can simple optical switching fabrics scale to terabit per second

B56 J. OPT. COMMUN. NETW./VOL. 1, NO. 3 /AUGUST 2009 Gaudino et al.

Can Simple Optical Switching FabricsScale to Terabit per Second Switch

Capacities?Roberto Gaudino, Guido A. Gavilanes Castillo, Fabio Neri, and Jorge M. Finochietto

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Abstract—The design of fabrics for terabit packetswitches and routers needs to consider the limita-tions imposed by electronic technologies. In particu-lar, attention has to be paid to information densityand to power consumption and dissipation, as well asto power supply and footprint requirements. Opticaltechnologies can overcome some of these limitations.We analyze the use of optical fabrics to interconnectline cards in terabit packet switches and routers. Forthis purpose, single-plane and multiplane optical in-terconnection architectures are proposed that ex-ploit wavelength agility at line cards to implementthe required switching functionality. The physical-layer scalability and feasibility of these architecturesare studied by using realistic models, mostly based onthe characteristics of commercially available opto-electronic devices. As a result, the considered archi-tectures can be characterized in terms of power bud-get and signal-to-noise ratio, enabling the computat-ion of the maximum achievable port count and aggre-gate switching capacity. Our results show that aggre-gate capacities of the order of a few terabits per sec-ond are possible in very simple optical switchingfabrics and that the multiplane architectures permita complexity trade-off between the wavelength andspace domains, making the overall design more fea-sible.

Index Terms—Optical interconnects; Opticalswitching fabrics; Optical packet switching;Broadcast-and-select architectures.

I. INTRODUCTION

T he use of optical fabrics to interconnect line cardsin packet switches and routers is still an open

area of debate and research. Although packet switches

Manuscript received November 30, 2008; revised June 22, 2009;accepted June 23, 2009; published July 31, 2009 �Doc. ID 113579�.

R. Guadino, G. A. Gavilanes Castillo, and F. Neri are with theDipartimento di Elettronica, Politecnico di Torino, Corso Duca degliAbruzzi, 29-10129, Torino, Italy.

J. M. Finochietto (e-mail: [email protected]) is with theUniversidad Nacional de Córdoba-CONICET, Avenida VélezSarsfield, 1611-5000, Córdoba, Argentina.

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ith capacities above several terabits per second ofggregate bandwidth are currently commerciallyvailable, the number of backplane interconnectionsnd the power and information density are reachinghysical limits. Indeed, each new generation of com-ercial routers consumes more power than the previ-

us one, and it is more difficult to package them in aingle rack of equipment. Thus, high-end routers oftenomprise several racks of equipment: one or moreacks host the electronic switching fabric and the con-rol logic, while the other racks host the line cards. Inhis configuration, optical links are sometimes used tonterconnect the fabric with the line cards, evenhough they are used as pure optical wires, withoutny networking scope. These solutions occupy valu-ble space, consume too much power, and pose reli-bility concerns because of the large number of activeomponents in the switching fabric. Packet switchesith optical fabrics can potentially scale better toigher capacities, increase reliability, and at the sameime significantly reduce the footprint and power con-umption [1,2].

In this paper we consider optical interconnection ar-hitectures that make use of broadcast-and-selectnd/or wavelength-routing approaches [3] and exploitavelength agility at line cards to actually control

witching through an optical fabric. We consider dif-erent alternatives to implement the optical fabric,nd we evaluate their feasibility and scalability inerms of the maximum achievable port count and ag-regate bandwidth. For this purpose, the character-zation of the relevant optical components and theirenalties is discussed, resulting in the definition of re-listic device models that can be used to evaluate theverall performance of a given optical fabric. The pro-osed architectures belong to the well-known familysually referred to as “tunable transmitter, fixed re-eiver” (TT-FR) architectures, which have been deeplynvestigated in past years, but mostly from the net-orking side. The novelty of this paper is thehysical-layer scalability analysis based on today’sommercial optoelectronic component performance.

These architectures take advantage of the ex-

2009 Optical Society of America

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Gaudino et al. VOL. 1, NO. 3 /AUGUST 2009/J. OPT. COMMUN. NETW. B57

tremely large bandwidth that optical technologies canpotentially offer and, at the same time, consider theinherent difficulties in realizing fundamental routerfunctions in the optical domain such as queuing, con-tention resolution, labeling, etc. Indeed, while manyoptical switching experiments published in the past10–15 years propose to use optical processing tech-niques such as wavelength conversion or 3R regenera-tion, these approaches, although often successfullydemonstrated in a laboratory environment, are stillvery far from stable commercial applications, sincethey require optical components that are either intheir infancy or simply too expensive. In contrast, thearchitectures proposed in this paper require opticalcomponents that are commercially available nowa-days. The only significant exceptions are fast tunablelasers that, even though already demonstrated inmany experimental projects [1], do not yet have widecommercial availability. We will assume in this paperthe availability of tunable lasers that can switch in anegligible fraction of the packet duration.

An experimental prototype of a variant of the archi-tectures considered here was developed at the Photon-Lab and LIPAR laboratories of Politecnico di Torino[4,5]; however, it will not be described here because ofspace limitations.

The paper is organized as follows. Section II pro-vides a general framework for the proposed optical in-terconnection architectures. Sections III and IV intro-duce the different alternatives for implementingsingle-plane and multiplane optical fabrics usingmainly passive optical devices. Section V discusses thetypical transmission characteristics of these devicesand proposes realistic models based on the informa-tion available from commercial components. SectionVI analyzes specific issues of multiplane architec-tures. Section VII describes the general analyticalmodels used to evaluate the actual feasibility andscalability of the proposed optical fabrics. Section VIIIdiscusses the main results of the proposed analysis interms of the maximum port count and aggregatebandwidth. Finally, Section IX concludes the paper.

II. OPTICAL INTERCONNECTION ARCHITECTURE

We introduce in this section the switching architec-tures considered throughout the paper. The commonprinciple is the use of a simple WDM all-optical fabricthat interconnects N line cards in a nonblocking fash-ion. The optical fabric does not require any activeswitching element; thus, packet switching is actuallycontrolled at each line card transmitter by means offast tunable lasers (i.e., in the wavelength domain)and fast optical switches (i.e., in the space domain). Inthe case of single-plane architectures, only the wave-length domain is exploited; thus, no optical switches


re required. The basic scheme for the single-planease is shown in Fig. 1. Each line card is equippedith one (wavelength) tunable transmitter and oneurst-mode receiver (BMR) operating at the data ratef a single WDM channel. The optical fabric performsltering adequately to select the proper wavelength

at most one wavelength at any time) to be sent toach BMR. Consequently, all the BMR subblocks thatre present in our architectures are wavelength inde-endent (i.e., the optoelectronic front-end of the BMRs a traditional photodiode able to receive any of theavelengths used). Burst-mode operation is required

or these receivers, on a packet-by-packet basis. Byeans of fast tunable lasers, each packet is sent on a

pecific wavelength such that after traversing the op-ical fabric, the correct destination receiver is reached.ead-of-the-line blocking can be avoided by imple-enting virtual output queuing at the line cards [6];

hus, transmitters queue packets on a per-destinationasis.

