Zakład Teletransmisji i Technik Optycznych (Z-14) Badania w zakresie zaawansowania infrastruktury sieci fotonicznych (COST-291) Praca nr

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1 Zakład Teletransmisji i Technik Optycznych (Z-14) Badania w zakresie zaawansowania infrastruktury sieci fotonicznych (COST-291) Praca nr Warszawa, grudzień 2007

2 Badanie zaawansowanych formatów modulacji optycznej, metod symulacji propagacji sygnału oraz mechanizmów zapewnienia jakości usług w sieciach z grupową komutacją pakietów (OBS), stosowanych w optycznych sieciach telekomunikacyjnych Zadanie 3: Badanie efektywnych obliczeniowo metod symulacji propagacji sygnału w światłowodzie Praca nr Słowa kluczowe: telekomunikacja optyczna, symulacja systemów światłowodowych Kierownik pracy: Wykonawcy pracy: doc. dr hab. Marian Marciniak dr inż. Marek Jaworski mgr inż. Marcin Chochół spec. Hanna Skrobek mgr inż. Mariusz Zdanowicz mgr inż. Mirosław Klinkowski Kierownik Zakładu: dr hab. Marian Marciniak Copyright by Instytut Łączności, Warszawa

3 Zakład Teletransmisji i Technik Optycznych (Z-14) Badania w zakresie zaawansowania infrastruktury sieci fotonicznych (COST-291) Etap 1. Studium potencjalnych architektur całkowicie optycznego przetwarzania sygnału Etap 2. Analiza parametrów fizycznych przezroczystej sieci optycznej w aspekcie ich roli i wykorzystania w platformie GMPLS Zadanie 3. Projektu COST 291:Badanie efektywnych obliczeniowo metod symulacji propagacji sygnału w światłowodzie Zadanie 1. Projektu COST 291:Badanie wielopoziomowych formatów modulacji optycznej Etap 3. Badanie bezpieczeństwa informacji i odporności optycznej sieci cyfrowej na atak i zagrożenia Praca nr

4 Etap 1. Studium potencjalnych architektur całkowicie optycznego przetwarzania sygnału

5 Instytut ¾ AcznoŚci Zak ad Teletransmisji i Technik Optycznych (Z-14) Streszczenie Gwarantowana jakość us ug (QoS) i routing w sieciach optycznych z komutacj a¾ grupow a¾ pakietów (OBS - Optical Burst Switching) - projekt COST 291 Etap 1: Badanie mechanizmów zapewniania jakości us ug (QoS) w sieciach OBS Kwiecień 2007

