ETSI has considered a new set of services for the Release 2, which cannot be implemented using the single control channel. Therefore, it is necessary to regulate the operation of applications on multiple channels, what is called Multi-Channel Operation (MCO). In this case the interference from the first adjacent channel is not negligible and is recommended to manage it by congestion control mechanisms. We propose an elastic channel usage scheme for MCO, based on an optimal scheduler whose goal is to maximize the traffic on the channels while minimizing the adjacent channel interference generated by that load and controlling the congestion. We formulate the interference and congestion control as a constrained convex optimization problem and derive as solution a distributed algorithm called MINOS (MultI-chaNnel operation Optimal Scheduler). MINOS seamlessly work when vehicles have a different number of network interfaces available, and constraints and priorities can be set individually and dynamically, which provides flexibility to implement more sophisticated services on top of the framework. Our results show that MINOS effectively controls the congestion and reduces the interference, achieving an increased packet reception ratio across all channels and a higher allocated traffic, compared to other proposals.

To support inter-vehicular applications, vehicles broadcast beacons with information about their state. Congestion may occur when the load on the channel due to beaconing can prevent the transmission of other types of messages. In this paper, we propose a distributed algorithm for optimal joint adaptation of transmit power and beaconing rate for congestion and awareness control. Our approach is based on a network utility formulation of the congestion control problem, which allows us to induce a desired fairness notion and set different priorities for vehicles. We formulate the general problem but, since it is not convex, we assume Rayleigh fading and derive an algorithm, called PRAIOS, that solves the optimization problem in a decentralized way with convergence guarantees. Our results, validated with realistic simulations in both static and dynamic scenarios and compared with other proposals, show that PRAIOS quickly converges to close to optimal allocations, while keeping the maximum beaconing load at the desired level. They also show that it can control the load when the fading is not Rayleigh. Applications can dynamically set their requirements as constraints, that are enforced by the algorithm while complying with the maximum load, which allows seamless integration of operational requirements into the control framework.

Traffic growth forecasts announce a dramatic future for core networks, struggling to keep the pace of traffic augmentation. Internet traffic growth primarily stems from the proliferation of cloud services and the massive amounts of data distributed by the content delivery networks (CDNs) hosting these services. In this paper, we investigate the evolution of core traffic in the presence of growing CDNs. Expanding the capacities of existing data centers (DCs) directly translates the forecasted compound-annual-growth-rate (CAGR) of user traffic to the CAGR of carried core link traffic. On the other hand, expanding CDNs by building new geographically dispersed DCs can significantly reduce the predicted core traffic growth rates by placing content closer to the users. However, reducing DC-to-user traffic by building new DCs comes at a trade-off with increasing inter-DC content synchronization traffic. Thus, the resulting overall core traffic growth will depend on the types of services supported and their associated synchronization requirements. In this paper, we present a long-term evolution study to assess the implications of different CDN expansion strategies on core network traffic growth considering a mix of services in proportions and growth rates corresponding to well-known traffic forecasts. Our simulations indicate that CDNs may have significant incentive to build more DCs, depending on the service types they offer, and that current alarming traffic predictions may be somewhat overestimated in core networks in the presence of expanding CDNs.

Cooperative inter-vehicular applications rely on the exchange of broadcast single-hop status messages among vehicles, called beacons. The aggregated load on the wireless channel due to periodic beacons can prevent the transmission of other types of messages, what is called channel congestion due to beaconing activity. In this paper, we approach the problem of controlling the beaconing rate on each vehicle by modeling it as a Network Utility Maximization (NUM) problem. This allows us to formally apply the notion of fairness of a beaconing rate allocation in vehicular networks and to control the trade-off between efficiency and fairness. The NUM methodology provides a rigorous framework to design a broad family of simple and decentralized algorithms, with proved convergence guarantees to a fair allocation solution. In this context, we focus exclusively in beaconing rate control and propose the Fair Adaptive Beaconing Rate for Intervehicular Communications (FABRIC) algorithm, which uses a particular scaled gradient projection algorithm to solve the dual of the NUM problem. The desired fairness notion in the allocation can be established with an algorithm parameter. Simulation results validate our approach and show that FABRIC converges to fair rate allocations in multi-hop and dynamic scenarios.

