1,721,037 research outputs found
Architetture per Reti Ottiche ad Elevata Efficienza Energetica
No full textIl settore dell’informatica e delle telecomunicazioni svolgerà un ruolo fondamentale nel ridurre i consumi energetici della nostra società. Tuttavia il consumo energetico dovuto al settore stesso è tuttora significativo ed aumenterà rapidamente con il proliferare di dispositivi collegati ad Internet e con l’apparizione di nuove applicazioni. Il consumo energetico del settore dell’informatica e delle telecomunicazioni è dovuto a: (i) periferiche, (ii) reti di telecomunicazione e (iii) data center. Sebbene le periferiche (es. computer, stampanti, ecc.) consumino la maggioranza dell’energia del settore, le reti di telecomunicazione e i data center consumano insieme più della metà del totale. Con l’attesa crescita del traffico Internet, il loro impatto energetico è destinato a crescere e per tale motivo risulta essenziale definire nuove architetture per reti di telecomunicazione e data center che presentino un basso impatto energetico.
Le reti di telecomunicazione possono essere suddivise in: (i) reti di accesso, (ii) reti metropolitane e (iii) reti di trasporto. Il traffico Internet viene aggregato nelle reti di accesso e metropolitane e trasmesso a grande distanza attraverso le reti di trasporto. Per questo motivo le reti di trasporto devono supportare grandi quantità di traffico e di conseguenza consumano una grande quantità di energia. Al fine di incrementare l’efficienza energetica nelle reti di trasporto, nella prima parte di questo elaborato viene proposto un nuovo meccanismo di trasmissione ottico definito Hybrid Optical Switching (HOS). HOS integra sulla stessa rete commutazione ottica di pacchetto, burst e circuito e prevede l’utilizzo di due switch in parallelo, uno switch ottico “lento” per la trasmissione di circuiti e burst lunghi ed uno “veloce” per la trasmissione di pacchetti e burst corti. Ciascuna applicazione Internet può scegliere il meccanismo di commutazione più adatto alle proprie caratteristiche e gli elementi di commutazione a più basso consumo vengono scelti ed utilizzati dinamicamente dai nodi della rete. Un architettura di rete basata su HOS viene proposta ed analizzata utilizzando un approccio analitico-simulativo. I risultati mostrano che HOS migliora notevolmente l’efficienza energetica rispetto alla soluzioni attuali.
Il consumo di energia dei data center può essere suddiviso in (i) energia consumata dai dispositivi ICT, (ii) energia consumata dal sistema di raffreddamento ed (iii) energia consumata dal sistema di alimentazione. In base alle ultime specifiche costruttive, l’energia consumata dai moderni data center è quasi interamente dovuta ai dispositivi ICT. Ne consegue che per ridurre il consumo energetico dei data center è importante definire nuove tecnologie ed architetture che consentano di ridurre il consumo dei componenti ICT ed in particolare il consumo della rete di interconnessione interna. A tale scopo, nella seconda parte di questo elaborato vengono proposte due nuove architetture di interconnessione ottiche per data center. La prima architettura si basa sul meccanismo di trasmissione HOS e viene indicata con il nome HOSDC, mentre la seconda si basa sul concetto di reti ottiche elastiche e viene indicata con il nome di EODC. L’energia consumata dalle due architetture proposte viene valutata e confrontata con quella consumata dalle soluzioni tradizionali, mostrando in entrambi i casi un notevole miglioramento. Infine, nell’ultima parte di questo elaborato viene proposta un architettura di rete interamente ottica che consente di massimizzare l’efficienza energetica sia nelle comunicazione interne ai data center che nelle comunicazioni tra data center situati in diverse posizioni geografiche.Although the Information and Communications Technologies (ICT) sector can play a fundamental role in enabling a low carbon economy, the energy and carbon impact of the sector itself is significant and is expected to grow rapidly with the proliferation of devices connected to the Internet and emergence of new services. The energy consumption of the ICT sector can be divided in: (i) energy consumed by the user devices, (ii) energy consumed by the telecommunication network infrastructure, and (iii) energy consumed by the data centers. Even if end-user devices (such as computers, printers, etc.) are the major contributors, the sum of the energy consumed by the telecommunication networks and data centers is today estimated to be more than a half of the total ICT energy consumption. With the expected growth in the Internet and data center traffic the energy consumption of telecommunication networks and data centers is destined to drastically increase if the energy efficiency would not be improved. In this work energy efficient network architectures for telecommunication networks and data centers are proposed and analyzed.
