Papers by Luciano Lenzini
European Transactions on Telecommunications, Jul 1, 1991
This paper reports on an extended simulation analysis of the asynchronous part of the DQDB MAC pr... more This paper reports on an extended simulation analysis of the asynchronous part of the DQDB MAC protocol. The analysis is divided into three parts. The first and second part deal with one priority level, while in the third part we analyze DQDB behavior with multiple priority level. In the first part we study DQDB in underload conditfons i.e.. when the offered load is lower than the medium capacity. Our results show that in underload, the access delay is not always as low as expected. In the second part we study DQDB in overload conditions, i.e., when the offered load is higher than the medium capacity. Our results show that DQDB without the Bandwidth Balancing mechanism (BWB) h unfair and that the unfairness is dependent on the medium capacity and the bus length. When the BWB is enabled, DQDB fairness and performance, in the steady state, improve significantly. However, DQDB takes some time (depending on the BWB-MOD value) to achieve the steady state during which the node quality of service is degraded. In the third part we show that the DQDB priority mechanism is not always effective.
Performance Evaluation, Oct 1, 1996
Analysis of communication systems with timed token protocols using the power-series algorithm. Pe... more Analysis of communication systems with timed token protocols using the power-series algorithm. Performance Evaluation, 27&28, 391-409. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.-Users may download and print one copy of any publication from the public portal for the purpose of private study or research-You may not further distribute the material or use it for any profit-making activity or commercial gain-You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright, please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Computer Networks and Isdn Systems, Mar 1, 1992
ABSTRACT
Abstract In this paper we investigate link scheduling for Wireless Mesh Networks (WMNs) carrying ... more Abstract In this paper we investigate link scheduling for Wireless Mesh Networks (WMNs) carrying real-time (ie, delay-constrained) traffic. We show that the problem of computing a conflict-free link schedule with end-to-end delay constraints can be formulated as a mixed-...
Performance Evaluation, Mar 1, 1997
The MetaRing is a Medium Access Control (MAC) protocol for high- speed LANs and MANs. The MetaRin... more The MetaRing is a Medium Access Control (MAC) protocol for high- speed LANs and MANs. The MetaRing MAC protocol offers its users synchronous, and asynchronous types of services and can operate under two basic access control modes: buffer insertion for variable size packets, and slotted for fixed length packets (i.e., cells). The latter mode of operation is considered in this
Lecture Notes in Computer Science, 1996
Springer eBooks, Jan 15, 2009
The IEEE 802.16e standard specifies a connection-oriented centralized Medium Access Control (MAC)... more The IEEE 802.16e standard specifies a connection-oriented centralized Medium Access Control (MAC) protocol, based on Time Division Multiple Access (TDMA), which adds mobility support defined by the IEEE 802.16 standard for fixed broadband wireless access. To this end, Orthogonal Frequency Division Multiple Access (OFDMA) is specified as the air interface. In OFDMA, the MAC frame extends over two dimensions: time, in units of OFDMA symbols, and frequency, in units of logical sub-channels. The Base Station (BS) is responsible for allocating data into the frames so as to meet the Quality of Service (QoS) guarantees of the Mobile Stations’ (MSs) admitted connections. This is done on a frame-by-frame basis by defining the content of map messages, which advertise the position and shape of data regions reserved for transmission to/from MSs. We refer to the process of defining the content of map messages as frame allocation. Through a detailed analysis of the standard, we show that the latter is an overly complex task. We then propose a modular framework to solve the frame allocation problem, which decouples the constraints of data region allocation into the MAC frame, i.e. the definition of the position and shape of the data regions according to a set of scheduled grants, from the QoS requirements of connections. Allocation is carried out by means of the Sample Data Region Allocation algorithm (SDRA), which also supports Hybrid Automatic Repeat Request (H-ARQ), an optional feature of IEEE 802.16e. Finally, we evaluate the effectiveness of SDRA by means of Monte Carlo analysis in several scenarios, involving mixed Voice over IP (VoIP) and Best Effort (BE) MSs with varied modulations, with different sub-carrier permutations and frequency re-use plans.
Computer Communications, 1993
This paper reports oh pn extended simulation analysis ofthe Cyclic Reservation Multiple Access (C... more This paper reports oh pn extended simulation analysis ofthe Cyclic Reservation Multiple Access (CRMA) Media Access Control (MAC) protocol. The analysis is divided into two parts. In the first part we study CRMA in underloadconditions, i.e. when the offered load is lower than the medium capacity. In the second part we study CRMA in overload conditions, i.e. when the offered load is higher than the medium capacity. Our results show that in underload conditions the behaviour of CRMA depends on load distribution and node position, but it is quite predictable and basically fair. In overload conditions the node buffer may be a critical parameter and the network becomes fair only ifthe buffer size is greater than a threshold. The value of this threshold depends on the workload and on network parameters. Finally, we present a case study to show that CRMA is suitable to service integration.
