1,720,987 research outputs found
Wavelength conversion in WDM optical networks: strategies and algorithms for limiting the number of converters in optical cross-connects
No full textThis paper considers the problem of wavelength conversion in optical networks using wavelength division multiplexing technique. In the previous literature, two main wavelength routing and assignment strategies have been introduced: wavelength path (WP) and virtual wavelength path (VWP), depending on whether the signal stays on the same wavelength or is converted to another during its travel throughout the network. While the former method does not require any wavelength conversion, the latter needs wavelength conversion in each optical node and, in particular, a wavelength converter per each signal handled by the node itself. From the previous literature emerged that the VWP leads to optical cross-connect (OXC) with lower dimensions compared to the ones required by the WP scheme, and that the difference between the WP and VWP schemes increases as the number of wavelengths carried by each ®ber increases. In this paper a new strategy is introduced, named partial virtual wavelength path (PVWP), with the related wavelength routing and assignment algorithm, which makes limited use of wavelength conversion compared to the VWP scheme, and allows the same advantages of VWP to be attained with lower OXC dimensions. The paper reports a comparative analysis among the different strategies, considering both the cases of a network without failures and a network with the possibility of failure restoration. The main result is that the proposed PVWP strategy allows the same advantages of the VWP scheme with a strongly reduced number of wavelength converters (around 5% of the number required by VWP scheme). This ®gure does not vary appreciably if failure restoration is considered. The new strategy can be adopted by using an opportune OXC architecture, as illustrated in the paper, which allow a limited number of converters to be shared among all the channels as a common pool
Optical Data Network Based on the Switchless Concept: Analysis and Dimensioning
No full textThe switchless all optical network aims to provide a future single-layer advanced transport architecture on a national scale. In this paper we present a model which contains innovative elements and report original results assuming to deal with data traffic of two different types: Constant Bit Rate (CBR) and Variable bit rate (VBR)
Strategies and Algorithms for routing both Unicast and Multicast Paths in WDM Networks
No full textThis paper introduces the concept of the multicast optical path in WDM networks, and treats the strategies and the algorithms, which allow the routing of plural multicast paths together with unicast paths. This analysis was motivated by the possibility of exploit the optical layer facilities in the transport network, to carry distributive services, such as video channels (e.g. CATV), without the need of dedicated transmission networks. The strategies and algorithms reported in this paper arise from a generalisation of those ones, which have been previously reported in literature. They are wavelength path (WP: which does not make use of wavelength conversion), virtual wavelength path (VWP: which make full use of wavelength conversion), and partial virtual wavelength path (PVWP: making a parsimonious use of wavelength conversion). The analysis shows the characteristics and performance of those strategies and algorithms considering, as a figure of merit, either the number of wavelengths or the system scale (dimensions of the optical nodes), and compare one to each other in order to point out advantages and disadvantages. The main result is that multicast optical paths can favourably be accommodated in a WDM network, and the strategy we propose, making a parsimonious use of wavelength conversion, allows the lowest system scale to be obtained with a very low number of wavelength converters
Fast Downloading of Large Files via Multi-Channel Wireless Mesh Networks
No full textIn this contribution, the problem of download time minimization, by considering channel state, is solved for application scenario where the downlink channel is slotted and continuous-state, while the resulting conveyed throughput is measured by any desired increasing concave rate-function. Specifically, the optimal energy-allocation policy minimizing the download-time is found and its performance is compared against that of a basic On-Off type heuristic scheduler for some Rayleigh-faded multi-antenna downloading systems of practical interest. © 2006 IEEE
Analysis and dimensioning of switchless networks for single-layer optical architecture
No full textThe “switchless” all-optical network is an alternative networking approach being developed in the framework of the ACTS project named SONATA, which aims to provide a future single layer, advanced transport architecture on a national scale. The single hop, shared access network employs time and wavelength agility (a WDMA/TDMA scheme), using fast tunable transmitters and receivers, to set up individual customer connections through a single wavelength router (suitably replicated for resilience). The dimensioning of this type of network is one of the main tasks for the design of networks serving a certain number of customers, connected together by means of passive optical networks (PON’s). This paper reports an analytical model which allows the network dimensioning according to some relevant design parameters: the number of customers per PON, the number of PON’s, the offered traffic per single user (either considering residential or business user), and the required system performance expressed in terms of blocking probability. Furthermore, relevant issues related to the dimensioning of switchless networks are discussed and some results achieved for relevant network scenarios are reported, to assess the feasibility of the system concept
Fine protection of data-paths in multi-layer networks based on the GMPLS paradigm
No full textThe telecommunications world is expecting the take off of broadband services, beyond typical telephone, both mobile and fixed, and IPTV. The expectations on huge growth of data traffic will lead the evolution of the network towards the next generation multi-service network. The cornerstone of future network infrastructure will be the possibility of provide carrier grade performance, for those services that require such features. This means to guarantee the QoS performance and the resilience of a circuit-switched network even in a packet-based scenario. Beyond that, key requirements are the capacity of tailoring the QoS to different services, and flexibility, that is the effective utilization of network resources, as well as the ability to react to changes in the traffic demands. This paper addresses the issue of providing adequate levels of protection to data flows in multi-layer networks composed of MPLS and optical layers and based on the GMPLS paradigm. A new approach is proposed allowing for an efficient use of network resources and providing adequate levels of protection, starting from the high standard required for real-time traffic. (C) 2008 Elsevier B.V. All rights reserved
Impact of transmission performances on path routing in all-optical transport networks
No full textThe impact of transmission related issues on the routing strategies for transparent all-optical wavelength division multiplexed (WDM) transport networks is analyzed in this paper. Three different categories of routing algorithms are analyzed: algorithms based on the wavelength path (WP) strategy, based on the virtual wavelength path (VWP) strategy and requiring only a limited number of wavelength converters in the network partial virtual wavelength path (PVWP). It results that the PVWP allows a saving in network devices with respect to the WP similar those permitted by the VWP also attaining transmission performances near those attained by the WP that are quite better that those attained by the VWP
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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