A method of transferring control data between a master device and a slave device over a path including at least one intermediate device, such that the path includes multiple path segments between successive pairs of devices. Data is transferred on each path segment in a plurality of frames of data, wherein the frames are synchronized between said path segments. The control data is transmitted in command slots of each frame, wherein a command slot comprises a set of control data bit slots, and wherein a control data bit slot is a time window associated with the transfer of a single control data bit over a single path segment between the devices on the path segment. The control data bit slots for each command slot are subdivided into: a first set of bit slots reserved for the transfer of control data in the direction from the master device to the slave device, and a second set of bit slots reserved for the transfer of control data either in the direction from the master device to the slave device or in the direction from the slave device to the master device. The time positions of the command slots on each path segment are offset from the positions of the command slots on each respective adjacent path segment by at least one control data bit slot.