Optical link time-of-flight and traffic latency determination using optical transceiver

Abstract

A method for determining timing information in an optical communication link includes transmitting a falling edge from a transceiver positioned at a near end of the optical communication link and simultaneously starting a first timer at the transceiver positioned at the near end of the link. The transmitted falling edge is received at a transceiver positioned at a far end of the link. A falling edge is transmitted from the transceiver positioned at the far end of the link after a response delay. The transmitted falling edge is received at the transceiver positioned at the near end of the link while the first timer is simultaneously terminated at the transceiver positioned at the near end of the link and the elapsed time is recorded. The total link delay is determined based on the elapsed time.

What is claimed is: 
     
         1 . A system for determining a path delay of an optical link between transceivers, the system comprising:
 an optical interface in communication with a first path and a second path of the optical link between a first transceiver and a second transceiver; and   a processing unit connected to the optical interface and configured to determine an indication of a shorter path delay of the first path and the second path based upon:
 transmission, from the first transceiver via the first path, of a first edge and a second edge separated by a total optical link delay; 
 receipt, at the first transceiver via the second path, of a third edge associated with transmission through the optical link; and 
 receipt, at the first transceiver via the second path, of a fourth edge associated with optical signal transmission through the optical link after the total optical link delay. 
   
     
     
         2 . The system of  claim 1 , wherein the processing unit is configured to calculate a total link length based upon the total optical link delay and a speed of light at an effective refractive index associated with the optical link. 
     
     
         3 . The system of  claim 1 , wherein the processing unit is configured to receive, at the first transceiver, the total optical link delay from the second transceiver. 
     
     
         4 . The system of  claim 3 , wherein the processing unit is configured to set a wait time at the first transceiver equal to the total optical link delay. 
     
     
         5 . The system of  claim 1 ,
 wherein the third edge is associated with an optical signal transmission delayed by a response time after the receipt of the second edge, and   wherein the processing unit is configured to subtract the response time from an elapsed time of a first timer to determine the path delay.   
     
     
         6 . The system of  claim 1 , wherein the processing unit is configured to determine a path length based on the path delay. 
     
     
         7 . A communication system comprising:
 an optical link;   an optical interface in communication with a first path and a second path of the optical link;   a processing unit connected to the optical interface and configured to determine an indication of a shorter path delay of the first path and the second path based upon:
 transmission, from a transceiver via the first path, of a first edge and a second edge separated by a total optical link delay; 
 receipt, at the transceiver via the second path, of a third edge associated with transmission through the optical link; and 
 receipt, at the transceiver via the second path, of a fourth edge associated with optical signal transmission through the optical link after the total optical link delay. 
   
     
     
         8 . The communication system of  claim 7 , wherein the processing unit is configured to calculate a total link length based on multiplication of the total optical link delay times a speed of light at an effective refractive index associated with the optical link. 
     
     
         9 . The communication system of  claim 7 , wherein the processing unit is configured to receive, at the transceiver, the total optical link delay from another transceiver. 
     
     
         10 . The communication system of  claim 9 , wherein the processing unit is configured to configure a wait time at the transceiver equal to the total optical link delay. 
     
     
         11 . The communication system of  claim 7 , wherein:
 the third edge is associated with an optical signal transmission delayed by a response time after the receipt of the second edge; and   the processing unit is configured to subtract the response time from an elapsed time of a first timer to determine the shorter path delay.   
     
     
         12 . The communication system of  claim 7 , wherein the processing unit is configured to determine a shorter path length based on the shorter path delay. 
     
     
         13 . A communication system between a plurality of transceivers, the communication system comprising:
 an optical link between the plurality of transceivers;   an optical interface in communication with a first path and a second path of the optical link;   a processing unit connected to the optical interface and configured to determine an indication of a shorter path delay of the first path and the second path based upon:
 storing, at a first of the plurality of transceivers, a total link delay of the optical link; 
 receiving, at the first of the plurality of transceivers via the first path of the optical link, a first edge through the optical link and simultaneously starting a wait timer for the total link delay; 
 receiving, at the first of the plurality of transceivers via the first path, a second edge through the optical link at a time period after the first edge; 
 transmitting, from the first of the plurality of transceivers via the second path of the optical link, a third edge in response to receipt of the second edge; 
 transmitting, from the first of the plurality of transceivers via the second path, a fourth edge after the wait timer has elapsed; and 
 determining a first indication of a shorter path delay of the first path and the second path based on an elapsed time between the third and fourth edges. 
   
     
     
         14 . The communication system of  claim 13 ,
 wherein transmitting the third edge comprises transmitting the third edge delayed by a response time after the receipt of the second edge, and   wherein determining the first indication of a shorter path delay comprises subtracting the response time from the elapsed time.   
     
     
         15 . The communication system of  claim 13 , wherein the fourth edge is transmitted after the third edge. 
     
     
         16 . The communication system of  claim 13 , wherein the processing unit is configured to determine the total link delay in the optical link. 
     
     
         17 . The communication system of  claim 16 , wherein determining the total link delay in the optical link comprises:
 transmitting, from the first of the plurality of transceivers via the first path, an initial edge and simultaneously starting an initial timer at the first of the plurality of transceivers;   receiving, at the first of the plurality of transceivers via the second path, a subsequent edge and simultaneously terminating the initial timer, the subsequent edge being associated with transmission through the optical link in response to receipt of the initial edge; and   determining the total link delay of the first and second paths based on an elapsed time of the initial timer.   
     
     
         18 . The communication system of  claim 13 , wherein the processing unit is configured to determine a total link length based on the total link delay. 
     
     
         19 . The communication system of  claim 18 , wherein the processing unit is configured to determine the total link length based upon multiplication of the total link delay times a speed of light at an effective refractive index associated with the optical link. 
     
     
         20 . The communication system of  claim 13 , wherein the processing unit is configured to receive, at the first of the plurality of transceivers, the total link delay from a second of the plurality of transceivers.