Gérard Maral

ATM-based routing in LEO/MEO satellite networks with intersatellite links

An asynchronous transfer mode (ATM)-based concept for the routing of information in a low Earth orbit/medium Earth orbit (LEO/MEO) satellite system including intersatellite links (ISLs) is proposed. Specific emphasis is laid on the design of an ATM-based routing scheme for the ISL part of the system. The approach is to prepare a virtual topology by means of virtual path connections (VPCs) connecting all pairs of end nodes in the ISL subnetwork for a complete period in advance, similar to implementing a set of (time dependent) routing tables. The search for available end-to-end routes within the ISL network is based on a modified Dijkstra (1959) shortest path algorithm (M-DSPA) capable of coping with the time-variant topology. With respect to the deterministic time variance of the considered ISL topologies, an analysis of optimization aspects for the selection of a path at call setup time is presented. The performance of the path search in combination with a specific optimization procedure is-by means of extensive simulations-evaluated for example LEO and MEO ISL topologies, respectively.

Delay analysis for interlan traffic using two suitable TDMA satellite access schemes

SUMMARY Two d emand assignment TDMA satellite acce ss s chemes that are suitable for providing flexible interconnections of local area networks are c ompared by means of simulation: FODA/IBEA and CFRA. A unique simulation tool was used, a meshed network of VSATs under the control of a master station was considered and similar networking conditions were applied to both access schemes. The generated traffic had two components having different level of burstiness: bulk traffic a nd interactive traffic. The performance e valuated is the delay for each traffic component. We show that CFRA is best when connecting clusters of only a few stations and even individual ones exchanging light traffic. FODA/IBEA, on the other hand, is better suited to interconnect networks, o r within n etworks with many ho sts, where heavy traffic is more likely.

Response-time evaluation of transaction-oriented applications in VSAT networks

The authors present modeling of an integrated terrestrial-satellite network using very small aperture terminals (VSATs), for transaction-oriented computer applications. They address the analytical and simulation modeling techniques used to study the network performance. More specifically, these models are used to obtain network response times for an integrated terrestrial-VSAT network for inquiry-response applications under various load conditions at the cluster controller units. The major result obtained through this analytical and simulation modeling suggests that communications satellite channels can be used efficiently for the interactive inquiry-response traffic at an acceptable response time, provided that the system parameters including the link transmission rates are chosen appropriately. >

Méthode de calcul rapide de convolution entre deux séquences dont l’une est binaire

RésuméCet article présente une méthode de calcul rapide de produits de convolution apériodique entre deux séquences de valeurs numériques dans le cas où l’une des séquences est composée d’éléments binaires de valeurs +1 et -1. La méthode utilise une décomposition de la séquence non binaire en segments élémentaires et une combinaison des produits polynomiaux issus de cette décomposition. Dans ces conditions les seules opérations élémentaires sont des additions et soustractions, et la méthode présentée réduit le nombre de ces opérations par un facteur 4 à 10 par rapport au calcul direct, pour des longueurs de séquences comprises entre 100 et 10000 éléments.AbstractThis article presents a method for the fast calculation of the convolution between two numerical sequences when one of the sequence is made up of binary elements with values +1 and -1. The method is based on the decomposition of the non binary sequence into segments and the combination of the polynomial products resulting from this decomposition. Under these conditions, the only operations needed are additions and substructions. Compared to the direct calculation, this method involves a reduced number of such operations and results in the order of 4 to 10-fold reductions in calculation load for sequence lengths ranging from 100 to 1 000.

Performance modelling of a cell multiplexer for bursty ATM traffic

Abstract A cell multiplexer handling bursty asynchronous transfer mode (ATM) traffic is analysed by simulation to evaluate the relationship between the cell delay and the input traffic parameters. The traffic on an input line of the multiplexer is characterized by three parameters: the average burst length (L a) expressed in terms of the number of cells; the peak bit rate (R p) in bits−1; and the average inter-arrival time between two bursts (IATa) in seconds. The performance measures are the average and the 99% values of the queueing delay of a cell. The cell multiplexer is assumed to have an infinite buffer capacity, which means there are no cell losses due to buffer overflow. Besides the particular traffic configuration in which the inputs have the same traffic type (identical inputs or homogeneous traffic configuration), the study addresses some other traffic configurations in which the inputs do not have the same traffic type (non-identical inputs or inhomogeneous traffic configuration).