M. De Leenheer

A Survey on OFDM-Based Elastic Core Optical Networking

Orthogonal frequency-division multiplexing (OFDM) is a modulation technology that has been widely adopted in many new and emerging broadband wireless and wireline communication systems. Due to its capability to transmit a high-speed data stream using multiple spectral-overlapped lower-speed subcarriers, OFDM technology offers superior advantages of high spectrum efficiency, robustness against inter-carrier and inter-symbol interference, adaptability to server channel conditions, etc. In recent years, there have been intensive studies on optical OFDM (O-OFDM) transmission technologies, and it is considered a promising technology for future ultra-high-speed optical transmission. Based on O-OFDM technology, a novel elastic optical network architecture with immense flexibility and scalability in spectrum allocation and data rate accommodation could be built to support diverse services and the rapid growth of Internet traffic in the future. In this paper, we present a comprehensive survey on OFDM-based elastic optical network technologies, including basic principles of OFDM, O-OFDM technologies, the architectures of OFDM-based elastic core optical networks, and related key enabling technologies. The main advantages and issues of OFDM-based elastic core optical networks that are under research are also discussed.

Design of Disaster-Resilient Optical Datacenter Networks

Survivability against disasters-both natural and deliberate attacks, and spanning large geographical areas-is becoming a major challenge in communication networks. Cloud services delivered by datacenter networks yield new opportunities to provide protection against disasters. Cloud services require a network substrate with high capacity, low latency, high availability, and low cost, which can be delivered by optical networks. In such networks, path protection against network failures is generally ensured by providing a backup path to the same destination (i.e., a datacenter), which is link-disjoint to the primary path. This protection fails to protect against disasters covering an area which disrupts both primary and backup paths. Also, protection against destination (datacenter) node failure is not ensured by a generic protection scheme. Moreover, content/service protection is a fundamental problem in a datacenter network, as the failure of a datacenter should not cause the disappearance of a specific content/service from the network. So content placement, routing, and protection of paths and content should be addressed together. In this work, we propose an integrated Integer Linear Program (ILP) to design an optical datacenter network, which solves the above-mentioned problems simultaneously. We show that our disaster protection scheme exploiting anycasting provides more protection, but uses less capacity than dedicated single-link failure protection. We show that a reasonable number of datacenters and selective content replicas with intelligent network design can provide survivability to disasters while supporting user demands. We also propose ILP relaxations and heuristics to solve the problem for large networks.

A view on enabling-consumer oriented grids through optical burst switching

As grid computing continues to gain popularity in the research community, it also attracts more attention from the enterprise and consumer levels. Applications in these domains generate large amounts of jobs, with individual jobs having only modest resource requirements. In this article, a novel architecture to realize a highly scalable and flexible platform for consumer-oriented grids is proposed. The architecture is based on an optical burst switched network, complemented with an advanced control and signaling plane. The architecture, functionality, and interfaces of all the relevant entities are presented and issues, current initiatives, and future directions for the control and management of these grid networks are discussed.

Multi-Granular Optical Cross-Connect: Design, Analysis, and Demonstration

A fundamental issue in all-optical switching is to offer efficient and cost-effective transport services for a wide range of bandwidth granularities. This paper presents multi-granular optical cross-connect (MG-OXC) architectures that combine slow (ms regime) and fast (ns regime) switch elements, in order to support optical circuit switching (OCS), optical burst switching (OBS), and even optical packet switching (OPS). The MG-OXC architectures are designed to provide a cost-effective approach, while offering the flexibility and reconfigurability to deal with dynamic requirements of different applications. All proposed MG-OXC designs are analyzed and compared in terms of dimensionality, flexibility/reconfigurability, and scalability. Furthermore, node level simulations are conducted to evaluate the performance of MG-OXCs under different traffic regimes. Finally, the feasibility of the proposed architectures is demonstrated on an application-aware, multi-bit-rate (10 and 40 Gbps), end-to-end OBS testbed.

Optical traffic grooming in OFDM-based elastic optical networks [Invited]

Orthogonal frequency-division multiplexing (OFDM) is a multi-carrier modulation technology that transmits a high-speed data stream using multiple spectrally overlapped lower-speed subcarriers. Optical OFDM (O-OFDM) technology is a promising candidate for future high-speed optical transmission. Based on O-OFDM, a novel elastic optical network architecture with immense flexibility and scalability in spectrum allocation and data rate accommodation can be built to support diverse services and the rapid growth of Internet traffic. This architecture can provide various services directly at the optical layer in a spectrum-efficient way through bandwidth-elastic optical paths. However, carrying various data rate services using a single type of bandwidth-variable transponder might not be cost-efficient. Electrical traffic grooming is a traditional approach for sub-wavelength service accommodation in wavelength division multiplexing networks. However, it places additional electrical switching and optical-electrical-optical conversion requirements on the network, which may lead to higher cost and energy consumption. In contrast, grooming traffic optically is an attractive option for elastic optical networks. In this paper, we propose a novel optical grooming approach to aggregate and distribute traffic directly at the optical layer in OFDM-based elastic optical networks. We study routing and spectrum allocation algorithms of optical grooming to show the benefits of this approach. Our results demonstrate that significant transmitter and spectrum savings can be achieved by the optical grooming versus the non-grooming scenario, and a trade-off between optimizing the number of transmitters and optimizing spectrum usage should be considered during network planning.

