A communication system comprising a master apparatus and a slave apparatus, wherein: the slave apparatus is configured, in an upstream period, to transmit a slave data signal to the master apparatus based on a slave clock signal; and the master apparatus is configured to: during reception of the slave data signal from the slave apparatus in the upstream period, extract timing information from the slave data signal and adjust a phase and/or frequency of a master clock signal or a definition thereof relative to a reference phase and/or frequency based on the extracted timing information to enable decoding of the received slave data signal based on the master clock signal or that definition; in a downstream period, transmit a master data signal to the slave apparatus based on the master clock signal according to the adjustment carried out during reception of the slave data signal in the upstream period; and adjust the phase and/or frequency of the master clock signal during transmission of the master data signal in the downstream period to reduce a change in the phase and/or frequency of the master clock signal effected according to the adjustment carried out during reception of the slave data signal in the upstream period.