The embodiments herein relate to a method in a communications network comprising a communications link connecting a first device to a second device. The communications link comprises an upper layer having a variable delay and a lower layer having a constant delay. The first device comprises a first clock and the second device comprises a second clock. The communications network synchronizes the first clock via the lower layer of the communications link with the second clock. The communications network determines, at the second device, a residence time for a first message when transmitted from the first device to the second device via the upper layer of the communications link.