All proposed architectures have a synchronous be-avior, with time-slotted operation, as depicted in Fig.[7]. For this purpose, all line cards are synchronized

o a common clock signal that can be distributed ei-her optically or electrically. Receiver contention isolved at transmitters, since packets are scheduled sohat at most one packet is sent to each receiver on aime slot. Switching speeds for tunable lasers atransmitters are assumed to be negligible with re-pect to time slot duration. The architecture can behown to be equivalent to a distributed crossbarwitch, which is able to connect at each time up to Nisjoint input–output pairs. Given this behavior, anycheduling scheme suited for an electronic crossbaran be applied to our optical fabrics. Switching deci-ions will translate into wavelengths to which tunableransmitters will have to tune and/or into open/closeommands for optical gates. Although in this paper weocus mostly on the optical physical layer, the remain-er of this section will discuss general issues relatedo the control of the switching fabric.

ig. 1. Single-plane architecture with distributed sequentialcheduling.


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Packet scheduling can be implemented in a central-ized fashion as in most current packet switches. Inthis case, an electronic scheduler is required so that,after receiving status information from line cards, itdecides a new permutation, i.e., an input–output portconnection pattern, for each time slot. Centralizedschemes can potentially offer excellent performance interms of throughput, but the electronic complexity ofthe scheduler implementation can upper bound theactual performance [2]. Indeed, in electronic switchesoptimal algorithms such as maximum weight match-ing [6] are impractical because of their complexity,and suboptimal ones, such as iSLIP [8], are in generalpreferred. Centralized arbitration schemes requiresignaling bandwidth to collect status information andto distribute scheduling decisions, and they introducelatencies due to the time needed to propagate such in-formation and to execute the scheduling algorithm.

In this context, the implementation of a distributedscheduling scheme becomes a crucial issue for assess-ing the actual value of the proposed optical intercon-nection architectures. Distributed schemes (see, e.g.,[9,10]) have been proposed for similar architecturesthat exhibit fair access among line cards using only lo-cally available information. These schemes share thecommon principle of requiring line cards to decide in astrictly sequential order which wavelength would beused for packet transmission in a given time slot. Asan example of a possible implementation, the time slotboundaries generated by a slot clock signal are de-layed by a fraction D (sufficient to make an access de-cision) of the time slot at each line card on the dashedsignal path, as depicted in Fig. 1. To avoid packet col-lisions (i.e., line cards sending packets to the samedestination), each line card must indicate which wave-length has been selected so that the following linecards can consider only unused (free) ones. This infor-mation can be written (read) on (from) a specific low-bit-rate channel. Although scheduling decisions arehandled sequentially in time, all packets in one timeslot must be received in parallel (at the same time) byall receivers. Thus, each line card introduces in thedata path a fixed delay, depending on its position inthe sequential access, to compensate scheduling times(see again Fig. 1). These delays, which can be esti-mated to be in the tens of nanoseconds range [4,5], canbe obtained by (fixed) short spools of fiber as depictedin Fig. 1 or by electronic delays inside line cards.

It can be shown that further variations of this basicscheme permit the transmission of variable-size pack-ets despite the slotted behavior of the architecture. Infact, variable-size packets can easily fit in successivetime slots without collisions problems, since each in-put has full control of the channel access during trans-mission. In particular, the scheme proposed in [10]


as shown good performance in terms of throughputnd latency.

The optical fabric architectures proposed in this pa-er preserve the capability of sequential schedulingecisions that are the base for this distributed sched-ling approach.

The single-plane optical fabrics can be extended toultiple planes by introducing active optical space

witching at line cards to select one of the availablewitching planes as shown in Fig. 2. One of the mainotivations behind multiplane extensions is to reduce

he number of required wavelengths (tuning range),hich can be a limiting factor for practical realiza-

ions of the proposed single-plane architectures. In-eed, as of today, the maximum tuning range for (evenrototypes of) tunable lasers are of the order of a fewens of wavelengths [11]. Adding space diversity to ourasic configuration permits us to use fewer wave-engths with respect to the number of line cards. It be-omes possible to reuse the same set of wavelengthsn each space-diverse entity (switching plane). Theumber of switching planes (from now on called S)ermits us to use N /S wavelengths, instead of the Nhat single-plane architectures require, and still ob-ain the same aggregate capacity.

III. SINGLE-PLANE OPTICAL FABRIC ARCHITECTURES

We propose five different alternatives to implementsingle-plane optical fabric. Each fabric uses passive

ptical devices, without any active switching element.oreover, to keep the optical plane simple, we propose

o use, at most, a single optical amplifier. Besides pre-enting the different architectures, we derive the ex-ression for the L�N� parameter that accounts forower penalties on an optical fabric with N line cards.he L�N� parameter is used in Section VII to assess

he architecture scalability when considering powerudget and signal-to-noise-ratio constraints.

Fig. 2. Multiplane optical fabric architecture.


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A. Single-Plane Broadcast-and-Select

The first proposed architecture uses an N :N passivestar coupler, i.e., a wavelength-independent N-input,N-output coupler, as shown in Fig. 3. In the rest of thepaper, this architecture will be referred as the “single-plane broadcast-and-select” (SBS) architecture. Thestar coupler is used to combine all optical signals fromtransmitters and broadcast them to all output ports.By means of a suitable optical filter before each re-ceiver, tuned to a specific wavelength, only one wave-length reaches each receiver. As a result, each outputreceiver is associated with a specific wavelength thattunable transmitters select when sending packets tothis destination. The scheduling algorithm must en-force that at most one transmitter is tuned to a givenwavelength in each time slot. The power loss of theSBS architecture LSBS�N� can be expressed on loga-rithmic scale as

LSBS��N��dB = Lstar��N��dB + �Lfilter�dB, �1�

where Lstar�N� is the power loss of the N-port star cou-pler and Lfilter is the loss of the single WDM channeloptical filter, assumed to be independent of N.

B. Single-Plane Couple-and-Demultiplex

While N :N star couplers so far have only a few com-mercial applications, standard 1:N splitters are muchmore common because of their use in passive opticalnetworks (PONs), which also makes their cost muchlower as a result of larger production volumes. Wethus propose a second architecture based on these de-vices, dubbed “single-plane couple-and-demultiplex”(SCD), shown in Fig. 4. An N :1 coupler is used to com-bine all inputs on a single fiber, and a 1:N WDM de-multiplexer distributes each wavelength to a specificreceiver. With respect to the previous architecture, theoptical filtering function is implemented by the WDMdemultiplexer itself, and no further filtering is re-quired. The power loss in decibels of the SCD archi-tecture LSCD�N� can be expressed as

Fig. 3. SBS optical fabric.


