Papers by Luciano Lenzini
OSILAB: an OSI prototyping laboratory
ABSTRACT
Experimentation of the STELLA /Satellite Transmission Experiment Linking Laboratories/ project using the SIRIO satellite
AlFr, Oct 1, 1980
ABSTRACT
Springer eBooks, 2009
Many technological standards for Wireless Mesh Networks include the possibility to use several no... more Many technological standards for Wireless Mesh Networks include the possibility to use several nonoverlapping channels for data transmission. This represents an opportunity that can be exploited by equipping the terminals with multiple network interfaces. This opens up an interesting challenge, namely, how to simultaneously use different frequencies, so as to limit collisions and therefore activate multiple simultaneous transmissions in the same geographic area. At the same time, this poses new issues; for example, network connectivity is reduced, because nodes that do not interfere are also unable to communicate with each other. Thus, more complex interface management techniques are required. Moreover, a paradigm shift from the classic routing schemes is needed. Usual approaches are not always satisfactory because they often use shortest-path heuristic and tend to concentrate transmissions to certain nodes. To efficiently exploit the presence of multiple channels instead, a proper routing algorithm should avoid congested links and possibly make use of an estimation of the actual network traffic. Therefore, cross-layer information exchange can be useful for an efficient functioning of the routing protocols. In this chapter, we will analyze all these issues and propose and identify possible solutions.
Efficient Two-Dimensional Data Allocation in IEEE 802.16 OFDMA
IEEE ACM Transactions on Networking, Oct 1, 2014
ABSTRACT The IEEE 802.16 standard uses Orthogonal Frequency Division Multiple Access (OFDMA) for ... more ABSTRACT The IEEE 802.16 standard uses Orthogonal Frequency Division Multiple Access (OFDMA) for mobility support. Therefore, the medium access control frame extends in two dimensions, i.e., time and frequency. At the beginning of each frame, i.e., every 5 ms, the base station is responsible both for scheduling packets, based on the negotiated quality of service requirements, and for allocating them into the frame, according to the restrictions imposed by 802.16 OFDMA. To break down the complexity, a split approach has been proposed in the literature, where the two tasks are solved in separate and subsequent stages. In this paper we focus on the allocation task alone, which is addressed in its full complexity, i.e., by considering that data within the frame must be allocated as bursts with rectangular shape, each consisting of a set of indivisible sub-bursts, and that a variable portion of the frame is reserved for in-band signaling. After proving that the resulting allocation problem is NP-hard, we develop an efficient heuristic algorithm, called Recursive Tiles and Stripes (RTS), to solve it. RTS, in addition to handle a more general problem, is shown to perform better than state-of-the-art solutions via numerical analysis with realistic system parametrization.
This paper has three parts: first, it presents an up to date characterization of the BGP visibili... more This paper has three parts: first, it presents an up to date characterization of the BGP visibility obtained from the three largest public sources: routeviews, RIPE, and PCH. Next, it proposes a criterion for a good monitoring infrastructure: one in which no AS is more than one provider-customer hop away from a monitor. It derives for the pubicly available dataset, the minimal set of ASes that meet this coverage goal. It discusses the properties of ASes that should be monitored. The question of BGP monitor placement is important, hard to study, and not often examined. This paper sheds important light on this question. Weaknesses: The paper's results are somewhat misstated, and the ultimate output is an approximation of unknown quality. The first part of the paper is helpful but doesn't really contain anything new. The discussion about the differences between routeviews/RIPE and PCH is helpful for folks who are using that data. As regards Section 3, the results are presented in a strange way. The authors are solving a set-cover problem. Clearly there is no efficient algorithm to solve this problem (unless P = NP). So it is strange for the authors to discuss an "algorithm" for this problem. Rather, what they have done is apply brute-force search to one specific dataset and found that they can obtain the optimal solution for that dataset. In particular, the authors provide no guarantees that their algorithm will run in acceptable time on any other dataset. So the claims (eg in the abstract) that they have "designed a novel algorithm for selecting the optimal number of ASes" should be removed. Further, the results are optimal only with respect to the constraint that no AS is more than one producer-consumer hop away from a monitor. This provides no guarantees on the fraction of links that will be observed using this monitor set. It is simply a heuristic that may or may not work well. The authors have not considered the effects of missing p2c links in their dataset. It would seem that the optimal set remains a set cover when missing links are added (good) but is no longer optimal (bad). The authors should acknowledge this fact and discuss the limitations due to missing p2c links.
