Pablo Pavon-Marino

A Geometric Distribution Reader Anti-Collision Protocol for RFID Dense Reader Environments

Dense passive radio frequency identification (RFID) systems are particularly susceptible to reader collision problems, categorized by reader-to-tag and reader-to-reader collisions. Both may degrade the system performance decreasing the number of identified tags per time unit. Although many proposals have been suggested to avoid or handle these collisions, most of them are not compatible with current standards and regulations, require extra hardware and do not make an efficient use of the network resources. This paper proposes the Geometric Distribution Reader Anti-collision (GDRA), a new centralized scheduler that exploits the Sift geometric probability distribution function to minimize reader collision problems. GDRA provides higher throughput than the state-of-the-art proposals for dense reader environments and, unlike the majority of previous works, GDRA is compliant with the EPCglobal standard and ETSI EN 302 208 regulation, and can be implemented in real RFID systems without extra hardware.

Offline Impairment Aware RWA Algorithms for Cross-Layer Planning of Optical Networks

Transparent optical networks are the enabling infrastructure for converged multi-granular networks in the future Internet. The cross-layer planning of these networks considers physical impairments in the network layer design. This is complicated by the diversity of modulation formats, transmission rates, amplification and compensation equipments, or deployed fiber links. Thereby, the concept of quality of transmission (QoT) attempts to embrace the effects of the physical layer impairments, to introduce them in a multi-criterium optimization and planning process. This paper contributes in this field by the proposal and comparative evaluation of two novel offline impairment aware planning algorithms for transparent optical networks, which share a common QoT evaluation function. The first algorithm is based on an iterative global search driven by a set of binary integer linear programming formulations. Heuristic techniques are included to limit the binary programming complexity. The second algorithm performs different pre-orderings of the lightpath demand, followed by a sequential processing of the lightpath demands. The performance and the scalability of both approaches are investigated. Results reveal great scalability properties of the global search algorithm, and a performance similar to or better than the sequential schemes.

Performance evaluation of MAC transmission power control in wireless sensor networks

In this paper we provide a method to analytically compute the energy saving provided by the use of transmission power control (TPC) at the MAC layer in wireless sensor networks (WSN). We consider a classical TPC mechanism: data packets are transmitted with the minimum power required to achieve a given packet error probability, whereas the additional MAC control packets are transmitted with the nominal (maximum) power. This scheme has been chosen because it does not modify the network topology, since control packet transmission range does not change. This property also allows us to analytically compute the expected energy savings. Besides, this type of TPC can be implemented in the current sensor hardware, and it can be directly applied to several MAC protocols already proposed for WSN. The foundation of our analysis is the evaluation of L ratio, defined as the total energy consumed by the network using the original MAC protocol divided by the total energy consumed if the TPC mechanism is employed. In the L computation we emphasize the basic properties of sensor networks. Namely, the savings are calculated for a network that is active for a very long time, and where the number of sensors is supposed to be very large. The nodes position is assumed to be random - a normal bivariate distribution is assumed in the paper - and no node mobility is considered. In the analysis we stress the radio propagation and the distribution of the nodes in the network, which will ultimately determine the performance of the TPC. Under these conditions we compute the mean value of L. Finally, we have applied the method to evaluate the benefits of TPC for TDMA and CSMA with two representative protocols, L-MAC and S-MAC using their implementation reference parameters. The conclusion is that, while S-MAC does not achieve a significant improvement, L-MAC may reach energy savings up to 10-20%.

On the Myths of Optical Burst Switching

This paper discusses merits and drawbacks of the Optical Burst Switching (OBS) paradigm, which received so much attention by the academic research community. Since the topic is hot, and given the several flavors of OBS available in the literature, we first define what we mean by OBS. Then, we carefully design a reference scenario and a set of evaluation experiments that can be used to obtain quantitative answers to interesting questions in a repeatable way. Within this framework, we motivate our skepticism towards two frequent assertions about the OBS paradigm: its ability to (i) exploit the network bandwidth more efficiently than Optical Circuit Switching (OCS) alternatives, and (ii) to efficiently solve contentions without optical buffers.

Net2plan: an open source network planning tool for bridging the gap between academia and industry

The plethora of network planning results published in top-ranked journals is a good sign of the success of the network planning research field. Unfortunately, it is often difficult for network carriers and ISPs to reproduce these investigations on their networks. This is partially because of the absence of a software planning tool, meeting the requirements of industry and academia, which can make the adaptation and validation of planning algorithms less time consuming. We describe how a paradigm shift to an open source view of the network planning field emphasizes the power of distributed peer review and transparency to create high-quality software at an accelerated pace and lower cost. Then we present Net2Plan, an open source Java-based software tool. Built on top of a technology-agnostic network representation, it automates the elaboration of performance evaluation tests for userdefined or built-in network design algorithms, network recovery schemes, connection-admission-control systems, or dynamic provisioning algorithms for timevarying traffic. The Net2Plan philosophy enforces code reutilization as an open repository of network planning resources. In this article, a case study in a multilayer IP-over-WDM network is presented to illustrate the potential of Net2Plan. We cover standard CAPEX studies, and more advanced aspects such as a resilience analysis of the network under random independent failures and disaster scenarios, and an energy efficiency assessment of “green” schemes that switch off parts of the network during low load periods. All the planning algorithms in this article are publicly available on the Net2Plan website.