LSCD��N��dB = Lsplit��N��dB + Lmux��N��dB, �2�

here Lsplit�N� and Lmux�N� are the losses of a 1:Nplitter and a 1:N WDM demultiplexer, respectively.

. Single-Plane Couple-Amplify-Demultiplex

To overcome the significant power loss introducedy the splitter in the SCD architecture, an erbium-oped fiber amplifier (EDFA) can be used to amplifyll wavelengths that enter the WDM demultiplexer.he resulting architecture, dubbed “single-planeouple-amplify-demultiplex” (SCAD), is shown in Fig..

In this case, owing to the presence of the EDFA, welso need to consider optical signal-to-noise-ratioOSNR) constraints, as will be detailed in Section VII.

e will show that it is useful to evaluate power losseseparately before and after the EDFA. The power lossn the path from the EDFA output to the receivers ishus denoted La�N� (after the EDFA), while that fromransmitters to the EDFA input is Lb�N� (before theDFA). They are given by

LSCADa ��N��dB = Lmux��N��dB, �3�

LSCADb ��N��dB = Lsplit��N��dB. �4�

Fig. 4. SCD optical fabric.

Fig. 5. SCAD optical fabric.


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D. Single-Plane Couple-Amplify-Split (SCAS)

The “single-plane couple-amplify-split” (SCAS) ar-chitecture, shown in Fig. 6, is a simpler alternative toSCAD, that uses simpler components such as couplersand filters instead of the WDM demultiplexer. Thepower loss should again be split in two parts as fol-lows:

LSCASa ��N��dB = Lsplit��N��dB + �Lfilter�dB, �5�

LSCASb ��N��dB = Lsplit��N��dB. �6�

E. Single-Plane Wavelength-Routing

A well-known alternative to the previously proposedarchitectures is the use of an N :N arrayed waveguidegrating (AWG) [1]. Indeed, the inherent cyclic prop-erty of N :N AWGs enables the routing of packets bytuning the transmitter to a proper wavelength. There-fore, by means of a N :N AWG, a “single-planewavelength-routing” (SWR) architecture can be con-sidered as shown in Fig. 7. In the previous architec-tures, a unique wavelength is associated with each re-ceiver; thus, all transmitters use the same wavelengthto reach a given destination. To avoid receiver colli-sions, the adopted protocol must ensure that on agiven time slot all transmitters select different wave-lengths to send packets. The situation for the SWR ar-chitecture is different, since the actual routing of agiven wavelength through the N :N AWG also dependson the input port. The scheduling scheme shouldagain guarantee that a single packet is routed to eachoutput on each time slot. It is worth mentioning here,for reasons that will become clear below, that the situ-ation in which all transmitters are tuned on the samewavelength simultaneously is allowed in the SWR ar-chitecture from a scheduling point of view (i.e., thisconfiguration is collision-free for SWR), but poses sig-nificant limitations to physical layer scalability, asdiscussed in Subsection V.A.

The power loss of the SWR architecture can be sim-ply formulated as:

Fig. 6. SCAS optical fabric.


LSWR��N��dB = LAWG��N��dB, �7�

here LAWG�N� is the power loss of an N�N AWG de-ice.

IV. MULTIPLANE OPTICAL FABRIC ARCHITECTURES

The previous single-plane architectures can be ex-ended to multiplane ones if space switching capabili-ies are added to line cards, as previously discussed inection II. We assumed a simple architecture for theptical space switching element as illustrated in Fig.. The switch is based on a 1:S splitter with one semi-onductor optical amplifier (SOA) on–off gate on eachutput port, a solution that has already seen someommercial solutions, such as in [12]. The physicalharacterization of the components of this device isiscussed in Subsection V.B.

In multiplane architectures, each line card trans-itter is connected to all S switching planes, while

ach receiver is connected to only one switching plane.hus, each plane is associated with a unique group of/S different receivers. As a result, each plane can

ransfer at most N /S packets on each time slot; hencets switching capacity is reduced by a factor S with re-pect to the entire switch. In order to share each planemong all transmitters, S :1 couplers can be used toroom incoming signals from different transmitters ashown in Fig. 9. To control switching, line cards selecthe output switching plane to which the destinationeceiver is connected, and the line cards tune their la-ers to the corresponding wavelength to select the out-ut receiver.

Fig. 7. SWR optical fabric.

Fig. 8. Space diversity switch configuration.


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Multiplane fabrics make use of the previously de-scribed single-plane architectures on each plane, butnow for a given N each individual plane has to handleonly N /S wavelengths. Thus, all optical devices arescaled from N to N /S input–output ports, a featurethat, besides improving overall capacity, as detailedbelow, also reduces the tunability requirements (tun-ing range) on the transmitter lasers from N to N /Swavelengths. To illustrate the multiplane concept,Fig. 10 shows the multiplane solution for the SCADproposal. The resulting power penalty, denotedL�N ,S� for multiplane architectures, is similar to theanalogous single-plane case if components are scaleddown to N /S input–output ports, while an additionalpenalty is considered because of the introduction onthe data path of an S :1 coupler to connect transmit-ters to planes. The resulting multiplane fabrics aredefined as follows:

• Multiplane broadcast-and-select (MBS),• Multiplane couple-and-demultiplex (MCD),• Multiplane couple-amplify-demultiplex (MCAD),• Multiplane couple-amplify-split (MCAS),• Multiplane wavelength-routing (MWR).

V. OPTICAL DEVICES

All the proposed optical fabrics do not include anysignal regeneration besides pure linear optical ampli-fication. Using the common terminology introduced in[3], we are proposing no regeneration or at most 1R re-generation of the signal inside the optical fabric, whilewe exclude 2R and 3R regeneration. As a result,physical layer impairments may accumulate when in-creasing the port count N or the number of planes S,so that the characterization of the optical devices usedbecomes crucial to effectively assess the architecture’sultimate scalability. In performing our study, we ob-served that a first-order scalability assessment basedon theoretical insertion loss (IL) values gives unreal-istic results. As a clear example, the SWR architecturehas an IL that ideally does not depend on the numberof input–output ports, thus leading to a theoretical in-finite scalability. Clearly, we needed a more accurate

Fig. 9. General multiplane configuration.


econd-order assessment capable of capturing othermportant effects that characterize commercial de-ices, such as polarization dependence, excess losses,hannel uniformity, and crosstalk. Despite their dif-erent nature, all of these effects can be expressed asn input–output equivalent power penalty that ac-ounts for both actual physical power loss and thequivalent power penalty introduced by other second-rder transmission impairments, as described below.

. Power Penalties

Insertion Loss (IL). We indicate as IL the totalorst-case power loss, which includes all effects re-

ated to internal scattering due to the splitting processnd nonideal splitting conditions, such as material de-ects or manufacturing inaccuracies. In the case of-port splitters, the splitting process gives a mini-um theoretical loss increasing with 10 log �N� dB,

ut extra loss contributions due to nonideal effects, of-en referred to as excess losses (EL), must also be con-idered.