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7 Streszczenie Rozwoju sieci transportowych zorientowanych na przesy anie danych wynika z faktu, ze Internet jest bezpo ¾ aczeniowa ¾siecia¾ oparta¾ na transmisji pakietów. W tym kontekście obiecujacym ¾ rozwiazaniem ¾ jest model sieci z komutacj a¾ grupowa¾ pakietów (OBS, ang. optical burst switching). Korzyści p yn ace ¾ z elastycznego prze ¾ aczania stosunkowo krótkich grup pakietów optycznych (ang. bursts) w modelu OBS sa¾ okupione znaczna¾ z o zoności a¾ systemu i trudnościami w implementacji. Stad ¾ istnieje potrzeba opracowania skutecznych metod pozwalajacych ¾ na dzia anie sieci OBS. To opracowanie poświ ¾econe jest problemowi gwarantowania jakości us ug (QoS, ang. quality of service) w sieciach OBS. W szczególności analizowane sa ró zne mechanizmy QoS ze wzgl ¾edu na ich wydajność. Dalsza cz ¾eść badań poświ ¾econa jest mechanizmowi ró znicowania us ug oparta na wyw aszczaniu burstu (ang. burst preemption). Wprowadzenie Ogólna koncepcja komutacji grupowej pakietów, zaproponowana na poczatku ¾ lat osiemdziesia- ¾ tych, by a przewidywana pierwotnie do zastosowań w komunikacji g osowej. Warto wymienić trzy g ówne ró znice miedzy komutacj a¾ grupowa¾ pakietów burst a innymi technikami (np. komutacja¾ po ¾ aczeń i komutacja ¾pakietów), a mianowicie: grupa pakietów burst ma pośrednia¾ ziarnistość w porównaniu z podstawowymi jednostkami komutowanymi (lub przenoszonymi) w przypadku komutacji po ¾ aczeń lub pakietów, którymi sa¾ odpowiednio wywo ania (badź ¾ sesje) i pakiety; w przypadku komutacji grupowej pakietów pasmo rezerwowane jest w jednostronnym procesie, tzn. ze grupa pakietów mo ze być wys ana do sieci bez potwierdzenia pomyślnej rezerwacji zasobów, natomiast w przypadku komutacji po ¾ aczeń pasmo dla po ¾ aczenia jest rezerwowane w procesie dwustronnym; dane moga¾ zostać wys ane dopiero po ustanowieniu i potwierdzeniu po ¾ aczenia (co zwi ¾eksza opóźnienia); podczas komutacji grupowej pakietów, pakiety danych b ¾ed a¾ przechodzić (ang. cutthrough) przez w¾ez y pośredniczace ¾ bez poddawania procesowi buforowania, inaczej ni z w typowej komutacji pakietów, gdzie pakiet jest magazynowany i kierowany w ka zdym w¾eźle pośrednicz acym, ¾ co powoduje wzrost z o zoności sprz ¾etowej w¾ez ów. Komutacja grupowa pakietów optycznych OBS [1] uwa zana jest obecnie za jedna¾ z g ównych koncepcji realizacji telekomunikacyjnej sieci szkieletowej nowej generacji, w której nie zachodzi konieczność stosowania buforowania pakietów [2]. Komutacja OBS odbywa si¾e na nast¾epuj acych ¾ zasadach: informacja jest przekazywana w postaci du zych pakietów o zmiennej d ugości, określanych nazwa¾ grupy pakietów burst;

8 w¾eze dzia a w sposób asynchroniczny; nast ¾epuje oddzielenie treści zasadniczej (ang. payload) od treści kontrolnej (zwanej BCP - Burst Control Packet) zawieraj acej ¾ informacj ¾e sterujac ¾ a. ¾ Ka zde wys anie grupy pakietów poprzedzone jest, z pewnym odst ¾epem czasowym (ang. o set time), wys aniem pakietu BCP, którego zadaniem jest kon guracja komutatorów i rezerwacja ście zki optycznej dla nadchodzacej ¾ grupy pakietów. Pakiet BCP podlega przetwarzaniu w ka zdym w¾eźle sieci, ¾ acznie ze zmiana¾ postaci sygna u z optycznej na elektroniczna ¾, podczas gdy grupa pakietów jest komutowana w postaci optycznej w sposób transparentny. Obecnie trwaja¾ intensywne badania majace ¾ na celu zapewnianie odpowiedniej jakości us ug sieci OBS, m.in. zmniejszenie opóźnienia i stopnia utraty pakietów. Cel pracy Zapewnianie jakości us ug jest jednym z najwi ¾ekszych problemów w sieciach OBS. Przy komutacji pakietów stosowane jest zwielokrotnianie statystyczne i zachodzi rywalizacja pakietów o dost ¾ep, skutkujaca ¾ utrata¾ przesy anych w sieci danych. Z tego powodu niezb ¾edne jest stosowanie specjalnych mechanizmów QoS ochrony ruchu o wysokim priorytecie. Celem tej pracy jest poszukiwanie mechanizmów zapewniajacych ¾ wydajne i stabilne, ze wzgl ¾edu na nat ¾e zenie obs ugiwanego ruchu, charakterystyki ró znicowania parametrów QoS takich, jak stopień utraty pakietów, zarówno dla ruchu o niskim (LP) jak i wysokim priorytecie (HP High Priority); w kontekście efektywności (wykorzystanie ¾ aczy, poziom zró znicowania klas) oraz mo zliwości wdro zenia. Wyniki pracy 1. W literaturze mo zna spotkać wiele ró znych mechanizmów poświeconych gwarantowaniu jakości us ug w sieciach OBS. Mechanizmy te sa¾ zwykle badane w specy cznych kon guracjach i stad ¾ ich wzajemne porównanie jest trudne do przeprowadzenia. W pracy dokonujemy bezpośredniego porównania wydajność najcz ¾eściej spotykanych mechanizmów QoS w ujednoliconej kon guracji pojedynczego, izolowanego prze ¾ acznika OBS. Otrzymane wyniki wykazuja, ¾ ze najni zszy stopień utraty pakietów, zarówno dla ruchu LP jak i HP, osiagany ¾ jest przy zastosowaniu mechanizmu z wyw aszczeniem burstu. Mechanizm z ró znicowaniem o setu czasowego (ang. o set-time di erentiation), który cz ¾esto jest wymieniany w literaturze, zapewnia wysoka¾ wydajność dla ruchu HP. Nie mniej jednak, jego wydajność przy alokacji zasobów ¾ acza, i stad ¾ przepustowość (ang. throughput), ulega pogorszoniu z powodu uktuacji o set-u. Ostatecznie, mechanizm oparty na alokacji kana ów optycznych (wavelengths) z progiem decyzyjnym (ang. threshold) charakteryzuje si ¾e najgorsza ¾ wydajnościa, ¾ która w du zej mierze zale zy od wartości progu decyzyjnego.

