Investigation of dynamic routing and spectrum allocation methods in elastic optical networks

The introduction of flexible frequency grids and advanced modulation techniques to optical transmission, namely an elastic optical network, requires new routing and spectrum allocation techniques. In this paper, we investigate dynamic two-step routing and spectrum allocation (RSA) methods for elastic optical networks. K-shortest path-based methods as well as spectrum allocation methods are analysed and discussed. Experimental verified of the investigated techniques is provided using simulation software. Based on the obtained experimental results, it can be seen that effectiveness of routing and spectrum allocation methods depend on network topologies. Moreover, performance of shortest path first methods improves considerably when a number of candidate paths increases in a topology with high nodal degree

Elastyczne sieci optyczne. Telekomunikacja i Techniki Informacyjne, 2013, nr 1-2

Artykuł przybliża koncepcję elastycznej sieci optycznej i charakterystyczne zagadnienia związane z jej implementacją. Przedstawiono w nim standardy styków optycznych sieci Ethernet 40 Gbit/s i 100 Gbit/s zawarte w dokumencie IEEE 802.3ba. Następnie opisano szczelinowy charakter widma elastycznej sieci optycznej, porównując ze sztywnym podziałem częstotliwości DWDM. Nakreślono problem planowania i dynamicznej alokacji zasobów w sieci

Automatic hidden bypasses in software-defined networks

As global internet traffic continues to increase, network operators face challenges on how to efficiently manage transmission in their networks. Even though attempts are underway to make optical networks automatic, the majority of actions related to traffic engineering are still performed manually by the administrators. In this paper we propose an Automatic Hidden Bypasses approach to enhance resource utilization in optical networks. Our solution uses the software-defined networking concept to automatically create or remove hidden bypasses which are not visible at the network layer. The mechanism increases throughput and reduces transmission delays

Conceptualizing multidimensional barriers: a framework for assessing constraints in realizing recreational benefits of urban green spaces

This article was supported by the German Research Foundation (DFG) and the Open Access Publication Fund of Humboldt-Universität zu Berlin.Although potential urban green space accessibility is being discussed widely, specific barriers that affect accessibility are often under-estimated. They do not equate to limited or uneven accessibility nor are they exclusively related to physical settings. Rather, the range of barriers and their complex interactions, including people’s perceptions, personal conditions, and institutional frameworks, make this topic less clear cut and difficult to put into practice for planning purposes. Given the importance of barriers when people make decisions, we present a conceptual framework to capture the cumulative and interactive effects of different barriers on realizing recreational benefits of urban green spaces. The framework classifies physical, personal, and institutional barriers and highlights their interactions based on three case studies: Stockholm, Leipzig, and Lodz. We argue that constraints to the accessibility of urban green spaces are not so much the interactions between various physical, personal, and institutional barriers, but more the significance that beneficiaries assign to them as perceived barrier effects. Studying barriers seeks to improve the knowledge about the non-use of urban green spaces and to enable us to draw conclusions about the actual accessibility of recreational benefits. Deduced from the conceptual framework, three pathways are contrasted for improving accessibility to the recreational benefits of urban green spaces: the environment, knowledge, and engagement. We argue that these pathways should not be a diffuse objective, but a sensitive and scale-dependent re-balance of individual, physical, and institutional factors for considering justice in environmental and green space planning and management. Our systematic conceptualization and classification of multidimensional barriers enables a more comprehensive understanding of individuals’ decisions in terms of accessing recreational benefits.Peer Reviewe

Popular but exclusive : How can lower socio-economic status groups win access to urban green spaces?

Territorial conflicts related to the use of urban green spaces typically result from conflicting preferences and institutions not being able to account for the equitable distribution of benefits. Our study focuses on the value conflicts and contestations around using an urban green space as a "social good" and the political processes of defining what makes it "good." It investigates the institutional setting and the preferences of 415 forest users in a series of entertainment events organized in a large municipal forest (Lagiewniki) in Lodz, Poland. The low socioeconomic status group benefited at the cost of the high socio-economic group, whose members typically chose to change their routes in the forest to avoid the nuisance related to these events. The fact that the lower socioeconomic status group benefited seems to have been an unplanned side effect of leasing the deteriorating site (to reduce municipal costs) to a company that chose to pick a low-hanging fruit and not invest in developing the site but only cater to the less picky clientele. The local authorities responsible for leasing the site turned a blind eye to the various nuisances caused by these events and disregarded local conservation provisions. We put this case in the context of the "lumpengeography of capital" (Walker, 1978), which suggests that due to the relative scarcity of capital and the abundance of green spaces, some areas remain in a stage of disinvestment, perhaps only temporarily awaiting the next wave of capitalist redevelopment.Peer reviewe