Summary739(O/E) conversions, particularly at the higher bit rates, it makes sense to minimizethe number of these converters in the network. The first step in this direction wasthe development of ultra-long-haul systems, which provided longer reach betweenregenerators. The second step was to handle as much of the traffic passing througha node in the optical domain as possible. An all-optical OADM or OXC performsthis function. Having optical passthrough instead of electrical processing can leadto an order of magnitude savings in the cost, given that the cost of O/E conversionsdominates the cost of the node itself. There are associated savings in power and ﬂoorspace as well, given that the O/E devices consume most of the power and occupy mostof the ﬂoor space in WDM equipment. Even further cost savings can be realized bypassing signals through in bands of wavelengths, instead of individual wavelengths.
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