A data transmission method and apparatus, a network device, and a storage medium are provided. In the method, a first network device determines whether there is a packet to be sent at a switching moment of a current time window; and the first network device sends a preset identification packet to a second network device in a case where there is no packet to be sent at the switching moment of the current time window, wherein the preset identification packet carries a window value of the current time window, and the window value is used for enabling the second network device to determine switching moments of different time windows of the first network device. By means of the solution, the problem that a downstream device cannot detect a time window exception of an upstream device is solved, thereby achieving the effects of shortening fault recovery time and improving communication efficiency.