We show that the accuracy of the international atomic time (TAI) system imposes no conditions on the one-way speed of light. The TAI is given by a network of atomic clocks distributed around the world that communicate with one another using radio synchronization signals. The synchronization signals sent by a transmitting station always arrive at the receiving station ?on time,' at any time of day and in any season, despite the motion of the earth. For certain authors this means that these signals propagate isotropically (with one-way velocity c), even on earth. In fact this may not be so; we shall show that the proper working of the TAI network says nothing about the one-way velocity c, as it is consistent with another theory, empirically equivalent to special relativity, in which the one-way speed of light has a directional dependence in moving frames.
