Optical Networks - _10_5 Maximum Load Dimensioning Models_121

Optical Networks - _10_5 Maximum Load Dimensioning Models_121

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10.5 Maximum Load Dimensioning Models 609 Table 10.2 Reuse factor for 1% block- ing for different RWA algorithms for the 20-node network considered in [RS95]. RWA Algorithm Reuse Factor Random-1 6.9 Random-2 7.8 Max-used-1 7.5 Max-used-2 8.3 In addition to the choice of routes, the wavelength assignment algorithm also plays an important role in determining the reuse factor. Note that for the same number of available paths, the max-used algorithms have a distinct advantage over the random algorithms. The intuitive reason for this phenomenon is that the max- used strategy provides a higher likelihood of finding the same free wavelength on all the links along a particular route. A drawback of the max-used algorithm is that it requires knowledge of the wavelengths in use by all other connections in the network. When the routing and wavelength assignment is performed in a distributed manner, such information typically has to be obtained by means of periodic updates broadcast by each node. This again increases the control traffic load on the network. 10.5 Maximum Load Dimensioning Models As discussed above, from a dimensioning perspective, the fundamental property that distinguishes wavelength-routing networks from traditional electronic circuit- switched networks is the absence of full wavelength conversion. A number of studies have been undertaken to determine how networks using no, or limited, wavelength conversion should be dimensioned in order to support the same set, or sets, of lightpaths as an optical layer with full conversion. In this section, we will present some of the results obtained in this direction. We assume that both the lightpaths and the network edges are undirected. The results can be broadly classified into two categories: offline requests and on- line requests. The offline problem corresponds to a “static” network design problem, where only a single set of lightpaths is to be supported. This set is constrained to be such that it can be supported in a network with nodes capable of full wavelength conversion, with at most L wavelengths per link, since there is a routing that places no more than L routes on any link. Thus, the maximum load of this set of lightpaths is said to be L . In a network with nodes incapable of wavelength conversion, more
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610 WDM Network Design than L wavelengths per link would be needed, in general, to support the same set of lightpaths. We are interested in determining the additional number of wavelengths that would be required to support every set of such lightpaths, with nodes that do not have any wavelength conversion capability. Online RWA corresponds to the “dynamic” network design case where light- paths arise one at a time and have to be assigned routes and wavelengths when the request arrives, without waiting for future requests to be known. However, the requests and routing are such that no more than L lightpaths use any link at any given time. Thus a network with fully wavelength-converting crossconnects that provide L wavelengths on each link would be able to support all the requests. In
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This note was uploaded on 01/15/2011 for the course ECE 6543 taught by Professor Boussert during the Spring '09 term at Georgia Institute of Technology.

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Optical Networks - _10_5 Maximum Load Dimensioning Models_121

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