Computer Networks, Aug 1, 2013
We investigate the problem of joint routing and link scheduling in Time-Division Multiple Access ... more We investigate the problem of joint routing and link scheduling in Time-Division Multiple Access (TDMA) Wireless Mesh Networks (WMNs) carrying real-time traffic. We propose a framework that always computes a feasible solution (i.e. a set of paths and link activations) if there exists one, by optimally solving a mixed integer-non linear problem. Such solution can be computed in minutes or tens thereof for e.g. grids of up to 4x4 nodes. We also propose heuristics based on Lagrangian decomposition to compute suboptimal solutions considerably faster and/or for larger WMNs, up to about 50 nodes. We show that the heuristic solutions are near-optimal, and we exploit them to gain insight on the schedulability in WMN, i.e. to investigate the optimal placement of one or more gateways from a delay bound perspective, and to investigate how the schedulability is affected by the transmission range.
arXiv (Cornell University), Nov 25, 2022
The primary task of a quantum repeater network is to deliver entanglement among end nodes. Most o... more The primary task of a quantum repeater network is to deliver entanglement among end nodes. Most of existing entanglement distribution protocols do not consider purification, which is thus delegated to an upper layer. This is a major drawback since, once an end-to-end entangled connection (or a portion thereof) is established it cannot be purified if its fidelity (F) does not fall within an interval bounded by Fmin (greater than 0.5) and Fmax (less than 1). In this paper, we propose the Ranked Entanglement Distribution Protocol (REDiP), a connection-oriented protocol that overcomes the above drawback. This result was achieved by including in our protocol two mechanisms for carrying out jointly purification and entanglement swapping. We use simulations to investigate the impact of these mechanisms on the performance of a repeater network, in terms of throughput and fidelity. Moreover, we show how REDiP can easily be configured to implement custom entanglement swapping and purification strategies, including (but not restricted to) those adopted in two recent works.
IEEE transactions on quantum engineering, 2022
In a paper published in 2009, Brun et al. proved that in the presence of a D-CTC one can map K di... more In a paper published in 2009, Brun et al. proved that in the presence of a D-CTC one can map K distinct non-orthogonal states (hereafter input set) to the standard orthonormal basis of a Kdimensional state space. To implement this result, the authors propose a quantum circuit which includes, among SWAP gates, a fixed set of controlled operators (boxes) and an algorithm for determining the unitary transformations carried out by such boxes. To our knowledge, what is still missing to complete the picture is an analysis evaluating the performance of the above circuit from an engineering perspective. The objective of this paper is therefore to address this gap throughout an in-depth simulation analysis which exploits the approach proposed by Brun et al. in 2017. This approach relies on multiple copies of an input state, multiple iterations of the circuit until a fixed point is (almost) reached. The performance analysis led us to a number of findings. First, the number of iterations is significantly high even if the number of states to be discriminated against is small, such as 2 or 3. Second, we envision that such a number may be shortened as there is plenty of room to improve the unitary trasformation acting in the aforementioned controlled boxes. Third, we also revealed a relationship between the number of iterations required to get close to the fixed point and the Chernoff limit of the input set used: the higher the Chernoff bound the smaller the number of iterations. A comparison, although partial, with another quantum circuit discriminating the non-orthogonal states, proposed by Nareddula et al. in 2018, is carried out and differences are highlighted. INDEX TERMS Classical simulation of quantum systems, Benchmarking and performance characterization.
Computer Communications, Dec 1, 1995
This paper analyses bandwidth allocation schemes for managing real-time applications (Variable Bi... more This paper analyses bandwidth allocation schemes for managing real-time applications (Variable Bit Rate video and voice) in a CRMA network. A methodology to compute the Quality of Service (QoS) experienced by variable bit rate (VBR) video and voice sources is proposed. As VBR video applications only tolerate extremely low packet loss rates (< lo-*), we need a computational approach to estimate very low tail probabilities. Studying the QoS with a simulation technique is not feasible, because computational costs make it almost impossible to estimate tail distribution probabilities lower than 1O-2-1O-3. Therefore, to achieve this target, we propose a model which represents a CRMA network's worst case behaviour (i.e. a scenario with maximum network congestion), and which can be solved analytically. By solving this model for different bandwidth allocation schemes, we can obtain the corresponding bounds on the QoS experienced by VBR video users. Finally, for those bandwidth allocation schemes which provide an acceptable QoS for VBR video traffic, we also estimate (via a trace-driven simulation) the QoS achieved by voice users.
