Gabriel Junyent

Challenges and requirements for introducing impairment-awareness into the management and control planes of ASON/GMPLS WDM networks

The absence of electrical regenerators in transparent WDM networks significantly contributes to reduce the overall network cost. In transparent WDM networks, a proper resource allocation requires that the presence of physical impairments in routing and wavelength assignment (RWA) and lightpath provisioning be taken into account. In this article a centralized, a hybrid centralized-distributed and two distributed approaches that integrate information about most relevant physical impairments in RWA and lightpath provisioning are presented and assessed. Both centralized and hybrid approaches perform a centralized path computation at the management-plane level, utilizing physical impairment information, while the lightpath provisioning is done by the management plane or the control plane, respectively. The distributed approaches fall entirely within the scope of the ASON/GMPLS control plane. For these two approaches, we provide functional requirements, architectural functional blocks, and protocol extensions for implementing either an impairment-aware real-time RWA, or a lightpath provisioning based on impairment-aware signaling.

Integrated IP/WDM routing in GMPLS-based optical networks

Future transport networks will have to cope with the continuous growth of IP traffic. Furthermore, transport networks need to evolve so as to drastically reduce both deployment costs and operating expenses. A reasonable strategy to achieve this goal consists of simplifying the network architecture by reducing the number of layers. Assuming a peer model IP over optical network, we propose an integrated routing strategy that takes into account constraints and dynamic occupancy of both the IP and optical layers. The collaboration of both layers in the routing process leads to optimization of network performance. The main emphasis is on the implementation requirements of this grooming functionality using GMPLS-TE mechanisms. Simulation results show the benefits obtained by applying this strategy.

Novel Power Efficient Optical OFDM Based on Hartley Transform for Intensity-Modulated Direct-Detection Systems

We present a novel optical orthogonal frequency division multiplexing (O-OFDM) scheme, suitable for intensity-modulated direct-detection systems, where the modulation/demodulation processing takes advantage of the fast Hartley transform algorithm. Due to the properties of the discrete Hartley transform (DHT), the conventional transmission scheme can be streamlined. We demonstrate that asymmetrically clipping (AC) technique can also be applied to DHT-based OFDM; the signal can be transmitted without the need of a DC bias, resulting in a power-efficient system, not affected by clipping noise. Hermitian symmetry is not required for the input signal. Therefore, this technique supports the double of input symbols compared to both AC and DC-biased O-OFDM, based on standard Fourier processing. The analysis in an additive white Gaussian noise channel shows that the same performance can be achieved by replacing 4, 16, and 64 QAM (quadrature-amplitude modulation) AC optical-OFDM with a simpler system based on DHT, using binary phase-shift keying (BPSK), 4 and 8 PAM (pulse-amplitude modulation), respectively.

Solving Routing and Spectrum Allocation Related Optimization Problems: From Off-Line to In-Operation Flexgrid Network Planning

Compared to wavelength switched optical networks (WSON), flexgrid optical networks provide higher spectrum efficiency and flexibility. To properly analyze, design, plan, and operate flexgrid networks, the routing and spectrum allocation (RSA) problem must be solved. The RSA problem involves two different constraints: the continuity constraint to ensure that the allocated spectral resources are the same along the links in the route and the contiguity constraint to guarantee that those resources are contiguous in the spectrum. As a consequence of its complexity, it is crucial that efficient methods are available to allow solving realistic problem instances in practical times. In this paper, we review different RSA-related optimization problems that arise within the life-cycle of flexgrid networks. Different methods to solve those optimization problems are reviewed along with the different requirements related to where those problems appear. Starting from its formulation, we analyze network life-cycle and indicate different solving methods for the kind of problems that arise at each network phase: from off-line to in-operation network planning. We tackle two representative use cases: i) a use case for off-line planning where a flexgrid network is designed and periodically upgraded, and ii) multilayer restoration as a use case for in-operation planning. Three solving methods are proposed for the off-line planning problem: mathematical programming, column generation and metaheuristics, whereas, as a result of its stringent required solving times, two heuristic methods are presented for the on-line problem.

The ADRENALINE testbed: integrating GMPLS, XML, and SNMP in transparent DWDM networks

This article presents a brief overview, state of the art, and taxonomy of optical WDM testbeds, and outlines the differences between them and the ADRENALINE testbed. ADRENALINE is an optical circuit-switched WDM testbed that deploys reconfigurable OADMs based on various technologies (e.g., AWG and tunable lasers). In ADRENALINE, end-to-end lightpaths are set up and torn down dynamically and in real time by means of a GMPLS-based control plane (switched connections) and a distributed management plane (soft-permanent connections). ADRENALINE supports the request of SPCs under user initiative by combining GMPLS, SNMP, and XML. ADRENALINE allows both the topology and major characteristics of the data communications network to be modified, enabling control and management related experiments with varying DCN. In our experiments we investigate user management of lightpaths and address its performance in terms of basic SLA parameters related to connection establishment (delay and availability). Finally, we address remaining challenges and outline exciting avenues of future work on ADRENALINE.

