No. 2 (2002)

Preface

The paper presents trial experiments with IP QoS network services (NS) defined and implemented in the AQUILA pilot installation. The AQUILA NSs (premium CBR, premium VBR, premium multimedia and premium mission critical) provide a framework for supporting a variety of applications generating both streaming and elastic traffic. The measurement experiments confirm that AQUILA architecture differentiates the QoS offered to these NSs. The presented numerical results were obtained in the test network installed in the Polish Telecom (Warsaw) consisting of 8 CISCO routers.

In the paper, we present the results of research of MPEG-2 streams transmission through CBR and VBR channel in ATM network. We applied not only experimental and measurement methods but analytical ones as well. A description of the proposed measurement station includes: installed hardware, created software and prepared experimental data. Next, we present the applied measurement method. In the following section, we define a term of the quality of multimedia transmission. The measurement results were compared with the results of the analytical station model. We proposed a functional description of dependence between ATM traffic parameters, video stream bit rate, and quality of multimedia transmission.

The backbone networks evolution to high-speed DWDM networks generates new problems for switching. This function element must be also based on optical technology. For large capacity this cannot be realized by a single matrix, but by multistage switching networks. In the paper three types of optical matrices have been described: fiber switch FX, wavelength fiber switch WSX and wavelength interchanging fiber switch WIX. Based on these matrices, four switching network constructions were considered. The connection properties of these switching networks were evaluated, determining the electronic equivalent switching network for which these properties are well known.

In this paper, the IP/MPLS network cost optimisation problem of selecting localisation of nodes and links, combined with link`s dimensioning, is discussed. As the considered problem is hard, we discuss and propose greedy randomised adaptive search procedure (GRASP) based solution method. GRASP is an iterative randomised sampling technique which combines adaptive randomised greedy function in constructing initial solution with local search optimisation. The effectiveness of the method is illustrated by means of a~numerical study. We compare the GRASP results with results for both exact and heuristic methods obtained in previous research concerning topological design problem.

Future IP QoS (quality of service) networks are aiming at differentiating transfer quality of packets belonging to different flows. For this purpose, a set of network services (NS) with different QoS objectives is defined and implemented in the network. To a NS a certain amount of network resources, i.e. dedicated link capacity with associated buffer size, is allocated. Moreover, the resources dedicated for one NS are not available for other NSs. Traditional approach for admission control algorithm corresponding to given NS takes into account current traffic conditions inside considered NS. This can lead to the situation, due to traffic fluctuations, that temporary overloaded NS cannot use the spare bandwidth from underloaded in this time other NSs. This paper describes a conditional admission control algorithm (C-AC),allowing us to admit new packet flow conditionally in the case where no available capacity inside a given NS. For conditionally accepted flow currently unused capacity, dedicated to other NS, is allocated. This can be done only in the case when QoS requirements for both the conditionally accepted flow and the flows in progress are satisfied. The conditions for effective using of C-AC algorithm are discussed in the paper, like characteristics of NS borrowing and lending capacity and their current traffic load. To show potential benefits of the approach, exemplary numerical results are included, corresponding to hypothetical NSs using REM (rate envelope multiplexing) scheme.

In this paper, we present a new approach for capacitance matrix calculation of lossy multilayer VLSI interconnects based on quasi-static analysis and Fourier projection technique. The formulation is independent from the position of the interconnect conductors and number of layers in the structure, and is especially adequate to model 2D and 3D layered structures with planar boundaries. Thanks to the quasi-static algorithms considered for the capacitance analysis and the expansions in terms of convergent Fourier series the tool is reliable and very efficient; results can be obtained with relatively little programming effort. The validity of the technique is verified by comparing its results with on-surface MEI method, moment method for total charges in the structure, and CAD-oriented equivalent-circuit methodology, respectively.

Recently, digital streams have become widely used to make audio, video, and other media available in real-time over the Internet. As with other transmission methods, the recipient needs to have a possibility to verify the source and authenticity of the received information. Several techniques have been proposed to deal with this issue. Most of them are vulnerable to packet losses or they introduce unacceptable computational and/or communication overheads. Some of the graph-based techniques provide immunity to burst losses of certain length. However, these techniques are not immune to the loss of packets containing signatures or occasional burst of lengths greater than the assumed one. In the paper, we propose a modification to one of the graph-based techniques that introduces immunity to the loss of packets containing signatures, without introducing any additional overheads.

In this paper a simple analytical expression based on E-model is applied to analyse the impact of packet loss and delay on voice transmission quality. The relationship between overall transmission quality rating, packet loss and delay G.711, G.723 and G.729 codecs is presented.