The present invention discloses a method and system for communication. The method includes: according to a network resource and a signal type of a label switched path to be established, generating, by a first optical communication device, a label indicating that a first optical channel data unit is multiplexed to a second optical channel data unit, wherein the label comprises a tributary slot assignment indication field indicating a tributary slot occupied in the second optical channel data unit, and a length of the tributary slot assignment indication field is equal to the number of tributary slots of the second optical channel data unit; sending the label to a second optical communication device; obtaining, by the second optical communication device, the label; and multiplexing, by the second optical communication device, the first optical channel data unit to the second optical channel data unit based on the label.