Method and apparatus for time synchronization in a network data processing system

Abstract

A method, apparatus, and computer implemented instructions for synchronizing time in a network data processing system. A request for time synchronization is received at a target data processing system. A current target time at the target data processing system is placed in a reply. The reply is sent to the source data processing system. A current source time from when the reply is received at the source data processing system is compared to the current target time to generate a comparison. A synchronization factor is generated using the comparison.

What is claimed is:  
     
         1 . A method for synchronizing time in a network data processing system comprising the data processing system implemented steps of: 
 receiving a request for time synchronization at a target data processing system, wherein the request is received from a source data processing system;    placing a current target time at the target data processing system in a reply;    sending the reply to the source data processing system;    comparing a current source time from when the reply is received at the source data processing system to the current target time to generate a comparison; and    generating a synchronization factor using the comparison.    
     
     
         2 . The method of claim Al, wherein the synchronization factor is determined as follows: 
         SF=T   3 − T   2   
       wherein SF is the synchronization factor, T 2  is the current target time, and T 3  is the current source time when the reply is received.  
     
     
         3 . The method of claim Al, wherein the synchronization factor is determined as follows: 
         SF=T   3 − T   2 −( T   3 − T   1 )/2 
       wherein SF is the synchronization factor, Tl is a source time when the request is sent, T 2  is the current source time, and T 3  is the current source time when the reply is received.  
     
     
         4 . The method of claim A 1  further comprising: 
 generating a time stamp for a message using the synchronization factor and a current time in the target data processing system.  
 
     
     
         5 . The method of claim A 1  further comprising: 
 storing the synchronization factor.  
 
     
     
         6 . A method in a data processing system for synchronizing time, the method comprising: 
 sending a synchronization request to a target;    receiving a reply, wherein the reply includes a current time from the target;    identifying a clock skew using the current time from the target; and    generating a time stamp for a message using the clock skew.    
     
     
         7 . The method of  claim 6  further comprising: 
 sending the message to a server.  
 
     
     
         8 . The method of  claim 6 , wherein the message is a request for authentication.  
     
     
         9 . The method of  claim 6 , wherein the target is a key distribution center server.  
     
     
         10 . The method of  claim 6 , wherein the clock skew is identified as follows: 
         CS=T   3 − T   2   
       wherein CS is the clock skew, T 2  is the current time from the target, and T 3  is a current time at the data processing system when the reply is received.  
     
     
         11 . The method of  claim 6 , wherein the request is sent a selected time and wherein the clock skew is determined as follows: 
         CS=T   3 − T   2 −( T   3 − T   1 )/2 
       wherein CS is the clock skew, T 1  is the selected time, T 2  is the current time from the target, and T 3  is a current time at the data processing system when the reply is received.  
     
     
         12 . The method of  claim 7  further comprising: 
 determining whether the server is located in a different realm from the target, prior to sending the message to the server; and  
 responsive to the server being located in the different realm, sending a synchronization request to a new target in the different realm; receiving a reply, wherein the reply includes a new current time from the new target; identifying a new clock skew using the current time from the new target; and generating a new time stamp for the message using the new clock skew.  
 
     
     
         13 . The method of  claim 12 , wherein the new target is a key distribution center server.  
     
     
         14 . A data processing system comprising: 
 a bus system;    a communications unit connected to the bus, wherein data is sent and received using the communications unit;    a memory connected to the bus system, wherein a set of instructions are located in the memory; and    a processor unit connected to the bus system, wherein the processor unit executes the set of instructions to send a synchronization request to a target; receive a reply, wherein the reply includes a current time from the target; identify a clock skew using the current time from the target; and generate a time stamp for a message using the clock skew.    
     
     
         15 . The data processing system of  claim 14 , wherein the bus system includes a primary bus and a secondary bus.  
     
     
         16 . The data processing system of  claim 14 , wherein the processor unit includes a single processor.  
     
     
         17 . The data processing system of  claim 14 , wherein the processor unit includes a plurality of processors.  
     
     
         18 . The data processing system  claim 14 , wherein the communications unit is an Ethernet adapter.  
     