Uniformity (U). Because of the large wavelengthange typically covered by splitters, demultiplexers,nd AWGs, different transmission coefficients exist,ither for different wavelengths or even from port toort. Over all input–output paths, the propagationonditions vary slightly on the same device. This dif-erence is taken into account by the U penalty, whichs often referred to as the maximum IL variation overhe full set of physical paths on the full wavelengthange; note that the wavelength dependency loss is in-luded in U.

Polarization-Dependent Loss (PDL). The attenua-ion of the light crossing a device depends on its polar-zation state due to construction geometries or to ma-erial irregularities. Losses due to polarization effectsre counted as a penalty in the worst propagationase.

Crosstalk (X). When considering a signal out of aDM demultiplexing port, there is always an amount

f power, other than the useful one, belonging to otherhannels passing through the device. This effect, gen-

Fig. 10. MCAD architecture.


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erally referred as crosstalk, is due to the nonideal fil-tering effect inside demultiplexers, given that allchannels diffract nonideally through the same inter-nal concave slab waveguide [13]. For a given usefulsignal at wavelength �, the crosstalk is usually classi-fied [3] as either out of band, when the spurious inter-fering channels appear at wavelengths spectrallyseparated from �, or as in band, when they appeararound �. For the same amount of crosstalk power,this second situation is much more critical in terms ofoverall performance [13]. The contribution tocrosstalk is usually higher for wavelength-adjacentchannels XA than for nonadjacent channels XN. Fol-lowing the formalism presented in [14], the overallcrosstalk relative to the channel level, expressed in di-mensionless linear units, can be approximated as fol-lows:

X�N� = 2XA + �N − 3�XN. �8�

Out-of-band crosstalk, also called incoherentcrosstalk, is present on any WDM filtering devices,such as WDM demultiplexers, 1:N AWGs, and opticalfilters, because their ability to transmit or reject out-of-band signals does not behave as an ideal step trans-fer function. As such, out-of-band crosstalk is presentin all our fabric architectures. Typical values for mul-tiplexers [15] are −25 and −50 dB for adjacent XA andnonadjacent XN channels, respectively.

Equation (8) can be transformed into an equivalentout-of-band crosstalk power penalty (OX, in decibels)following the approximations presented in [14], givingrise to

OX��N��dB = 10 log10�1 + X�N��. �9�

In-band crosstalk, or coherent crosstalk, is due tointerference from other channels working on the samewavelength as the channel under consideration. Inour optical fabrics, in-band crosstalk is relevant forthe SWR architecture and for the multiplane architec-tures. In the first case, the same wavelength can begenerated simultaneously at the input of many AWGports. Due to the AWG actual transfer functions, someamount of in-band power leaks to other device ports.In the second case, nonideal space switching can injecta small portion of line card output into other switch-ing planes, as will be explained in Subsection VI.A.The impact of in-band crosstalk is typically high givenits in-band characteristics, and the equivalent powerpenalty (IX, in decibels) for the optimized decisionthreshold in the receiver can be estimated [13] as

IX��N��dB = − 10 log10�1 − X�N�Q2�, �10�

where Q is the target quality factor in linear units, de-termining the target bit error rate (typically, Q lies inthe range from 6 to 7 on a linear scale for a bit error


ate between 10−9 and 10−12). In the case of multiplanerchitectures, we consider X�S� to represent therosstalk contribution from other sources (for ex-mple, multiplane nonideal switches) relative to thehannel under consideration (see Subsection VI.A).

. Device Characterization

The previously described power penalties enable theharacterization of passive optical devices in terms ofhe overall power penalty they introduce for a givenumber of ports N. This penalty takes into account allctual passive losses introduced by the componentslus equivalent losses introduced by crosstalk impair-ents. To this end, a detailed study has been carried

ut in order to find reasonable values for realistic com-ercial devices, by analyzing a large number of data

heets for commercial devices [15–18]. As a result, weollected typical realistic values of each parameter forhe different devices. Linear and logarithmic regres-ion methods have been used to derive analytical for-ulas that fit data sheet values well and can estimate

nknown ones. For the same device type, the valueseported in data sheets from different vendors weresually very similar, since the reported values are of-en those that allow the specifications of some rel-vant international standard to be met. For instance,ost commercial 1:N splitters have values that are

et by current PON standards. Thus, the values thate have considered in this paper can be assumed to be

airly general and consistent among different opticalomponent vendors.

Results of this study for the star coupler and split-er devices are shown in Figs. 11 and 12, respectively.hese plots report the contribution of each of the indi-idual effects described in Subsection V.A, and the re-ulting total equivalent power penalty. In both cases,he ideal log�N�-like loss dominates the contributionsf other parameters such as U, polarization-ependent loss, and excess losses. However, as theumber of ports increases, so does the relative contri-

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bution of these second-order parameters. For in-stance, 20 ports contribute 3–4 dB of additional pen-alty with respect to the ideal case.

The characterization of WDM demultiplexers andAWGs is shown in Figs. 13 and 14. Ideally, the powerpenalty of these devices should be independent of thenumber of ports owing to the wavelength routingproperty. However, in both cases the IL values thatwere inferred from data sheets show a dependency onthe number of ports that contributes logarithmicallyto the power penalty.

Regarding crosstalk effects, we found thatcrosstalk-related contributions to penalty are veryweak for all architectures that create only out-of-bandcrosstalk, while they have a significant impact only onthe N :N AWG, which suffers from in-band crosstalk.The crosstalk power penalty in this case increases ex-ponentially, limiting the realistically useful size of theAWG device to about 10–15 ports �13–18 dB�. Thisrather strong limit is confirmed by several experimen-tal studies, such as [1,13], and it is in contrast withmany studies on switching architectures in whichAWGs with large port counts are indicated as very

0 10 20 30 400

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romising components for the implementation of largeptical switches (see, for instance, [19]).

Single-input single-output optical filters, such ashose requested by the SBS architecture, are typicallyuite ideal devices, with attenuation of adjacent chan-els of around 40 dB, so that we simply assumed anL value of 3 dB [20] and negligible crosstalk. Fromhe optical noise point of view, optical filtering devicesuch as demultiplexers, AWGs, and filters were con-idered to have the typical good performance of cur-ent commercial components used for dense WDMDWDM) applications. Thus, we assume flattop opti-al filters having an equivalent optical bandwidthhat is slightly larger than the bit rate carried on eachavelength.

