Comparison of transparent versus opaque interconnecting nodes of OADM rings with respect to failure location

Optical communication systems have evolved towards ring networks interconnected through fully optical add-drop multiplexers (OADM). These networks offer advantages from the restoration point of view and allow the transparent exchange of data. The next step in the evolution is the interconnection of OADM rings through nodes being either opaque or transparent optical crossconnects (OXC). As it will be shown, both opaque and transparent OXC show advantages and disadvantages from the network flexibility, cost and failure management point of view. The objective of this study is to find the analytical expressions that give the maximum number of interconnected elements between monitoring points, called maximum segment size (MSS). Lower MSS is associated to better failure location, whereas higher MSS is associated to less precise failure location. The analytical expressions are confirmed with a set of simulations in a Pan-European network. The decrease of the MSS with respect to the installation of new monitoring equipment is also shown.