9 2. Problemem mechanizmu z wyw aszeniem burstu jest nadmierna rezerwacja zasobów wymagajaca ¾ zastosowania dodatkowych procedur sygnalizacyjnych w przypadku pomyślnego wyw aszczania. Problem ten mo zna uniknać ¾ przy zastosowaniu proponowanego mechanizmu z oknem wyw aszczeniowym (PW, ang. preemption window). W pracy przedstawiamy model analityczny mechanizmu PW oraz znajdujemy wielkość o setu, po wprowadzeniu którego mechanizm PW oferuje wydajność porównywaln a¾ z wydajnościa¾ klasycznego mechanizmu z wyw aszczeniem burstu. Wyniki uzyskano z wykorzystaniem stworzonego programu komputerowego symulujacego ¾ mechanizmy QoS jak i w oparciu o analiz ¾e matematyczn a. ¾ Publikacje przedstawiajace ¾ wyniki pracy: 1. Porównanie mechanizmów QoS: [3], [4], [5]; 2. Mechanizm PW z wyw aszczeniem burstu: [6]. References [1] C. Qiao and M. Yoo, Optical burst switching (obs) - a new paradigm for an optical internet, Journal of High Speed Networks, vol. 8, no. 1, pp , March [2] M. Klinkowski, D. Careglio and J. Solé-Pareta, Wavelength vs Burst vs Packet Switching: comparison of optical network models, ephoton/one Summer School 05, Aveiro (Portugal), February, [3] M. Klinkowski, D. Careglio, S. Spadaro and J. Solé-Pareta, Impact of Burst Length Di erentiation on QoS Performance in OBS Networks, in Proceedings of 7th IEEE International Conference on Transparent Optical Networks (ICTON2005), Barcelona, Spain, July [4] M. Klinkowski, D. Careglio, M. Marciniak and J. Solé-Pareta, Comparative Study of QoS Mechanisms in OBS Networks, in Proceedings of 11th European Conference on Networks and Optical Communications (NOC 2006), Berlin, Germany, July [5] J. Aracil, N. Akar, S. Bjørnstad, M. Casoni, K. Christodoulopoulos, D. Careglio, J. Fdez-Palacios, C. Gauger, O. Gonzalez de Dios, G. Hu, E. Karasan, M. Klinkowski, D. Morato, R. Nejabati, H. Øverby, C. Ra aelli, D. Simeonidou, N. Stol, G. Tosi-Bele, K. Vlachos, "Research in Optical Burst Switching within the e-photon/one Network of Excellence", Elsevier Optical Switching and Networking (OSN) journal, vol. 4, no. 1, pp. 1-19, February [6] M. Klinkowski, D. Careglio, D. Morató and J. Solé-Pareta, E ective Burst Preemption in OBS Network, in Proceedings of 2006 IEEE International Workshop on High Performance Switching and Routing (HPSR 2006), Poznan, Poland, June 2006.