PHOSPHORUS: single-step on-demand services across multi-domain networks for e-science

The Phosphorus project focuses on delivering advanced network services to Grid users and applications interconnected by heterogeneous infrastructures. The project is addressing some of the key technical challenges to enable on-demand end-to-end network services across multiple domains. The Phosphorus network concept makes applications aware of their complete Grid resources environment -computational and networking- and its capabilities. Phosphorus enables and tests dynamic adaptive and optimised use of the heterogeneous network infrastructure interconnecting various high-end resources. The project will demonstrate on-demand service delivery across access-independent multi-domain/multi-vendor research network test-beds on a European and worldwide scope. Phosphorus enhances and demonstrates solutions that facilitate vertical and horizontal communication among applications middleware and the network resources across different domains, managed by existing Network Resource Provisioning Systems (NRPS), or domains that integrate a new Grid-GMPLS (G2MPLS) Control Plane, both under a new AAA architecture to support policy based on-demand network resource provisioning. This G2MPLS extends ASON/GMPLS in order to provide part of the functionalities related to the selection, co-allocation and maintenance of both Grid and network resources, by exposing upgraded interfaces at the UNI and E-NNI network reference points -i.e. G.OUNI and G.E-NNI-. The project outcomes are going to be demonstrated in a worldwide test-bed.

Multi-cost job routing and scheduling in Grid networks

A key problem in Grid networks is how to efficiently manage the available infrastructure, in order to satisfy user requirements and maximize resource utilization. This is in large part influenced by the algorithms responsible for the routing of data and the scheduling of tasks. In this paper, we present several multi-cost algorithms for the joint scheduling of the communication and computation resources that will be used by a Grid task. We propose a multi-cost scheme of polynomial complexity that performs immediate reservations and selects the computation resource to execute the task and determines the path to route the input data. Furthermore, we introduce multi-cost algorithms that perform advance reservations and thus also find the starting times for the data transmission and the task execution. We initially present an optimal scheme of non-polynomial complexity and by appropriately pruning the set of candidate paths we also give a heuristic algorithm of polynomial complexity. Our performance results indicate that in a Grid network in which tasks are either CPU- or data-intensive (or both), it is beneficial for the scheduling algorithm to jointly consider the computational and communication problems. A comparison between immediate and advance reservation schemes shows the trade-offs with respect to task blocking probability, end-to-end delay and the complexity of the algorithms.

Providing resiliency for optical grids by exploiting relocation: A dimensioning study based on ILP

Grids use a form of distributed computing to tackle complex computational and data processing problems scientists are presented with today. When designing an (optical) network supporting grids, it is essential that it can overcome single network failures, for which several protection schemes have been devised in the past. In this work, we extend the existing Shared Path protection scheme by incorporating the anycast principle typical of grids: a user typically does not care on what specific server this job gets executed and is merely interested in its timely delivery of results. Therefore, in contrast with Classical Shared Path protection (CSP), we will not necessarily provide a backup path between the source and the original destination. Instead, we allow to relocate the job to another server location if we can thus provide a backup path which comprises less wavelengths than the one CSP would suggest. We assess the bandwidth savings enabled by relocation in a quantitative dimensioning case study on an European and an American network topology, exhibiting substantial savings of the number of required wavelengths (in the order of 11-50%, depending on network topology and server locations). We also investigate how relocation affects the computational load on the execution servers. The case study is based on solving a grid network dimensioning problem: we present Integer Linear Programming (ILP) formulations for both the traditional CSP and the new resilience scheme exploiting relocation (SPR). We also outline a strategy to deal with the anycast principle: assuming we are given just the origins and intensity of job arrivals, we derive a static (source,destination)-based demand matrix. The latter is then used as input to solve the network dimensioning ILP for an optical circuit-switched WDM network.

Energy efficiency considerations in integrated IT and optical network resilient infrastructures

The European Integrated Project GEYSERS - Generalised Architecture for Dynamic Infrastructure Services - is concentrating on infrastructures incorporating integrated optical network and IT resources in support of the Future Internet with special emphasis on cloud computing. More specifically GEYSERS proposes the concept of Virtual Infrastructures over one or more interconnected Physical Infrastructures comprising both network and IT resources. Taking into consideration the energy consumption levels associated with the ICT today and the expansion of the Internet in size and complexity, that incurring increased energy consumption of both IT and network resources, energy efficient infrastructure design becomes critical. To address this need, in the framework of GEYSERS, we propose energy efficient design of infrastructures incorporating integrated optical network and IT resources, supporting resilient end-to-end services. Our modeling results quantify significant energy savings of the proposed solution by jointly optimizing the allocation of both network and IT resources.

Using Divisible Load Theory to Dimension Optical Transport Networks for Grid Excess Load Handling

An important aspect of grid deployment is the allocation and activation of installed network capacity. Due to the data-intensive nature of grid jobs, it is expected that optical transport networks will play an important role in grid deployment. As grids possibly consist of high numbers of re sources and users, solving the network dimensioning problem using straight forward integer linear programs (ILP) does not scale well with increasing number of jobs. There fore, we propose the use of divisible load theory (DLT) when modeling this OCS (with wavelength translation) dimensioning problem. We establish the suitability of this approach as an optical transport network dimensioning tool in an excess load scenario for varying wavelength granularity, fiber/wavelength cost models, network topology, traffic demand asymmetry and Grid scheduling strategy