Impact of the access network topology on the handoff performance

Micromobility protocols such as Cellular IP, Hawaii and Hierarchical Mobile IP are developed to solve problems of high handoff latency and control overhead, which occur when Mobile IP is used in combination with frequent handoffs. Up to now, tree access network topologies are considered to evaluate the protocol performance. However, for reasons of robustness against link failures and load balancing, extra uplinks and mesh links in the topology are desired. This article makes a classification of several topology types and gives a model that points out to which extent the topology influences the protocol performance in terms of handoff latency and handoff packet loss. Simulations confirm the results calculated by the model. Performance metrics such as load balancing, end-to-end delay and robustness against link failures are also evaluated. The study points to several shortcomings of the existing micromobility protocols for different topology types. Several aspects of the studied handoff schemes, their advantages and drawbacks are identified. L. Peters is a Research Assistant of the Fund for Scientific Research – Flanders (F.W.O.-V., Belgium) Liesbeth Peters was born in Temse, Belgium, in 1978. She received her Master of Science degree in Electrotechnical Engineering from Ghent University, Gent, Belgium in 2001. Since August 2001, she has been working as a doctoral researcher with the Department of Information Technology (INTEC) of the Faculty of Applied Sciences, Ghent University, where she joined the Broadband Communications Networks Group. Since October 2002, she works there as a research assistant of the Fund for Scientific Research—Flanders (F.W.O.-V., Belgium). Her current research interests are in broadband wireless communication and the support of IP mobility in wired cum wireless networks. Ingrid Moerman was born in Gent, Belgium, in 1965. She received the degree in Electro-technical Engineering and the Ph.D degree from the Ghent University, Gent, Belgium in 1987 and 1992, respectively. Since 1987, she has been with the Interuniversity Micro-Electronics Centre (IMEC) at the Department of Information Technology (INTEC) of the Ghent University, where she conducted research in the field of optoelectronics. In 1997, she became a permanent member of the Research Staff at IMEC. Since 2000 she is part-time professor at the Ghent University. Since 2001 she has switched her research domain to broadband communication networks. She is currently involved in the research and education on broadband mobile & wireless communication networks and on multimedia over IP. Her main research interests related to mobile & wireless communication networks are: adaptive QoS routing in wireless ad hoc networks, personal networks, body area networks, wireless access to vehicles (high bandwidth & driving speed), protocol boosting on wireless links, design of fixed access/metro part, traffic engineering and QoS support in the wireless access network. Ingrid Moerman is author or co-author of more than 300 publications in the field of optoelectronics and communication networks. Bart Dhoedt received a degree in Engineering from the Ghent University in 1990. In September 1990, he joined the Department of Information Technology of the Faculty of Applied Sciences, University of Ghent. His research, addressing the use of micro-optics to realize parallel free space optical interconnects, resulted in a PhD degree in 1995. After a 2 year post-doc in opto-electronics, he became professor at the Faculty of Applied Sciences, Department of Information Technology. Since then, he is responsible for several courses on algorithms, programming and software development. His research interests are software engineering and mobile & wireless communications. Bart Dhoedt is author or co-author of more than 100 papers published in international journals or in the proceedings of international conferences. His current research addresses software technologies for communication networks, peer-to-peer networks, mobile networks and active networks. Piet Demeester finished his PhD thesis at the Department of Information Technology (INTEC) at the Ghent University in 1988. At the same department he became group leader of the activities on Metal Organic Vapour Phase Epitaxial growth for optoelectronic components. In 1992 he started a new research group on Broadband Communication Networks. The research in this field resulted in already more than 300 publications. In this research domain he was and is a member of several programme committees of international conferences, such as: ICCCN, the International Conference on Telecommunication Systems, OFC, ICC, and ECOC. He was Chairman of DRCN’98. In 2001 he was chairman of the Technical Programme Committee ECOC’01. He was Guest Editor of three special issues of the IEEE Communications Magazine. He is also a member of the Editorial Board of the Journals “Optical Networks Magazine” and “Photonic Network Communications”. He was a member of several national and international PhD thesis commissions. Piet Demeester is a member of IEEE (Senior Member), ACM and KVIV. His current research interests include: multilayer networks, Quality of Service (QoS) in IP-networks, mobile networks, access networks, grid computing, distributed software, network and service management and applications (supported by FWO-Vlaanderen, the BOF of the Ghent University, the IWT and the European Commission). Piet Demeester is currently full-time professor at the Ghent University, where he is teaching courses in Communication Networks. He has also been teaching in different international courses.     

X-masking during logic BIST and its impact on defect coverage

We present a technique for making a circuit ready for logic built-in self test by masking unknown values at its outputs. In order to keep the silicon area cost low, some known bits in output responses are also allowed to be masked. These bits are selected based on a stuck-at n-detection based metric, such that the impact of masking on the defect coverage is minimal. An analysis based on a probabilistic model for resistive short defects indicates that the coverage loss for unmodeled defects is negligible for relatively low values of n.     

