Provisioning strategies for Translucent Elastic Optical Networks (EONs) should consider both spectrum and transponder costs. End-to-end connections that support user demands may be obtained on the one hand via transparent paths, which avoid regeneration costs but may require more spectrum slot, thus increasing the blocking probability, on the other hand via opaque paths that can reduce spectrum requirements, but at the cost of additional transponders for regeneration purposes. In this context, a wise provisioning strategy needs to consider translucent paths that can provide a good trade-off between transparent and opaque solutions. We propose a provisioning strategy that considers a multi-objective optimization problem aiming at the joint minimization of spectrum resources and regenerators. We show that the proposed strategy can significantly reduce regeneration costs while achieving low blocking probability.

Elastic Optical Networks (EONs) permit a trade-off between spectrum and regeneration use. Provisioning strategies for translucent EONs can reduce spectrum requirements at the cost of additional Bandwidth Variable Transponders (BVTs) used for regeneration. In this context, Sliceable Bandwidth Variable Transponders (SBVTs) can enable transponder sharing among multiple demands, potentially reducing regeneration costs. In this paper, we analyze the impact of SBVTs on the translucent provisioning process of EONs. In particular, we demonstrate that the use of SBVTs can improve blocking probability at almost no extra cost. We discuss simulation results for dynamic traffic over an EON when using different provisioning strategies that use SBVTs with respect to BVTs. Results reflect that the translucent strategy can significantly reduce the blocking probability even without the need of extra transponder deployment.

Delay Tolerant Networking (DTN) has been proposed to provide efficient and autonomous store-carry-and-forward data transport in space networks. Since these networks relay on scheduled contact plans, Contact Graph Routing (CGR) can be used to optimize routing and data delivery performance. However, transient or permanent faults can occur in large space networks, thus introducing uncertainties on the original contact plan reducing CGR performance. In this work, we propose alternative CGR metrics and study a novel replication-based CGR formulation that improves data delivery when operating under uncertain contact plans. This proposal is analyzed by means of simulation and compared with other scheduled and opportunistic routing approaches. Results provide a baseline to develop more specialized probabilistic CGR routing strategies that could cope with unplanned and transient faults in future space DTN networks.

Survivability of optical networks is considered among the most critical problems that telecommunications operators need to solve at a reasonable cost. Survivability can be enhanced by increasing the amount of network links and its spare capacity, nevertheless this deploys more resources on the network that will be used only under failure scenarios. In other words, these spare resources do not generate any direct profit to network operators as they are reserved to route only disrupted traffic. In particular, the case of dual link failures on fiber optic cables (i.e., fiber cuts) has recently received much attention as repairing these cables typically requires much time, which then increases the probability of a second failure on another link of the network. In this context, survivability schemes can be used to recover the network from a dual link failure scenario. In this work, we analyze the case of protection and restoration schemes, which are two well-known recovery strategies. The former is simpler to implement as it considers a fixed set of backup paths for all failure scenarios; however, it cannot take into account the spare capacity released by disrupted connections. Instead, the latter computes the best recovery path considering not only the spare capacity but also the released one due to failures. Achieving 100% survivability (i.e., recovery from all possible dual link failures) requires a triconnected network, where three disjoint paths for each connection are required. Since these networks can become extremely expensive since they can require a huge number of network links (i.e., fibers connections), a more realistic case of non-triconnected networks is assumed. In these networks, full network recovery is not be feasible, but achieving the maximum possible survivability is desired. Spare capacity can then be allocated to existing network links, which represents the actual cost of the survivability. We propose optimization models that take into account these different recovery strategies, and demonstrate that restoration has the potential to provide a much better recovery capability with almost the same amount of spare capacity required in protection schemes.

Elastic Optical Networks (EONs) can increase the efficiency of already deployed optical fibers thanks to transponders that adjust the modulation format, baud-rate and number of optical carriers to achieve the desired transmission rate, bandwidth and reach. Due to the high cost of these transponders, transparent end-to-end lightpaths are usually desired, which can require a large amount of spectrum when provisioned over long distances. In this paper, we consider the case of translucent lightpaths, which make use of flexible regeneration schemes to reduce the amount of required spectrum. We analyze the trade-off between the spectrum usage and the number of transponder devices. In particular, we propose a proactive approach to provision EONs that considers the spectrum availability. Thus, it is possible to explore the referred trade-off with a load-incremental perspective, which may be relevant for network operators. Results show how the proposed approach can increase the supported capacity in the network at the cost of additional transponder devices.

