From a high-level view, core nodes are optical-electrical-optical based. This means that all optical traffic is converted to the electronic domain and processed by the node, whether the traffic is terminated at this node or not. In general, a node consists of a number of WDM transmit and receive cards, also referred to as transponders or transceivers, which are connected to an IP router. The IP router in turn can be connected to a number of access routers.