On properties of multicast routing trees

In the last several years we witnessed the proliferation of multimedia applications on the Internet. One of the unavoidable techniques to support this type of communication is multicasting. However, even a decade after its initial proposal, multicast is still not widely deployed. One of the reasons is the lack of a solid business model. If the gain and the cost of multicast could be predicted, network operators might be encouraged to deploy multicast on a larger scale. In this paper we propose analytical expressions that could be used to estimate the gain of network‐layer multicast. We show that the theoretical model matches extensive simulation and Internet measurement results remarkably well. Furthermore, we examine the reliability of traceroute data and of traceroutes‐based conclusions. We investigate the node degree distributions in the Internet maps obtained from CAIDA and RIPE and we show the divergency of our results with those obtained by other researchers. We further focus on the analysis of multicast trees based on traceroute data. Only few results have been available on the node degree distribution of multicast routing trees which provided contradictory conclusions. Our results seem to indicate that the node degrees follow power laws only for a large number of multicast users. Copyright © 2005 John Wiley & Sons, Ltd.     

Block position dithering in DCT-coded sequences

An attempt has been made to hide the false edges perceived at block borders in DCT-coded image sequences. The standard H.261 codec is extended by simple pre- and postprocessing: shifting the input image over small pseudo-random horizontal and vertical distances and shifting back the output image by the same amount. A subjective comparison by a panel of 20 observers has established a quality improvement for interframe coding, if both the current image and the previous image are subjected to the same shift. Masking the block borders by adding a time-invariant noise image to the output is found to be a desirable option.     

The influence of lactoperoxidase,heat and low pH on survival of acid-adapted and non-adapted Escherichia coli O157:H7 in goat milk

In hot climates where quality of milk is difficult to control, a lactoperoxidase (LP) system can be applied in combination with conventional preservation treatments at sub-lethal levels to inhibit pathogenic microbes. This study investigated the effect of combined heat treatments (55 °C, 60 °C and 72 °C) and milk acidification (pH 5.0) on survival of acid-adapted and non-adapted Escherichia coli O157:H7 strains UP10 and 1062 in activated LP goat milk. Heat treatment at 72 °C eliminated E. coli O157:H7. Acid-adapted strains UP10 and 1062 cells showed resistance to combined LP and heat at 60 °C in fresh milk. The inhibition of acid-adapted and non-adapted E. coli O157:H7 in milk following combined LP-activation, heat (60 °C) and milk acidification (pH 5.0) suggests that these treatments can be applied to reduce E. coli O157:H7 cells in milk when they occur at low numbers (<5 log₁₀ cfu mL^?1) but does not eliminate E. coli O157:H7 to produce a safe product.     

Extraction and fractionation of wheat flour proteins

Extraction of wheat flour with 1.5% sodium dodecyl sulphate (SDS) solution dissolved 65–67% of the total flour nitrogen. The SDS-insoluble proteinaceous material was separated into glycoproteins-I, II and III by ultracentrifugation. Part of the SDS-soluble proteinaceous material was precipitated by addition of ethanol and separated into glycoproteins-IV, glutenins and globulins. The rest of the dissolved proteinaceous material was separated into glycoproteins-V, gliadins, glycoproteins-VI, and albumins by (NH₄)₂SO₄-precipitation and gel filtration chromatography.     

A New Technique for the Suppression of the MECG

After a review of the different techniques in use up to now for the detection of an interference-free abdominal fetal electrocardiogram (FECG), with the limitations of these techniques indicated, a new technique is described which does not suffer from these limitations. This technique is based on an optimization procedure applied to the multiplication coefficients of six independent abdominal signals which are added together. The theoretical background of this method is given, as well as the required operational conditions and electrode positions, leading to an FECG reading guaranteed free of maternal electrocardiogram (MECG).     

The use of thermal analysis techniques for the validation of phase transformation models

In the study of the phase transformation of steel several methods can be used to obtain information about the behaviour of steel during heating and cooling. In this research several conventional methods, e.g. dilatometry, were studied together with an in-situ thermal analysis method (ISTA). This method, which can be applied to any cooling curve, enables us to draw conclusions as to the transformation behaviour of the steel. Using a continuous annealing simulator (Casim) a range of cooling rates can be investigated with the resulting mechanical properties. It will be demonstrated that ISTA can be performed on the results of a variety of experimental techniques and therefore under very different experimental conditions. It is possible to investigate transformation behaviour and mechanical properties on a single test piece. Using the pressurized air cooling of the Casim proves to be a good compromise between the possibilities of determining the mechanical properties and flexibility in cooling conditions of the specimens.