A method is provided for seamless migration from a scaleable optical add/drop multiplexer to a network switching node in an optical transport network. The method includes: providing a pre-deployed optical add/drop multiplexer (OADM) at a network node in the optical transport network; introducing an additional optical add/drop multiplexer (OADM) at the network node; and interconnecting the pre-deployed OADM to the additional OADM using a photonic cross-connect switch, where the photonic cross-connect switch is operable to route optical signals amongst the optical transport lines connected to the pre-deployed OADM and the upgraded OADM.