Improving Routing Efficiency, Fairness, Differentiated Servises And Throughput In Optical Networks

Wavelength division multiplexed (WDM) optical networks are rapidly becoming the technology of choice in next-generation Internet architectures. This dissertation addresses the important issues of improving four aspects of optical networks, namely, routing efficiency, fairness, differentiated quality of service (QoS) and throughput. A new approach for implementing efficient routing and wavelength assignment in WDM networks is proposed and evaluated. In this approach, the state of a multiple-fiber link is represented by a compact bitmap computed as the logical union of the bitmaps of the free wavelengths in the fibers of this link. A modified Dijkstra\u27s shortest path algorithm and a wavelength assignment algorithm are developed using fast logical operations on the bitmap representation. In optical burst switched (OBS) networks, the burst dropping probability increases as the number of hops in the lightpath of the burst increases. Two schemes are proposed and evaluated to alleviate this unfairness. The two schemes have simple logic, and alleviate the beat-down unfairness problem without negatively impacting the overall throughput of the system. Two similar schemes to provide differentiated services in OBS networks are introduced. A new scheme to improve the fairness of OBS networks based on burst preemption is presented. The scheme uses carefully designed constraints to avoid excessive wasted channel reservations, reduce cascaded useless preemptions, and maintain healthy throughput levels. A new scheme to improve the throughput of OBS networks based on burst preemption is presented. An analytical model is developed to compute the throughput of the network for the special case when the network has a ring topology and the preemption weight is based solely on burst size. The analytical model is quite accurate and gives results close to those obtained by simulation. Finally, a preemption-based scheme for the concurrent improvement of throughput and burst fairness in OBS networks is proposed and evaluated. The scheme uses a preemption weight consisting of two terms: the first term is a function of the size of the burst and the second term is the product of the hop count times the length of the lightpath of the burst

Design of Routers for Optical Burst Switched Networks

Optical Burst Switching (OBS) is an experimental network technology that enables the construction of very high capacity routers using optical data paths and electronic control. In this dissertation, we study the design of network components that are needed to build an OBS network. Specifically, we study the design of the switches that form the optical data path through the network. An OBS network that switches data across wavelength channels requires wave-length converting switches to construct an OBS router. We study one particular design of wavelength converting switches that uses tunable lasers and wavelength grating routers. This design is interesting because wavelength grating routers are passive devices and are much less complex and hence less expensive than optical crossbars. We show how the routing problem for these switches can be formulated as a combinatorial puzzle or game, in which the design of the game board determines key performance characteristics of the switch. In this disertation, we use this formu-lation to facilitate the design of switches and associated routing strategies with good performance. We then introduce time sliced optical burst switching (TSOBS), a variant of OBS that switches data in the time domain rather that the wavelength domain. This eliminates the need for wavelength converters, the largest single cost component of systems that switch in the wavelength domain. We study the performance of TSOBS networks and discuss various design issues. One of the main components that is needed to build a TSOBS router is an optical time slot interchanger (OTSI). We explore various design options for OTSIs. Finally, we discuss the issues involved in the design of network interfaces that transmit the data from hosts that use legacy protocols into a TSOBS network. Ag-gregation and load balancing are the main issues that determine the performance of a TSOBS network and we develop and evaluate methods for both

Design And Analysis Of Effective Routing And Channel Scheduling For Wavelength Division Multiplexing Optical Networks