Regarding WDM tunable transmitters, we modeledhem as optical sources characterized by a givenSNRTx, corresponding to the ratio between the use-

ul laser power and the noise floor due to spontaneousmission inside the laser. Though in standard WDMransmission OSNRTx gives negligible effects, we willhow later that it can be relevant for very large opticalabrics, because of the presence of N lasers, each oneontributing to a low (but nonnegligible) noise floor. Inur analysis, we have assumed a flat noise behavior ofhe transmitter lasers, characterized by an OSNRTxalue of 40 dB over a 0.1 nm reference bandwidth.he actual sidelobes of tunable lasers are not flat.hey are usually characterized by the side-mode sup-ression ratio (SMSR) parameter [21], which has typi-al values below 40 dB for good devices. We have in-roduced a worst-case model in which this spuriousaser noise is upper bounded by a flat noise whoseevel is determined by the side-mode suppression ra-io. Therefore, the typical OSNRTx is consistent withractical lasers.

Finally, for what regards the SOA-based spacewitches, we based our analysis on the characteristicsf one of the few commercially available specific SOA-ased switches [12], on the basis of the block diagram

0 10 20 30 400

5

10

15

20

25

30

Number of ports (N)

LA

WG

[dB

]

Total PenaltyILUPDLIX+OX Penalty

Fig. 14. Power penalties for N :N AWG devices.


dio

Ttoterascvtf

FaF�iccd

A

fsMtt

B

pboa(tpbtp

to


shown in Fig. 8. In the on state, the SOA is assumedto have a noisy behavior characterized by a noise fig-ure of 9 dB. In the off state, a realistic switching ex-tinction ratio of 35 dB is considered. This ratio turnsout to be relevant for large multiplane solutions, sinceit generates in-band and out-of-band crosstalk. Be-sides, we assumed a gain transparency condition forthe full switch, where the SOA gain compensates thepassive losses of the 1:S splitter required to imple-ment space switching inside the line card (as shown inFig. 8).

VI. MULTIPLANE SPECIFIC ISSUES

A. Switching Extinction Ratio

Due to the finite extinction ratio (ER) of the SOA-based switching devices, crosstalk arises acrossplanes. In the worst case, the number of crosstalk con-tributions is one in-band component for each plane,and the resulting crosstalk impact is given by the co-herent expression IX shown before, which here de-pends on S and on the nominal switch ER (in linearunits). As a result, the crosstalk penalty in multiplaneconfigurations due to this effect can be estimated as

IX��S��dB = − 10 log10�1 − �S − 1�ERQ2�. �11�

B. Cross Noise Floor Accumulation

Beside acting as a space switch, each SOA gate gen-erates amplified spontaneous emission noise when op-erating in the on state, which in turn is sent to allplanes. Though individually the resulting noise floorlevels are quite low, for a high number of planes all ofthese small contributions add up over a very largebandwidth, resulting in an intrinsic limitation to thescalability in some situations. We took this effect intoaccount in our model. The maximum number of noisefloor sources per plane is N /S; therefore, when all linecards are transmitting, the noise accumulates N /Stimes on each switching plane.

VII. SCALABILITY ANALYSIS

In this section, we consider the feasibility and scal-ability of the optical fabric architectures described inSections III and IV when taking into account the de-vice characterization and multiplane issues discussedin Sections V and VI , respectively. With this target inmind, we still need to introduce some other param-eters and assumptions for the transmitter–receiverpair.

For the transmitter, a typical average transmittedpower PTX of 3 dBm is assumed. This is consistentwith typical tunable laser peak output power of the or-


er of +10 dBm, and with the 6–7 dB equivalent lossntroduced by an external modulator (3 dB due to on–ff keying and 3–4 dB due to additional IL).

For the receiver, we assume a target bit error rateBER=10−12, for which the best receivers at 10 Gbits/s

oday have a typical reference receiver sensitivity PSf around −26 dBm (without any optical amplifica-ion). Since we wanted to address scalability at differ-nt bit rates, we looked for a suitable model on howeceiver sensitivity scales with the bit rate Rb. This is

nontrivial task, and we followed the analysis pre-ented in [22], which, inferring from many differentommercial data sheets, proposes a sensitivity slopeersus Rb of 13.5 dB/decade. Following this model,he receiver sensitivity in dBm can be determined asollows:

PS��Rb��dBm = − 26 dBm + 13.5 log� Rb

10 Gbits/s�.

�12�

or instance, given the aforementioned PS=−26 dBmt 10 Gbits/s, we infer PS=−17.8 dBm at 40 Gbits/s.inally, we considered an additional system margin=3 dB, accounting for any other nonideality, includ-

ng, for instance, components aging, burst-mode re-eiver penalty with respect to standard continuous re-eivers, laser misalignments, and wavelength-ependent gain in the EDFA.

. Nonamplified Fabrics

Given all the assumptions and models presented soar, the power budget analysis for the completely pas-ive optical fabrics (SBS, SCD, SWR, MBS, MCD,WR) can be evaluated quite simply by imposing that

he received power PRx must satisfy PRx�PS includinghe margin; i.e., on a logarithmic scale,

�PTx�dBm − �L�dB − � � �PS�dBm. �13�

. Optically Amplified Fabrics

In the case of amplified architectures, because of theresence of the EDFA and/or SOA, the analysis shoulde treated differently. We first observed that for mostptical transmission systems, the performance is usu-lly bounded by either the OSNR at the EDFA outputdue to amplified spontaneous emission noise) or byhe useful signal power at the input of the receiverhotodiode. Consequently, a typical system is limitedy either the lowest acceptable OSNR at the output ofhe last optical amplifier present in the transmissionath or by the receiver sensitivity.

To account for receiver sensitivity, we assume thathe EDFA operating point is maintained at a constantutput power of P =17 dBm by using proper
EDFA

efp

wsOta

faomrpe

1mclttmt

tpar

Fs


EDFA gain locking techniques. This power, when all NWDM channels are simultaneously active, is evenlydistributed among the N WDM channels, giving riseto a power per channel of

�PEDFA,out�dBm = �PEDFA�dBm − 10 log��N��dB. �14�

The OSNR-related constraint is slightly more com-plex to take into account. We assumed a (commonlyaccepted) target OSNR TOSNR=17 dB, defined over abandwidth equal to the bit rate, in order to have a nu-merical target value that is, to a good extent, indepen-dent from the bit rate. To this end, it is useful to per-form calculations by evaluating the noise spectraldensity GN�f� (in linear units) in order to account forall optical noise sources present in the systems and toapply the multiplane considerations described in Sec-tion VI.

Assuming that the noise power spectral density isflat over the full spectral window of interest, and thusassuming GN�f�=GN, we can express the noise powerPN integrated on a bandwidth equal to the bit rate Rbas

PN = GNRb. �15�

We now need a model to account for the accumula-tion of the different sources of amplified spontaneousemission noise. For an optical amplifier we have thatthe output noise spectral density can be estimated as

GN,out�f� = GN,in�f�GAmp + hf�GAmp − 1�FAmp, �16�

where h is Planck’s constant, FAmp is the amplifiernoise figure, and f is the optical frequency in hertz. Inour calculations, the EDFA is assumed to have a noisefigure of 5 dB, while the SOAs have a noise figure of9 dB.

