Clock synchronizaton using codeword marker
Aspects of the present disclosure includes a method and program product for clock synchronization of a networked computer system. The method records a time (t 1 ) when a first codeword marker in a datastream is sent from a master computer to a slave computer and records a second time (t 2 ) when the slave computer receives the first codeword marker. The method includes recording a third time (t 3 ) when a third codeword marker in a datastream is sent from the slave computer to the master computer. The method includes recording a fourth time t 4 when the master receives the third codeword marker from the slave. The method calculates a time offset θ, according to; θ = ( t 2 - t 1 ) + ( t 4 - t 3 ) 2 , and a roundtrip delay δ, according to δ=(t 4 −t 1 )−(t 3 −t 2 ). The clock in the slave computer is synchronized with a clock in the master computer using θ and δ.
1. A method for clock synchronization of a networked computer system, the method comprising:
recording a time (t 1 ) when a first codeword marker in a datastream is sent from a master computer to a slave computer;
recording a second time (t 2 ) when the slave computer receives the first codeword marker;
sending a second codeword marker in the datastream from the master computer to the slave computer, the second codeword marker containing the first time (t 1 ), wherein sending the second codeword marker includes inserting the second codeword marker into a stream of transcoded blocks transmitted over a network computer system at predefined locations within the datastream;
recording a third time (t 3 ) when a third codeword marker in the datastream is sent from the slave computer to the master computer, wherein the third codeword marker is a first available codeword marker after receipt of slave computer of the second codeword marker;
recording a fourth time (t 4 ) when the master computer receives the third codeword marker from the slave;
sending a fourth codeword marker in the datastream from the master computer to the slave computer, the fourth codeword marker containing the fourth time (t 4 ), wherein sending the fourth codeword marker includes inserting the fourth codeword marker into a stream of transcoded blocks transmitted over a network computer system at predefined locations within the datastream;
calculating a time offset θ, according to
θ
=
(
t
2
-
t
1
)
+
(
t
4
-
t
3
)
2
;
calculating a roundtrip delay δ, according to δ=(t 4 −t 1 )−(t 3 −t 2 ); and
synchronizing a clock in the slave computer with a clock in the master computer using θ and δ to adjust the clock in the slave computer from an initial setting to a synchronized setting; and
continuing operation of the master computer and the slave computer after adjusting the clock of the slave computer to the synchronized setting.
2. The method of claim 1 , wherein the slave computer determines an elapsed time (T mm ) from receipt of the first codeword marker from the master computer to receipt of the second codeword marker from the master computer and if T mm is less than a predetermined value, clock synchronization is not initiated.
3. The method of claim 2 , wherein the predetermined value is twice a time between two consecutive codeword markers.
4. The method of claim 1 , wherein the master computer determines an elapsed time (T ms ) from sending of the second codeword marker to the slave computer to receipt of the third codeword marker from the slave computer and if T ms is less than a predetermined value, clock synchronization is not initiated.
5. The method of claim 4 , wherein the predetermined value is triple a time between two consecutive codeword markers.
6. The method of claim 1 , wherein the slave computer determines an elapsed time (T sm ) from sending of the third codeword marker to the master computer to receipt of the fourth codeword marker from the master computer and if T sm is less than a predetermined value, clock synchronization is not initiated.
7. The method of claim 6 , wherein the predetermined value is triple a time between two consecutive codeword markers.
8. A program product stored on a non-transitory computer readable medium, the program product operative to synchronize clocks within a computer network containing a master computer and a slave computer, the non-transitory computer readable medium comprising program code for:
recording a time (t 1 ) when a first codeword marker in a datastream is sent from the master computer to the slave computer;
recording a second time (t 2 ) when the slave computer receives the first codeword marker;
sending a second codeword marker in the datastream from the master computer to the slave computer, the second codeword marker containing the first time (t 1 ), wherein the program code for sending the second codeword marker inserts the second codeword marker into a stream of transcoded blocks transmitted over a network computer system at predefined locations within the datastream;
recording a third time (t 3 ) when a third codeword marker in the datastream is sent from the slave computer to the master computer, wherein the third codeword marker is a first available codeword marker after receipt of slave computer of the second codeword marker;
recording a fourth time (t 4 ) when the master computer receives the third codeword marker from the slave;
sending a fourth codeword marker in the datastream from the master computer to the slave computer, the fourth codeword marker containing the fourth time t 4 , wherein the program code for sending the fourth codeword marker inserts the fourth codeword marker into a stream of transcoded blocks transmitted over a network computer system at predefined locations within the datastream;
calculating a time offset θ, according to
θ
=
(
t
2
-
t
1
)
+
(
t
4
-
t
3
)
2
;
calculating a roundtrip delay δ, according to δ=(t 4 −t 1 )−(t 3 −t 2 ); and
synchronizing a clock in the slave computer with a clock in the master computer, wherein the program code for synchronizing of the clock in the slave computer uses θ and δ to adjust the clock in the slave computer from an initial setting to a synchronized setting; and
continuing operation of the master computer and the slave computer after adjusting the clock of the slave computer to the synchronized setting.
