TOWARDS TRANSPARENT OPTICAL NETWORKS : STILL SOME CHALLENGES AHEAD

In the recent past, optical transparency -and more specifically the possible migration of incumbent opaque optical network towards optical transparency- have been intensively discussed and have drawn major interest from both optical systems vendors and network operators since they are expected to provide major cost reduction [1,2]. In first approximation, this cost reduction is of CAPEX nature and results from the elimination of costly optical-electrical-optical (OEO) located in the network nodes when a significant part of the traffic i.e wavelengths is maintained in the optical domain and transparently bypasses electrical switching and routing elements, which then need to be replaced by optical elements such a newly-developed Reconfigurable Optical Add-Drop Multiplexer (ROADM) or Wavelength Selective Switches (WSS) [3]. The consequences of such an evolution of optical networks towards transparency are a generation of a new set of constraints for the optical transport layer -since transmission distances are potentially significantly longer in transparent networks than in opaque ones- and the emergence of new technical challenges that we propose to discuss in this paper. These considerations will translate in increased complexity for the transmission layer and -to some extendincreased network management, that will lead to higher OPEX then counterbalancing the aforementioned cost benefits of transparent networks