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Optimization Scheme for WDM-Based Transmission Technology Selection in Future Passive Optical Networks
No full textA Multi-Threaded Dynamic Bandwidth and Wavelength Allocation Scheme With Void Filling for Long Reach WDM/TDM PONs
No full textDynamic bandwidth and wavelength allocation with coexisting transceiver technology in WDM/TDM PONs
Get PDFPassive Optical Networks (PONs) are continuously evolving. One important requirement of these systems is the possibility to smoothly upgrade the network infrastructure as technologies evolve. During the process of network upgrade, a coexistence of new and old end-users, i.e., Optical Network Units (ONU), with diverse transceiver technologies, is expected. In this work, we focus on a scenario where the network is upgraded from a TDM PON to a hybrid WDM/TDM PON (both short-reach and long-reach), and where the transceivers used in the old TDM PON can coexist with the new transceivers adopted in the hybrid WDM/TDM PON. Therefore, we consider that three different types of transceivers can be installed at the ONUs: single fixed tuned lasers, array of fixed tuned lasers, and tunable lasers. In particular, we propose new Dynamic Bandwidth and Wavelength Allocation (DBWA) algorithms which solve the problem of managing the traffic originated by end-users equipped with transceivers with different characteristics. In this paper we focus on the case of transceivers characterized by different tuning times. To investigate the importance of a DBWA able to manage transceivers with different tuning times, we also compare them to DBWAs which are not aware that different transmission technologies coexist in the network. Then, we test these DBWAs in different network scenarios, and discuss what are the network parameters that mostly affect the algorithms performance. After showing the importance of having a DBWA that supports transceivers characterized by different values of TTs, we investigate also the practical case of tunable lasers that have different values of TT depending on the wavelength they have to retune to (i.e., higher distances between two wavelengths require higher TTs). Finally, we evaluate the performance of the previously proposed DBWAs when the arrays of fixed tuned lasers can transmit over a limited number of wavelengths, i.e., the number of lasers of the array is limited
Dynamic Bandwidth and Wavelength Allocation with Coexistence of Transmission Technologies in TWDM PONs
No full textOptimization of long-reach TDM/WDM passive optical networks
Get PDFLong-Reach Passive Optical Network (LR-PON) using hybrid TDM/WDM techniques is one of the candidates for the future optical access that can solve the expected increase in terms of traffic demand and area coverage. One of its advantages is the possibility to share the capacity of any wavelength among more than one user, through TDM/WDM hybrid multiplexing. However, it is still an open issue which transmission technology (DWDM transmitters, colorless transmitters, coherent detection, direct detection) can more effectively satisfy the requirements and characteristics of the future long-reach access network. In this article we propose a new optimization model based on Mixed Integer Linear Programming (MILP) that formalizes the problem of selecting the most cost-effective transmission technology in LR TDM/WDM PONs while also assigning the wavelength-channels line rate and the splitting ratio of the remote nodes at different levels, under bandwidth and power budget constraints. Using this proposed MILP formulation we can identify the optimal transmission technology for a wide set of possible LR-PON scenarios of interest. In this work we provide an evaluation of the optimal transmission technologies under several PON scenarios with varying traffic loads and area coverage. We also analyze the cost sensitivity of the optimization process for coherent-detection technology since it is still under research and development
Dynamic bandwidth and wavelength allocation strategies for long reach WDM TDM passive optical network
Get PDFLAUREA SPECIALISTICADurante la migrazione dai sistemi d'accesso ottici passivi (PON) verso reti d'accesso a lungo raggio (LR-PON), uno dei campi di ricerca che si apre è quello relativo ai metodi di allocazione dinamici della banda. Questo tema è ancora più importante se si considerano sistemi d'accesso che utilizzano come tecniche di multiplazione sia il TDM che il WDM (LR WDM/TDM PON). In questi sistemi, il design di nuovi sistemi di allocazione dinamica della banda deve essere rivolto, in particolare, alla soluzione di due problemi principali: la ricerca di metodi per assegnare gli slot di trasmissione su reti con più lunghezze d'onda e la ricerca di metodi che siano in grado di sfruttare efficientemente la banda disponibile in presenza di scenari a lunga e lunghissima distanza (fino a 100 km).
Molte soluzioni di allocazione della banda sono già state proposte in sistemi LR-PON a singola lunghezza d'onda (LR TDM PON) e in reti ibride WDM/TDM passive, senza però tener conto dei problemi introdotti dalla lunga distanza. Per quel che riguarda gli algoritmi di allocazione dinamica della banda e della lunghezza d'onda in sistemi LR WDM/TDM PON, invece, esistono in letteratura solo poche soluzioni già proposte.
Per questo motivo, e considerato l'elevato interesse da parte del mondo scientifico per questi nuovi sistemi d'accesso LR WDM/TDM PON, in questo lavoro di tesi proponiamo e valutiamo diversi schemi di allocazione dinamica della banda e della lunghezza d'onda.
Gli algoritmi studiati in questo lavoro hanno come obiettivo quello di cercare di utilizzare la banda disponibile quanto più efficientemente possibile e, contemporaneamente, quello di trovare metodi per ridurre il ritardo medio in rete delle trasmissioni. Le strategie proposte sono valutate attraverso simulazioni e confrontate con algoritmi esitenti per reti LR WDM/TDM PON.
In particolare i sistemi considerati possono essere classificati QoS-unaware, cioè che non differenziano il servizio fornito agli utenti sulla base delle diverse richieste di QoS. Tuttavia, gli algoritmi proposti sono in grado di garantire una stessa capacità minima di trasmissione, in modo da assicurare la fairness tra tutti gli utenti finali.Dynamic Bandwidth Allocation is a major open research challenge in
the migration of Passive Optical Network (PON) systems towards
Long Reach PON, especially when hybrid WDM/TDM is used (Long Reach
WDM/TDM PON). New and efficient solutions for Dynamic Bandwidth
and Wavelength Assignment are sought to address two main critical
issues of such PON system: how to schedule the transmissions over
multiple wavelengths and how to efficiently exploit the bandwidth
in presence of long propagation delays that characterize long
reach scenarios. While several DBAs have been proposed for
long-reach single-wavelength PON systems or for WDM/TDM hybrid PONs
(with no regard to the long reach aspect), only few DBAs have been
investigated in the case of combined LR WDM/TDM PON scenario.
In this work we propose and evaluate a number of Dynamic Bandwidth and Wavelength Allocation schemes with the aim of utilizing the available bandwidth efficiently while reducing as much as possible the average packet delay within a LR WDM/TDM PON. In particular, the algorithms proposed in this thesis are QoS-unaware, which means that QoS requirement of different ONUs are not taken into account. However, the proposed schemes do guarantee a bandwidth to each user
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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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