Albert Pagès

Optimal allocation of virtual optical networks for the future internet

Optical network infrastructures can be partitioned into multiple parallel, dedicated virtual networks for a physical infrastructure sharing purpose. However, different transport technologies may impact in both the amount and the characteristics of the different virtual instances that can be built on top of a single physical infrastructure. To analyse the impact of the transport technology in this regard, we present exact Integer Linear Programming (ILP) formulations that address the off-line problem of optimally allocate a set of virtual networks in two kind of substrates: wavelength switching and spectrum switching. Both formulations serve the purpose to provide opaque transport services from the virtual network point of view, where electronic terminations are assumed in the virtual network nodes. We carry out a series of experiments to validate the presented formulations and determine which is the impact of both substrates in the number of virtual networks that can be optimally allocated in the transport network.

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.

Lightpath fragmentation for efficient spectrum utilization in dynamic elastic optical networks

The spectrum-sliced elastic optical path network (SLICE) architecture has been presented as an efficient solution for flexible bandwidth allocation in optical networks. An homologous problem to the classical Routing and Wavelength Assignment (RWA) arises in such an architecture, called Routing and Spectrum Assignment (RSA). Imposed by current transmission technologies enabling the elastic optical network concept, the spectrum contiguity constraint must be ensured in the RSA problem, meaning that the bandwidth requested by any connection must be allocated over a contiguous portion of the spectrum along the path between source and destination nodes. In a dynamic network scenario, where incoming connections are established and disconnected in a quite random fashion, spectral resources tend to be highly fragmented, preventing the allocation of large contiguous spectrum portions for high data-rate connection requests. As a result, high data-rate connections experience unfairly increased bocking probability in contrast to low data-rate ones. In view of this, the present article proposes a lightpath fragmentation mechanism that makes use of the idle transponders in the source node of a high data-rate connection request to fragment it into multiple low data-rate ones, more easily allocable in the network. Besides, aiming to support such an operation, a light-weight RSA algorithm is also proposed so as to properly allocate the generated lightpath fragments over the spectrum. Benefits of the proposed approach are quantified through extensive simulations, showing drastically reduced high data-rate connection blocking probability compared to a usual contiguous bandwidth allocation, while keeping the performance of low data-rate requests to similar levels.

Optimal route, spectrum, and modulation level assignment in split-spectrum-enabled dynamic elastic optical networks

The spectrum fragmentation effect in elastic optical networks is one of their main limitations. Multiple techniques have been proposed to address this problem, with the split spectrum approach (SSA) being a very interesting candidate among them. This technique is based on splitting a demand into smaller sub-demands when a blocking situation arises. In split-spectrum-enabled networks, the route, spectrum, and modulation level assignment (RSMLA) problem that appears in elastic optical networks is further complicated due to the signal splitting operation. In this paper we present novel mechanisms to optimally attack this problem; various possible implementations of the SSA are also discussed. We highlight the benefits of the proposed mechanisms through illustrative results and compare the various implementation solutions in terms of average network cost.

Flex-grid/SDM backbone network design with inter-core XT-limited transmission reach

Spatial division multiplexing (SDM) has been presented as a key solution to circumvent the nonlinear Shannon limit of standard single-core fibers. To implement SDM, multi-core fiber (MCF) technology becomes a top candidate that is leveraged by the very low inter-core crosstalk (XT) measurements obtained in real laboratory MCF prototypes with up to 22 cores. In this work, we concentrate on the design of MCF-enabled optical transport networks. To this goal, we present a methodology to estimate the worst-case transmission reach of the optical signals (at different bit rates and modulation formats) across MCFs given real laboratory XT measurements. Next, we present an optimal integer linear programming (ILP) formulation for the design of a flex-grid/SDM optical transport network that makes use of the transmission reach estimations. Additionally, an effective simulated annealing (SA)-based heuristic able to solve large problem instances with reasonable execution times is presented. Once the proposed heuristic is adequately tuned and validated, we use it to compare the resource utilization in MCF-enabled network scenarios against currently available multi-fiber link solutions. Numerical results reveal very close performances with up to 19 cores/fibers in national backbone network scenarios and up to 12 cores/fibers in long-haul continental ones.

Enabling multi-tenancy in hybrid optical packet/circuit switched data center networks

In a flattened optical data center network employing hybrid technologies, multi-tenancy is enabled by a new virtual data center embedding method that is equipped with network-aware VM placement exploiting the advanced but complex characteristics of diverse optical technologies.

Power consumption reduction through elastic data rate adaptation in survivable multi-layer optical networks

Network survivability requires the provisioning of backup resources in order to protect active traffic against any failure scenario. Backup resources, however, can remain unused most of the time while the network is not in failure condition, inducing high power consumption wastage, if fully powered on. In this paper, we highlight the power consumption wastage of the additional resources for survivability in IP/multi-protocol label switching (MPLS) over dense wavelength division multiplexing multi-layer optical networks. We assume MPLS protection switching as the failure recovery mechanism in the network, a solution interesting for current network operators to ensure fast recovery as well as fine-grained recovery treatment per label switched path. Next, we quantitatively show how elastic optical technologies can effectively reduce such a power consumption by dynamically adjusting the data rate of the transponders to the carried amount of traffic.

Virtual network embedding in optical infrastructures

Optical network virtualisation has recently become a hot topic among the research community due to its potential to enable the shaping of the Infrastructure as a Service (IaaS) concept. A major challenge that arises of paramount importance when virtualising a network is the so called Virtual Network (VN) embedding problem. While this problem has been extensively treated for electrical networks, there is very little work regarding Virtual Optical Network (VONs) embedding. This paper addresses the VON embedding problem, giving an insight about the potential challenges and presenting solutions that allow to optimally solving this problem in dynamic network scenarios.

Split spectrum-enabled route and spectrum assignment in elastic optical networks

The Split Spectrum Approach (SSA) in elastic optical networks is based on splitting a demand into smaller sub-signals when a blocking situation arises, either due to the lack of spectral resources or transmission reach reasons. In this paper, we propose a mechanism based on a Mixed Integer Linear Programming (MILP) formulation for efficiently serving incoming demands in SSA-based elastic optical networks. Moreover, we also present a lightweight heuristic mechanism for scenarios where the MILP mechanism may suffer from scalability issues. The benefits of the proposal are highlighted through illustrative results. Furthermore, we compare two SSA implementations available in the literature in terms of relative transponder cost.

Optimal VDC Service Provisioning in Optically Interconnected Disaggregated Data Centers

Virtual data center (VDC) is a key service in modern data center (DC) infrastructures. However, the rigid architecture of traditional servers inside DCs may lead to blocking situations when deploying VDC instances. To overcome this problem, the disaggregated DC paradigm is introduced. In this letter, we present an integer linear programming (ILP) formulation to optimally allocate VDC requests on top of an optically interconnected disaggregated DC infrastructure, aiming to quantify the benefits that such an architecture can bring when compared with traditional server-centric DCs. Moreover, a lightweight simulated annealing-based heuristic is provided for the scenarios where the ILP scalability is challenged. The obtained numerical results reveal the substantial benefits yielded by the resource disaggregation paradigm.