Delay and disruption tolerant networks (DTNs) are becoming an appealing solution for extending Internet boundaries so as to embrace disruptive communications. In particular, if node trajectory can be predicted as in space networks, routing schemes can take advantage of the a-priori knowledge of a contact plan. Despite mechanisms such as Contact Graph Routing (CGR) exist, they might derive in harmful overbooking of forthcoming contacts, also known as congestion. In order to tackle congestion, we initially formulate the problem by means of a linear programming (LP) model so as to establish an upper theoretical bound of performance. Next, we survey existing congestion mitigation mechanisms for predictable DTNs to later contribute with a CGR extension named PA-CGR. Finally, in the pursuance of an optimal congestion avoidance approach, we also propose and evaluate in a realistic scenario a novel multi-graph technique (MG-CGR) that outperforms existing solutions by exploiting traffic predictability.

In-network filtering schemes can be used for computing type-threshold functions in wireless sensor networks. Instead of relaying all data to a sink node, sensor nodes can filter measurements to provide only the set of data required to compute a given function (e.g., maximum, range). In this context, the network can progressively learn where relevant data are available and use this information to compute the function over time by only querying a subset of nodes. Trails between sink and these nodes can be obtained based on bio-inspired strategies, reducing the energy consumption and prolonging the network lifetime. The adaptive behavior of swarm intelligence allows to overcome a lot of obstacles presented in wireless communication networks. In this work, we evaluate the PhINP (Pheromone-based in Network Processing) mechanism, which drives the filtering process based on the integration of metaheuristic and learning algorithms. MAX function computation in oneand multiple-source environment monitoring is used as a case study. We show by simulation that communication cost can be significantly reduced respect to traditional mechanisms, increasing the network lifetime, while keeping a low computational error. Finally, node density requirements for efficient event detection in real applications are analyzed.

Packet processing is becoming much more challenging as networks evolve towards a multi-service platform. In particular, packet classification demands smaller processing times as data rates increase. To successfully meet this requirement, hardware-based classification architectures have become an area of extensive research. Even if Field Programmable Logic Arrays (FPGAs) have emerged as an interesting technology for implementing these architectures, existing proposals either exploit maximal concurrency with unbounded resource consumption, or base the architecture on distributed RAM memory-based schemes which strongly undervalues FPGA capabilities. Moreover, most of these proposals target best-match classification and are not suited for high-speed updates of classification rulesets. In this paper, we propose a new approach which exploits rich logic resources available in modern FPGAs while reducing memory consumption. Our architecture is conceived for multi-match classification, and its mapping methodology is naturally suited for high-speed, simple updating of the classification ruleset. Analytical evaluation and implementation results of our architecture are promising, demonstrating that it is suitable for line speed processing whith balanced resource consumption. With additional optimizations, our proposal has the potential to be integrated into network procesing architectures demanding all aforementioned features.

Packet classification techniques are continuously challenged as network bandwidth increases and new services are deployed. Ternary Content Addressable Memories (TCAMs) have traditionally been used for scenarios requiring high-speed packet processing. However, TCAM-based classification suffers from high power consumption and clock rate limitations. Among several proposed solutions, TCAM emulation through RAM has emerged as a more flexible and energy-efficient strategy. On the other hand, Field-Programmable Gate Array (FPGA) devices have been evolving providing not only abundant logical resources but also an increasing number of integrated RAM blocks. This paper investigates performance and trade-offs related to TCAM emulation in FPGAs. In particular, we analyze the impact of encoding different key ranges on rules for different configurations in terms of the search key length and the number of rules. To validate and evaluate actual performance, we report and discuss results of real implementations on FPGA devices. Our work shows that classification rates above 300Mpps for both large keys and rule sets can be implemented with only a few megabits of RAM when considering up to medium size range matching intervals.

The use of wireless sensor networks for information discovery and monitoring of continuous physical fields has emerged as a novel and efficient solution. To this end, a sink node disseminates a query message through the network to fetch data from sensor nodes. As several applications only require a limited subset of the available data in the network, the query could be ideally routed to obtain only relevant information, hence minimizing energy consumption. In this work, we apply computational intelligence algorithms to adapt the query process to the characteristics of the network in order to direct queries to relevant nodes, thus, limiting the routing space. This proposal is validated by extensive simulations which show that the routing cost can be reduced by approximately 60% over flooding with an error less than 5%.