     
         19 . A network data processing system for synchronizing time comprising: 
 receiving means for receiving a request for time synchronization at a target data processing system, wherein the request is received from a source data processing system;    placing means for placing a current target time at the target data processing system in a reply;    sending means for sending the reply to the source data processing system;    comparing means for comparing a current source time from when the reply is received at the source data processing system to the current target time to generate a comparison; and    generating means for generating a synchronization factor using the comparison.    
     
     
         20 . The network data processing system of  claim 19 , wherein the synchronization factor is determined as follows: 
         SF=T   3 − T   2   
       wherein SF is the synchronization factor, T 2  is the current target time, and T 3  is the current source time when the reply is received.  
     
     
         21 . The network data processing system of  claim 19 , wherein the synchronization factor is determined as follows: 
         SF=T   3 − T   2 −( T   3 −- T   1 )/2 
       wherein SF is the synchronization factor, T 1  is a source time when the request is sent, T 2  is the current source time, and T 3  is the current source time when the reply is received.  
     
     
         22 . The network data processing system of  claim 19 , wherein the generating means is a first generating means and further comprising: 
 second generating means for generating a time stamp for a message using the synchronization factor and a current time in the target data processing system.    
     
     
         23 . The network data processing system of  claim 19  further comprising: 
 storing the synchronization factor.  
 
     
     
         24 . The network data processing system of  claim 19 , wherein the receiving means, placing means, and sending means are located in the target data processing system and wherein the comparing means and the generating means are located in the source data processing system.  
     
     
         25 . A data processing system for synchronizing time, the data processing system comprising: 
 sending means for sending a synchronization request to a target;    receiving means for receiving a reply, wherein the reply includes a current time from the target;    identifying means for identifying a clock skew using the current time from the target; and    generating means for generating a time stamp for a message using the clock skew.    
     
     
         26 . The data processing system of  claim 25 , wherein the sending means is a first sending means and further comprising: 
 second sending means for sending the message to a server    
     
     
         27 . The data processing system of  claim 25 , wherein the message is a request for authentication.  
     
     
         28 . The data processing system of  claim 25 , wherein the target is a key distribution center server.  
     
     
         29 . The data processing system of  claim 25 , wherein the clock skew is identified as follows: 
         CS=T   3 − T   2   
       wherein CS is the clock skew, T 2  is the current time from the target, and T 3  is a current time at the data processing system when the reply is received.  
     
     
         30 . The data processing system of  claim 25 , wherein the request is sent a selected time and wherein the clock skew is determined as follows: 
         CS=T   3 − T   2 −( T   3 − T   1 )/2 
       wherein CS is the clock skew, T 1  is the selected time, T 2  is the current time from the target, and T 3  is a current time at the data processing system when the reply is received.  
     
     
         31 . The data processing system of  claim 26  further comprising: 
 determining means for determining whether the server is located in a different realm from the target, prior to sending the message to the server; and  
 execution means, responsive to the server being located in the different realm, for sending a synchronization request to a new target in the different realm; receiving a reply, wherein the reply includes a new current time from the new target; identifying a new clock skew using the current time from the new target; and generating a new time stamp for the message using the new clock skew.  
 
     
     
         32 . The data processing system of  claim 31 , wherein the new target is a key distribution center server.  
     
     
         33 . A computer program product in a computer readable medium for synchronizing time in a network data processing system, wherein the computer program product: 
 first instructions for receiving a request for time synchronization at a target data processing system, wherein the request is received from a source data processing system;    second instructions for placing a current target time at the target data processing system in a reply;    third instructions for sending the reply to the source data processing system;    fourth instructions for comparing a current source time from when the reply is received at the source data processing system to the current target time to generate a comparison; and    fifth instructions for generating a synchronization factor using the comparison.    
     
     
         34 . A computer program product in a computer readable medium for synchronizing time, the computer program product comprising: 
 first instructions for sending a synchronization request to a target;    second instructions for receiving a reply, wherein the reply includes a current time from the target;    third instructions for identifying a clock skew using the current time from the target; and    fourth instructions for generating a time stamp for a message using the clock skew.