A method for generating a frame signal includes monitoring a first frame signal and obtaining a first parameter based on the monitoring result; setting a second parameter based on the type of the first frame signal; when the first frame signal is being input, generating a second frame signal with a bit rate different from that of the first frame signal by determining data and stuff byte positions based on the first parameter and performing frame processing on data and stuff bytes corresponding to the first frame signal based on the determined data and stuff byte positions; and when the first frame signal is not being input, generating the second frame signal by determining the data and stuff byte positions based on the second parameter and performing the frame processing on data and stuff bytes corresponding to a maintenance signal based on the determined data and stuff byte positions.