Telecommunication networks can be divided into three domains: (i) access, (ii) metro, and (iii) core. Core networks are the central part of the network hierarchy, providing nationwide or global coverage, and are based on optical transmission technologies. They contribute significantly to the energy consumption of the telecommunication infrastructure since they must support very high capacities. To increase the energy-efficiency in optical core networks, in the first part of the thesis a novel core network paradigm, referred to as Hybrid Optical Switching (HOS), is presented. HOS integrates optical packet, burst, and circuit switching on the same network and envisages the use of two parallel switches, a slow optical switch for the transmission of circuits and long bursts, and a fast switch for the transmission of packets and short bursts. The most appropriate switching method is selected for the traffic generated by different applications and the less power consuming elements are utilized for transmission, ensuring flexibility, QoS differentiation, and low energy consumption. The HOS architecture is analyzed and compared with traditional solutions based on electronic switching through a combined simulation and analytical approach. Results show the effectiveness of the proposed solution.
The energy consumption of a data center is divided in (i) energy consumed by the ICT equipment, (ii) energy consumed by the cooling system and (iii) energy consumed by the power supply chain. According to the latest specifications data centers are designed in such a way that the ICT equipment consumes nearly all the energy within the data center. As a consequence, major energy savings in modern data centers can be achieved by reducing the energy consumption of the ICT equipment and in particular the energy consumption of the internal interconnection network. To this aim, in the second part of this thesis two novel optical switched data center interconnects are proposed. The first, referred to as HOS data center (HOSDC) interconnect, is based on the HOS switching paradigm while the second, referred to as Elastic Optical Data Center (EODC) interconnect, is based on the elastic optical networking concept. The energy consumption of the two architectures is evaluated in order to show the advantages with respect to existing solutions. Finally, an integrated all-optical network that provides both intra-data-center and inter-data-center connectivity together with interconnection toward legacy IP networks is proposed for achieving high overall energy improvements
Spatial division multiplexing for high capacity optical interconnects in modular data centers
Full text linkModular design has recently emerged as an efficient solution to build large data center (DC) facilities. Modular DCs are based on stand-Alone prefabricated modules (i.e., PODs) that can be easily installed and interconnected. PODs can generate a large amount of traffic and thus require an ultra-high-capacity interconnection network. However, current electronic and optical interconnect architectures applied to modular DCs may experience major scalability problems in terms of high energy consumption and cabling complexity. To address these problems, we investigate five optical interconnect architectures based on spatial division multiplexing (SDM), and for each architecture, we propose a resource allocation strategy. We also present an extensive comparison among the SDM architectures in terms of cost and performance (i.e., blocking probability and throughput), with the objective to find the architecture offering the best trade-off between cost and performance for given DC sizes and traffic load values. Our results demonstrate that, in small modular DCs with low traffic load, an architecture based only on SDM is the best option, while in medium DCs with medium traffic load, an architecture based on coupled SDM and flexgrid wavelength division multiplexing (WDM) with spectral flexibility is the best solution. Finally, for large DCs with high traffic load values, the best trade-off between cost and performance is achieved by an SDM architecture that is based on uncoupled SDM and flexgrid WDM
TCP Performance in Multi-EPON Access Networks under Different Optical Core Switching Paradigms
No full textIn this paper the end-to-end TCP performance of a hybrid network composed of multiple Ethernet Passive Optical Networks (EPONs) in the access segment connected to the same edge node of a core network is evaluated.
Three possible core network paradigms are considered: Optical Circuit Switching (OCS), Optical Burst Switching (OBS) and Optical Packet Switching (OPS). TCP performance is evaluated through simulations with ns-2.