10 Instytut Šaczno±ci Zakªad Teletransmisji i Technik Optycznych (Z-14) Sprawozdanie Gwarantowana jako± usªug (QoS) i routing w sieciach optycznych z komutacj grupow pakietów (OBS - Optical Burst Switching) - projekt COST 291 Etap 1: Badanie mechanizmów zapewniania jako±ci usªug (QoS) w sieciach OBS Kwiecie«2007

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12 Contents List of Figures Summary and structure iii v I Introduction 1 1 Optical networking Motivations Internet trac growth Limitations of electronic technology Advances in photonic technology Optical transport networks Optical switching architectures Principle of operation OPS vs. OBS Characteristics of switching architectures Optical burst switching Overview of general OBS concepts Signalling Architectures and functions of OBS nodes Oset time provisioning Resources reservation Contention resolution Burst scheduling Quality of service provisioning Network routing II Quality of service provisioning 25 3 QoS provisioning in OBS networks Basic concepts of QoS in OBS networks QoS metrics Absolute vs. relative QoS guarantees i

13 3.1.3 QoS in connection-oriented and connection-less OBS Categories of QoS mechanisms in OBS networks with one-way signalling Control plane-related mechanisms Edge-based mechanisms Core-based mechanisms Performance of QoS mechanisms in E-OBS Overview QoS scenario details Simulation scenario Threshold selection in BD-W mechanism Performance results Burst loss probability and throughput Burst preemption vs. oset time dierentiation Summary Eective burst preemption in E-OBS Preemption rate in a buer-less OBS node Preemption Window (PW) mechanism Principles The length of preemptive window A single-wavelength model of PW mechanism Blocking probability of LP bursts Blocking probability of HP burst Some inferences from analytical model Computer simulation of PW mechanism Simulation scenario Numerical results PW and FDL buering Summary Conclusions 57 A Acronyms 59 B Related publications 61 Bibliography 64 ii

14 List of Figures 1.1 Generic architecture of optical DWDM network The trend of migration in optical networking Optical circuit switching network Optical packet switching network Optical burst switching network Overview over key parameters determining circuit/burst/packet granularity and required switching technology Signalling protocols in OBS networks OBS ingress edge node Burst control packet format OBS core switching node Oset time provisioning architectures Resources reservation schemes Contention resolution mechanisms Burst scheduling algorithms Categories of QoS mechanisms in OBS networks Selected QoS mechanisms in OBS networks Evaluated QoS network scenario Performance of BD-W mechanism (c = 8), a) HP class BLP, b) LP class BLP, c) throughput, d) threshold value guaranteeing BLP HP Performance of QoS mechanism vs. link dimensioning (ρ = 0.8, α HP = 30%), a) HP class BLP, b) LP class BLP, c) overall BLP, d) eective data throughput Burst loss probabilities vs. HP class relative load in OTD and BP mechanisms (ρ = 0.8, c = 8), a) HP class, b) LP class Eective throughout vs. HP class relative load in OTD and BP mechanisms, with overall trac load: a) 0.5, b) Percentage of additional signalling necessary to release preempted burst at each node, with HP class load: a) 30%, b) 50% Principles of the preemption window mechanism The length of preemptive window in PW mechanism iii