Survivable IP/MPLS-Over-WSON Multilayer Network Optimization

Network operators are facing the problem of dimensioning their networks for the expected huge IP traffic volumes while keeping constant or even reducing the connectivity prices. Therefore, new architectural solutions able to cope with the expected traffic increase in a more cost-effective way are needed. In this work, we study the survivable IP/multi-protocol label switching (MPLS) over wavelength switched optical network (WSON) multilayer network problem as a capital expenditure (CAPEX) minimization problem. Two network approaches providing survivability against optical links, IP/MPLS nodes, and opto-electronic port failures are compared: the classical overlay approach where two redundant IP/MPLS networks are deployed, and the new joint multilayer approach which provides the requested survivability through an orchestrated interlayer recovery scheme which minimizes the over-dimensioning of IP/MPLS nodes. Mathematical programming models are developed for both approaches. Solving these models, however, becomes impractical for realistic networks. In view of this, evolutionary heuristics based on the biased random-key genetic algorithm framework are also proposed. Exhaustive experiments on several reference network scenarios illustrate the effectiveness of the proposed approach in minimizing network CAPEX.

UCLPv2: a network virtualization framework built on web services [web services in telecommunications, part II]

User controlled LightPaths version 2 provides a network virtualization framework upon which communities of users can build their own services or applications without dealing with the complexities of the underlying network technologies and still can maintain the functionality that the network provides. The system has been designed as a service-oriented architecture where Web services and Web services workflows are the basic building blocks. Articulated private networks are presented as the first services built upon the UCLPv2 network virtualization middleware. APNs can be considered as a next generation VPN where a user can create a complex, multi-domain network topology by binding together network resources, computers, time slices, and virtual or real routing and/or switching nodes. A first implementation of the UCLPv2 software was deployed on CAnet 4, Canadas research and education network, and currently, it is being used by Environment Canada, a federal government department, to enable an APN that links its research facilities across the country.

Strategies for Virtual Optical Network Allocation

This paper presents Integer Linear Programming (ILP) formulations to optimally allocate Virtual Optical Networks (VONs) over a transparent optical network substrate. These formulations serve the purpose of building either completely transparent VONs or opaque ones, where electrical termination capabilities are assumed at each virtual network node. In addition, a lightweight Greedy Randomized Adaptive Search (GRASP) heuristic is provided for the transparent case. The obtained results validate the accuracy of the proposed heuristic and reveal the benefits of the presented solutions against simpler shortest-path-based VON allocation strategies.

Using spectrum fragmentation to better allocate time-varying connections in elastic optical networks

Elastic optical network (EON) technology arises as a promising solution for future high-speed optical transport, since it can provide superior flexibility and scalability in the spectrum allocation for seamlessly supporting diverse services, while following the rapid growth of Internet traffic. This work focuses on lightpath adaptation under time-variable traffic demands in EONs. Specifically, we explore the possibility of utilizing the spectral fragmentation to increase the spectrum allocation (SA) capabilities of EONs. In this context, a heuristic SA algorithm, which intentionally increases the spectral fragmentation in the network, is proposed and validated. In our proposal, the spectrum assigned to each new connection is in the middle of the largest free spectral void over the route, aiming to provide considerable spectral space between adjacent connections. These free spectral spaces are then used to allocate time-varying connections without requiring any lightpath reallocation. The obtained simulation results show a significant improvement in terms of network blocking probability when utilizing the proposed algorithm.

Saving CAPEX by extending flexgrid-based core optical networks toward the edges [invited]

National IP/multiprotocol label switching (MPLS) networks have been designed using a multilayer approach to take advantage of the optical layers longer reach. In that approach, the IP/MPLS layer performs routing and flow aggregation, whereas the optical layer, based on wavelength division multiplexing technology, transports those aggregated flows into optical connections. However, the flexgrid technology, featuring a finer granularity, also allows the performance of grooming at the optical layer, and hence, the aggregation level of the incoming flows can be reduced. Taking advantage of that fact, in this paper we propose a new network architecture consisting of a number of IP/MPLS areas performing routing and aggregating flows to the desired level and a flexgrid-based core network connecting the areas among them. A two-step procedure to design the whole network is presented where locations are first partitioned into a set of areas, and then each area network and the flexgrid core is designed separately. Mixed-integer linear programming models are developed for the resulting optimization problems. Solving these models, however, becomes impractical for real-sized scenarios so evolutionary heuristics based on the biased random-key genetic algorithm framework are also proposed. Extending the core toward the edges results in significant savings in both the core and IP/MPLS networks.