For the single-plane optically amplified architec-tures (SCAD, SCAS), we need to take into account theaccumulation of the noise floors generated by thetransmitters, resulting in a noise spectral density atthe input of the EDFA given by

GN,in�f� =GN,Tx

Lb�N�N.

Similarly, for the multiplane configurations (MCAD,MCAS), we have

GN,in�f� =GN,in,SOAGSOA + hf�GSOA − 1�FSOA

Lb�N,S�

N

S.

For both equations, the last multiplicative term ac-counts for worst-case noise accumulation from differ-ent sources. Input noise power spectral density GN,Txand GN,in,SOA depend directly on the transmitter’snoise spectral density, which can be derived from thedefinition of OSNR . By combining all the previous
Tx

quations, we have all input values to be used in theollowing two scalability constraints for optically am-lified architectures:

�PEDFA,out�dBm − �La�dB − � � �PS�dBm, �17�

�PEDFA,out�dBm − �PN,EDFA,out�dBm − � � �TOSNR�dB,

�18�

here La are power penalties after the amplificationtage. These equations set sensitivity and targetSNR limits and account for the previously men-

ioned power margin � of 3 dB to consider componentging and other possible effects.

VIII. RESULTS

We report in this section the performance of the dif-erent architectures in terms of the maximum achiev-ble aggregate bandwidth and port count. Dependingn the different architectures, the scalability limitsay be set by the power sensitivity threshold at the

eceivers, by the OSNR at the optical amplifier out-uts, or by the onset of excessively high crosstalk lev-ls.

We first consider single-plane architectures. Figure5 shows for the five proposed architectures the maxi-um aggregate bandwidth versus the individual

hannel bit rates (called “line card bit rate” in the fol-owing). As the line card bit rate increases, all archi-ectures tend to a maximum constant value. In par-icular, the gain obtained beyond 40 Gbits/s isinimal. This result has interesting implications in

he design of future switching architectures.

The best performance for the single-plane architec-ures can be obtained on the SCAD architecture; theerformance reaches slightly more than 1 Tbit/s forny line card bit rate of the order of 10 Gbits/s, and itemains stable until 100 Gbits/s. Considering its sim-

2.5 10 2025 40 50 1000.01

0.1

1

Channel Bit Rate [Gbps]

Agg

rega

teB

andw

idth

[Tbp

s]

SCADSCDSBSSWRSCAS

ig. 15. Total aggregate bandwidth versus line card bit rate foringle-plane architectures.


msab

saSgsfifiSfcippa

tprBwptttwdtctOtvar

Ft


plicity, the SCAD architecture appears the most prom-ising one among all single-plane architectures.

All other architectures remain below 1 Tbit/s of ag-gregate bandwidth. The SWR architecture can offerresults similar to SCAD, but only when the line cardbit rate is very high, such as 100 Gbits/s, since thisallows a low N, which in turn keeps in-band crosstalkunder control. For lower line card bit rates and thus ahigher number of ports, the SWR architecture is se-verely limited by crosstalk. For instance, at a line cardbit rate equal to 10 Gbits/s, it is limited to below150 Gbits/s (i.e., N=15).

For the SBS architecture, the larger the line cardbit rate, the lower the aggregate bandwidth, since theincrease in the receiver sensitivity strongly penalizesthe maximum number of ports on the star coupler.This is compensated in the SCAD and SCAS architec-ture, since the EDFA power gain is useful when fewerchannels (ports) are present, and the per-channel gainis reasonably high. The behavior of the SCAS archi-tecture is top bounded by the SCAD architecture(which has an enhanced power budget by having onlydemultiplexer losses). The good performance of theSCAD architecture is further supported by the factthat it is in the end a simplified version of a single-span DWDM transmission system, for which stablecomponents, massive commercial deployments, andmany theoretical studies exist.

These results show that, for some architectures, therequired number of ports N for line card bit rates of10 Gbits/s can reach very high numbers (of the orderof 100), imposing very strict requirements on the tun-ability of WDM transmitters. When the number ofwavelengths N is very high, say above the maximumlevel of today’s standard WDM systems (80 wave-lengths), it is clear that the actual port count can bedirectly limited by the laser tunability range and canthus result in values lower than those shown by ourphysical scalability analysis.

2.5 10 2025 40 50 1000.01

0.1

1

Channel Bit Rate [Gbps]

Agg

rega

teB

andw

idth

[Tbp

s]

MCADMCDMBSMWRMCAS

Fig. 16. Total aggregate bandwidth versus line card bit rate formultiplane architectures �S=2,OSNRTx=40 dB�.


These considerations introduce the rationale forultiplane solutions, which try to overcome these is-

ues by introducing spatial switching at transmittersnd thus reduce the number of wavelengths requiredy the switch.

As a first example we considered the case S=2. Re-ults are shown in Fig. 16 for the different multiplanerchitectures. From this graph, we can deduce that for=2 optically amplified architectures double their ag-regate bandwidth, while nonamplified ones do nothow any significant bandwidth increase. The ampli-ed architectures benefit from dividing signal ampli-cation on more than one EDFA (e.g., two EDFAs for=2); thus, the amplifier gain is distributed among

ewer signals as the number of planes increases. Inontrast, the introduction of multiple planes does notmprove the available power budget much on nonam-lified architectures, since the passive losses are stillroportional to N. For this reason we focus only onmplified solutions from here on.

Figure 17 shows the maximum fabric capacities forhe MCAD architecture as a function of the number oflanes S and for different line card bit rates. Similaresults can also be obtained for the MCAS solution.oth architectures reach a maximum aggregate band-idth close to 5 Tbits/s for configurations with 10–20lanes. The curves show an optimum point versus Shat can be explained as follows. For low S, the limi-ations are similar to those of single-plane architec-ures and, up to a given point, the aggregate band-idth increases with S thanks to the previouslyiscussed better distribution of the optical amplifica-ion. Anyway, for large S (e.g., S�20), in-bandrosstalk and transmitter noise floors start pushinghe operation conditions of the power budget and theSNR toward its operation limits. As a result from

hese two different impairment sources, the optimal Salue for bit rates above 2.5 Gbits/s is around S=20nd aggregated capacities close to 5 Tbits/s wereeached.

ig. 17. Aggregate bandwidth comparison for the MCAD architec-ure (OSNRTx=40 dB).


mutcesppct

awha

eamuf

hntprcice

blprs

pecCgvba


The somehow counterintuitive behavior of thegraph for S higher than the optimal value, where thecurve is not monotonically decreasing but actually fol-lows a saw-tooth-like behavior, has the following ex-planation. The aggregate bandwidth is the result ofconsidering the actual number of wavelengths W tra-versing each plane multiplied by the number of planesS and the line card bit rate. Since W= �N /S� (i.e., wemust always assume an integer number of wave-lengths), W may turn out to be higher than N /S.Thus, an increment in S may not affect the value of Wbut may impact the resulting aggregate capacity,which actually increases linearly with S while thevalue of W remains unchanged. This phenomenon ismore visible for high bit rates (40, 100 Tbits/s), wherethe port count N is typically low, and the ratio N /Schanges smoothly as S increases.

