Method and apparatus for reducing data burst overhead in an ethernet passive optical network

Abstract

One embodiment of the present invention provides a system that reduces data burst overhead in an Ethernet passive optical network which includes a central node and at least one remote node, wherein downstream data from the central node is broadcast to the remote nodes, and wherein upstream data from a remote node is transmitted to the central node in a unicast manner. During operation, the central node transmits grant messages to a number of remote nodes, wherein a grant message for a specified remote node assigns a start time and a duration of a transmission timeslot in which the specified remote node may transmit an upstream data burst. In response to the grant messages, the central node then receives a number of upstream data bursts, wherein the time gap between two consecutive upstream data bursts is less than the summation of a default laser turn-on time, a default laser turn-off time, an AGC period, and a CDR period.

1 . A method for reducing data burst overhead in an Ethernet passive optical network, the method comprising:
 transmitting grant messages to a number of optical network units (ONUs), wherein a grant message for a specified ONU assigns a start time and a duration of a transmission timeslot in which the specified ONU may transmit a upstream data burst; and   receiving a number of upstream data bursts, wherein the time gap between two consecutive upstream data bursts is less than the summation of a default laser turn-on time, a default laser turn-off time, an automatic gain control (AGC) period, and a clock and data recovery (CDR) period.   
     
     
         2 . The method of  claim 1 , wherein a preceding upstream data burst's laser turn-off period overlaps with a subsequent data burst's laser turn-on period. 
     
     
         3 . The method of  claim 1 , wherein the non-overlapping portion of the preceding data burst's laser turn-off period is equal to or greater than twice the allowed maximum jitter of the round-trip time between the central node and an ONU; and
 wherein the non-overlapping portion of the subsequent data burst's laser turn-on period is equal to or greater than twice the allowed maximum jitter of the round-trip time between the central node and an ONU.   
     
     
         4 . The method of  claim 1 , wherein a grant message specifies a transmission timeslot start time that is earlier than the ending time of an immediately preceding transmission timeslot. 
     
     
         5 . The method of  claim 1 , wherein receiving a number of upstream data bursts involves receiving a number of consecutive data bursts from an ONU, and wherein the ONU is allowed to transmit the number of consecutive data bursts without turning off and turning on its laser between two consecutive data bursts. 
     
     
         6 . The method of  claim 5 , further comprising detecting the time gap between two consecutive transmission timeslots assigned to the ONU; and
 if the time gap is less than a pre-defined value, allowing the ONU to transmit upstream data during the time gap without turning off and turning on its laser.   
     
     
         7 . The method of  claim 1 , wherein if one or more ONUs are virtual remote nodes located in a common physical ONU, and if these virtual ONUs transmit upstream data through a common laser belonging to the common physical ONU, the method further comprises:
 allowing the common laser to keep transmitting upstream data without being turned off between consecutive transmission timeslots assigned to one or more virtual ONUs located in the common physical remote node.   
     
     
         8 . The method of  claim 7 , wherein a grant message contains a laser-turn-on flag and a laser-turn-off flag;
 wherein if a grant message's laser-turn-on flag is true, the corresponding ONU turns on its laser at the start time of its assigned transmission timeslot and transmits an AGC bit sequence and a CDR bit sequence before transmitting upstream data;   wherein if a grant message's laser-turn-on flag is false, the corresponding ONU immediately starts transmitting upstream data at the start time of its assigned transmission timeslot without transmitting an AGC bit sequence and a CDR bit sequence;   wherein if a grant message's laser-turn-off flag is true, the corresponding ONU turns off its laser after transmitting upstream data; and   wherein if a grant message's laser-turn-off flag is false, the corresponding ONU continues transmitting data until the end of its assigned transmission timeslot without turning off its laser.   
     
     
         9 . The method of  claim 7 , wherein if one or more ONUs are virtual ONUs located in a common physical ONU, and if these virtual ONUs transmit upstream data through a common laser belonging to the common physical ONU, the method further comprises allowing the common laser to keep transmitting the upstream data bursts without being turned off between consecutive transmission timeslots assigned to one or more virtual ONUs located in the common physical ONU. 
     
     
         10 . The method of  claim 1 , further comprising receiving an actual laser turn-on time and an actual laser turn-off time from an ONU;
 wherein the actual laser turn-on and turn-off times specify the amount of time required by the ONU to turn on and turn off its laser, respectively.   
     
