Communicating time information in a network to enable synchronization

Abstract

A first node in a network receives a timing packet containing time information, where the timing packet is originated by a time server. The first node then updates the time information in the timing packet to reflect a delay associated with communicating the timing packet over a network link. The first node then updates the time information in the timing packet to reflect the delay associated transfer of the timing packet through the node. The first node sends the timing packet with the updated time information to a second node to enable the second node to use the updated time information for synchronization of the second node. The process repeats across an arbitrary number of nodes to enable time alignment between the first node and final destination node.

We claim: 
     
         1 . A method comprising:
 receiving, at a first node in a network, a timing packet comprising time information, the timing packet being originated by a time server;   updating, by the first node, the time information in the timing packet to indicate a cumulative delay comprising:
 a delay associated with communicating the timing packet to the first node over a network link to which the first node is connected; and 
 a delay experienced by the timing packet in transit through the first node determined using a local clock of the first node, the local clock of the first node having a lower accuracy than a clock associated with the time server; and 
   sending, by the first node, the timing packet with the updated time information to a second node to enable the second node to use the updated time information for synchronization of the second node.   
     
     
         2 . The method of  claim 1 , wherein the time information in the received timing packet comprises information indicating a time at which the timing packet was originated by the time server. 
     
     
         3 . The method of  claim 2 , wherein:
 the timing packet is received from a third node of the network; and   the time information in the received timing packet comprises information indicating a cumulative delay experienced by the timing packet before transmission of the timing packet from the third node to the first node.   
     
     
         4 . The method of  claim 3 , wherein the delay associated with communicating the timing packet to the first node over a network link to which the first node is connected is a delay associated with communicating the timing packet over a network link connecting the third node to the first node. 
     
     
         5 . The method of  claim 1 , wherein the timing packet comprises information indicating that the timing packet is a timing packet. 
     
     
         6 . The method of  claim 1 , comprising:
 receiving the timing packet with the updated timing information at the second node; and   
       using the updated time information to synchronize the second node. 
     
     
         7 . The method of  claim 6 , wherein using the updated time information to synchronize the second node comprises using the updated time information to synchronize a local clock of the second node to a reference time source of the time server. 
     
     
         8 . The method of  claim 6 , wherein using the updated time information to synchronize the second node comprises determining a time epoch for the second node. 
     
     
         9 . The method of  claim 1 , wherein the first node maintains a delay table, the delay table indicating respective delays associated with network links to which the first node is connected. 
     
     
         10 . The method of  claim 1 , wherein the first node is a packet network node and the second node is a base station of a mobile communications system connected to the packet network node. 
     
     
         11 . A system comprising, at a first node of a communications network:
 a local clock; and   characterization logic adapted:
 to receive a timing packet comprising time information, the timing packet being originated by a time server; 
 to update the time information in the timing packet to indicate a cumulative delay comprising:
 a delay associated with communicating the timing packet to the first node over a network link to which the first node is connected; and 
 a delay experienced by the timing packet in transit through the first node determined using the local clock of the first node, the local clock of the first node having a lower accuracy than a clock associated with the time server; and 
 
 to send the timing packet with the updated time information to a second node to enable the second node to use the updated time information for synchronization of the second node. 
   
     
     
         12 . The system of  claim 11 , wherein the time information in the received timing packet comprises information indicating a time at which the timing packet was originated by the time server. 
     
     
         13 . The system of  claim 12 , wherein:
 the timing packet is received from a third node of the network; and   the time information in the received timing packet comprises information indicating a cumulative delay experienced by the timing packet before transmission of the timing packet from the third node to the first node.   
     
     
         14 . The system of  claim 13 , wherein the delay associated with communicating the timing packet to the first node over a network link to which the first node is connected is a delay associated with communicating the timing packet over a network link connecting the third node to the first node. 
     
     
         15 . The system of  claim 11 , wherein the timing packet comprises information indicating that the timing packet is a timing packet. 
     
     
         16 . The system of  claim 11 , comprising the second node and a network link connecting the second node to the first node, the second node being adapted:
 to receive the timing packet with the updated timing information at the second node; and   to use the updated time information to synchronize the second node.   
     
     
         17 . The system of  claim 16 , wherein the second node comprises a local clock and is adapted to use the updated time information to synchronize the second node by using the updated time information to synchronize the local clock of the second node to a reference time source of the time server. 
     
     
         18 . The system of  claim 16 , wherein the second node is adapted to use the updated time information to synchronize the second node by determining a time epoch for the second node. 
     
     
         19 . The system of  claim 11 , wherein the first node is adapted to maintain a delay table, the delay table indicating respective delays associated with network links to which the first node is connected. 
     
     
         20 . The system of  claim 11 , wherein the first node is a packet network node and the second node is a base station of a mobile communications system connected to the packet network node.