Abstract: For use in a multi-node digital network wherein the local clocks of all the nodes are required to be maintained in synchronism, and corrections are required to be effected for changes in propagation times of inter-node links. A clock deviation at either of two link-connected nodes is oppositely detected at both nodes, and this results in each node transmitting, in place of a normal "do-nothing" signal, an "advance" or a "retard" signal (i.e. opposite types) to the other to correct for the deviation. Each signal transmitted is allowed to be operative on the clock at the receiving node only if no other link, terminated on that node, is producing a contrary signal. Thus the clock of the node which has drifted is subjected to correction by a signal from the partner node. As regards a change in propagation-delay of the link (same for each direction of transmission) this results in both nodes of the effected link transmitting identical "advance" or "retard" signals to the partner.