Optical networking, employing wavelength division multiplexing (WDM), is seen as the technology of the future for the Internet. This dissertation investigates several important problems affecting optical circuit switching (OCS) and optical burst switching (OBS) networks. Novel algorithms and new approaches to improve the performance of these networks through effective routing and channel scheduling are presented. Extensive simulations and analytical modeling have both been used to evaluate the effectiveness of the proposed algorithms in achieving lower blocking probability, better fairness as well as faster switching. The simulation tests were performed over a variety of optical network topologies including the ring and mesh topologies, the U.S. Long-Haul topology, the Abilene high-speed optical network used in Internet 2, the Toronto Metropolitan topology and the European Optical topology. Optical routing protocols previously published in the literature have largely ignored the noise and timing jitter accumulation caused by cascading several wavelength conversions along the lightpath of the data burst. This dissertation has identified and evaluated a new constraint, called the wavelength conversion cascading constraint. According to this constraint, the deployment of wavelength converters in future optical networks will be constrained by a bound on the number of wavelength conversions that a signal can go through when it is switched all-optically from the source to the destination. Extensive simulation results have conclusively demonstrated that the presence of this constraint causes significant performance deterioration in existing routing and wavelength assignment (RWA) algorithms. Higher blocking probability and/or worse fairness have been observed for existing RWA algorithms when the cascading constraint is not ignored. To counteract the negative side effect of the cascading constraint, two constraint-aware routing algorithms are proposed for OCS networks: the desirable greedy algorithm and the weighted adaptive algorithm. The two algorithms perform source routing using link connectivity and the global state information of each wavelength. Extensive comparative simulation results have illustrated that by limiting the negative cascading impact to the minimum extent practicable, the proposed approaches can dramatically decrease the blocking probability for a variety of optical network topologies. The dissertation has developed a suite of three fairness-improving adaptive routing algorithms in OBS networks. The adaptive routing schemes consider the transient link congestion at the moment when bursts arrive and use this information to reduce the overall burst loss probability. The proposed schemes also resolve the intrinsic unfairness defect of existing popular signaling protocols. The extensive simulation results have shown that the proposed schemes generally outperform the popular shortest path routing algorithm and the improvement could be substantial. A two-dimensional Markov chain analytical model has also been developed and used to analyze the burst loss probabilities for symmetrical ring networks. The accuracy of the model has been validated by simulation. Effective proactive routing and preemptive channel scheduling have also been proposed to address the conversion cascading constraint in OBS environments. The proactive routing adapts the fairness-improving adaptive routing mentioned earlier to the environment of cascaded wavelength conversions. On the other hand, the preemptive channel scheduling approach uses a dynamic priority for each burst based on the constraint threshold and the current number of performed wavelength conversions. Empirical results have proved that when the cascading constraint is present, both approaches would not only decrease the burst loss rates greatly, but also improve the transmission fairness among bursts with different hop counts to a large extent

Architectures and protocols for sub-wavelength optical networks: contributions to connectionless and connection-oriented data transport