     
         11 . The method of  claim 10 , wherein the actual laser turn-on and turn-off times are transmitted with a registration message from the ONU when the central node initially registers the ONU. 
     
     
         12 . The method of  claim 10 , wherein a grant message assigns a start time and a duration of a transmission timeslot based on the actual laser turn-on and turn-off times of the ONU to which the grant message is destined. 
     
     
         13 . An apparatus for reducing data burst overhead in an Ethernet passive optical network, comprising:
 at least one ONU; and   an optical line terminal (OLT) configured to,
 transmit grant messages to a number of ONUs, wherein a grant message for a specified ONU assigns a start time and a duration of a transmission timeslot in which the specified ONU may transmit a upstream data burst; and 
 receive a number of upstream data bursts, wherein the time gap between two consecutive upstream data bursts is less than the summation of a default laser turn-on time, a default laser turn-off time, an AGC period, and a CDR period. 
   
     
     
         14 . The apparatus of  claim 13 , wherein a preceding upstream data burst's laser turn-off period overlaps with a subsequent data burst's laser turn-on period. 
     
     
         15 . The apparatus of  claim 13 , wherein the non-overlapping portion of the preceding data burst's laser turn-off period is equal to or greater than twice the allowed maximum jitter of the round-trip time between the central node and an ONU; and
 wherein the non-overlapping portion of the subsequent data burst's laser turn-on period is equal to or greater than twice the allowed maximum jitter of the round-trip time between the central node and an ONU.   
     
     
         16 . The apparatus of  claim 13 , wherein a grant message specifies a transmission timeslot start time that is earlier than the ending time of an immediately preceding transmission timeslot. 
     
     
         17 . The apparatus of  claim 13 , wherein an ONU is configured to transmit a number of consecutive data bursts without turning off and turning on its laser between two consecutive data bursts. 
     
     
         18 . The apparatus of  claim 17 , wherein the ONU is further configured to detect the time gap between two consecutive transmission timeslots assigned to the ONU; and
 if the time gap is less than a pre-defined value, allow the ONU to transmit upstream data during the time gap without turning off and turning on its laser.   
     
     
         19 . The apparatus of  claim 13 , wherein if one or more ONUs are virtual ONUs located in a common physical ONU, and if these virtual ONUs transmit upstream data through a common laser belonging to the common physical ONU, the common physical ONU is configured to:
 allow the common laser to keep transmitting upstream data without being turned off between consecutive transmission timeslots assigned to one or more virtual ONUs located in the common physical ONU.   
     
     
         20 . The apparatus of  claim 19 , wherein a grant message contains a laser-turn-on flag and a laser-turn-off flag;
 wherein if a grant message's laser-turn-on flag is true, the corresponding ONU is configured to turn on its laser at the start time of its assigned transmission timeslot and transmits an AGC bit sequence and a CDR bit sequence before transmitting upstream data;   wherein if a grant message's laser-turn-on flag is false, the corresponding ONU is configured to start immediately transmitting upstream data at the start time of its assigned transmission timeslot without transmitting an AGC bit sequence and a CDR bit sequence;   wherein if a grant message's laser-turn-off flag is true, the corresponding ONU is configured to turn off its laser after transmitting upstream data; and   wherein if a grant message's laser-turn-off flag is false, the corresponding ONU is configured to continue transmitting data until the end of its assigned transmission timeslot without turning off its laser.   
     
     
         21 . The apparatus of  claim 19 , wherein if one or more ONUs are virtual ONUs located in a common physical ONU, and if these virtual ONUs transmit upstream data through a common laser belonging to the common physical ONU, the physical ONU is further configured to allow the common laser to keep transmitting the upstream data bursts without being turned off between consecutive transmission timeslots assigned to one or more virtual ONUs located in the common physical ONU. 
     
     
         22 . The apparatus of  claim 13 , wherein the central node is further configured to receive an actual laser turn-on time and an actual laser turn-off time from an ONU; and
 wherein the actual laser turn-on and turn-off times specify the amount of time required by the ONU to turn on and turn off its laser, respectively.   
     
     
         23 . The apparatus of  claim 22 , wherein the actual laser turn-on and turn-off times are transmitted with a registration message from the ONU when the central node initially registers the ONU. 
     
     
         24 . The apparatus of  claim 22 , wherein a grant message assigns a start time and a duration of a transmission timeslot based on the actual laser turn-on and turn-off times of the ONU to which the grant message is destined.