In an SDH transmission unit, a tributary block includes a plurality of routing blocks for accommodating low speed line signals of a predetermined capacity and performing line selection processing of the low speed line signals to be interfaced with a high speed block in accordance with a form of a tributary...http://www.google.fr/patents/US6600742?utm_source=gb-gplus-shareBrevet US6600742 - Add-drop multiplexer in an SDH transmission unit