La ràpida evolució d’Internet i l’àmplia gamma de noves aplicacions (per exemple, multimèdia, videoconferència, jocs en línia, etc.) ha fomentat canvis revolucionaris en la manera com ens comuniquem. A més, algunes d’aquestes aplicacions demanden grans quantitats de recursos d’ample de banda amb diversos requeriments de qualitat de servei (QoS). El desenvolupament de la multiplexació per divisió de longitud d’ona (WDM) en els anys noranta va fer molt rendible la disponibilitat d’ample de banda. Avui dia, les tecnologies de commutació òptica de circuits són predominants en el nucli de la xarxa, les quals permeten la configuració de canals (lightpaths) a través de la xarxa. No obstant això, la granularitat d’aquests canals ocupa tota la longitud d’ona, el que fa que siguin ineficients per a proveir canals de menor ample de banda (sub-longitud d’ona). Segons la comunitat científica, és necessari augmentar la transparència dels protocols, així com millorar l’aprovisionament d’ample de banda de forma dinàmica. Per tal de fer això realitat, és necessari desenvolupar noves arquitectures. La commutació òptica de ràfegues i de paquets (OBS/OPS), són dues de les tecnologies proposades. Aquesta tesi contribueix amb tres arquitectures de xarxa destinades a millorar el transport de dades sub-longitud d’ona. En primer lloc, aprofundim en la naturalesa sense connexió en OBS. En aquest cas, la xarxa incrementa el seu dinamisme a causa de les transmissions a ràfega. A més, les col·lisions entre ràfegues degraden el rendiment de la xarxa fins i tot a càrregues molt baixes. Per fer front a aquestes col·lisions, es proposa un esquema de resolució de col·lisions pro actiu basat en un algorisme d’encaminament i assignació de longitud d’ona (RWA) que balanceja de forma automàtica i distribuïda la càrrega en la xarxa. En aquest protocol, el RWA i la transmissió de ràfegues es basen en l’explotació i exploració de regles de commutació que incorporen informació sobre contencions i encaminament. Per donar suport a aquesta arquitectura, s’utilitzen dos tipus de paquets de control per a l’encaminament de les ràfegues i l’actualització de les regles de commutació, respectivament. Per analitzar els beneficis del nou algorisme, s’utilitzen quatre topologies de xarxa diferents. Els resultats indiquen que el mètode proposat millora en diferents marges la resta d’algorismes RWA en funció de la topologia i sense penalitzar altres paràmetres com el retard extrem a extrem. La segona contribució proposa una arquitectura híbrida sense i orientada a connexió sobre la base d’un protocol de control d’accés al medi (MAC) per a xarxes OBS (DAOBS). El MAC ofereix dos mètodes d’accés: arbitratge de cua (QA) per a la transmissió de ràfegues sense connexió, i pre-arbitratge (PA) per serveis TDM orientats a connexió. Aquesta arquitectura permet una àmplia gamma d’aplicacions sensibles al retard i al bloqueig. Els resultats avaluats a través de simulacions mostren que en l’accés QA, les ràfegues de més alta prioritat tenen garantides zero pèrdues i latències d’accés molt baixes. Pel que fa a l’accés PA, es reporta que la duplicació de la càrrega TDM augmenta en més d’un ordre la probabilitat de bloqueig, però sense afectar en la mateixa mesura les ràfegues sense connexió. En aquest capítol també es tracten dos dels problemes relacionats amb l’arquitectura DAOBS i el seu funcionament. En primer lloc, es proposa un model matemàtic per aproximar el retard d’accés inferior i superior com a conseqüència de l’accés QA. En segon lloc, es formula matemàticament la generació i optimització de les topologies virtuals que suporten el protocol per a l’escenari amb tràfic estàtic. Finalment, l’última contribució explora els beneficis d’una arquitectura de xarxa òptica per temps compartit (TSON) basada en elements de càlcul de camins (PCE) centralitzats per tal d’evitar col·lisions en la xarxa. Aquesta arquitectura permet garantir l’aprovisionament orientat a connexió de canals sub-longitud d’ona. En aquest capítol proposem i simulem tres arquitectures GMPLS/PCE/TSON. A causa del enfocament centralitzat, el rendiment de la xarxa depèn en gran mesura de l’assignació i aprovisionament de les connexions. Amb aquesta finalitat, es proposen diferents algorismes d’assignació de ranures temporals i es comparen amb les corresponents formulacions de programació lineal (ILP) per al cas estàtic. Per al cas de tràfic dinàmic, proposem i avaluem mitjançant simulació diferents heurístiques. Els resultats mostren els beneficis de proporcionar flexibilitat en els dominis temporal i freqüencial a l’hora d’assignar les ranures temporals.The rapid evolving Internet and the broad range of new data applications (e.g., multimedia, video-conference, online gaming, etc.) is fostering revolutionary changes in the way we communicate. In addition, some of these applications demand for unprecedented amounts of bandwidth resources with diverse quality of service (QoS). The development of wavelength division multiplexing (WDM) in the 90's made very cost-effective the availability of bandwidth. Nowadays, optical circuit switching technologies are predominant in the core enabling the set up of lightpaths across the network. However, full-wavelength lightpath granularity is too coarse, which results to be inefficient for provisioning sub-wavelength channels. As remarked by the research community, an open issue in optical networking is increasing the protocol transparency as well as provisioning true dynamic bandwidth allocation at the network level. To this end, new architectures are required. Optical burst/packet switching (OBS/OPS) are two such proposed technologies under investigation. This thesis contributes with three network architectures which aim at improving the sub-wavelength data transport from different perspectives. First, we gain insight into the connectionless nature of OBS. Here, the network dynamics are increased due to the short-lived burst transmissions. Moreover, burst contentions degrade the performance even at very low loads. To cope with them, we propose a proactive resolution scheme by means of a distributed auto load-balancing routing and wavelength assignment (RWA) algorithm for wavelength-continuity constraint networks. In this protocol, the RWA and burst forwarding is based on the exploitation and exploration of switching rule concentration values that incorporate contention and forwarding desirability information. To support such architecture, forward and backward control packets are used in the burst forwarding and updating rules, respectively. In order to analyze the benefits of the new algorithm, four different network topologies are used. Results indicate that the proposed method outperforms the rest of tested RWA algorithms at various margins depending on the topology without penalizing other parameters such as end-to-end delay. The second contribution proposes a hybrid connectionless and connection-oriented architecture based on a medium access control (MAC) protocol for OBS networks (DAOBS). The MAC provides two main access mechanisms: queue arbitrated (QA) for connectionless bursts and pre-arbitrated (PA) for TDM connection-oriented services. Such an architecture allows for a broad range of delay-sensitive applications or guaranteed services. Results evaluated through simulations show that in the QA access mode highest priority bursts are guaranteed zero losses and very low access latencies. Regarding the PA mode, we report that doubling the offered TDM traffic load increases in more than one order their connection blocking, slightly affecting the blocking of other connectionless bursts. In this chapter, we also tackle two of the issues related with the DAOBS architecture and its operation. Firstly, we model mathematically the lower and upper approximations of the access delay as a consequence of the connectionless queue arbitrated access. Secondly, we formulate the generation of the virtual light-tree overlay topology for the static traffic case.Postprint (published version

