A method includes: determining a target code block in a code block stream that is in a first rate mode and includes a plurality of code blocks, where the target code block includes a code block of a start type in the first rate mode; modifying information carried in a code block type field of the target code block to target information, where the target information includes information carried in a code block type field of a code block of a start type in a second rate mode; or the target information includes information carried in a code block type field of a code block of a terminate type in a second rate mode; and transmitting a code block stream in the second rate mode to a transport network, where the code block stream in the second rate mode includes a modified target code block.