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Optical multi-band OFDM switching technology
Sofiene Blouza, Esther Le Rouzic, Nicolas Brochier, Bernard Cousin
To cite this version:
Sofiene Blouza, Esther Le Rouzic, Nicolas Brochier, Bernard Cousin. Optical multi-band OFDM switching technology. 17th European Conference on Network and Optical Communications (NOC 2012), Jun 2012, Vilanova i la Geltru, Spain. �10.1109/NOC.2012.6249935�. �hal-01183350�
Optical Multi-band OFDM Switching Technology
Sofiene Blouza, Esther Le Rouzic, Nicolas Brochier Orange Labs Networks and Carriers
2, Avenue Pierre Marzin Lannion, France Sofiene.blouza@orange.com
Bernard Cousin University of Rennes 1, Irisa
Campus de Beaulieu Rennes, France
Abstract— With the continuing growth in the amount of traffic, improving the flexibility and the transparency of optical networks is a very important problem facing operators today. In this paper, we present a networking technique based on optical multi-band Orthogonal Frequency Division Multiplexing. The optical multi-band OFDM approach enables optical switching at fine granularity in a highly spectrum-efficient manner. We study the performance of this approach in term of blocking compared to mono-band opaque and mono-band transparent OFDM technologies in an optical core network. We show that the flexibility offered by optical multi-band OFDM is efficient in term of blocking and that the sub-band granularity has an important impact on the blocking ratio.
Keywords: All-optical network, multi-band optical Orthogonal Frequency Division Multiplexing, Wavelength/sub-band conversion, optical aggregation/disaggregation, wavelength continuity constraint.
I. INTRODUCTION
The telecommunication area has been marked in the last years by an important increase in traffic, doubling every two years approximately [1]. The massive emergence of new services with high capacity requirements, like audiovisual services such as video on demand, will certainly sustain this growth in the next years. To support this growth, optical core networks have to increase their link capacity up to 100 Gbps per optical channel. Around a hundred of WDM channels per fibres that is becoming the next standard for optical transmission systems.
In order to support the regular traffic growth, optical networks have already evolved towards wavelength routed networks, introducing Reconfigurable Optical Add Drop Multiplexers equipment and dynamicity thanks to a control plane. However, in a wavelength-routed network, the minimum granularity of an optical connection is the capacity of a wavelength. With capacity growing up to 100 Gbps per wavelength, this granularity is even larger than it was from traffic flows generated by users. Thus the requirement for aggregation into the wavelength “tunnels” is expected to grow. Today, this aggregation is done at the end points thanks to electrical switching [2]. But with traffic increase, the use of electrical switching generates an important growth in power consumption and network cost [3]. Netrwork operators aim thus to find solutions that offer such functionality with reduced impact on power consumption and cost. These
solutions should switch in the optical layer which may indeed provide these reductions thanks to the corresponding savings of optical-electrical conversions.
In this context optical multi-band OFDM (orthogonal frequency division multiplexing) technology can be an interesting candidate for future optical core networks. Optical multi-band OFDM can handle ultra high bitrates (as high as 100 Gbps and above). Itbenefits from an access to finer granularity than the aggregated 100 Gbps data rate while remaining in the optical domain. Using adequate add and drop sub-band functions in nodes, optical multi-band OFDM offers all optical switching and aggregation flexibility at granularities finer than the original generated 100 Gbs data stream. OFDM technology appears to be a particularly well adapted technology to sub bands generation thanks to a low modulation rate per carrier leading to very square sub-band spectrums [4]. We have introduced this concept in [5]. In this paper, we analyze the performance of this solution in terms of blocking probability compared to legacy scenario based on mono-band opaque or mono-band transparent techniques.
The paper is organized as follows. First we describe the concept of the optical multi-band OFDM technique and present the major network flexibilities offered by this approach. We then explain the advantages of the concept with respect to state of the art solutions. In Section III, we describe the network model and the reference scenarios used to evaluate the proposed solution. In Section IV, we present the network performances of the optical multi-band OFDM approach compared to the reference scenarios. Section V concludes the paper.
II. OPTICAL MULTI-BAND OFDM NETWORKING TECHNIQUE In this part, we present the concept of optical multi-band OFDM networking approach. Then we discuss the other technologies that can compete the optical multi-band OFDM technique.
A. Concept
The principle of OFDM is to split a high-rate data streaminto a number of lower-rate data streams that are transmitted over a number of sub-carriers.