Monitoring spatio-temporal continuous fields using wireless sensor networks has emerged as a novel and efficient solution. The development of energy efficient query dissemination and data collection algorithms for environments where only a small subset of nodes has relevant readings is a challenging problem if no information about the location of these nodes is available. Monitoring these data requires not only an initial discovery but also a continuous search for new relevant data due to field variations in time. One solution to this problem is to let nodes cooperate and decide jointly which data are relevant and their location. Trails to relevant data can be distributively marked as insect colonies do using pheromone-based schemes. In this work, we propose PhINP, a probabilistic pheromone-based in-network processing scheme to monitor information on WSNs. Our proposal takes advantage of both query-based innetwork filtering to select nodes to answer, and a pheromone-based strategy to direct queries towards nodes with relevant readings. Additionally, nodes use reinforcement learning to improve the routing performance of queries. We demonstrate by extensive simulations that the routing cost can be reduced by approximately 70% over flooding with an error below 1%.

Medium access control (MAC) protocols for wireless sensor networks (WSNs) have been extensively investigated in the last years. Although several different protocols have been proposed, and some have been implemented as proprietary protocols in commercial devices, the IEEE 802.15.4 MAC protocol is widely adopted in today's devices. As a result, energy-saving strategies that can be implemented in compliance with IEEE 802.15.4 can be considered of great relevance. In particular, in beacon-enabled networks much energy can be wasted due to contention among nodes sending data to the coordinator. In this paper, we investigate strategies that can reduce this energy waste by splitting the contention window into multiple contention-limited slots. We consider two different alternatives, and propose efficient algorithms that can be used to assign nodes to these slots based on their traffic conditions. The resulting strategies are evaluated by simulation in terms of energy consumption. Finally, a proof-of-concept is discussed to illustrate the feasibility of our proposal.

Passive optical networks (PONs) represent a step forward in "first mile" networks; indeed, by using optical technologies, PONs can transfer a large amount of data, and by being completely passive, they reduce management costs and failure probabilities. Access network is logically a point-to-multipoint network and the tree topology emerged as the winning solution; however, it naturally lacks protection capability and requires local traffic to be processed by the optical line terminal. In this paper, we present WONDER, a novel PON architecture based on a folded bus topology, which offers fault resilience and efficient local traffic support, and we discuss WONDER strengths and weaknesses.

Designing switching architectures for network routers and switches needs to consider limits imposed by the electronic technology, like small bandwidth x distance factors, power density constraints, energy consumption and dissipation issues. Introducing optical technologies to implement switching functions can overcome several of the current design limits. We propose a cost-effective architecture implementing an optical switch without any need for optoelectronic conversion within the switching fabric. We further propose a distributed scheduling scheme, based on an extension of the Fasnet protocol, and we compare it to classical centralized scheduling algorithms, showing that a distributed scheduler can provide performance comparable to the ones offered by more complex centralized schedulers.

The design of fabrics for Terabit packet switches and routers needs to consider the limitations imposed by the electronic technology; in particular, more and more attention has to be paid to information density and to power consumption and dissipation, as well as to power supply and footprint requirements. These issues make more difficult to package a packet switch in one single rack of equipment; thus, optical links start being used to interconnect the line cards with the switching fabric. In this paper, we consider optical interconnection architectures that exploit wavelength agility at line cards to control switching decisions. The actual feasibility and physical layer scalability of this approach is analyzed by considering different optical fabric alternatives to interconnect the line cards. The main contribution of the paper is the characterization of these optical fabrics in terms of their power budget, and the analysis of the port count and of the aggregate bandwidth offered by these architectures to build Terabit packet switches.

Disaster recovery and business continuity issues are becoming fundamental in networks since the importance and social value of digital data is continuously increasing. On the one hand, there is an obvious need of backing up data for resilience against major failures; in many situations the process of storing backup data is also enforced by the law. On the other hand, providing services that allow the migration of applications in real-time through virtualization techniques is becoming a mandatory feature in several business situations. In this paper we analyze the problems and the challenges of off-site data replication and virtual machine migration. In particular, we discuss the issue of optimizing network planning to support disaster recovery and business continuity. ILP (IntegerLinearProgramming) formulations for the optimization problem are presented with different objective functions. Heuristics are also proposed and analyzed taking into account both network cost minimization and fault recovery efficiency.