15 5.4 Preemption window scheme (the processing times are neglected for simplicity), T is the duration of the Preemption Window, l LP and l HP are the durations of the LP and HP bursts respectively, t is the arrival time of the HP control packet Simulation vs. modeling results (ρ = 0.8, α = 0.3, µ = 2) Burst blocking probability as a function of T comparing Gaussian and Exponential trac models (α = 30%, ρ = 0.8, W = 16) Burst blocking probability as a function of T and of W (α = 30%, ρ = 0.8, Gaussian trac model) Burst blocking probability as a function of ρ comparing Gaussian and Exponential trac models and dierent α (T = 10µs and W = 32) Burst blocking probability as a function of T (normalized to 1/µ) for dierent W and FDL buer size (α = 25%) iv

16 Summary and structure The evolution of the transport networking is driven by continuously increasing traf- c demand due to the introduction of broadband Internet access and new end-user business applications as well as the continuing paradigm shift from voice to data services. This trend has emerged at the same time as the advance in optical technology which has enabled the development of high-capacity transmission systems. The role of optics in communication networks is often limited to the realization of transmission functions, however, the next-generation networks will perform either some or all the switching and control functions in the optical domain. As a result the optical transport networks will provide a global transport infrastructure for legacy and new IP services (IP over DWDM). Optical burst switching (OBS) technology is a promising solution for reducing the gap between transmission and switching speeds in future networks. It oers both exibility and eciency through the exploitation of statistical multiplexing in optical domain. Nonetheless, due to the limitations in optical processing and queuing, OBS networks need a special treatment so that they could solve problems typical for datacentric networks. The problem of data loss is not uncommon in data-centric networks. As the network, or even some of its links and nodes, becomes congested, router buers ll and start to drop packets. Another cause can be the changes of routes as a result of inoperative network links. For non-real-time applications, such as le transfer and , packet loss is not critical. Packet protocols provide retransmission to recover dropped packets. However, in the case of real-time information, for instance in voice, video, telemedicine applications, packets must arrive within a relatively narrow time window to be useful to reconstruct the multimedia signal. Retransmission in this case would add extensive delay to the reconstruction and would cause clipping or unintelligible speech as well as discontinuous picture. Packets lost means lost of some information for these services. Discussed questions led to the introduction of dierent quality of service (QoS) classes. The transmission in OBS networks is very fast and in general the burst delays could be lower than in electronic packet networks (because of transparent optical switching without O/E conversion in intermediate nodes). Nevertheless, since there is no equivalent to the random access memories in optical networks the problem of excessive burst losses appears in OBS networks. In order to preserve the qualitydemanding applications from the best-eort data transmissions some dedicated QoS mechanisms have to be introduced to the network. First, in order to motivate the application of optical burst switching concept, Chapter 1 reviews the general characteristics, requirements, and trends of switching architectures considered for next generation optical networks. In particular, it introduce optical circuit switching, optical packet switching, and optical burst switching v

17 architectures. Then Chapter 2 discusses the features of optical burst switching as well as the-state-of-research solutions that are considered for OBS networks. The fundamental part of this work addresses the problem of QoS provisioning in OBS networks. Chapter 3 discusses some basic concepts of QoS as well as it presents the state of the art mechanisms dealing with QoS in OBS. The discussion is supported by a qualitative comparison of the mechanisms. Chapter 4 complements the study with a quantitative comparison of the performance of selected, most addressed in literature, QoS mechanisms in an OBS scenario. As an outcome the burst preemption mechanism, which is characterized by the highest overall performance, is qualied for operating in OBS networks. Since the preemptive mechanism may produce the overbooking of resources in any OBS network, Chapter 5 discusses this issue. Particularly, it proposes the preemption window scheme to solve the problem. Then it provide an analytical model which legitimates correctness of the solution. vi

