A transceiver unit (101, 201) for a slave-end of a phase synchronized loop, the transceiver unit comprising: - an optoelectronic transmitter (102, 202) for producing, according to a transmission line-code, a first light signal carrying a bit stream to be transmitted and for directing the first light signal into an optical data transfer link between the slave-end and a master-end of the phase synchronized loop, - an optoelectronic receiver (103, 203) for receiving a second light signal from the optical data transfer link and for detecting, according to a reception line-code, a received bit stream from the second light signal, - electrical connectors (104, 204) for receiving from an external device at least part of the information contained by the bit stream to be transmitted and for delivering to the external device at least part of the information contained by the received bit stream, and - a processor (105, 205) for including a first timing signal into the bit stream to be transmitted, for detecting a second timing signal from the received bit stream, and for calculating a phase difference between a phase signal prevailing at the transceiver unit and a reference phase signal prevailing at the master-end on the basis of (i) a transmission moment of the first timing signal at the transceiver unit, (ii) a first time-stamp indicating a reception moment of the first timing signal at the master-end, (iii) a reception moment of the second timing signal at the transceiver unit, and (iv) a second time-stamp indicating a transmission moment of the second timing signal at the master-end, wherein the transmission line-code defines the manner the bit stream to be transmitted is encoded to the properties of the first light signal and the reception line-code defines the manner the received bit stream is encoded to the properties of the second light signal, characterized in that the processor is configured to read information indicating the values of the first and second time stamps directly from the received bit stream that is in a form corresponding to the second light signal according to the reception line-code. - an optoelectronic transmitter (102, 202) for producing, according to a transmission line-code, a first light signal carrying a bit stream to be transmitted and for directing the first light signal into an optical data transfer link between the slave-end and a master-end of the phase synchronized loop, - an optoelectronic receiver (103, 203) for receiving a second light signal from the optical data transfer link and for detecting, according to a reception line-code, a received bit stream from the second light signal, - electrical connectors (104, 204) for receiving from an external device at least part of the information contained by the bit stream to be transmitted and for delivering to the external device at least part of the information contained by the received bit stream, and - a processor (105, 205) for including a first timing signal into the bit stream to be transmitted, for detecting a second timing signal from the received bit stream, and for calculating a phase difference between a phase signal prevailing at the transceiver unit and a reference phase signal prevailing at the master-end on the basis of (i) a transmission moment of the first timing signal at the transceiver unit, (ii) a first time-stamp indicating a reception moment of the first timing signal at the master-end, (iii) a reception moment of the second timing signal at the transceiver unit, and (iv) a second time-stamp indicating a transmission moment of the second timing signal at the master-end,