One-way delay time estimation method and apparatus and clock synchronization method and apparatus using the same
View Patent ↗An apparatus for and method of estimating a one-way delay time between two hosts and an apparatus and method of clock synchronization using the same. The two hosts are connected to a network and communicate a predetermined packet; k-th, (k+1)-th, and (k+2)-th transmission times are measured at the first host, and k-th, and (k+1)-th transmission times are measured at the second host; a time difference of the m-th transmission time is measured at the first and second host, where m is k or k+1, and by using the measured transmission times, an m-th one-way delay time is calculated. If the time difference is identical to the calculated one-way delay time, a value equal to or less than the calculated one-way delay time is determined as the estimated one-way delay time. Accordingly, the estimation error of a one-way delay time is reduced for both symmetrically and asymmetrically connected hosts.
1. A method of estimating a one-way delay time between first and second hosts connected to a network and communicating a predetermined packet, the method comprising:
measuring k-th, (k+1)-th, and (k+2)-th transmission times of the packet at the first host, using a clock of the first host, and measuring k-th, and (k+1)-th transmission times of the packet at the second host, using a clock of the second host;
calculating a time difference between the m-th transmission time measured at the first host and the m-th transmission time measured at the second host, where m is k or k+1;
using one or more of the measured transmission times, to calculate k-th and (k+1)-th round-trip delay times at the first host, and a k-th round-trip delay time at the second host;
calculating one or more m-th one-way delay times, using the round-trip delay times;
determining whether the calculated time difference is identical to the calculated one-way delay times; and
when the calculated time difference is determined to be identical to the calculated one-way delay times, determining a value equal to or less than the calculated one-way delay times, as the estimated one-way delay time; and
synchronizing the clocks of the first and second hosts using the estimated one-way delay time.
2. The method of claim 1 , wherein in the determining of the value as the one-way delay time, a one-half value of the calculated one-way delay time is determined as the estimated one-way delay time.
3. The method of claim 1 , wherein the determining of the value as the one-way delay time comprises:
when the calculated time difference is determined to be identical to the calculated one-way delay time,
determining a one-half value of the lowest calculated m-th one-way delay time, as the estimated one-way delay time.
4. The method of claim 1 , wherein the first host is disposed in a different layer than the second host.
5. The method of claim 1 , further comprising: changing the m-th transmission time measured at the second host into the m-th transmission time measured at the first host.
6. The method of claim 5 , wherein in the changing of the m-th transmission time measured at the second host, the m-th transmission time measured at the second host is changed to a value obtained by adding a predetermined positive value to the m-th transmission time measured at the first host.
7. The method of claim 1 , further comprising: determining whether a loss exists in the packet, and if the loss exists in the packet, correcting the loss.
8. The method of claim 1 , further comprising:
incrementing k by 1 to a predetermined value;
calculating the time difference and the m-th one-way delay time at each increment of k; and
determining a minimum value of the calculated m-th one-way delay times as the estimated one-way delay time.
9. An apparatus to estimate a one-way delay time between first and second hosts connected to a network and communicating a predetermined packet, the apparatus comprising:
a time measuring unit to measure k-th, (k+1)-th, and (k+2)-th transmission times at the first host, and to measure k-th, and (k+1)-th transmission times at the second host;
a calculation unit to calculate a time difference of the m-th-transmission time measured at the first host and the m-th transmission time measured at the second host, where m is k or k+1, to calculate k-th round-trip delay times at the first host, and a k-th round-trip delay time at the second host, by using the measured transmission times, and to calculate one or more m-th one-way delay times, by using the round-trip delay times;
an examination unit to examine whether the calculated time difference is identical to the calculated one-way delay times;
a delay time estimation unit, to output a value equal to or less than the smallest calculated one-way delay time, as the estimated one-way delay time, in response to the examined result; and
a clock adjusting unit to synchronize the two hosts using the estimated one-way delay time.
10. The apparatus of claim 9 , wherein the delay time estimation unit outputs a one-half value of the smallest calculated one-way delay time, as the estimated one-way delay time.
11. The apparatus of claim 10 , further comprising:
a comparison unit to compare the calculated m-th one-way delay times, and to output a value that is a not greater value of the compared one-way delay times, as a one-way minimum delay time,
wherein the delay time estimation unit outputs a one-half value of the one-way minimum delay time as the estimated one-way delay time.
12. The apparatus of claim 9 , further comprising:
an offset setting unit to change the m-th transmission time measured at the second host into the m-th transmission time measured at the first host.
13. The apparatus of claim 12 , wherein the offset setting unit changes the m-th transmission time measured at the second host into a value obtained by adding a predetermined positive value to the m-th transmission time measured at the first host.