Methods for the Analysis of Network-wide Models: Polling Models
Springer eBooks, 1997
Polling models are used throughout this book to represent the behavior of MAC protocols with a cy... more Polling models are used throughout this book to represent the behavior of MAC protocols with a cyclic behavior, such as Token Ring (see Chapter 1) and FDDI (see Chapter 5). To guarantee fair access to all the network stations and to limit access delay, MAC protocols with a cyclic behavior are based on limited service disciplines. For this reason hereafter only polling systems with an l-limited (gated or exhaustive) service discipline are taken into consideration. For a complete overview of the analysis of polling systems with gated or exhaustive service disciplines see Takagi ([145], [146], [147], [151]).
Ieee 802.16 OFDMAにおける効率的な2次元のデータ割当
International Conference on Computer Communications, 2010
Scheduling algorithm for providing real-time QoS guarantees in 802.11e WLANs
Broadband Communications, Networks and Systems, 2005
In this paper we propose a scheduling algorithm for supporting quality of service (QoS) in an IEE... more In this paper we propose a scheduling algorithm for supporting quality of service (QoS) in an IEEE 802.11e network using the HCF controlled channel access (HCCA) function. The algorithm consists of an offline procedure that generates a service schedule over a base period, and an online procedure that applies the latter to actually schedule transmission opportunities to HCCA flows
Game Based Self-Coexistence Schemes in Cognitive Radio Networks
Springer eBooks, 2011
... This analysis highlighted the fact that, in contrast to unlicensed bands, most licensed bands... more ... This analysis highlighted the fact that, in contrast to unlicensed bands, most licensed bands are ... The basic requirement of CRNs is the need to evolve over time which imposes a ... that devices are worried only about their own outcome instead of the overall network performance. ...
A model to evaluate the effects of the BWB mechanism in a DQDB network in underload conditions
This paper analyzes how the BWB mechanism influences the status of slots traveling on the bus (sl... more This paper analyzes how the BWB mechanism influences the status of slots traveling on the bus (slot-occupancy-pattern process) in a DQDB network. To capture the most important dependencies between consecutive slots at light-moderate load [CONTI91c] we have modeled the slot-occupancy-pattern process via a discrete-time first-order Markov process. In this paper we use a simplified DQDB network [CONTI91b] for which we
Springer eBooks, Nov 19, 2007
Lessons learned from the design, implementation, and management of a smartphone-based crowdsourcing system
ABSTRACT Ubiquitousness of smartphones, when combined with the power of crowdsourcing, enables ra... more ABSTRACT Ubiquitousness of smartphones, when combined with the power of crowdsourcing, enables radically novel application scenarios, where a massive amount of mobile users scattered over wide geographical regions cooperate towards a single goal. Nevertheless these new possibilities come at the cost of additional complexity, such as the presence of humans in the control loop, scarce resources of mobile devices, increased management costs due the large number of users. In this paper we report and discuss the lessons learned from the design, implementation and management of Portolan, a smartphone-based crowdsourcing system aimed at monitoring large-scale networks.
S-BITE: A Structure-Based Internet Topology gEnerator
Computer Networks, Feb 1, 2015
ABSTRACT The modeling and analysis of large-scale complex systems, such as the Internet, has rece... more ABSTRACT The modeling and analysis of large-scale complex systems, such as the Internet, has recently become a hot research topic. We propose a Structure-Based Internet Topology gEnerator (S-BITE) aimed at accurately reproducing the Internet at the Autonomous System (AS) level. The proposed generator exploits a technique that partitions the network topology into two distinct blocks: the Core, which captures the underlying community structure of the Internet, and the Periphery, representing the “tendrils” of the topology. The benefits of this innovative technique are twofold. First, it deals with the high heterogeneity of the Internet by highlighting a small yet well-structured core. This leads to a huge reduction in complexity and shows that the core of the large-scale Internet is not that large, and can further be broken down into a two-layer graph. Second, thanks to the simplifications introduced by the topology layering, it leads us to the definition of a new topology generator, first at the core level and then for the whole Internet.
A significant challenge for researchers analysing the Internet AS-level topology graph is how to ... more A significant challenge for researchers analysing the Internet AS-level topology graph is how to interpret the global organization of the graph as the coexistence of its structural blocks (communities) associated with more highly interconnected parts. While a huge number of papers have already been published on the issue of community detection, very little attention has so far been devoted to the discovery and interpretation of Internet communities at the various levels of abstractions. We believe that by discovering and interpreting a priori these unknown building blocks (i.e. communities), this will then pave the way for new types of analysis which are crucial in understanding of the structural and functional properties of the Internet at least at the AS level of abstraction. We thus propose a novel type of analysis of the Internet AS-level topology graph by exploiting the k-clique community definition. First, we show that detected communities can be described by a tree representation. Then we show the presence of two classes of k -clique communities: those that are strictly affected by the nesting process which is embedded in the k -clique community definition, and, on the other hand, those that appear as branches in the tree. We conclude our analysis by highlighting the properties that characterize k -clique communities with different k values by exploiting both geographical data and information related to IXPs.
