System, method, and article of manufacture for synchronizing time of day clocks on first and second computers

1. A method for synchronizing first and second time-of-day clocks on first and second computers, respectively, the first computer having a third clock on a first network interface card, the second computer having a fourth clock on a second network interface card, the first and second network interface cards communicating with one another via a communication network, the method comprising:

generating a first message having a first time difference value and a second time stamp value and transmitting the first message from the first network interface card, the first time difference value corresponding to a time difference between the first time-of-day clock and the third clock, the second time stamp value corresponding a time determined by the third clock on the first network interface card when the first message is transmitted from the first network interface card;

receiving the first message at the second interface card of the second computer;

generating a second message having the first time difference value, the second time stamp value, a third time stamp value, a fourth time difference value, and a fifth time stamp value and transmitting the second message from the second network interface card, the third time stamp value corresponding to a time determined by the fourth clock on the second network interface card when the first message is received by the second network interface card, the fourth time difference value corresponding to a time difference between the second time-of day clock and the fourth clock, the fifth time stamp value corresponding to a time determined by the fourth clock when the second message is transmitted from the second network interface card;

receiving the second message at the first network interface card and determining a sixth time stamp value associated with the second message, the sixth time stamp value corresponding to a time determined by the third clock when the second message is received by the first network interface card; and

determining a seventh time difference value corresponding to a time difference between the first and second time-of-day clocks based on the first time difference value, the second time stamp value, the third time stamp value, the fourth time difference value, the fifth time stamp value, and the sixth time stamp value.

2. The method of claim 1 , wherein the first message further comprises first and second port addresses, the first port address being associated with a first communication port of the first computer, the second port address being associated with a second communication port of the second computer.

3. The method of claim 2 , wherein the first message further includes first and second buffer addresses, the first buffer address being associated with a first buffer in the first computer for receiving messages containing time stamp values, the second buffer address being associated with a second buffer in the second computer for receiving messages containing time stamp values.

4. The method of claim 1 , further comprising:

modifying the first time-of-day clock based on the seventh time difference value to synchronize the first time-of-day clock with the second time-of-day clock.

5. A networked system, comprising:

a first computer having a first network interface card and a first time-of-day clock and a second computer having a second network interface card and a second time-of-day clock, the first network interface card having a third clock, the second network interface card having a fourth clock;

the first computer configured to generate a first message having a first time difference value and a second time stamp value and to transmit the first message from the first network interface card, the first time difference value corresponding to a time difference between the first time-of-day clock and the third clock, the second time stamp value corresponding a time determined by the third clock on the first network interface card when the first message is transmitted from the first network interface card;

the second computer configured to receive the first message at the second interface card, the second computer further configured to generate a second message having the first time difference value, the second time stamp value, a third time stamp value, a fourth time difference value, and a fifth time stamp value and to transmit the second message from the second network interface card, the third time stamp value corresponding to a time determined by the fourth clock on the second network interface card when the first message is received by the second network interface card, the fourth time difference value corresponding to a time difference between the second time-of day clock and the fourth clock, the fifth time stamp value corresponding to a time determined by the fourth clock when the second message is transmitted from the second network interface card; and

the first computer further configured to receive the second message at the first network interface card and to determine a sixth time stamp value associated with the second message, the sixth time stamp value corresponding to a time determined by the third clock when the second message is received by the first network interface card, the first computer further configured to determine a seventh time difference value corresponding to a time difference between the first and second time-of-day clocks based on the first time difference value, the second time stamp value, the third time stamp value, the fourth time difference value, the fifth time stamp value, and the sixth time stamp value.

6. The system of claim 5 , wherein the first message further includes first and second port addresses, the first port address being associated with a first communication port of the first computer, the second port address being associated with a second communication port of the second computer.

7. The system of claim 6 , wherein the first message further includes first and second buffer addresses, the first buffer address being associated with a first buffer in the first computer for receiving messages containing time stamp values, the second buffer address being associated with a second buffer in the second computer for receiving message containing time stamp values.

8. The system of claim 5 , wherein the first computer is further configured to modify the first time-of-day clock based on the seventh time difference value to synchronize the first time-of-day clock with the second time-of-day clock.

9. An article of manufacture, comprising:

a computer storage medium having a computer program encoded therein for synchronizing first and second time-of-day clocks on first and second computers, respectively, the first computer having a third clock on a first network interface card, the second computer having a fourth clock on a second network interface card, the first and second network interface cards communicating with one another via a communication network, the computer storage medium comprising:

code for generating a first message having a first time difference value and a second time stamp value and transmitting the first message from the first network interface card, the first time difference value corresponding to a time difference between the first time-of-day clock and the third clock, the second time stamp value corresponding a time determined by the third clock on the first network interface card when the first message is transmitted from the first network interface card;

code for receiving the first message at the second interface card of the second computer;

code for generating a second message having the first time difference value, the second time stamp value, a third time stamp value, a fourth time difference value, and a fifth time stamp value and transmitting the second message from the second network interface card, the third time stamp value corresponding to a time determined by the fourth clock on the second network interface card when the first message is received by the second network interface card, the fourth time difference value corresponding to a time difference between the second time-of day clock and the fourth clock, the fifth time stamp value corresponding to a time determined by the fourth clock when the second message is transmitted from the second network interface card;

code for receiving the second message at the first network interface card and determining a sixth time stamp value associated with the second message, the sixth time stamp value corresponding to a time determined by the third clock when the second message is received by the first network interface card; and

code for determining a seventh time difference value corresponding to a time difference between the first and second time-of-day clocks based on the first time difference value, the second time stamp value, the third time stamp value, the fourth time difference value, the fifth time stamp value, and the sixth time stamp value.

10. The article of manufacture of claim 9 , wherein the first message further includes first and second port addresses, the first port address being associated with a first communication port of the first computer, the second port address being associated with a second communication port of the second computer.

11. The article of manufacture of claim 9 , wherein the first message further includes first and second buffer addresses, the first buffer address being associated with a first buffer in the first computer for receiving messages containing time stamp values, the second buffer address being associated with a second buffer in the second computer for receiving messages containing time stamp values.

12. The article of manufacture of claim 9 , further comprising code for modifying the first time-of-day clock based on the seventh time difference value to synchronize the first time-of-day clock with the second time-of-day clock.