João Pedro

An overview of routing methods in optical burst switching networks

In this article we present a survey of routing methods in Optical Burst Switching (OBS) networks. We begin with a description of routing approaches and follow the discussion with a detailed classification of routing algorithms in OBS. Afterwards, we discuss common OBS network loss models that are frequently used in routing optimization. As examples of such application, we present a linear and a non-linear formulation of a multi-path routing optimization problem with an indication on convenient resolution methods. The presented algorithms are appropriate for proactive load balancing routing and aim at the improvement of network-wide burst loss performance. To compare performance results, both methods are evaluated by simulation in a set of unified network scenarios.

Design of survivable flexible-grid DWDM networks with joint minimization of transponder cost and spectrum usage

We present a multi-objective framework to jointly optimize cost and spectrum in a survivable flexible-grid network with multiple transponder profiles. Through the use of an evolutionary algorithm, the sharing of spectral and interface resources is explored to clearly show the cost/spectrum design trade-off according to different sharing policies.

A comparison of remote radio head optical transmission technologies for next generation wireless systems

A performance and cost comparison is made between analogue and digital optical transmission technologies for linking remote radio heads to digital base stations for future wireless systems with wide channel bandwidth and multiple MIMO channels.

Optimized design of multistage passive optical networks

The large investments required for deploying passive optical networks (PONs) render the disposal of appropriate planning tools for designing such networks in a cost-effective way a necessity. This paper addresses the problem of finding the least costly tree topology time-division multiplexing PON (TDM-PON) deployment configurations considering equipment and installation costs (CAPEX) and operational exploration costs. With this purpose, an integer linear programing model is developed, which is capable of designing not only common single-stage PON configurations, but also PONs with multiple stages of optical splitting. In order to reduce the computation time for problems of larger size, a two-stage heuristic is also proposed. The simulation results for the cases studied reveal that an optimal multistage splitting strategy can lead to cost savings of up to 15% in CAPEX expenditures in comparison with the traditional single-stage approach. Furthermore, the heuristic procedure proposed is shown to obtain results within acceptable bounds relative to the optimum solutions, hence validating its use for larger sized networks. The results also show that the average CAPEX cost savings between the two-stage and single-stage approaches are quite dependent on the strategies used to choose candidate locations for the splitters, with values ranging from 5 to 12% depending on whether random candidate placement or k-means-based placement is used.

On the modelling and performance evaluation of optical burst-switched networks

The future prospects of optical burst switching (OBS) architectures depend on several crucial factors, such as their performance versus their complexity and implementation cost. This paper presents a framework for evaluating the performance of OBS core networks, comprising an analytic performance model and a network simulator. The framework is used for evaluating the performance of several different network topologies and the analytic evaluation model is validated by the simulation results. Two resource reservation mechanisms for burst transmission, the just enough time (JET) mechanism, and a centralized mechanism, are examined using the performance evaluation framework. It is shown that the lack of awareness of global state information, characteristic of the JET mechanism, only significantly hampers the performance of OBS networks if limited range wavelength conversion is deployed in the network

OPNp1-5: Wavelength Contention Minimization Strategies for Optical Burst-Switched Networks

The future prospects of optical burst switching (OBS) networks would greatly benefit, in terms of cost and ease of implementation, from limiting or even avoiding the deployment of wavelength conversion capabilities at the network nodes. This paper proposes a new strategy for minimizing wavelength contention in OBS networks. Simulation results suggest that this strategy can significantly reduce the performance penalty of avoiding wavelength conversion at the network nodes. Moreover, the new strategy is shown to outperform a previously proposed strategy, in some cases by several orders of magnitude, in terms of average burst blocking probability.

Impact of add/drop port utilization flexibility in DWDM networks [Invited]

Optical transport networks are at the turning point from providing semi-permanent connections to being engineered to efficiently support dynamic optical connection services. Vital to this transition is the availability of node architectures that improve the flexibility of add/drop port utilization, thereby enabling the transponder connected to a port to be reused to realize connections with different wavelength channels or using different input/output fiber links (directions). This paper assesses the network-wide blocking performance provided by node architectures with different degrees of freedom for port reuse. The performance assessment not only clearly highlights the relevance of maximizing the chances of transponder sharing in transport networks, but also shows that the network topology determines which of the degrees of freedom for port reuse is more relevant.

Impact of node architecture in the power consumption and footprint requirements of optical transport networks

We evaluate and compare the power consumption and the number of required slots (footprint) of fixed and flexible transport nodes. The node architecture is assumed to comprise a grooming structure, and a reconfigurable optical add/drop multiplexer (ROADM). Fixed grooming is achieved using cascades of muxponders. Alternatively, flexible grooming is achieved with electrical switches. Fixed frequency and fixed direction ROADM, and colorless and directionless ROADM are considered. For all the architectures, we present an accurate dimensioning model that allows computation of the required modules. Results show that to optimize the total power consumption and footprint of the network, the architecture of each node has to be selected according to the amount and pattern of the add/drop and regenerated traffic and the number of pairs of fibers convergent to the node. An optimization method based on simple rules for node type selection is proposed.

Vendor-interoperable elastic optical interfaces: Standards, experiments, and challenges [Invited]

This paper aims to review the status of standardization activities on the black link (BL) and corresponding alien wavelength concepts. It discusses experimental work on filterless optical networks conducted within a dedicated Deutsche Telekom project. The general prospects and existing challenges concerning elastic extensions of the BL are also assessed. Furthermore, we present relevant work on control and management plane interoperability comprising generalized multi-protocol label switching and transport software defined networking aspects. In the second part of the article, we report on the latest dual-vendor experiments on data plane interoperability in terms of digital signal processing technology for next generation 1.28 Tb/s PM-16QAM super-channels. Finally, we present a network reachability analysis based on the widely used Gaussian noise model in the context of data plane interoperability. This analysis estimates the network-wide impact of the single-vendor versus the dual-vendor approach.

Multi-objective design of survivable flexible-grid DWDM networks

Emerging trends in optical transport networks aiming to support increasing data rates are reshaping the possibilities for network planning. The deployment of a flexible grid with multiple available channel bit rates and spectral widths gives way to a more clearly defined trade-off between spectrum and cost in the planning process. Furthermore, providing redundancy in these types of services is both crucial and costly. For this reason, it is important to consider all these aspects simultaneously in order to have an accurate view of the cost/spectrum trade-off in the optical backbone. This paper presents an evolutionary based multi-objective framework for optimizing network deployments with flexible-grid channel formats ranging from 40 to 400 Gbits/s with varying degrees of resilience to both link and transponder failures. The multi-objective algorithm can consider all these different aspects simultaneously and highlight the degree to which cost can be traded for spectrum, and how the protection/restoration schemes influence both parameters. After benchmarking the proposed algorithm on both objectives, we use it on two reference networks to trace the non-dominated front for multiple resilience schemes, offering different levels of protection against link and/or transponder failures. We also evaluate how the channel format selection for each demand evolves when considering single-rate or bit-rate variable transponders.