Conveying device having at least one movable transport device, wherein - the conveying device has an optical free-beam communication system having two transmission and reception units (101, 102), each of which comprises a transmitter, a receiver and a control unit and one of which is mounted on the movable transport device and the other of which is mounted on another section of the conveying device, and - the two transmission and reception units (101, 102) are in an optical free-beam connection and allow transmission of data packets, characterized in that - the control unit of at least one of the two transmission and reception units (101, 102), preferably the control unit of both transmission and reception units (101, 102), is configured such that it checks a received signal, in particular the data packets thereof or at least a prescribed type of data packets, for the presence of a device identifier that identifies the respective other transmission and reception unit (101, 102), and rejects the received signal, in particular the respective data packet, completely or in part if the received signal or the respective data packet contains no device identifier identifying the respective other transmission and reception unit (101, 102), and - the control unit of at least one of the two transmission and reception units (101, 102), preferably the control unit of both transmission and reception units (101, 102), is configured such that it generates a received clock signal from optical received signals received via the optical free-beam connection, captures the times of rising and/or falling edge changes in the received clock signal over a multiplicity of clock periods, uses the times in the past to estimate the time of the respective next edge change to form an estimated edge change time and uses the estimated edge change time and the actual edge change time to form a distance change value indicating a change of distance between the transmission and reception units (101, 102). - the conveying device has an optical free-beam communication system having two transmission and reception units (101, 102), each of which comprises a transmitter, a receiver and a control unit and one of which is mounted on the movable transport device and the other of which is mounted on another section of the conveying device, and - the two transmission and reception units (101, 102) are in an optical free-beam connection and allow transmission of data packets, - the control unit of at least one of the two transmission and reception units (101, 102), preferably the control unit of both transmission and reception units (101, 102), is configured such that it checks a received signal, in particular the data packets thereof or at least a prescribed type of data packets, for the presence of a device identifier that identifies the respective other transmission and reception unit (101, 102), and rejects the received signal, in particular the respective data packet, completely or in part if the received signal or the respective data packet contains no device identifier identifying the respective other transmission and reception unit (101, 102), and - the control unit of at least one of the two transmission and reception units (101, 102), preferably the control unit of both transmission and reception units (101, 102), is configured such that it generates a received clock signal from optical received signals received via the optical free-beam connection, captures the times of rising and/or falling edge changes in the received clock signal over a multiplicity of clock periods, uses the times in the past to estimate the time of the respective next edge change to form an estimated edge change time and uses the estimated edge change time and the actual edge change time to form a distance change value indicating a change of distance between the transmission and reception units (101, 102).