14. The apparatus of claim 9 , further comprising
an offset setting unit to change the (k+1)-th transmission time measured at the second host into a value obtained by adding the k-th round-trip delay time calculated at the second host to the (k+1)-th transmission time measured at the first host, and changing the k-th transmission time measured at the second host to a value obtained by subtracting the k-th round-trip delay time calculated at the second host from the changed (k+1)-th transmission time.
15. The apparatus of claim 14 , wherein:
the offset setting unit changes the (k+1)-th transmission time measured at the second host into a value obtained by subtracting a predetermined positive value from the addition result.
16. The apparatus of claim 9 , further comprising:
an error detection and correction unit to detect a loss in the packet, and to correct the detected loss.
17. The apparatus of claim 9 , wherein the predetermined packet comprises:
a transmission frequency data to count a number of times the transmission is performed;
a transmission time data to record a most recently measured transmission time;
a round-trip delay time data to record a most recently measured round-trip time; and
a jitter data to record the most recent jitter.
18. A computer readable recording medium having embodied thereon a computer program for executing a method of estimating a one-way delay time between first and second hosts connected to a network and communicating a predetermined packet, wherein the method comprises:
measuring k-th, (k+1)-th, and (k+2)-th transmission times at the first host, using a clock of the first host, and measuring the k-th, and (k+1)-th transmission times at the second host, using a clock at the second hose;
calculating a time difference of the m-th transmission time measured at the first host and the m-th transmission time measured at the second host, where m is k or k+1;
using the measured transmission times to calculate k-th and (k+1)-th round-trip delay times at the first host, and a k-th round-trip delay time at the second host; and
calculating one or more m-th one-way delay times using to the round-trip delay times;
determining whether the calculated time difference is identical to the calculated one-way delay times;
when the calculated time difference is determined to be identical to the calculated one-way delay times, determining a value equal to or less than the calculated one-way delay times, as the estimated one-way delay time; and
synchronizing the clocks of the first and second hosts using the estimated one-way delay time.
19. A method of estimating a one-way delay time between first and second hosts connected to a network and communicating a predetermined packet, the method comprising:
measuring a difference between successive sequential transmit times of the packet at the first and second hosts, using clocks of the first and second hosts, to obtain a time difference;
calculating a one-way delay time, by using one or more of the sequential transmit times;
comparing the time difference to the calculated one-way delay time;
when the time difference is determined to be identical to the calculated one-way delay time, determining a value equal to or less than the calculated one-way delay time, as the estimated one-way delay time; and
synchronizing the first and second hosts using the estimated one-way delay time.
20. The method of claim 19 , wherein the calculating of the one-way delay time comprises:
calculating two successive sequential round-trip delay times at the first host, and calculating a round-trip delay time at the second host, wherein the round-trip delay time at the second host occurs between the beginning and the end of the two successive sequential round-trip delay times at the first host; and
by using the calculated round-trip delay times, the one-way delay time is calculated.
21. A method of estimating a one-way delay time between first and second hosts connected to a network and communicating a predetermined packet, the method comprising:
measuring first, second, and third transmission times of the packet at the first host, using a clock of the first host, and measuring first and second transmission times of the packet at the second host, using a clock of the second host;
calculating a time difference between the first transmission time measured at the first host and the first transmission time measured at the second host or the second transmission time measured at the first host and the second transmission time measured at the second host;
using one or more of the measured transmission times to calculate first and second round-trip delay times at the first host and a first round-trip delay time at the second host, and using the calculated round-trip delay times to calculate a one-way delay time;
determining whether the calculated time difference is identical to the calculated one-way delay time;
when the calculated time difference is determined to be identical to the calculated one-way delay time, determining a value equal to or less than the calculated one-way delay time, as the estimated one-way delay time, and
synchronizing the first and second hosts using the estimated one-way delay time,
wherein the calculating of the one-way delay time further comprises:
calculating first and second round-trip delay times at the first host, and calculating a first round-trip delay time at the second host; and
by using the calculated round trip delay times, the one-way delay time.
22. The method of claim 1 , wherein the one or more m-th one-way delay times are calculated using,
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wherein a is a k-th one-way delay time calculated at the first host, R A (k) is the k-th round-trip delay time calculated at the first host, R B (k) is the k-th round-trip delay time calculated at the first host, b is the k-th one-way delay time calculated at the second host, a′ is the (k+1)-th one-way delay time calculated at the first host, b′ is a (k+1)-th one-way delay calculated at the second host, and the round-trip delay time is a time taken for the packet to make a round trip between the first host and the second host.