Compared to “simple” optical OFDM, the optical multi-band OFDM approach consists to “slice” the channel spectrum in
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le wavelengt um along the o he major cont , SLICE doesn e all op optical multi-t fiber channel of 5 potential he sub-band ropped in the λ1 of fibre hannel λ1 of fi h fiber 3. The come from W osition in the al position in ogether in the be by-passe The sub-band sub-bands an port. capability, OF prove the
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luate the sub-g such a data fine granu ynchronous D sport Network DM offers the mpared to SD ger (25 Gbps H or 1 Gbp elastic optical e “slicing” o E as defined i 100 Gbps ser on format.It o f the fixed IT made of spec LICE techniq ding on the dem
lightpath req nder which is necessary spe th cross con optical path,. tribution of SL n’t allow to a ptical -band ls (λ1 sub-5 of node 1 are ibre 2 e sub-WDM input n the same ed by d add-d can FDM -band neable radio their or/and very minal long crease avoid -band a-rate ularity Digital k) but e sub-DH or for 4 ps for l path f the in [9] rvices offers TU-T ctrum que is mand quest. used ectral nnects LICE access
to the slot entities independently. In this respect, SLICE is not suitable for all optical aggregation purpose.
Thanks to the OFDM modulation, multi-band optical OFDM can offer flexibility and adaptability of SLICE within the limit of technological constraint. In addition the multi-band optical OFDM approach allows access to sub-wavelength entities.
III. NETWORK MODEL PERFORMANCE STUDY
As explained in the previous section, optical multi-band OFDM switching technology can be viewed as a way to virtually multiply the number of independent optical channels with fine granualarity. On a networking point of view, this approach is expected to improve transparency. In this section, we compare the network performance of multi-band optical OFDM switching technology to two extreme switching technology: purely mono-band opaque and purely mono-band transparent networks. The optical switching technologies are defined as follow.
Mono-band opaque switching technologies: this
switching technology corresponds to an OTN case where O-E-O convertors are systematically deployed at intermediate nodes of the network. In this opaque network, we have thus the total flexibility to aggregate/disaggregate the carried traffic. Each demand is then aggregated to occupy a minimum of channels on each link. As a result, tributaries coming from different sources and going to the same destination are aggregated in the intermediate nodes. In the same way, tpurely transit traffic is also systematically converted. In the following studies, we suppose that the minimum granularity switched/aggregated by the network is 1 Gbps. Optical channels are thus expected to be well filled. Howevertrafic is expected to undergo a high number of OEO conversions (one at each switch along the lightpath).
Mono-band transparent switching technologies: In
mono-band transparent switching, O-E-O (optical-electrical-optical) conversions are not used to aggregate/disaggregate demands and the mono-band structure of the optical channel does not allow to access to any sub-wavelength granularity. Each demand uses a dedicated wavelength channel. Depending on the traffic distribution (for example if the traffic is made of many small demands), optical channels are not well filled in this kind of network which can cause a waste of optical resources.
Optical multi-band OFDM switching technologies: In
optical multi-band OFDM switching. Each demand can use a sub-band or a group of sub-bands of the optical channel. Thanks to optical switching, demands can be aggregated in the same optical channel while remaining in the optical domain. Optical multi-band OFDM can be considered as a trade-off between opaque networks and transparent networks.
The performance of the three previous network scenarios is evaluated using an event driven simulator based on OMNeT++ [10]. The following assumptions are made.
A. Assumptions
The bit-rate of each optical channel is 100 Gbps, except for the multi-band OFDM where it depends on the number of sub-bands effectively. The maximum bit-rate of multiband OFDM is 100 Gbps.
Every link is composed of maximum 10 optical channels (arbitrary limit selected to reduce simulation times).
Links are bidirectional.
Duration of connections: we assume that the connections have a finite duration. The duration of connections is drawn randomly following an exponential law with parameter values … and …. The probability of appearance of a demand between
two nodes is drawn randomly following a uniform law with parameter values … and … . and …
A connection between two nodes is deactivated at the end of the communication and the resources are released.
Generated demands have a bit-rate between 1Gbps and 100 Gbps. The bit-rate of each request is drawn randomly with a uniform law with parameter values … and … ..
Routing algorithm: a shortest path algorithm is used to calculate the path of each request. The shortest path is calculated based on the number of hops in a path.
For the transparent case:
Wavelength continuity is assured. This means that each request must use the same wavelength along its path. Wavelength conversion is not used except when specified.
Connections are setup based-on first fit wavelength assignment.
