A method includes: sending a first boundary bit block; sequentially sending an Ith bit block; determining a first parity check result and a second parity check result, where a check object of the first parity check result includes m consecutive bits of each bit block in the N bit blocks, a check object of the second parity check result includes n consecutive bits of each bit block in the N bit blocks, and at least one of m and n is greater than or equal to 2; and sending a second boundary bit block, the first parity check result, and the second parity check result.