Ramon Casellas

OpenSlice: an OpenFlow-based control plane for spectrum sliced elastic optical path networks

We present an OpenFlow-based control plane for spectrum sliced elastic optical path networks, called OpenSlice, for dynamic end-to-end path provisioning and IP traffic offloading. Experimental demonstration and numerical evaluation show its overall feasibility and efficiency.

Experimental demonstration of an OpenFlow based software-defined optical network employing packet, fixed and flexible DWDM grid technologies on an international multi-domain testbed

Software defined networking (SDN) and flexible grid optical transport technology are two key technologies that allow network operators to customize their infrastructure based on application requirements and therefore minimizing the extra capital and operational costs required for hosting new applications. In this paper, for the first time we report on design, implementation & demonstration of a novel OpenFlow based SDN unified control plane allowing seamless operation across heterogeneous state-of-the-art optical and packet transport domains. We verify and experimentally evaluate OpenFlow protocol extensions for flexible DWDM grid transport technology along with its integration with fixed DWDM grid and layer-2 packet switching.

Field Trial of an OpenFlow-Based Unified Control Plane for Multilayer Multigranularity Optical Switching Networks

Software defined networking and OpenFlow, which allow operators to control the network using software running on a network operating system within an external controller, provide the maximum flexibility for the operator to control a network, and match the carriers preferences given its centralized architecture, simplicity, and manageability. In this paper, we report a field trial of an OpenFlow-based unified control plane (UCP) for multilayer multigranularity optical switching networks, verifying its overall feasibility and efficiency, and quantitatively evaluating the latencies for end-to-end path creation and restoration. To the best of our knowledge, the field trial of an OpenFlow-based UCP for optical networks is a world first.

Experimental Translucent-Oriented Routing for Dynamic Lightpath Provisioning in GMPLS-Enabled Wavelength Switched Optical Networks

In the evolution from opaque networks, using 3R regenerators and OEO conversions for every wavelength channel, towards transparent networks, relying on end-to-end all-optical connections, translucent networks is considered as an intermediate step. A translucent network is a cost-efficient infrastructure between opaque and transparent networks, that aims at attaining an adequate trade-off between network construction cost (i.e., due to the high cost of 3R regenerators) and the service provisioning performance (i.e., end-to-end optical signal quality). This article addresses the dynamic provisioning of connections within a GMPLS-enabled translucent wavelength switched optical network with sparse 3R regenerators. To this end, translucent-oriented GMPLS protocol extensions are proposed to, on the one hand, disseminate required per node regenerator availability and OSNR-related link and node attributes and, on the other hand, allocate regenerator resources when setting up connections. An on-line OSNR-based impairment-aware RWA algorithm is devised to compute routes aiming at satisfying two constraints: the wavelength continuity constraint and the end-to-end optical signal quality. If either constraint cannot be satisfied, available regenerators along the route are used. To the best of our knowledge, the novelty and progress of this work is that, for the first time, both the proposed translucent GMPLS protocol enhancements and the performance of the RWA algorithm are combined within an experimental control plane network scenario (CTTCs ADRENALINE testbed). This allows validating and evaluating the feasibility of the described translucent GMPLS routing strategy when being potentially deployed into real WSON networks. Several configurations with numbers of 3R regenerators and wavelength channels per link, are experimentally evaluated and compared mainly in terms of the connection blocking probability. Although concrete details about the measured average setup delay are also discussed.

Control and management of flexi-grid optical networks with an integrated stateful path computation element and OpenFlow controller [invited]

A path computation element (PCE) is briefly defined as a control plane functional component (physical or logical) that is able to perform constrained path computation on a graph representing (a subset of) a network. A stateful PCE is a PCE that is able to consider the set of active connections, and its development is motivated by the fact that such knowledge enables the deployment of improved, more efficient algorithms. Additionally, a stateful PCE is said to be active if it is also able to affect (modify or suggest the modification of) the state of such connections. A stateful active PCE is thus able not only to use the knowledge of the active connections as available information during the computation, but also to reroute existing ones, resulting in a more efficient use of resources and the ability to dynamically arrange and reoptimize the network. An OpenFlow controller is a logically centralized entity that implements a control plane and configures the forwarding plane of the underlying network devices using the OpenFlow protocol. From a control plane perspective, an OpenFlow controller and the aforementioned stateful PCE have several functions in common, for example, in what concerns network topology or connection management. That said, both entities also complement each other, since a PCE is responsible mainly for path computation accessible via an open, standard, and flexible protocol, and the OpenFlow controller assumes the task of the actual data plane forwarding provisioning. In other words, the stateful PCE becomes active by virtue of relying on an OpenFlow controller for the establishment of connections. In this framework, the integration of both entities presents an opportunity allowing a return on investment, reduction of operational expenses, and reduction of time to market, resulting in an efficient approach to operate transport networks. In this paper, we detail the design, implementation, and experimental evaluation of a centralized control plane based on a stateful PCE, acting as an OpenFlow controller, targeting the control and management of optical networks. We detail the extensions toboth the OpenFlow and the PCE communication protocol (PCEP), addressing the requirements of elastic optical networks as well as the system performance, obtained when deployed in a laboratory trial.

