CLOCK MANAGEMENT BETWEEN TWO ENDPOINTS

• US 20090041020A1
• Filed: 08/07/2007
• Published: 02/12/2009
• Est. Priority Date: 08/07/2007
• Status: Active Grant

• Current Assignee: Avaya Incorporated
• Original Assignee: Avaya Incorporated
• Inventors: Tucker, Luke A., Gibbons, Lee D., Ong, Mei-Sing, Scholte, Alexander
• Granted Patent: US 7,936,794 B2
• Time in Patent Office: Days
• US Class Current: 370/394
• CPC Class Codes: H04J 3/0664 unidirectional timestamps
• CPC Class Codes: H04N 21/4305 Synchronising client clock from received content stream, e.g. locking decoder clock with encoder clock, extraction of the PCR packets arrangements for synchronising receiver with transmitter by comparing receiver clock with transmitter clock H04L7/0012; arrangements for synchronising receiver with transmitter wherein the receiver takes measures against momentary loss of synchronisation H04L7/0083
• CPC Class Codes: H04N 21/6437 Real-time Transport Protocol [RTP]
• CPC Class Codes: H04N 21/8547 involving timestamps for synchronizing content

Abstract

Clock correlation can be achieved, for example, utilizing the RTP stream between a sender and receiver by determining a baseline at the start of, for example, a communication. This baseline is derived as a point in time from an arriving packet and represents a point from which subsequent packets deviate. Using this baseline, an early packet or a late packet can be detected. An early packet pushes the baseline down to that earlier point, while late arriving packets, if they are arriving late for a continuous period of time, represents a shift in the opposite direction from the baseline, resulting in a baseline moving to the “earliest” packet out of the sequence of the late arriving packets.

Claims

1. A clock adjustment method comprising:

receiving a first packet;

extracting an RTP (Real-Time Transport Protocol) timestamp from the first packet;

establishing an initial baseline;

receiving a next packet; and

determining a delta from the baseline.

2. The method of claim 1, further comprising adjusting a clock based on the delta.

3. The method of claim 2, wherein the adjusting includes updating the baseline by a positive or a negative amount.

4. The method of claim 2, where the adjusting includes recording a positive delta in a current window.

5. The method of claim 2, wherein the adjusting includes talking no action for a zero value delta.

6. The method of claim 1, further comprising, if a window period has elapsed, updating the baseline by the smallest delta greater than zero.

7. The method of claim 1, further comprising determining a ratio of baseline deviation to elapsed time.

8. The method of claim 1, wherein the clock is a local clock, a digital PLL, a VCO or a conversion rate.

9. The method of claim 1, wherein the delta is positive or negative.

10. The method of claim 1, wherein the delta is zero.

11. A clock adjustment system comprising:

a device that receives a first packet;

a clock management module that extracts an RTP (Real-Time Transport Protocol) timestamp from the first packet and establishes an initial baseline, and upon receiving a next packet, determines a delta from the baseline.

12. The system of claim 11, wherein the clock management module adjusts a clock based on the delta.

13. The system of claim 12, wherein the adjusting includes updating the baseline by a positive or a negative amount.

14. The system of claim 12, where the adjusting includes recording a positive delta in a current window.

15. The system of claim 12, wherein the adjusting includes taking no action for a zero value delta.

16. The system of claim 11, wherein, if a window period has elapsed, the clock management module updates the baseline by the smallest delta greater than zero.

17. The system of claim 11, wherein the clock management module determines a ratio of baseline deviation to elapsed time.

18. The system of claim 11, wherein the clock is a local clock, a digital PLL, a VCO or a conversion rate.

19. The system of claim 11, wherein the delta is positive or negative.

20. The system of claim 11, wherein the delta is zero.

21. A clock adjustment means comprising:

means for receiving a first packet;

means for extracting an RTP (Real-Time Transport Protocol) timestamp from the first packet;

means for establishing an initial baseline;

means for receiving a next packet; and

means for determining a delta from the baseline.

22. The means of claim 21, further comprising means for adjusting a clock based on the delta.

23. A computer readable media including instructions that when executed:

receive a first packet;

extract an RTP (Real-Time Transport Protocol) timestamp from the first packet;

establish an initial baseline;

receive a next packet; and

determine a delta from the baseline.