Lecture Notes in Computer Science, 2003
In a DiffServ architecture, packets with the same marking are treated as an aggregate at core rou... more In a DiffServ architecture, packets with the same marking are treated as an aggregate at core routers, independently of the flow they belong to. Nevertheless, for the purpose of QoS provisioning, derivation of upper bounds on the delay of individual flows is of great importance. In this paper, we consider a case study network, composed by a tandem of rate-latency servers that is traversed by a tagged flow. At each different node, the tagged flow is multiplexed into a FIFO buffer with a different interfering flow. The tagged flow and the interfering flows are all leaky-bucket constrained at the network entry. We introduce a novel methodology based on well-known results on FIFO multiplexing from Network Calculus, by means of which we derive an end-to-end delay bound for tagged flow traffic. The delay bound assesses the contribution to the delay due to the interference of other flows precisely, and to the best of our knowledge, it is better than any other applicable result available from the literature. Furthermore, we utilize the delay bound formula to quantify the level of overprovisioning required in order to achieve delay bounds comparable to those of a flow-aware architecture.
IEEE Journal on Selected Areas in Communications, Jun 1, 1998
Networking science, Nov 15, 2013
Research to date has analyzed the Internet AS-level topology at a worldwide level of detail. Ever... more Research to date has analyzed the Internet AS-level topology at a worldwide level of detail. Every inference found for an AS is extrapolated from the global set of AS paths gathered from public monitors, independently of the geographic location of the ASes. This approach is useful when the Internet is analyzed at a very coarse level. However, it may be misleading if the analysis is more focused on a specific geographical region. The risk is that the particular characteristics that the Internet has in that region may be lost. An AS connection that has been identified in a global analysis may hide multiple connections located in different geographic regions, each with its own characteristics. Moreover, a couple of ASes may establish different economic relationships in each geographic region where they are connected. In this paper we propose an innovative technique to geolocate the AS connections retrieved from BGP raw data, in order to highlight the Internet characteristics both at a continental and national level. The analyses that we performed revealed some regional characteristics, in terms of graph properties and inter-AS economic relationships, that should be taken into account in a future analysis of the Internet.
Microprocessors and Microsystems, Mar 1, 2001
In this paper we study performance tradeoffs of fairness algorithms for ring networks with spatia... more In this paper we study performance tradeoffs of fairness algorithms for ring networks with spatial bandwidth reuse, by using two measures: (i) the fairness cycle size as a complexity measure, and (ii) the Max-Min optimal fairness criterion as a throughput measure. The fairness cycle size is determined by the number of communication links involved in every instance of the fairness algorithm (several identical fairness algorithms can be executed concurrently on the same ring). The study compares three fairness algorithms with different cycle sizes: the Globalcycle algorithm (implemented in the Serial Storage Architecture-SSA) in which the cycle size is equal to the number N of links in the ring; the Variable-cycle algorithm in which its cycle size changes between 1 and N links; the Onecycle, where there is a fairness cycle on every link. It is shown how varying the cycle size affects the network performance with respect to the Max-Min optimal fairness criterion. The results show that for non-homogeneous traffic patterns, decreasing the fairness cycle size, while increasing the complexity, can significantly improve the performance with respect to the Max-Min optimal fairness criterion.
Computer Networks, Jul 1, 2002
ABSTRACT Integrated services networks face the challenge of managing several traffic classes at t... more ABSTRACT Integrated services networks face the challenge of managing several traffic classes at the same time. Service disciplines devised for integrated services networks therefore need to be flexible, i.e. able to provide different types of service, in order to accommodate different traffic classes efficiently. In this paper we focus on the integration of rate-guaranteed and best-effort traffic, and we argue that service disciplines based on the generalized processor sharing paradigm, which schedule flows according to their weights, lack the flexibility needed to efficiently manage both classes at the same time. We propose that a different service paradigm, the dual-class paradigm, which considers the two traffic classes at the same time, be used as a reference to devise flexible and efficient service disciplines for integrated services networks. We then present and analyze an innovative packet timed token service discipline, which approximates a dual-class paradigm at a low computational complexity. PTTSD properties are described analytically: we derive minimum rate guarantees for rate-guaranteed traffic and propose rules to select the system parameters in order to achieve pre-specified guarantees. Finally, we show some of the PTTSD properties by means of simulation.
ABSTRACT Portolan is a crowdsourcing system, aimed at monitoring and measuring large-scale networ... more ABSTRACT Portolan is a crowdsourcing system, aimed at monitoring and measuring large-scale networks, that uses smartphones as mobile observation elements. Currently, Portolan is able to collect information about both wired and wireless networks, in particular it is used to obtain the graph of the Internet with unprecedented resolution and to associate performance indexes (received signal strength, maximum throughput) of cellular networks to geographic locations.
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Papers by Luciano Lenzini