss will have an important impact. Therefore, in order to determine the influence of delay jitter and packet loss on the perceived quality, an objective speech quality assessment system, called DSLA, is used to predict the mean opinion score for voice connections, which are set up on a test-bed, subject to artificially introduced network conditions. A decomposition of the voice degradation is made into different parts, due to sampling, digitization, encoding/decoding, packet loss and delay jitter, respectively. It is found that delay jitter has a devastating influence on the perceived quality, when no dejittering buffer is used. However, when the received signal is dejittered, the degradation due to jitter is similar to the one caused by packet loss.

A generic middleware-based platform for scalable cluster computing

Abstract In this paper, we address the design of a generic and scalable platform for cluster computing. The architecture of the platform is based on middleware technology in order to ensure easy distribution of the software components along the participating workstations and to exploit advanced communication techniques, such as event notification and object registration. The computational tasks are referred to as intelligent agents , which are software agents that are capable of executing particular algorithms on input data. The developed platform offers advanced features such as transparent load balancing, task scheduling, run time compilation of agent code and migration of tasks. The architecture of the platform will be outlined from a computational point of view and each component will be described in detail. Furthermore, the engineering aspects of the platform will be covered. In addition, a sample scenario for computational tasks in the area of telecommunication network design and management will be described, together with a performance evaluation of the platform.

Design and implementation of a generic connection management and service level agreement monitoring platform supporting the virtual private network service

In this paper we address the design of a generic and scalable architecture for connection management and SLA (service level agreement) monitoring of VPNs (virtual private networks). Layer-based design ensures that the architecture is independent of the network technology. Use of advanced software techniques such as run time compilation and intelligent agents allow easy integration of new monitoring and routing algorithms. The architecture offers advanced features such as VPN edge device capability matching, XML-based SLS (service level specification) language, load balancing of computational tasks, and programmable components. The architecture is compliant with the TINA (telecommunication information network architecture) recommendations and its implementation is based on CORBA (common object request broker architecture). In addition, a sample VPN setup and monitoring scenario will be detailed.

Design of a generic platform for efficient and scalable cluster computing based on middleware technology

We address the design of a generic and scalable platform for cluster computing. The architecture of the platform is based on middleware technology in order to ensure easy distribution of the software components along the participating workstations and to exploit advanced communication techniques, such as event notification and object registration. The computational tasks are referred to as intelligent agents, which are software agents that are capable of executing particular algorithms on input data. The developed platform offers advanced features such as transparent load balancing, task scheduling, run time compilation of agent code and migration of tasks. The architecture of the platform is outlined from a computational point of view and each component is described in detail. Furthermore, the engineering aspects of the platform are covered. In addition, a sample scenario for computational tasks in the area of telecommunication network design and management is described.

A generic end-to-end distributed QoS management architecture and its application to IP-DiffServ over a WDM access feeder network

The growing widespread use of advanced multimedia and interactive real-time applications is setting forth new challenges such as end-to-end quality-of-service (QoS) and broadband Internet access. The high bandwidth needs are pushing fiber closer and closer to the home, and as such WDM (wavelength division multiplexing) seems ideally suited to be used in the broadband access feeder network which interconnects the Internet core networks and the last mile networks. In the HARMONICS project (Hybrid Access Reconfigurable Multi-wavelength Optical Networks for IP-based Communication Services), a novel DWDM (dense wavelength division multiplexing) based optical access feeder network is investigated. This feeder network transports IP, guarantees QoS and can feed various last mile networks, stimulating the convergence of access networks. VDSL and Hiperlan/2 are studied within the project as last mile access networks. To support end-to-end QoS, a distributed CORBA-based generic network management framework is being developed as part of the project. This paper elaborates on the framework which is aligned with TINA, although adapted to be more consistent and applicable. End-to-end QoS is based on Differentiated Services (DiffServ) at layer 3, various QoS supporting technologies at layer 2 and QoS mappings between both layers.

Design of a generic architecture for service management and monitoring of service level agreements through distributed intelligent agents

We present a generic architecture for service management and monitoring of service level agreements (SLA). Special attention has been devoted to the efficient management of computational resources. The usage of an intelligent agent platform (IAP) with this respect is motivated. The case study of an adaptive distributed caching architecture is presented and the agent for adaptive distributed data caching is detailed. Furthermore, a sample scenario is provided to illustrate the different stages in the data caching process and how distributed intelligent agents are used in favor.