All previous results assume a reasonable OSNRTx of40 dB for the line card transmitters. To better analyzethe impact of this parameter and to show how such anapparently minor detail is actually important, Fig. 18shows the aggregated maximum bandwidth (achievedby the best N and S combination) as a function ofOSNRTx. This figure shows that, for the multiplanearchitectures (MCAD and MCAS), this parameter issignificant and, if increased, may lead to further im-provement on overall scalability. In contrast, for SWR,SCD, and SBS, this effect is not relevant, since perfor-mance is power-budget limited.

To sum up, we have shown that multiplane architec-tures can effectively increase their maximum aggre-gate bit rate compared with single-plane ones, despitethe additional limiting effects implied by plane multi-plicity described in Section VI. In particular, amplifiedarchitectures can benefit significantly from multi-plane configurations. Moreover, the multiplane solu-tions are advantageous in terms of reduction of thenumber of required wavelengths.

40 45 50 55 60

1

10

Tx OSNR [dB]

Agg

rega

ted

Ban

dwid

th[T

bps]

MCADSCDSBSSWRMCAS

Fig. 18. Aggregated bandwidth dependency of all architectures onOSNRTx at 100 Gbits/s. Aggregated bandwidth is the maximumachieved by the architectures with any line card bit rate (and S val-ues for multiplane architectures).


IX. CONCLUSIONS

In this paper we analyzed simple single-plane andultiplane optical interconnection architectures for

se inside high-capacity packet switches. These archi-ectures make use of simple and mainly passive opti-al components and are conceived in a manner thatnables distributed packet scheduling algorithms. Wetudied their scalability properties, using nontrivialhysical-layer modeling of the optical components, ca-able of capturing the significant behaviors of realommercial devices available at the time of publica-ion.

Among single-plane architectures, the best resultsre obtained by the SCAD and SCAS architectures,hich are shown to be able to support 1 Tbit/s whenigh-bit-rate line cards are used, such as 40 Gbits/s,nd 25 wavelengths.

Multiplane optical fabric architectures can reachven higher aggregate capacities (near 5 Tbits/s)nd/or reduce significantly wavelength agility require-ents of tunable devices (and the total number of

sed wavelengths), making the overall design moreeasible.

These switching capacities are adequate for today’sigh-end devices and will probably also suffice in theear future. To obtain higher aggregate bit rates withhe switching fabric architectures considered in thisaper, improvements in optical components would beequired. For instance, N :N AWG devices with lowerrosstalk would allow the current achievable switch-ng capacity to be significantly increased. Very benefi-ial would also be improvements of the SMSR param-ter in lasers.

While other optical interconnect architectures withetter performance may be identified and studied fol-owing the approach outlined in this paper, the resultsresented above show that optical technologies haveeached the maturity to play a role in the design ofwitching architectures.

ACKNOWLEDGMENT

This work was partially supported by the Italianroject OSATE and by the Networks of Excellence-Photon/ONe and BONE (“Building the Future Opti-al Network in Europe”), funded by the Europeanommission through the 6th and 7th Framework Pro-rammes. Part of the contents of this paper were pre-iously reported in [7,23], where, however, the contri-ution of transmitter noise GN,Tx was not taken intoccount (hence results were more optimistic).


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REFERENCES

[1] J. Gripp M. Duelk, J. E. Simsarian, A. Bhardwaj, P. Ber-nasconi, O. Laznicka, and M. Zirngibl, “Optical switch fabricsfor ultra-high-capacity IP routers,” J. Lightwave Technol., vol.21, no. 11, pp. 2839–2850, Nov. 2003.

[2] N. McKeown, “Optics inside routers,” presented at EuropeanConf. and Exhibition on Optical Communication 2003, Rimini,Italy, Sep. 2003.

[3] R. Ramaswami, and K. N. Sivarajan, Optical Networks—APractical Perspective, San Francisco, CA: Morgan Kaufman,1988.

[4] A. Antonino, R. Birke, V. De Feo, J. M. Finocchietto, R.Gaudino, A. La Porta, F. Neri, and M. Petracca, “The WON-DER testbed: architecture and experimental demonstration,”in Proc. European Conf. and Exhibition on Optical Communi-cation 2007, Berlin, Germany, Sept. 16–20, 2007, p. 116.

[5] A. Antonino, V. De Feo, J. M. Finocchietto, R. Gaudino, A. LaPorta, F. Neri, and M. Petracca, “Toward feasible all-opticalpacket networks: recent results on the WONDER experimentaltestbed,” in Nat. Fiber Optic Engineers Conf., San Diego, CA,Feb. 24, 2008, OSA Technical Digest (CD), Washington, DC:Optical Society of America, 2008, paper JWA86.

[6] N. McKeown A. Mekkittikul, V. Anantharam, and J. Walrand,“Achieving 100% throughput in an input-queued switch,”IEEE Trans. Commun., vol. 47, no. 8, pp. 1260–1267, Aug.1999.

[7] J. M. Finochietto, R. Gaudino, G. A. Gavilanes Castillo, and F.Neri, “Simple optical fabrics for scalable terabit packetswitches,” in IEEE Int. Conf. on Communications, 2008. ICC’08, Beijing, China, May 19–23, 2008, pp. 5331–5337.

[8] N. McKeown, “The iSLIP scheduling algorithm for input-queued switches,” IEEE/ACM Trans. Netw., vol. 7, no. 2, pp.188–201, Apr. 1999.

[9] M. Ajmone Marsan, A. Bianco, E. Leonardi, and L. Milia,“RPA: a flexible scheduling algorithm for input bufferedswitches,” IEEE Trans. Commun., vol. 47, no. 12, pp. 1921–1933, Dec. 1999.

[10] A. Bianco, E. Carta, D. Cuda, J. M. Finochietto, F. Neri, “A dis-tributed scheduling algorithm for an optical switching fabric,”in IEEE Int. Conf. on Communications, 2008. ICC ’08, Beijing,China, May 19–23, 2008, pp. 5427–5431.

[11] A. Bhardwaj, J. Gripp, J. Simsarian, and M. Zirngibl, “Demon-stration of stable wavelength switching on a fast tunable lasertransmitter,” IEEE Photon. Technol. Lett., vol. 15, no. 7, pp.1014–1016, July 2003.

[12] Alphion, QLight I-Switch Model IS22, Advance Product Infor-mation, http://www.alphion.com.

[13] H. Takahashi, K. Oda, and H. Toba, “Impact of crosstalk in anarrayed-waveguide multiplexer on NN optical interconnec-tion,” J. Lightwave Technol., vol. 14, no. 6, pp. 1097–1105, June1996.

[14] G. P. Agrawal, Fiber-Optic Communication Systems, New York,NY: Wiley, 2002.

[15] ACCELINK, 100 GHz DWDM Module, Product Datasheet,http://www.accelink.com.