18 Environment Optical Burst Switching (OBS): a photonic network architecture which overcomes the wavelength switching ineciency by a proper exploitation of the statistical multiplexing in the optical layer. On the contrary to optical packet switching, OBS uses large data bursts aggregated from the client packets in order to reduce the processing and switching requirements. Moreover, a burst control packet is transmitted in a dedicated control channel and delivered with some oset-time prior to the data burst. Contributions Related work: several QoS mechanisms for OBS networks burst preemption mechanisms with signalling overhead Our contributions: qualitative and quantitative comparison of the most referenced QoS mechanism estimation of the signalling overhead in a burst preemption mechanism proposal of a new preemption-based mechanism without signalling overhead Contents The content of this work is structured as follows: Part 1: gives an introduction to optical networking and in particular to OBS. In the beginning the drivers and trends in optical networking with a description of the main optical network models are discussed. Then an overview of OBS technology is presented. Part 2: is devoted to the problem of QoS guarantees in OBS network. The most addressed QoS mechanism are presented and their performance is studied. Then the proposal and analysis of a novel QoS preemption-based mechanism is provided. vii

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20 Part I Introduction 1

21 Chapter 1 Optical networking 1.1 Motivations Internet trac growth The telecommunication networks are experiencing a continuous increase in demand for transmission capacity. This trend is strictly related with the exponential growth of the Internet. The evolution of the Internet is accompanied by development of miscellaneous network applications; peer-to-peer (P2P) le exchange, video broadcasting, grid services are among the most bandwidth-demanding applications. Simultaneously we can observe a big progress in the deployment of access network technologies (e.g., ADSL, WLAN or FTTH). Broadband access networks place immense trac on the metro and core transport networks [KMM + 05]. As a consequence, the next generation networks must be able to cope with such increasing trac demands and so they should oer both high transmission and switching capacities. Another consequence of the expansion of the Internet is the continuing paradigm shift from voice to data services. This trend is followed by the migration of telecommunication industry from the voice-optimized to the IP-centric networks. In traditional voice-centric networks (such as SONET/SDH [G.700]) the connection-oriented circuit-switched operation is both powerful and ecient. In particular, the trac characteristic of a superposition of several dierent constant-bit-rate connections is the total sum and is still constant bit rate. In sharp contrast to, the trac characteristics in data-centric networks are typically characterized as being very bursty. Also, the packets, which are the basic data transport units, are often variable in length. Additionally, while a typical voice call is quite predictable in duration, i.e. the length of a conversation, the duration of the data transmission session in the Internet can vary by orders of magnitude and often have to be characterized by heavy-tailed distributions. All this results in so-called self-similar nature of Internet trac [LTWW94], which has a direct impact on network dimensioning; in particular, buer sizing is crucial. 2

22 Chapter 1. Optical networking 3 Client networks - IP, SONET/SDH, ATM,... Core node - All-optical switching function - Processing of control information (mainly electronically) Optical network Edge node - Adaptation function WDM links - Simultaneous data transmission on different wavelengths Figure 1.1: Generic architecture of optical DWDM network Limitations of electronic technology Electronic IP router architectures are not scalable enough and will suer from technological limitations when trying to reach the multi-terabit throughput range. Indeed when the bit rates increase the density of integration of electronic circuits increases as well. This may produce unwanted (parasitic) capacitances and impedances at small dimensions. Another problem is power consumption and heat dissipation at high integration level. Finally, electronic technology has its speed limitations Advances in photonic technology The observed trends have emerged at the same time with advances in optical transmission technologies which led to wavelength division multiplexing (WDM) systems [Cav00] [Kar02]. The dense WDM (DWDM), which is an extension of WDM, is able to accommodate up to hundreds of wavelengths; hence providing huge transmission capacities. Accelerated development of optical networking has been possible due to feasibility of integrated optics for both passive and active optical components [Chi01]. 1.2 Optical transport networks A generic architecture of optical transport network (see Figure 1.1) consists of source and destination edge nodes and intermediate core nodes that are connected by WDM links. Client networks (IP, ATM, SONET/SDH, etc.) are connected to the edge nodes