New contention resolution techniques for optical burst switching

Optical burst switching (OBS) is a technology positioned between wavelength routing and optical packet switching that does not require optical buffering or packet-level parsing, and it is more efficient than circuit switching when the sustained traffic volume does not consume a full wavelength. However, several critical issues still need to be solved such as contention resolution without optical buffering which is a key determinant of packet-loss with a significant impact on network performance. Deflection routing is an approach for resolving contention by routing a contending packet to an output port other than the intended output port. In OBS networks, when contention between two bursts cannot be resolved through deflection routing, one of the bursts will be dropped. However, this scheme doesn’t take advantage of all the available resources in resolving contentions. Due to this, the performance of existing deflection routing scheme is not satisfactory. In this thesis, we propose and evaluate three new strategies which aim at resolving contention. We propose a new approach called Backtrack on Deflection Failure, which provides a second chance to blocked bursts when deflection failure occurs. The bursts in this scheme, when blocked, will get an opportunity to backtrack to the previous node and may get routed through any deflection route available at the previous node. Two variants are proposed for handling the backtracking delay involved in this scheme namely: (a) Increase in Initial Offset and (b) Open-Loop Reservation. Furthermore, we propose a third scheme called Bidirectional Reservation on Burst Drop in which bandwidth reservation is made in both the forward and the backward directions simultaneously. This scheme comes into effect only when control bursts get dropped due to bandwidth unavailability. The retransmitted control bursts will have larger offset value and because of this, they will have lower blocking probability than the original bursts. The performance of our schemes and of those proposed in the literature is studied through simulation. The parameters considered in evaluating these schemes are blocking probability, average throughput, and overall link utilization. The results obtained show that our schemes perform significantly better than their standard counterparts

Cross-layer modeling and optimization of next-generation internet networks

Scaling traditional telecommunication networks so that they are able to cope with the volume of future traffic demands and the stringent European Commission (EC) regulations on emissions would entail unaffordable investments. For this very reason, the design of an innovative ultra-high bandwidth power-efficient network architecture is nowadays a bold topic within the research community. So far, the independent evolution of network layers has resulted in isolated, and hence, far-from-optimal contributions, which have eventually led to the issues today's networks are facing such as inefficient energy strategy, limited network scalability and flexibility, reduced network manageability and increased overall network and customer services costs. Consequently, there is currently large consensus among network operators and the research community that cross-layer interaction and coordination is fundamental for the proper architectural design of next-generation Internet networks. This thesis actively contributes to the this goal by addressing the modeling, optimization and performance analysis of a set of potential technologies to be deployed in future cross-layer network architectures. By applying a transversal design approach (i.e., joint consideration of several network layers), we aim for achieving the maximization of the integration of the different network layers involved in each specific problem. To this end, Part I provides a comprehensive evaluation of optical transport networks (OTNs) based on layer 2 (L2) sub-wavelength switching (SWS) technologies, also taking into consideration the impact of physical layer impairments (PLIs) (L0 phenomena). Indeed, the recent and relevant advances in optical technologies have dramatically increased the impact that PLIs have on the optical signal quality, particularly in the context of SWS networks. Then, in Part II of the thesis, we present a set of case studies where it is shown that the application of operations research (OR) methodologies in the desing/planning stage of future cross-layer Internet network architectures leads to the successful joint optimization of key network performance indicators (KPIs) such as cost (i.e., CAPEX/OPEX), resources usage and energy consumption. OR can definitely play an important role by allowing network designers/architects to obtain good near-optimal solutions to real-sized problems within practical running times

Adaptive traffic distribution in optical burst switching networks

Master'sMASTER OF ENGINEERIN

Performance issues in optical burst/packet switching

The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-642-01524-3_8This chapter summarises the activities on optical packet switching (OPS) and optical burst switching (OBS) carried out by the COST 291 partners in the last 4 years. It consists of an introduction, five sections with contributions on five different specific topics, and a final section dedicated to the conclusions. Each section contains an introductive state-of-the-art description of the specific topic and at least one contribution on that topic. The conclusions give some points on the current situation of the OPS/OBS paradigms

Efficient Control Routing and Wavelength Assignment in Loss-Less Optical Burst Switching Networks

Katedra telekomunikační technik