Continuous advances in network technologies challenge network architects in their attempt to foresee what new technologies deserve resources and investments, what existing infrastructure to keep, and their interplay during migration processes. Moreover, topics like energy efficiency, disaster resilience, or SDN/NFV are being intensively considered and investigated during the last years. As a result, R&D efforts have led to a number of solutions. Unfortunately, it is often difficult for operators to reproduce such results on their networks, maybe due to divergent philosophies between commercial planning tools used in the industry and academic tools. A paradigm shift to an open-source view of network planning could emphasize the power of peer-review and transparency to promote innovation at an accelerated pace and lower cost. This tutorial would focus on Net2Plan (http://www.net2plan.com), an open-source tool developed by the authors, and actively used in several courses (>200 students) and research projects since 2012. Built on top of a technology-agnostic multilayer network representation, Net2Plan is designed to assist users in the evaluation of built-in or original user-developed planning algorithms. In addition, users can analyze their designs using either reports or a simulation tool for in-operation scenarios like network resilience, connection-admission-control, time-varying traffic resource allocation, or even combinations of them. Besides, Net2Plan permits applying algorithms to orchestrate OpenFlow-enabled networks interacting with the northbound interface of OpenDaylight. Throughout the tutorial, attendees would have the opportunity to learn about the main features of Net2Plan, also discovering some of its applications. At the end of this tutorial, attendees would be guided through an intensive hands-on case study based on an IP-over-WDM network, e.g., including network dimensioning using built-in or user-developed algorithms, WDM line engineering (e.g., EDFA placement, impairment computations), automatic availability calculation under different failure patterns, and automatic simulation of the effects of time-varying traffic and assessment of energy-efficient switch-off techniques.

Long-reach passive optical networks (LR-PONs) are able to effectively support the growing demand of traffic originating from residential and business customers. Failures of metro/core (M/C) nodes serving the traffic to/from the access networks covered by LR-PONs, may potentially affect hundreds or thousands of customers. One way of guaranteeing 100% survivability from single-node failures is to apply dual-homing, where each LR-PON is connected to two M/C nodes, and combine it with node-disjoint dedicated-path protection (DPP). In this paper, we present a new approach to provide network survivability against single M/C node failures. Instead of applying dedicated path protection (DPP) strategy, which can require huge amount of extra resources, we combine an unprotected network design with a dynamic multilayer restoration algorithm. Our aim is to determine a suitable amount of resource overbuild (in terms of extra transponders) needed to provide average connection availability close to that guaranteed by DPP. Preliminary results show that dimensioning for the worst-case scenario among a set of predefined M/C node failures, i.e., the one disrupting the highest number of connections, yields to a cost-effective strategy requiring up to 35% less transponders than DPP, while offering the same average connection availability.

In this paper we describe the main features of the open-source Net2Plan tool. Built on top of a technology-agnostic vendor-neutral multilayer network representation, Net2Plan is designed to assist users in the evaluation of built-in or original user-developed planning algorithms. In addition, users can analyze their designs using either reports or a simulation tool for in-operation scenarios like network resilience, connection-admission-control, time-varying traffic resource allocation, or even combinations of them, using built-in or custom event generators or reaction algorithms. We motivate how a paradigm shift to an open-source view of network planning emphasizes the power of distributed peer-review, collaboration cycles and transparency to create high-quality software at an accelerated pace and lower cost.

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.

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.

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.

This paper investigates offline planning and scheduling in transparent optical networks for a given periodic traffic demand. The main objective is to minimize the number of transceivers needed which make up for the main network cost. We call this problem “Scheduled Virtual Topology Design” and consi

The deployment of optical packet switching (OPS) in dense wavelength division multiplexing (DWDM) backbone networks is perceived as a medium term promising alternative. Scalability restrictions imply that conventional switching architectures are unfeasible in this large-scale scenario. In a previous paper, the wavelength-distributed knockout architecture was proposed as a cost-effective scaling strategy for OPS switching fabrics. In this paper, this growable architecture is applied to OPS switching fabrics able to emulate output buffering. We also propose an scheduling algorithm which provides optimum performance if knockout packet losses are made negligible. The mathematical analysis to evaluate the knockout packet loss probability of this architecture is obtained, under uniform and non-uniform traffic patterns. To complement the switch dimensioning process, an upper bound assuring 0-knockout packet losses is compared with the exact analytical results.

Commercial applications of optical packet switching to backbone WDM networks are still far from reality due to hardware costs. The two envisaged alternatives for network control and operation of this type of networks is scattered wavelength path (SCWP) and shared wavelength path (SHWP). The advantages and drawbacks of both approaches involve many different issues. In this paper, the impact of SCWP and SHWP switching modes on performance and hardware costs is discussed and evaluated for three different prominent OPS switch fabric designs: KEOPS switch, space switch, and output-buffered wavelength-routed switch. To achieve it, we conduct a necessary set of modifications for these architectures, which were not originally conceived for SCWP/SHWP. This normalization process is unavoidable to provide a true comparison among the switch fabric designs, and to advance to a global comparison between SCWP and SHWP operation modes, that under knowledge of the authors do not exist yet.

The authors present DelfosnetX, an information retrieval (IR) system intended to evaluate different relevance analysis and ranking techniques for metadata-enabled IR, and more specifically, XML based IR. The theoretical background that supports the proposed model is also discussed.