9. The program product of claim 8 , wherein the slave computer determines an elapsed time (T mm ) from receipt of the first codeword marker from the master computer to receipt of the second codeword marker from the master computer and if T mm is less than a predetermined value, clock synchronization, is not initiated.
10. The program product of claim 9 , wherein the predetermined value is twice a time between two consecutive codeword markers.
11. The program product of claim 8 , wherein the master computer determines an elapsed time (T ms ) from sending of the second codeword marker to the slave computer to receipt of the third codeword marker from the slave computer and if T ms is less than a predetermined value, clock synchronization is not initiated.
12. The program product of claim 11 , wherein the predetermined value is triple a time between two consecutive codeword markers.
13. The program product of claim 8 , wherein the slave computer determines an elapsed time (T sm ) from sending of the third codeword marker to the master computer to receipt of the fourth codeword marker from the master computer and if T sm is less than a predetermined value, clock synchronization is not initiated.
14. The program product of claim 13 , wherein the predetermined value is triple a time between two consecutive codeword markers.
15. A computer-implemented method for synchronizing clocks within a computer network containing a master computer and a slave computer, the method comprising using a computing device to perform actions including:
recording a time (t 1 ) when a first codeword marker in a datastream is sent from the master computer to the slave computer;
recording a second time (t 2 ) when the slave computer receives the first codeword marker;
sending a second codeword marker in the datastream from the master computer to the slave computer, the second codeword marker containing the first time (t 1 ), wherein sending the second codeword marker includes inserting the second codeword marker into a stream of transcoded blocks transmitted over a network computer system at predefined locations within the datastream;
recording a third time (t 3 ) when a third codeword marker in the datastream is sent from the slave computer to the master computer, wherein the third codeword marker is a first available codeword marker after receipt of slave computer of the second codeword marker;
recording a fourth time (t 4 ) when the master computer receives the third codeword marker from the slave;
sending a fourth codeword marker in the datastream from the master computer to the slave computer, the fourth codeword marker containing the fourth time t 4 , wherein sending the fourth codeword marker includes inserting the fourth codeword marker into a stream of transcoded blocks transmitted over a network computer system at predefined locations within the datastream;
calculating a time offset θ, according to
θ
=
(
t
2
-
t
1
)
+
(
t
4
-
t
3
)
2
;
calculating a roundtrip delay δ, according to δ=(t 4 −t 1 )−(t 3 −t 2 ); and
synchronizing a clock in the slave computer with a clock in the master computer, wherein the synchronizing of the clock in the slave computer includes using θ and δ to adjust the clock in the slave computer from an initial setting to a synchronized setting; and
continuing operation of the master computer and the slave computer after adjusting the clock of the slave computer to the synchronized setting.
16. The computer-implemented method of claim 15 , wherein the slave computer determines an elapsed time (T mm ) from receipt of the first codeword marker from the master computer to receipt of the second codeword marker from the master computer and if T mm is less than a predetermined value, clock synchronization is not initiated.
17. The computer-implemented method of claim 16 , wherein the predetermined value is twice a time between two consecutive codeword markers.
18. The computer-implemented method of claim 15 , wherein the master computer determines an elapsed time (T ms ) from sending of the second codeword marker to the slave computer to receipt of the third codeword marker from the slave computer and if T ms is less than a predetermined value, clock synchronization is not initiated.
19. The computer-implemented method of claim 18 , wherein the predetermined value is triple a time between two consecutive codeword markers.
20. The computer-implemented method of claim 15 , wherein the slave computer determines an elapsed time (T sm ) from sending of the third codeword marker to the master computer to receipt of the fourth codeword marker from the master computer and if T sm is less than predetermined value clock synchronization is not initiated.