[16] FUTUREX, Single Mode Standard Star Coupler Module, Prod-uct Datasheet, http://www.futurexusa.com.

[17] JDSU, WDM Filter 100 GHz Multi-channel Mux/Demux Mod-ule and Tuneable Lasers, Product Datasheet, http://www.jdsu.com.

[18] ANDevices N�N, AWG Multiplexers and DemultiplexersRouter Module, Product Datasheet, http://www.andevices.com.

[19] D. Blumenthal and M. Masanovic, “Lasor (label switched opti-cal router): architecture and underlying integration technolo-gies,” presented at 31st European Conf. on Optical Communi-cation (ECOC 2005), Sept. 25–29, 2005.

[20] JDSU, WDM Filter 100 GHz Single-channel, ProductDatasheet, http://www.jdsu.com.


[21] S. L. Woodward, I. M. I. Habbab, T. L. Koch, and U. Koren,“The side-mode-suppression ratio of a tunable DBR laser,”IEEE Photon. Technol. Lett., vol. 2, no. 12, pp. 854–856, Dec.1990.

[22] E. Sackinger, Broadband Circuits for Optical Fiber Communi-cation, New York, NY: Wiley, 2005.

[23] J. M. Finochietto, R. Gaudino, G. A. Gavilanes Castillo, and F.Neri, “Multiplane optical fabrics for terabit packet switches,”in Int. Conf. on Optical Network Design and Modeling, 2008.ONDM 2008, Vilanova i la Geltru, Spain, March 12–14, 2008,pp. 1–6.

Fabio Neri (M’98-SM’08) was born in No-vara, Italy, in 1958. He holds an M.S. and aPh.D. in electrical engineering, both fromPolitecnico di Torino, Turin, Italy. His re-search interests are in the fields of perfor-mance evaluation of communication net-works, high-speed and all-optical networks,packet switching architectures, discreteevent simulation, and queuing theory. He isa Full Professor at the Electronics Depart-ment of Politecnico di Torino (www.tlc-

etworks.polito.it). His teaching duties include graduate-levelourses on computer communication networks and on the perfor-ance evaluation of telecommunication systems. He leads research

ctivities on optical networks and on switching architectures at Po-itecnico di Torino. He coordinated the participation of his researchroup to several national Italian research projects. He was involvedn a number of European projects on WDM networks and was theoordinator of the FP6 Network of Excellence e-Photon/ONe on op-ical networks, which involved 40 European institutions. He has co-uthored more than 150 papers published in international journalsnd presented in leading international conferences. Dr. Neri partici-ated to the technical program committees of several conferences,ncluding IEEE Infocom and IEEE Globecom. He was general co-hair of the 2001 IEEE Local and Metropolitan Area NetworksIEEE LANMAN) Workshop, of the 2002 and 2007 IFIP Workingonference on Optical Network Design and Modelling (ONDM), andf the Optical Networks and Systems Symposium at IEEE Globe-om 2008. He served on the editorial board of IEEE/ACM Transac-ions on Networking and is co-editor-in-chief of the Elsevier Opticalwitching and Networking Journal.

Roberto Gaudino was born in Turin, Italy,in 1968. He holds an M.S. and a Ph.D. inelectrical engineering, both from Politecnicodi Torino, Turin, Italy. Dr. Gaudino’s mainresearch interest is in the metro and long-haul DWDM systems, fiber nonlinearity,modeling of optical communication systems,and on the experimental implementation ofoptical networks. He is currently an Associ-ate Professor in the Optical CommunicationGroup at Politecnico di Torino, where he

orks on several research topics related to optical communications.e investigated new optical modulation formats, such as polariza-

ion or phase modulation, and on packet switched optical networks.r. Gaudino spent one year in 1997 at the Georgia Institute of Tech-ology, Atlanta, as a visiting researcher in the OCPN group, wheree worked in the realization of the MOSAIC optical network test-ed. From 1998, he has been for two years with the team that coor-inates the development of the commercial optical system simula-ion software OptSim. He is author or coauthor of more than 100apers in the fields of optical fiber transmission and optical net-orks; he is continuously involved in consulting for several compa-ies of the optical sector and in professional continuing education.e was the coordinator of the EU STREP project “POF-ALL” in006–2008, and he is currently the coordinator of its prosecutionPOF-PLUS,” both on short-reach optical transmission over plasticptical fibers.


cobCoc

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Guido A. Gavilanes Castillo (M’00) wasborn in Popayan, Colombia, in 1979. He ob-tained his M.S. degree in electronics andtelecommunication engineering from Uni-versidad del Cauca, Colombia, in 2002. Dur-ing the last year of his studies, he was amember of the Telematics EngineeringR&D Group within the same university. Be-ing awarded an ALPIP grant, he receivedhis second level masters degree in 2006 onOptical Communication and Photonic Tech-

nologies from Politecnico di Torino, Turin, Italy. During 2006, hewas awarded a research grant to investigate the use of optical tech-nologies in switching devices within the Telecommunication Net-works Group at Politecnico di Torino. He worked as a Network Man-agement Engineer in IT and network infrastructure for bankingand oil companies in 2003; this involved network service assess-ment and acquisition of new skills to cope with network automationdemands. As a developer, he participated in the integration of sev-eral networking applications, mainly enabling mobility in bankingbusiness in 2004. Since January 2007 he has been a Ph.D. studentin the Telecommunication Networks Group, where his main re-search area is focused on the assessment of optical technologies inenvironments beyond long-haul transmission, specifically in high-capacity switches and interconnects. He has been an active re-searcher in several initiatives, such as the Italian project OSATE(Optical Switching Architectures: Theory and Experimentation),the European 6th and 7th Framework Programme Networks of Ex-


ellence “e-Photon/ONe,” and “BONE,” respectively, specifically onptical networks. Mr. Gavilanes directed the faculty’s IEEE studentranch in 2001 as an IEEE student member at the Universidad delauca, Popayán, Colombia. As a volunteer, he was awarded in meritf his collaboration to the regional IEEE electronic communicationsommittee, IEEE Region 9, in 2004.

Jorge M. Finochietto was born in BuenosAires, Argentina, in 1978. He holds an M.S.and a Ph.D. in electrical engineering fromUniversidad Nacional de Mar del Plata, Ar-gentina, and from Politecnico di Torino,Turin, Italy, respectively. His research in-terests are in the field of performanceevaluation, high-speed networking andswitching, and optical and wireless net-works. He is currently an Associate Profes-sor in the Digital Communications Group at

niversidad Nacional de Cordoba, Argentina, and he is also an As-istant Researcher at the National Research Council (CONICET) ofrgentina. From 2005 to 2007, he was a post-doc student at theelecommunication Network Group of Politecnico di Torino. He haseen involved in several international research projects in the fieldsf communication networks. He has coauthored more than 40 pa-ers published in international journals and presented in leadingnternational conferences.


can simple optical switching fabrics scale to terabit per second

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