Portolan is a crowdsourcing-based system aimed at building an annotated graph of the Internet: th... more Portolan is a crowdsourcing-based system aimed at building an annotated graph of the Internet: the smartphones of participating volunteers are used as mobile monitors to collect measures about the network that surrounds them, then results are conveyed on a central server where they are aggregated. Thus, differently from all the other Internet monitoring systems, which are based on fixed infrastructure, Portolan rely on a multitude of mobile sensing nodes. While this paves the way to the opportunity of having detailed and geo-referenced measures, the design of the systems has to take into account additional difficulties such as scalability, coordination and smartphones' reachability. Besides describing the Portolan's architecture, this paper also shows some preliminary results that confirm the validity of the proposed approach.
IEEE ACM Transactions on Networking, Aug 1, 2015
In the last decade many studies have used the Internet AS-level topology to perform several analy... more In the last decade many studies have used the Internet AS-level topology to perform several analyses, from discovering its graph properties to assessing its impact on the effectiveness of worm-containment strategies. Yet, the BGP data used to reveal the topologies are far from complete. Our contribution is three-fold. Firstly, we analyse BGP data currently gathered by the most famous route collector projects, highlighting and explaining the causes of their incompleteness. We found that large areas of the Internet are not properly captured due to the geographical location of route collector feeders and due to BGP filters, such as export policies and decision processes. Secondly, we propose a methodology based on a new metric, named p2cdistance, which is able to i) identify the minimum number of ASes required to obtain an Internet AS-level topology that is closer to reality, and ii) identify a ranking list of these ASes to show that it is possible to obtain non negligible coverage improvements with a limited number of appropriately chosen feeding ASes. Thirdly, we characterize the ASes that were found to be part of the solution of the above covering problems. We found that the route collectors are rarely connected to these ASes, thus highlighting that much effort is needed to devise a route collector infrastructure that ideally would be able to capture a complete view of the Internet.
A Fully Distributed Game Theoretic Approach to Guarantee Self-Coexistence among WRANs
Although the proliferation of wireless applications operating in unlicensed spectrum bands has re... more Although the proliferation of wireless applications operating in unlicensed spectrum bands has resulted in overcrowding, recent analysis has shown that license bands are still underutilized. Cognitive Radio is seen as the key enabling technology to address the spectrum shortage problem, opportunistically using the spectrum allocated for TV bands. In this paper, we present a novel game theoretic framework that uses
Ad hoc networks, Jun 1, 2009
Wireless mesh networks are an attractive technology for providing broadband connectivity to mobil... more Wireless mesh networks are an attractive technology for providing broadband connectivity to mobile clients who are just on the edge of wired networks, and also for building selforganized networks in places where wired infrastructures are not available or not deemed to be worth deploying. This paper investigates the joint link scheduling and routing issues involved in the delivery of a given backlog from any node of a wireless mesh network towards a specific node (which acts as a gateway), within a given deadline. Scheduling and routing are assumed to be aware of the physical interference among nodes, which is modeled in the paper by means of a signal-to-interference ratio. Firstly, we present a theoretical model which allows us to formulate the task of deriving joint routing and scheduling as an integer linear programming problem. Secondly, since the problem cannot be dealt with using exact methods, we propose and use a technique based on genetic algorithms. To the best of our knowledge, these algorithms have never been used before for working out these kinds of optimization problems in a wireless mesh environment. We show that our technique is suitable for this purpose as it provides a good trade-off between fast computation and the overall goodness of the solution found. Our experience has in fact shown that genetic algorithms would seem to be quite promising for solving more complex models than the one dealt with in this paper, such as those including multiple flows and multi-radio multi-channels.
FDDI Models
Springer eBooks, 1997
Methods for the Analysis of Node-in-isolation Models
Telecommunication networks and computer systems, 1997
As pointed out in Chapter 2, a LAN or a MAN station is frequently analyzed in isolation and hence... more As pointed out in Chapter 2, a LAN or a MAN station is frequently analyzed in isolation and hence each station is modeled as an M/G/l queueing system with or without server vacation (node-in-isolation models). This chapter presents methods extensively used in the literature to analyze the performance figures of these systems. Specifically, it focuses on the study of the stochastic process {N(t),t≥0} which represents the number of packets queued in the system (e.g., a station of a MAN, a packet-switching node, etc.) at a random point in time.
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Papers by Luciano Lenzini