In this paper, the challenges and problems for the in-band and off-band adaptive coding will be studied. To provide the agile and fast in-band adaptive coding, the information of the channel is inserted as the preamble into the each frame. Pseudorandom noise is utilized as the preamble and it is distributed and updated by the SDN controller to the transmitters and the receivers. Deploying the parallel preamble mapping distributed by the SDN controller is not only for the channel synchronization and the clock recovery but also for serving the in-band adaptive coding. The proposed scheme for the cross-layer design of the centralized SDN controller for the adaptive coding system is demonstrated and discussed. The proposed adaptive coding system is implemented and tested in the 100Gbps DP-QPSK fiber-optics transmission system. The performances of the system with different codes and adaptive scheme in the system are examined and plotted. Also, the time-domain analysis for the LDPCs changing is performed to demonstrate its operational features based on the different channel conditions signal-to-noise ratio (SNR). By deploying the pseudonoise preamble detection, the system enables the rapidly in-band adaptive coding service with low overhead and short guard time. The cross-layer SDN controlling scheme, for updating the mapping between preamble and codes, provides the agile and robust service in the fiber-optics network.