A wireless sensor networks MAC protocol for real-time applications

Wireless sensor networks (WSN) are designed for data gathering and processing, with particular requirements: low hardware complexity, low energy consumption, special traffic pattern support, scalability, and in some cases, real-time operation. In this paper we present the virtual TDMA for sensors (VTS) MAC protocol, which intends to support the previous features, focusing particularly on real-time operation. VTS adaptively creates a TDMA arrangement with a number of timeslots equal to the actual number of nodes in range. Thus, VTS achieves an optimal throughput performance compared to TDMA protocols with fixed size of frame. The frame is set up and maintained by a distributed procedure, which allows sensors to asynchronously join and leave the frame. In addition, duty cycle is increased or decreased in order to keep latency constant below a given deadline. Therefore, a major advantage of VTS is that it guarantees a bounded latency, which allows soft real-time applications.

Virtual topology design and flow routing in optical networks under multihour traffic demand

This article addresses the problem of finding a static virtual topology design and flow routing in transparent optical wavelength division multiplexing networks under a time-varying (multihour) traffic demand. Four variants of the problem are considered, using fixed or dynamically adaptable (meaning variable) flow routing, which can be splittable or unsplittable. Our main objective is to minimize the number of transceivers needed which make up for the main network cost. We formulate the problem variants as exact integer linear programs (ILPs) and mixed ILPs. For larger problem instances, we also propose a family of heuristics based on the concept of domination between traffic matrices. This concept provides the theoretical foundations for a set of techniques proposed to reduce the problem complexity. We present a lower bound to the network cost for the case in which the virtual topology could be dynamically reconfigured along time. This allows us to assess the limit on the maximum possible benefit that could be achieved by using optical reconfigurable equipment. Extensive tests have been conducted, using both synthetically generated and real-traced traffic demands. In the cases studied, results show that combining variable routing with splittable flows obtains a significant, although moderate, cost reduction. The maximum cost reduction achievable with reconfigurable virtual topologies was shown to be negligible compared to the static case in medium and high loads.

Dimensioning the Add/Drop Contention Factor of Directionless ROADMs

Reconfigurable Optical Add/Drop Multiplexers (ROADM) are the optical switching equipment of transparent optical networks. Directionless ROADMs permit the network carriers to change the direction of an added and/or dropped lightpath without the need of a technician on-site intervention in the lightpath end nodes. Colorless ROADMs provide the same versatility for changing the lightpath transmission wavelength. Cost-effective directionless ROADM architectures (colorless or colored) can be built if the maximum number of lightpaths that can be added/dropped using the same wavelength is limited. We name this limit as the node add/drop contention factor, and denote it as C. In this paper we investigate the network lightpath blocking performance as a function of this add/drop contention factor of the nodes. The scenarios considered are the static planning of a network (i) with unprotected traffic, (ii) with traffic 1+1 protected for single-link failures, and (iii) with traffic 1+1 protected for single-link or single-node failures. Since for these scenarios, the wavelength of an existing lightpath does not have to be dynamically reconfigured, the work in this paper applies to both colorless and colored nodes. An ILP model and an effective heuristic are presented to solve the so-called Add/Drop Contention Aware RWA (ADCA-RWA) planning of the network. Extensive results are reported. In all the cases, an add/drop factor C = 2 is sufficient to provide the same performance as contentionless nodes (C = ∞). Furthermore, in all the tests a factor C = 1 was also sufficient, or produced a minor lightpath blocking performance degradation (below 0.5% in the unprotected cases, and below 2.5% in the 1 + 1 protected cases).

(Non-)reconfigurable virtual topology design under multihour traffic in optical networks

This paper investigates offline virtual topology design in transparent optical networks under a multihour traffic demand. The main problem variant addressed here designs a reconfigurable virtual topology that evolves over time to more efficiently utilize network resources (the MH-VTD-R problem). The case of designing a static non-reconfigurable virtual topology that can accommodate the time-varying traffic (the MH-VTD-NR problem) is also considered. The objectives are to minimize: 1) the number of transceivers, which make up for the main network cost; and 2) the frequency of reconfiguration (for MH-VTD-R), which incurs additional overhead and potential service disruption. We formulate this multiobjective problem as an exact mixed integer linear program (MILP). Due to its high complexity, we propose a very efficient heuristic algorithm called Greedy Approach with Reconfiguration Flattening (GARF). GARF not only solves both (non-)reconfigurable problem variants, but it allows for tuning of the relative importance of the two objectives. Exhaustive experiments on real and synthetic traffic and comparison to previous proposals and bounds reveal the merits of GARF with respect to both solution quality and execution time. Furthermore, the obtained results indicate that the maximal transceiver cost savings achieved by the fully reconfigurable case may not be enough to justify the associated increase in reconfiguration cost. However, results show that an advantageous tradeoff between transceiver cost savings and reconfiguration cost can be achieved by a allowing a small number of virtual topology reconfigurations over time.

MatPlanWDM: an educational tool for network planning in wavelength-routing networks

This paper presents the MatPlanWDM tool, an educational network planning tool for wavelength-routing WDM networks. It includes a set of heuristic algorithms for solving the virtual topology design, and the routing and grooming of traffic flows on top of it. In addition, an implementation of the linear programming problem to obtain the optimal solution of the complete design is included for comparison. The input parameters to the planning problem are the network physical topology, the traffic matrix, and technological constraints like the number of transmitters, receivers, optical converters and wavelengths available. The tool is implemented as a MATLAB toolbox. The set of heuristic algorithms can be easily extended. A graphical interface is provided to plot the results obtained from different heuristics and compare them with the optimal solution in small-scale topologies.