Network synchronization technique

Abstract

A network synchronization method allows reduced frequency fluctuations due to synchronization control in a network. Each node connected to the network has time information individually varying in a period of T. A time master node periodically notifies its own time information to time slave devices. Each time slave node prepares update-possible time points having a period of T/N (N>1). When receiving master time information, each time slave node updates its own time information using the master time information at an update-possible time point just after the master time information has been received.

1 . A network device connected to a network, comprising: 
 a clock generator for generating a clock signal;    a physical-layer circuit connected to the clock generator; and    a link-layer circuit connected to the physical-layer circuit,    wherein the link-layer circuit comprises:    a timing generator for generating a first timing signal and a second timing signal from a system clock signal inputted from the physical-layer circuit, wherein the first timing signal is generated in a period of T and the second timing signal is generated at a time point corresponding to a period of T/N (N is an integer greater than 1);    a time information memory for storing time information, which varies according to the first timing signal; and    a controller controlling the time information memory such that, when receiving reference time information from the network, the time information stored in the time information memory is updated using the reference time information at a time point according to the second timing signal just after the reference time information has been received.    
   
   
       2 . The network device according to  claim 1 , wherein the timing generator comprises: 
 a frequency divider for dividing the system clock signal in frequency by two to produce the first timing signal having the period of T; and    a frequency multiplier for multiplying the system clock signal in frequency by two to produce the second timing signal having a period of T/2.    
   
   
       3 . The network device according to  claim 1 , wherein the timing generator comprises: 
 a frequency multiplier for multiplying the system clock signal in frequency by two to produce a timing signal having a period of T/2; and    a base-4 counter for counting from 0 to 3 according to the timing signal to produce the first timing signal every time the base-4 counter is reset to 0,    wherein, when the reference time information has been received, the base-4 counter is reset to 0 to generate the second timing signal.    
   
   
       4 . The network device according to  claim 1 , wherein the timing generator comprises: 
 a binary counter for counting according to the system clock signal to produce the first timing signal every time the binary counter is reset to 0,    wherein, when the reference time information has been received, the binary counter is reset to 0 to generate the second timing signal.    
   
   
       5 . The network device according to  claim 1 , wherein the second timing signal is coincident to a time point when the time information varies in the predetermined time period of T.  
   
   
       6 . The network device according to  claim 1 , wherein the second timing signal is generated independently of a time point when the time information varies in the predetermined time period of T.  
   
   
       7 . The network device according to  claim 1 , wherein N is equal to 2.