Method and system for synchronization between network elements

Abstract

A system for synchronizing a first network device and a second network device. The first network device comprises an interface configured to release over a communication link a first signal carrying a first data stream clocked by a first clock signal. The second network device comprises an interface configured to receive the first signal over the communication link. The second network device also comprises a clock extraction module configured to generate an extracted clock signal from the received first signal; and a data coding module configured to clock a second data stream with an output clock signal selected based on a speed of a locally generated clock signal relative to the first clock signal or the extracted clock signal, thereby to produce a second signal for transmission from the second network element to the first network element.

1 . A method for synchronizing a plurality of network devices in a network, the method comprising:
 providing a communication link configured to transport signals in compliance with a standard that defines a first nominal frequency and a first tolerance;   transmitting from a first network device over the communication link a first signal carrying a first data stream clocked by a first clock signal expressly synthesized to have a frequency different from the first nominal frequency but within the first tolerance;   receiving the first signal at a second network device communicatively coupled to the communication link;   generating at the second network device an extracted clock signal from the first signal;   selecting at the second network device between a locally generated clock signal and the extracted clock signal based on a frequency of the locally generated clock signal relative to a frequency of the extracted clock signal to provide a selected clock signal; and   clocking a second data stream with the selected clock signal to produce a second signal for transmission from the second network device to the first network device.   
     
     
         2 . The method of  claim 1 , wherein selecting between the locally generated clock signal and the extracted clock signal comprises selecting the extracted clock signal when the frequency of the extracted clock signal is higher than the frequency of the locally generated clock signal. 
     
     
         3 . The method of  claim 1 , wherein selecting between the locally generated clock signal and the extracted clock signal comprises selecting the locally generated clock signal when the frequency of the locally generated clock signal is higher than the frequency of the extracted clock signal. 
     
     
         4 . The method of  claim 1 , wherein the first clock signal has a tolerance that is stricter than the first tolerance defined by the standard. 
     
     
         5 . The method of  claim 4 , wherein the first clock signal has a frequency that is higher than the first nominal frequency and within the first tolerance. 
     
     
         6 . The method of  claim 1 , wherein:
 the first signal comprises a first sequence of frames;   the second signal comprises a second sequence of frames;   the first network device introduces inter-frame gaps between successive frames in the first signal; and   the second network device introduces inter-frame gaps between successive frames in the second signal.   
     
     
         7 . The method of  claim 6 , wherein the inter-frame gaps each occupy a nominal number of bytes defined by the standard with which the first network device and the second network device are intended to be compliant. 
     
     
         8 . The method of  claim 6 , wherein the inter-frame gaps each occupy a number of bytes less than a minimum number of bytes defined by the standard with which the first network device and the second network device are intended to be compliant. 
     
     
         9 . The method of  claim 1 , wherein:
 the first signal comprises a first sequence of frames; and   the first network device refrains from introducing an inter-frame gap between successive frames in the first signal.   
     
     
         10 . The method of  claim 9 , wherein:
 the second signal comprises a second sequence of frames; and   the second network device refrains from introducing the inter-frame gap between successive ones of the second sequence of frames in the second signal.   
     
     
         11 . The method of  claim 1 , wherein the first network device synthesizes the first clock signal by adapting a high precision clock signal having a tolerance that is stricter than the first tolerance defined by the standard to a frequency that is higher than the first nominal frequency defined by the standard and within the first tolerance defined by the standard. 
     
     
         12 . The method of  claim 11 , wherein the first network device synthesizes the high precision clock signal. 
     
     
         13 . The method of  claim 12 , wherein the first network device adapts the high precision clock signal to the frequency that is higher than the first nominal frequency defined by the standard by multiplying the frequency of the high precision clock signal. 
     
     
         14 . The method of  claim 12 , wherein the first network device adapts the high precision clock signal to the frequency that is higher than the first nominal frequency defined by the standard by dividing the frequency of the high precision clock signal. 
     
     
         15 . The method of  claim 1 , wherein the first network device clocks the first data stream with the first clock signal to produce the first signal for transmission to the second network device. 
     
     
         16 . The method of  claim 1 , wherein the first network device and the second network device are intended to be compliant with the standard. 
     
     
         17 . The method of  claim 1 , wherein the first tolerance is less than or equal to plus or minus 100 parts per million. 
     
     
         18 . The method of  claim 1 , wherein the first nominal frequency is greater than or equal to 1.25 GHz.