For multi-band optical OFDM technology, we suppose that: Sub-band continuity is assured. Each request must
use the same sub-bands along its path. Sub-band conversion is not used except when specified.
Connections are setup based-on first fit wavelength and sub-band assignment on a chosen path. A connection is established using the shortest path and the first available continuous sub-band on this path. If no continuous sub-band is found, the connection is blocked.
The optical channel is composed of n sub-bands. The bit-rate of each sub-band is at maximum 100/n
Gbps (and since we do not consider data rate adaptation bit-rate of each sub-band is fixed to exactly this maximum).
The study is made on NSFnet network topology. The NSFnet network is composed of 14 nodes and 22 unidirectional links [11]. This network toplogy is one of the most used topology for similar studies. We suppose that each node of the network receives/transmits traffic from/to all other nodes.
Based on these assumptions we evaluate the performance of the proposed scenario.
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creasing the tical multi-ba h conversion multi-band O conversion gth conversio guess, this re on now favou multiple hops s reduce the a ngth/sub-band optical mu ub-bands have conside with 4 sub-b ave also bee mance. Now bands per op still keeping t e 7, we plotted with 10 sub-ba mance of optic 10 sub-bands mance is imp f 4 sub-bands number of su and OFDM w OFDM switc performs slig on (at most esult is due to urs demands s demands oc amount of use d conversion ulti-band OF ered a multi-ands. Wavele n investigate w we propos ptical channe the 100 Gbps d the perform ands. cal multi-ban s proved by ar . This result t ub-bands is m with ching ghtly 16% o the with ccupy eable does FDM -band ength ed to se to ls to s bit-mance nd round tends more effic conv H band the sub-aggr thus gran U opti mon tech effic how with Une imp num and swit be u T supp Fren [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] cient than im version However, the d is directly r number of su -band. So w regate-disaggr s a trade-off nularity. Using simula cal multi-ban no-band opaq hnology. Opti cient in term wever, it provi hout resortin expectedly, w rove much it mber of sub-ba steepness fix tching, but alr used for sub-b
The work des port of the 1 nch FUI Fram E. Le Rouzic, N Core Networks f S. Yao,”Design Electrical TDM A. Morea, Cont évaluation de le Ph.D. dissertatio S. L. Jensen, I. M OFDM Transmi SSMF,”, Journa 2009 S. blouza, E. Le “Multi-band OF Conference on C B. Ramamurthy networking," IE vol.16, no. 7, pp Yenista, http://w G. Bouyer, “Les B. Kozocki, H. T Yonenaga, M. Transmission in Photonics Techn Omnetpp, www Y. Yoon, T. Lee on Shortest Pa Conference on C mplementing c problem of related to tech ub-bands, we d we need very regate the sub
between tech
V. CO
ations, we stu d OFDM swi que and mon ical multi-ban m of blockin ide better resu g to electro wavelength/su s performance ands in the op the limit of t eady filters as and grooming ACKNOWL scribed in this 00G FLEX p ework page. REFER N. Brochier, B. A for Novel Applica n of Hybrid Op Switching”,GLO
tribution à l'étud eur faisabilité tec
on, Ecole Nationa Morita, C. W. Sch ssionwith 2-b/s/H l of Lightwave T Rouzic, N. Broc FDM for Optica Computer as a To y, B. Mukherjee EEE Journal on . 1061-1073, Sep www.yenista.com s réseaux synchro Takara, Y. Tsukis Jinno, “Op Spectrum-Sliced nology Letters, V .omnetpp.org. e, M. Young Chu ath in Optical W Computational Sc complex and increasing th hnological lim decrease the b ry selective b-bands. Numb hnical constra ONCLUSION udied first th itching techno no-band tran nd OFDM ap ng ratio as ult than mono onics at int ub-band conv es and less th ptical channel the feasibility s fine as 8 GH g. LEDGMENT s paper was ca project funded RENCES Arzur and P. Gav cations”, ECOC 2 ptical Networks OBECOM, 2003. de des réseaux o chnique et de le ale Supérieure de henk and H. Tan Hz Spectral Effic Technology, Vol. chier, B. Cousin, al Networking,” ool (EUROCON), e, “Wavelength n Selected Areas p. 1998. m. ones étendus”, He shima, T. Yoshim ptical Path Ag d Elastic Optical VOL. 22, NO. 17, ung, H. Choo, “T WDM Mesh Ne cience, 2005 costly wavele he number of mits. By incre bandwidth of optical filter ber of sub-ban aint and dem
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