Emerging Subsea Networks

Today’s undersea cable systems are increasingly complex and part of a much larger network topology that spans the continents. Operational efficiency can be significantly enhanced by integrating the undersea paths seamlessly into the overall network architecture. This implies that it is desirable to have one control plane for both the terrestrial and undersea parts of the network, one network management layer and similar transmission equipment. It is therefore not surprising that there is a tendency in the market to continue upgrading undersea cable systems with transmission equipment from the same supplier. This does not present a technical challenge as long as the undersea cable system is in operation and can be tested by prospective upgrade suppliers to ensure that capacity and system margin requirements can be met. However, a significant technical challenge exists if the cable is not yet in operation. In that case the cable is not available for testing and capacity and system margin must be predicted from specifications guaranteed by the cable supplier. A generally accepted performance metric for the undersea cable is the available optical signal to noise ratio (OSNR), which is a necessary but not sufficient parameter to characterize transmission performance. OSNR does not capture nonlinear transmission impairments and system designs with the same OSNR but very different transmission performance do exist. In this paper, we explore the two important cable implications of open cables: control plane requirements, and criteria for wet plant acceptance. We propose to use effective optical signal to noise ratio, which reflects a combination of linear and nonlinear transmission effects, to describe and guarantee cable performance for ultra-long haul and dispersion uncompensated transmission links.