The hybrid network scalability is assessed by varying the number of EPONs connected to the same edge node and the number of Optical Network Units (ONUs) per EPON. Interoperability issues between access and core are investigated and the impact of the most important network parameters is highlighted. The three transfer modes considered for the core network are properly compared under different input conditions, discussing the related trade-offs that may lead to the most suitable choice based on the specific
application scenario. Finally, some design issues are investigated with reference to emerging Long-Range EPON (LR-EPON) solutions
Network Performance Trade-Off in Modular Data Centers With Optical Spatial Division Multiplexing
Full text linkModular design based on spatial division-multiplexing switches is a promising way to improve the capacity and reduce the cabling complexity of data center networks. However, due to the coexistence of mice and elephant flows, in modular data center networks a trade-off between the blocking probability and total throughput arises. In fact, blocking elephant flows would lead to a relevant penalty on the throughput but a small penalty on the blocking probability. In this paper, we investigate the relation between the blocking and throughput in modular data center networks based on optical spatial division multiplexing. We combine the two metrics linearly by a weight factor that prioritizes them relatively. To solve the resource allocation problem, we propose both mixed integer linear programming formulations and close-to-optimal heuristics for three different spatial division multiplexing switching schemes. Simulation results demonstrate that a carefully chosen weight factor is necessary to achieve a proper balance between the blocking probability and throughput for all the schemes
Optical spatial division multiplexing for ultra-high-capacity modular data centers
No full textWe propose and evaluate four optical interconnect architectures based on spatial division multiplexing for ultra-high capacity modular data centers. It is shown in which way the best option depends on the network load and size
Benefits of joint planning of small cells and fiber backhaul in 5G dense cellular networks
No full textBase station (BS) densification is increasingly adopted by mobile operators in order to support increasing traffic demand. However, a large number of BSs requires many backhaul connections, which may be very expensive. For this reason, provisioning high speed backhaul connections to BSs in a cost-effective way is challenging, and it is important to efficiently utilize an existing fixed network infrastructure if possible. This paper proposes two optimized infrastructure-aware planning strategies for small cells and fiber backhaul. The first strategy is referred to as joint design (JD) and is based on the joint cost minimization of small cells and fiber backhaul. The JD strategy is compared to a traditional design (TD) solution based on a two-step optimization approach. In the latter a cost-optimal small cells placement is identified first, then the corresponding minimum cost fiber backhaul deployment is determined accordingly. A comparison between these two approaches in dense 5G urban scenarios shows that the relative performance of JD and TD largely depends on the expected traffic demand and on the existing infrastructure. In dense urban areas with the average traffic levels expected for the year 2020 and beyond, JD returns up to 50% lower deployment cost in a greenfield scenario, and up to 70% lower deployment cost in a brownfield scenario. Only in areas with extremely high traffic demand (e.g., open-air festivals and stadiums) JD returns deployment costs very similar to TD
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
Survivable BBU Hotel placement in a C-RAN with an Optical WDM Transport
No full textIn Centralized Radio Access Networks (C-RANs) Baseband Units (BBUs) are decoupled from Remote Radio Units (RRUs) and placed in BBU Hotels. In this way baseband processing resources can be shared among RRUs, providing opportunities for radio coordination and cost/energy savings. However, the failure of a BBU Hotel can affect a large number of RRUs creating severe outages in the radio network. For this reason, the design of a resilient C-RAN is extremely important. This paper focuses on the survivable BBU Hotel placement problem in C-RANs with an optical wavelength division multiplexing (WDM) transport. We first propose an algorithm that jointly decides (i) the placement of a minimum number of BBU Hotels and (ii) solves the Routing and Wavelength Assignment (RWA) problem for the fronthaul connections, ensuring that each RRU is connected to two different BBU Hotels (i.e., one primary and one backup). Then, we present a strategy for maximizing the sharing of backup BBU ports among RRUs, with the aim of reducing the total cost of the C-RAN while guaranteeing uninterrupted service provisioning in case of single BBU Hotel failure. Simulation results show that the proposed strategy helps reducing the overall C-RAN cost. On the other hand, it becomes also evident that the sharing benefits can be maximized only in the presence of a transport network with enough wavelength resources to handle potential bottlenecks that may occur when BBU Hotels are placed quite far from RRUs
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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