FIG. 5 is a schematic diagram showing how to synchronize timing with a peer communications device according to an embodiment of the invention. According to an embodiment of the invention, the back-end communications device 520 may perform protocol layer communications with the data flow relay device 510 based on the time stamp principal, so as to obtain the packet link delay Ti between the back-end communications device 520 and the data flow relay device 510 and the timing error Te between the reference clock and the local clock of the back-end communications device according to the time stamps carried in the packet.

For example, the back-end communications device 520 may comprise a time stamp generating device 520-1. The time stamp generating device 520-1 may generate a time stamp recording the time for the packet being received. In addition, the time stamp generating device 520-1 may also generate another time stamp recording the time for the packet being transmitted back to the data flow relay device 510. As discussed above, the packet may be transmitted to the data flow relay device 510 in a wired or wireless manner depending on how the data flow relay device 510 is coupled to the back-end communications device 520.