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UCLA COMSCI 218 - 10_2

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Integrated Dynamic 1P and Wavelength Routing in 1P over WDM NetworksMurali Kodialam T. V. LakshmanBell LaboratoriesLucent Technologies101 Crawfords Corner RoadHolmdel, NJ 07733, USA{muralik, lakshman}@bell-labs.comAbstractThis paper develops an algorithm for integrated dynamicrouting of bandwidth guaranteed paths in 1P over WDM net-works. By integrated routing, we mean routing taking intoaccount the combined topology and resource usage infor-mation at the 1P and optical layers. Typically, routing in1P over WDM networks has been separated into routing atthe IP layer taking only 1P layer information into account,and wavelength routing at the optical layer taking only op-tical network information into account. The motivation forintegrated routing is the potential for better network usage,and this is a topic which has not been been studied exten-sively. We develop an integrated routing algorithm that de-termines (1) whether to route an arriving request over theexisting topology or whether it is better to open new wave-length paths. Sometimes it is better to open new wavelengthpaths even V it feasible to mute the current demand overthe existing IP topology due to previously set-up wavelengthpaths. 2) For muting over the existing IP-level topolog~compute “good” routes. (3) If new wavelength paths are tobe set-up, determine the routers amongst which new wave-length paths are to be set-up and compute “good” routes forthese new wavelength paths. The pe~ormance objective isthe accommodation of as many requests as possible withoutrequiring any a pn”on knowledge regarding future am-vals.The mute computations account for the presence or absenceof wavelength conversion capabilities at optical crosscon-nects. We show that the developed scheme pe~orms verywell in terms ofpe~ormance metn”cs such as the number ofrejected demands.I. INTRODUCTIONWe develop an algorithm for integrated online routing ofbandwidth guaranteed paths in IP over WDM networks. Theproblem we consider is motivated by service provider needsfor fast deployment of bandwidth guaranteed services whichimply the need to dynamically set-up bandwidth guaranteedpaths between a network’s ingress-egress routers. Thoughbandwidth guaranteed paths can be set-up in a variety ofways, for ease of explanation we assume an MPLS network.Bandwidth guaranteed paths in this case are MPLS band-width guaranteed label switched paths (hereafter refered tomerely as LSPS). Since all potential LSP requests are notknown a priori, offline LSP routing algorithms cannot beused. Instead, on-line algorithms that handle requests ar-riving one-by-one and that satisfy as many potential futuredemands as possible are needed.The typical approach to routing LSPS is to separate therouting at each layer, i.e., routing at the IJYMPLS layer isindependent of routing of wavelengths at the optical layer.Wavelength-routing at the optical layer is used to set-up aquasi-static logical topology which is then used at the 1Player for IP routing. Algorithms for routing bandwidth guar-anteed paths considering only the IP layer topology and re-source information have been extensively studied. Someexamples are widest-shortest path routing [9], minimum-interference routing [11], and shortest-path routing withload-dependent weighting [15]. Wavelength routing at theoptical layer has also been extensively studied [12]. A keydifference, in an algorithmic sense, between LP layer LSProuting and wavelength routing is that in the optical networksome network elements may not be able to perform wave-length conversion and this has to taken into account by therouting algorithm.The prime difference between these previously consideredrouting problems, and the problem considered in this paperis that instead of separating routing at each layer we considerthe routing of LSPs taking into account the combined knowl-edge of resource and topology information in both the 1P andoptica~ layers. Clearly, this extra knowledge that is availableto an integrated routing algorithm can be exploited so thatthe integrated routing algorithm can extract better networkefficiencies than is possible with separated routing. An inte-grated dynamic routing scheme will be more robust to chang-ing traffic patterns at the II? layer, than a scheme which usesdynamic routing at the 1P layer only and uses a static wave-length topology determined by some a priori assumed trafficdistribution. The key issues in integrated routing, which thealgorithm that we develop addresses, are the following: (1)When a new request arrives, is this request to be routed overthe existing topology due to previously set-up wavelengthpaths? If it is to be routed over the existing topology, thenwhat is a “good” path? The measure of goodness is the se-lection of a path that permits as many future requests to berouted as possible. (2) If new wavelength paths are to beset-up then which are the routers amongst which new wave-length paths are to be set-up? (3) What are “good” routes int~e optical network for these new wavelength paths?0-7803-7018-8/01/$10.00 (C) 2001 IEEE IEEE INFOCOM 2001We develop a new integrated on-line routing algorithmwhich performs better than separated routing, and takes intoaccount all of the above issues. Also, it can take into accountrouter capacities and the presence or absence of wavelengthconversion capabilities at each of the optical network ele-ments. We show by simulation studies that the developed in-tegrated on-line routing scheme performs very well in termsof performance metrics such as the number of rejected de-mands.11. MOTIVATION FOR INTEGRATED ROUTINGThe network we consider consists of network elementswhich are either routers with WDM interfaces or opticalcross connects (OXCS). At the network edges, there area set of routers which we call ingress-egress routers. Forour purposes, the optical network can be thought of as afiber network with each fiber carrying multiple wavelengths,and where each network element is either an optical cross-connect (OXC) or a backbone router. Whereas a routercan handle traffic at any granularity and perform wavelengthconversion (i.e, route traffic from any incoming interface toany outgoing interface regardless of incoming and outgo-ing wavelengths), an OXC is a wavelength switch which canonly switch traffic at wavelength granularities. An OXC canswitch any wavelength from any input fiber link to any out-going link. Depending on the technology used, an OXC mayor may not be


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UCLA COMSCI 218 - 10_2

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