Method for synchronization in networks
View Patent ↗The invention relates to a method for synchronization in networks, whereby the local time (t loc ) which is valid at the particular node, is updated at different nodes. For that purpose, timing messages are regularly transmitted by a freely selectable superior node (N 1 ; N 3 ; N 6 ) and only by a superior node to an inferior node N 2 , N 3 ; N 4 -N 6 ; N 7 ), which receives the timing messages M 1 -M 8 ) and analyzes said messages for updating the local time (t loc ) thereof. A minimum propagation time (d min ) is determined for a timing message (M 1 -M 8 ) between an inferior node (N 1 ;N 3 ;N 6 ) and a superior node (N 2 , N 3 ; N 4 -N 6 ; N 7 ). When the inferior node (N 2 , N 3 ; N 4 -N 6 ; N 7 ) receives a timing message (M 1 -M 8 ), said inferior node extracts the local time of the superior node (N 1 ; N 3 ), which is contained in said timing message (M 1 -M 8 ) and adds the minimum propagation time (d min ) thereto, in order to generate a reference time (t comp, 1 -t comp, 8 ). Said reference time (t comp, 1 -t comp, 8 ) is then compared with the proper local time (t loc ). If the reference time is retarded in relation to the proper local time (t loc ), said proper local time (t loc ) is not updated. If said reference time is advanced in relation to the proper local time (t loc ).
1. A method for synchronization in a network in which a local time is updated at various nodes in the network, the method comprising:
determining, in a network, a higher-level node and a lower-level node;
receiving, at the lower-level node, a time message sent from the higher-level node;
reading, by the lower-level node, a local time of the higher-level node from the time message;
adding, by the lower-level node, a minimum delay time for a message to be transmitted between the higher-level node and the lower-level node, thereby generating a comparison time,
comparing, by the lower-level node, the comparison time to a local time of the lower-level node;
updating the local time of the lower-level node if the comparison time is newer than the local time of the lower-level node and not updating the local time of the lower-level node if the comparison time is older than the local time of the lower-level node;
if the local time of the lower-level node is not updated, monitoring, at the lower-level node, a non-zero time interval starting from a most recent update of the local time at the lower-level node;
producing a virtual local time at the lower-level node if the local time at the lower-level node has not been updated before the time interval exceeds a predetermined value, the virtual local time lagging behind the local time at the lower-level node; and
updating the local time of the lower-level node if the comparison time is newer than the virtual local time;
wherein the local time of the lower-level node is undated such that the local time of the lower-level node is set to the comparison time.
2. The method of claim 1 wherein the minimum delay time for a time message to be transmitted between the higher-level node and the lower-level node is either predetermined or is determined by a delay time measurement.
3. The method of claim 1 wherein a local clock is provided at both the higher-level node and the lower-level node, the local clock at the lower-level node having a speed slower than a speed of the local clock at the higher level node.
4. The method of claim 3 , wherein the speed of the local clock at the lower-level node is adjustable.
5. The method of claim 1 wherein the network comprises a first plurality of nodes each capable of acting only as a lower-level node, a second plurality of nodes each capable of acting as a higher-level node, and a third plurality of nodes each capable of acting as a lower-level node or as a higher-level node, synchronization of a node acting as a lower-level node occurring with respect to a single node acting as a higher-level node but in a manner decoupled from synchronization of the node acting as a higher-level node.
6. The method of claim 5 , wherein an independent local clock is provided at an intermediate node which acts both as a higher-level node and as a lower-level node in order to decouple synchronization of the intermediate node to a lower-level node from synchronization of the intermediate node to a higher-level node.
7. The method of claim 5 , further comprising the step of sending, from the higher-level node to the lower level node, (i) a total amount of update time corrections by which the higher-level node has been updated since a previous time message was sent by the higher-level node to the lower-level node until the current time message was sent by the higher-level node to the lower-level node, and (ii) a total amount of speed corrections by which a local clock at the higher-level node has been adjusted since the previous time message was sent by the higher-level node to the lower-level node until the current time message was sent by the higher-level node to the lower-level node.