Method for transmitting client data packets through an optical transmission network comprising multiple nodes (110a, 110b, 110c), the method comprising the steps of: - receiving (610, 705) a first container at a node (110a, 110b, 1 10c), the first container comprising a container header and a container payload portion, wherein the container header comprises at least information regarding a destination node of the first container and wherein the container payload portion includes a data portion comprising information associated with one or more client data packets directed to the destination node of the first container, the container header further comprising occupancy information indicative of the space occupied by the data portion in the container payload portion or about free space in the container payload portion, wherein a modular forward error correction, FEC, configuration is applied to the first container by including, in the first container, first FEC information referring only to the container header and second FEC information referring only to the container payload portion; - determining, at said node (110a, 110b, 110c), whether free space is available in the container payload portion for carrying a further data portion; - providing the further data portion, the further data portion comprising information associated with further client data packets directed to the destination node of the first container; and - transmitting (650, 760), in the optical domain, a second container comprising a container header including updated occupancy information and a container payload portion including the data portion and the further data portion to a further node (110a, 110b, 110c) and further containing updated first and second FEC information. - receiving (610, 705) a first container at a node (110a, 110b, 1 10c), the first container comprising a container header and a container payload portion, wherein the container header comprises at least information regarding a destination node of the first container and wherein the container payload portion includes a data portion comprising information associated with one or more client data packets directed to the destination node of the first container, the container header further comprising occupancy information indicative of the space occupied by the data portion in the container payload portion or about free space in the container payload portion, wherein a modular forward error correction, FEC, configuration is applied to the first container by including, in the first container, first FEC information referring only to the container header and second FEC information referring only to the container payload portion; - determining, at said node (110a, 110b, 110c), whether free space is available in the container payload portion for carrying a further data portion; - providing the further data portion, the further data portion comprising information associated with further client data packets directed to the destination node of the first container; and - transmitting (650, 760), in the optical domain, a second container comprising a container header including updated occupancy information and a container payload portion including the data portion and the further data portion to a further node (110a, 110b, 110c) and further containing updated first and second FEC information.