Design and Experimental Validation of a GMPLS/PCE Control Plane for Elastic CO-OFDM Optical Networks

ITU-T Recommendation G.694.1 defines normative DWDM frequency grids, each being a reference set of values that correspond to allowed nominal central frequencies, obtained using a fixed channel spacing (e.g., 12.5 GHz, 25 GHz, 50 GHz or 100 GHz). This rigid, grid-based approach does not seem well adapted for data rates beyond 100 Gb/s, is particularly inefficient when a whole wavelength is assigned to a lower rate optical path, and is not flexible enough for multi-rate systems . Consequently, the next generation of optical networks will require a flexible, highly efficient and adaptive management of the optical spectrum, along with advanced optical modulation schemes that efficiently use allocated spectrum slots, and recent progress on optical network technology justifies research on both new optical transmission systems as well as the applicability of control and management frameworks to such networks. We design and deploy a GMPLS control plane for flexible optical networks with coherent optical orthogonal frequency-division multiplexing (O-OFDM) transmission; we detail its functional architecture, which combines a centralized entity that performs path routing and modulation assignment, with a distributed spectrum allocation. The centralized entity (i.e., a path computation element) uses pre-configured static path characterizations, based on exhaustive OFDM transmission simulations, when performing dynamic path computation in line with GMPLS constrained shortest path mechanisms. The distributed spectrum allocation assigns frequency ranges (slots) to connection requests, by using dynamic signaling procedures and applying slot assignment policies. We summarize the control plane protocol extensions involved in the main functional aspects: routing and topology dissemination, path computation, signaling and resource reservation. We experimentally validate and evaluate the integrated centralized PCE and GMPLS control plane in a control plane testbed, obtaining key performance indicators such as path setup latency and blocking probability for different frequency slot assignment policies.

In-operation network planning

Current transport networks are statically configured and managed, because they experience a rather limited traffic dynamicity. As a result, long planning cycles are used to upgrade the network and prepare it for the next planning period. Aimed at guaranteeing that the network can support the forecast traffic and deal with failure scenarios, spare capacity is usually installed, thus increasing network expenditures. Moreover, results from network capacity planning are manually deployed in the network, which limits the network agility. In this article, we propose a control and management architecture to allow the network to be dynamically operated. Employing those dynamicity capabilities, the network can be reconfigured and reoptimized in response to traffic changes in an automatic fashion; hence, the resource overprovisioning can be minimized and overall network costs reduced.

Challenges for GMPLS lightpath provisioning in transparent optical networks: Wavelength constraints in routing and signaling

GMPLS has introduced several enhancements to the MPLS-TE routing and signaling control plane protocols to handle dynamic lightpath provisioning in wavelength-routed networks. Specifically, the GMPLS signaling protocol has been enhanced to support two new provisioning functionalities, namely, the minimization of the setup delay, and the setup of bidirectional connection requests. In both cases, the source node must perform a wavelength allocation for either minimizing the setup delay (i.e., the suggested label) or requesting a bidirectional connection (i.e., the upstream label). However, these GMPLS provisioning functionalities present important deficiencies when applied to wavelength-routed networks with the wavelength continuity constraint, degrading the network performance considerably. The reason is that the standard GMPLS routing protocols flood link attributes only at bandwidth granularity, that is, no per-wavelength channel granularity is disseminated. Therefore, the source node is unable to perform an optimal wavelength assignment that fulfils the wavelength continuity constraint along the complete route toward the destination. In this article we present and experimentally evaluate an enhanced routing-based solution in the ADRENALINE testbed to handle the wavelength continuity constraint.

GMPLS/PCE control of flexi-grid DWDM optical networks using CO-OFDM transmission [Invited]

Current optical transport networks use optical channel carriers (wavelengths) that are defined and constrained by a fixed ITU-T dense wavelength division multiplexing (DWDM) grid. Such a grid is not adapted to high data rates (beyond 100 Gb/s) and is inefficient when a wavelength is assigned to a low-rate optical signal. Consequently, the ITU-T is updating the set of DWDM reference frequencies with the inclusion of a smaller channel spacing (e.g., 6.25 GHz) while allowing the allocation of frequency slots, that is, variable-sized frequency ranges composed of a number of slices. In this paper, we propose the design, implementation, and experimental validation of a Generalized Multi-Protocol Label Switching/path computation element (GMPLS/PCE) control plane for such flexible optical networks, using optical orthogonal frequency division multiplexing transmission technology, given its unique flexibility, bit-rate/bandwidth scalability, and subwavelength granularity. The control plane uses a distance-adaptive and PCE-based routing and modulation assignment, combined with distributed frequency slot (spectrum) selection. A comparative analysis of path computation algorithms is carried out, highlighting the benefits of extending the path computation function with the knowledge of the status of the slices and the spectral efficiency of the modulation formats.

Enhanced Backwards Recursive Path Computation for Multi-area Wavelength Switched Optical Networks Under Wavelength Continuity Constraint

In the context of the future Internet, all-optical wavelength switched optical networks will play an important role in either evolutionary or revolutionary design paradigms. In any paradigm, dense wavelength domain multiplexing (DWDM) is the most cost-effective technology to increase bandwidth capacity. DWDM provides the basis for a core optical transport infrastructure supporting a wide range of heterogeneous services. However, such all-optical networks raise well-known challenges such as the wavelength continuity constraint (WCC). The WCC is hard to address in a multiarea scenario when provisioning an end-to-end lightpath owing to network topology hiding requirements and the limited exchange of information between areas. The Internet Engineering Task Force (IETF) is currently standardizing the path computation element (PCE) architecture, a good candidate to perform multidomain path computation. In such an architecture, the approach named backwards recursive path computation (BRPC), also under standardization at the IETF, aims at overcoming the limitations of the per-domain mechanism. However, although BRPC does provide end-to-end shortest paths, it fails to take into account the WCC, which is the main motivation for this work. We extend the BRPC algorithm and the companion PCE protocol in order to address the end-to-end WCC efficiently. We perform a quantitative comparative analysis of the different approaches, experimentally showing the improvements of the conceived solution, which has been evaluated in a GMPLS-controlled network of the ADRENALINE testbed.