We focus on metropolitan area networks operating in packet mode and exploiting a single-hop wavelength division multiplexing (WDM) architecture. First, we briefly describe a specific slotted WDM optical network, based on a folded bus topology. Then, we address the fairness problem arising in this architecture and propose an extension of the MetaRing protocol to a WDM scenario. Two possible strategies are defined and analyzed. Finally, we show that both fair access and high aggregate network throughput can be achieved by properly handling node access through all WDM channels.

Single-hop wavelength division multiplexing (WDM) ring networks operating in packet mode are a promising architecture for the design of innovate metropolitan area networks. They allow a cost-effective design, with a good combination of optical and electronic technologies, while supporting features like restoration and reconfiguration that are essential in any metropolitan scenario. In this article, we address the fairness problem in a slotted WDM optical network. We introduce the multi-fasnet fairness protocol, we discuss its limitations and we propose an extension, based on a dynamic strategy, that achieves high aggregate network throughput, throughput fairness, and bounded and fair access delays.

Software routers are becoming an important alternative to proprietary and expensive network devices, because they exploit the economy of scale of the PC market and open-source software. When considering maximum performance in terms of throughput, PC-based routers suffer from limitations stemming from the single PC architecture, e.g., limited bus bandwidth, and high memory access latency. To overcome these limitations, in this paper we present a multistage architecture that combines a layer-2 load-balancer front-end and a layer-3 routing back-end, interconnected by standard Ethernet switches. Both the front-end and the back-end are implemented using standard PCs and open- source software. After describing the architecture, evaluation is performed on a lab test-bed, to show its scalability. While the proposed solution allows to increase performance of PC- based routers, it also allows to distribute packet manipulation functionalities, and to automatically recover from component failures.

DAVID is a research project sponsored by the European Union aimed at the design of an optical packet-switched network for the transport of IP traffic. The DAVID network has a two-level hierarchical structure, with a backbone of optical packet routers interconnected in a mesh, and metropolitan areas served by sets of optical rings interconnected by passive memoryless devices called Hubs. The paper focuses on the metropolitan area network and its components: the nodes and the Huh. Access is regulated by a dynamic time-division multiple-access scheme allocating slots in sets of wavelengths that provide multichannel pipes among ring pairs. This paper proposes a new resource allocation scheme capable of transporting variable-size packets without segmentation into fixed-size data units. Resource sharing among nodes is granted by two scheduling algorithms running on different time scales: the first one is centralized at the Hub and provides coarse connectivity among ring pairs; the second one runs at nodes and provides finer node-to-node connectivity. The Hub scheduling algorithm is derived from well known algorithms in the literature; a novel heuristic scheduling algorithm running at nodes is proposed for datagram (not-guaranteed) traffic and its performance is studied by simulation.

The data and voice integration over dense wavelength-division-multiplexing (DAVID) project proposes a metro network architecture based on several wavelength-division-multiplexing (WDM) rings interconnected via a bufferless optical switch called Hub. The Hub provides a programmable interconnection among rings on the basis of the outcome of a scheduling algorithm. Nodes connected to rings groom traffic from Internet protocol routers and Ethernet switches and share ring resources. In this paper, we address the problem of designing efficient centralized scheduling algorithms for supporting multiclass traffic services in the DAVID metro network. Two traffic classes are considered: a best-effort class, and a high-priority class with bandwidth guarantees. We define the multiclass scheduling problem at the Hub considering two different node architectures: a simpler one that relies on a complete separation between transmission and reception resources (i.e., WDM channels) and a more complex one in which nodes fully share transmission and reception channels using an erasure stage to drop received packets, thereby allowing wavelength reuse. We propose both optimum and heuristic solutions, and evaluate their performance by simulation, showing that heuristic solutions exhibit a behavior very close to the optimum solution.

This paper presents Ring Optical Network (RingO), a wavelength-division-multiplexing (WDM), ring-based, optical packet network suitable for a high-capacity metro environment. We present three alternative architectural designs and elaborate on the effectiveness of optic with respect to electronic technologies, trying to identify an optimal mix. We present the design and prototyping of a simple but efficient access control protocol, based upon the equivalence of the proposed network architecture with input-buffering packet switches. We discuss the problem of node allocation to WDM channels, which can be viewed as a particular optical network design problem. We, finally, briefly illustrate the fault protection properties of the RingO architecture. The main contribution of this paper is the identification and experimental validation of an innovative optical network architecture, which is feasible and cost effective with technologies available today, and can be a valid alternative to more consolidated solutions in metro applications.