International Business Machines Corporation

Rudiger Karl Reischuk

Danny Dolev

Hovey Raymond Strong

Hovey Ramond Strong, Jr

A computer program product, such as a floppy disk with pre-recorded software, is provided. The computer program product is for use with a computer or processing system which is to function as a node within a network. Synchronization of a local time maintained at the node with a reference time is facilitated through execution of the prerecorded software by the node. Bursts of synchronization messages containing reference time stamps are transmitted over the network, or over a communication link, according to a predetermined protocol. The node receives and time stamps the messages. Thus, times according to a first time scale and a second time scale are obtained. The protocol defines temporal relationships between certain ones of the times. In accordance with the protocol, the node determines a difference between a first time according to one of the time scales and a time related to second and third times according to the other time scale. The node then updates its local time based on the difference. This synchronization method provides a well-defined upper bound of synchronization error, and allows the node to synchronize its internal time based only on information contained in the received messages and the internally generated local time stamp marks. No 'round trip' or handshaking messages are necessary to define the needed temporal relationships between the times according to the first and second scales. Thus, it is not necessary that the reference time source know the identity of the node which is synchronizing itself. The node also maintains a global precision value, which estimates its time synchronization error, by resetting the value when the node is synchronized, and updating the value as the node operates. Responsive to the global precision exceeding various theresholds, the node requests resynchronization or sends synchronization messages based on its internal time.

Computer program product for use with a network node for performing

A method is provided for synchronizing a local time maintained at a node within a network architecture with a reference time. Bursts of synchronization messages containing reference time stamps are transmitted over a network or communication link according to a predetermined protocol. A node to be synchronized receives and time stamps the messages. Thus, times according to a first time scale and a second time scale are obtained, and the protocol defines temporal relationships between certain ones of the times. In accordance with the predetermined protocol, the node determines a difference between a first time according to one of the time scales and a time related to second and third times according to the other time scale. The node then updates its local time based on the difference between the first time and the related time. This synchronization method provides a well-defined upper bound of synchronization error, and allows the nodes receiving the messages to synchronize their internal times based only on information contained in the received messages and their internally, generated local time stamp marks. Therefore, no 'round trip' or handshaking messages are necessary to define the needed temporal relationships between the times according to the first and second scales. Thus, it is not necessary that the reference time source know the identities of the nodes which synchronize themselves based on the messages. The node also maintains a global precision value, which estimates its time synchronization error, by resetting the value when the node is synchronized, and updating the value as the node operates. Responsive to the global precision exceeding various thresholds, the node requests resynchronization or sends synchronization messages based on its internal time.

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Munich, Georgia

Rudiger Karl Reischuk