23 Chapter 1. Optical networking 4 time 2015 Static NG- Dyn. (OCS) BS over dynamic SDH WR-OBS APSON ORION G.709FS All-optical OBS OPS Field deployment Standards, product status 2010 Research, lab status 2005 From semi-static to dynamically re-configurable optical networks technology Figure 1.2: The trend of migration in optical networking. where there is some adaptation function responsible for conversion of data signal from its input form to an optical format used in the optical network. This function can perform for instance a simple conversion of wavelength, if the client network is an optical network, or more sophisticated data aggregation/assembly operation. The data in its optical form is transmitted through WDM links towards core nodes; the WDM technology allows to transmit simultaneously several data signals on dierent wavelengths at the same time. The core nodes are responsible for processing of control information and all-optical switching of the data signal. The processing of control information in most cases is performed electronically. When the data reaches the destination edge node it is converted back to its client signal format Optical switching architectures Optical networks adopt several switching models that were developed successfully in electronic networks. In traditional voice-communication networks, which apply a circuit-switching model of operation, the communication between end users is achieved with assistance of dedicated, and established in the connection-setup phase, circuit (or channel) connections. Such dedicated circuits cannot be used by other users during the connection duration even if no communication is taking place at the moment. Thanks to relatively simple maintenance of circuit-connections the adaptation of circuit-switching model to optical circuit switching (OCS) networks was considered from the very beginning [CGK92].

24 Chapter 1. Optical networking 5 On the contrary to the voice-oriented networks, the data-centric networks apply a packet-switching paradigm. In such networks the end-to-end communication is achieved through the transmission of small packets that carry portioned information. The packets are routed between network nodes over data links that are shared with other trac. Since the collision of packets may occur in the network a packet buering is applied in order to solve it. As a consequence of the success of electronic data packet networks, an immense eort has took place, beginning from the mid of 1990s, in the research on optical packet switching (OPS) technology [Chi95][CVG + 98]. A burst switching, applied e.g., for a block transfer in asynchronous transfer mode (ATM) networks [I.300], is another switching paradigm adopted to optical networks. A burst switched network is a packet-like network where each switching node extracts control information from incoming packet header in advance in order to establish and maintain the appropriate switch connection for the duration of incoming burst of data packets. Optical burst switching (OBS) architectures were proposed in the late 1990s [QY99][Tur99] with the objective to overcome both the low exibility of OCS architectures and technological limitations of OPS architectures. The expected migration of switching functions from electronic to optics will be gradual and will take place in several phases (see Figure 1.2) [KM01]. Nowadays, transport networks (SDH/ATM/IP) are based mainly on static point-to-point and ring connections. While the role of optics in these networks is limited mainly to the realization of transmission functions the next-generation networks are expected to perform dynamic optical switching as well. The functions related with node and network control will remain in the electronic domain. Nevertheless, it is very likely that some simple control operation will be also performed by means of optical processing [DHL + 03]. Looking for a transport architecture of future optical Internet a few network architectures have been proposed [LES00]. These optical network architectures differ with respect to the degree of optical transparency and the exibility of optical interconnection [GDW03]. Taking into account the status of the optical technology development the nearest solution will apply a circuit-switching model in optical circuit-switched (OCS) networks [CGK92][VKM + 01]. The fact that the Internet is a packet-based connection-less network is the main driver to develop a data-centric transport network. In this context two other switching architectures are considered by the research community, namely optical packet switching (OPS) and optical burst switching (OBS) [XPR01]. In the perspective of network optimization the implementation of packet/burst switching techniques directly in the transport network will bring more statistical sharing of physical resources and will reduce the connection costs Principle of operation Optical circuit switching (OCS) The operation of optical circuit switching networks is connection-oriented. In particular, the transmission of data from a source node to a destination node is realized on