Methods and systems for jitter minimization in streaming media

• US 20040052209A1
• Filed: 09/13/2002
• Published: 03/18/2004
• Est. Priority Date: 09/13/2002
• Status: Active Grant

• Current Assignee: Dialogic, Inc. (Enghouse Systems Limited)
• Original Assignee: Dialogic, Inc. (Enghouse Systems Limited)
• Inventors: Ortiz, Luis
• Granted Patent: US 7,567,509 B2
• Time in Patent Office: Days
• US Class Current: 370/230
• CPC Class Codes: H04L 43/026 using flow identification
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04L 47/11 Identifying congestion
• CPC Class Codes: H04L 47/225 Determination of shaping rate, e.g. using a moving window
• CPC Class Codes: H04L 47/2416 Real-time traffic
• CPC Class Codes: H04L 47/283 in response to processing delays, e.g. caused by jitter or round trip time [RTT]
• CPC Class Codes: H04L 47/33 using forward notification
• CPC Class Codes: H04L 65/80 Responding to QoS

Abstract

A method and system for avoiding variance in transmission times of real-time, packet-based communications is disclosed. Transmissions such as voice and videoconferencing generally require a substantially constant delivery rate in order to be satisfactory to end users. When occurring via a packet-based network, such transmissions often experience unacceptable levels of variation in delay in their transmission times, and this variation in delay is known as jitter. One cause of jitter relates to collisions between packets generated by a first source and sent via a packet transport medium and other packets, generated by one or more other sources and transmitted by the same transport medium. The method and system disclosed allow data sources to independently establish their respective transmission timings so as to avoid these collisions, without a need for a master clock shared between all of the data sources. By operating in such a peer-to-peer manner, the data sources establish a reduction in jitter in a manner that is reliable, efficient, inexpensive, scaleable, and easy to implement.

Claims

1. A method for transmitting data, the method comprising:

monitoring a packet-based traffic flow to obtain traffic flow information;

calculating, based on the traffic flow information and a clock signal obtained from a clock, a transmission interval for transmitting a packet-based communication into the packet-based traffic flow; and

transmitting the packet-based communication into the packet-based traffic flow during the transmission interval, based on the clock signal.

2. The method of claim 1, wherein the transmission interval provides a time period having a reduced chance of collision between the packet-based communication and the packet-based traffic flow relative to an uncorrelated transmission of the packet-based communication into the packet-based traffic flow.

3. The method of claim 1, wherein transmitting the packet-based communication comprises:

determining a phase adjustment sufficient to alter a transmission timing of the packet-based communication to coincide with transmission into the transmission interval; and

adjusting a phase of the packet-based communication by the phase adjustment.

4. The method of claim 1, further comprising:

detecting a collision between the packet-based communication and the packet-based traffic flow; and

selecting a modified transmission timing of the packet-based communication relative to the packet-based traffic flow.

5. The method of claim 4, wherein the modified transmission timing provides a reduction in the chance of collision relative to a non-modified transmission timing.

6. The method of claim 1, wherein calculating a transmission interval comprises performing a correlation analysis based on the clock signal and the packet-based traffic flow.

7. The method of claim 6, wherein the clock is a high-speed clock local to a source of the packet-based communication.

8. The method of claim 6, wherein the clock is a packet-generation clock and the clock signal provides a timing for packet generation.

9. The method of claim 6, wherein performing the correlation analysis comprises inputting a sample threshold determining a length of time over which the monitoring of the packet-based traffic flow occurs.

10. The method of claim 1, further comprising:

minimizing a drift in the clock signal relative to a second clock signal based on a master clock signal having a timing that is known relative to the clock signal and the second clock signal.

11. The method of claim 1, wherein the packet-based traffic flow and the packet-based communication occur via a contention-based network.

12. The method of claim 1, wherein the packet-based traffic flow and the packet-based communication occur via a isochronous network.

13. The method of claim 1, wherein calculating a transmission interval comprises:

communicating with one of a plurality of data sources to establish a virtual clock, the virtual clock thereafter being maintained by each of the plurality of data sources and being operable to govern a timing of transmission of the packet-based communication; and

adjusting a phase of packets in the packet-based communication in accordance with the virtual clock.

14. A system for transmitting data, the system comprising:

a packet detector operable to monitor a packet-based traffic flow and thereby obtain traffic flow information;

a clock operable to output a clock signal;

a correlation determination circuit operable to calculate a transmission interval, based on the traffic flow information and the clock signal; and

a packet generator operable to generate a packet-based communication in approximate synchronization with the transmission interval.

15. The system of claim 14, further comprising:

a phase shifter operable to adjust a transmission timing of the packet generator to thereby achieve approximate synchronization between the packet-based communication and the transmission interval.

16. The system of claim 15, further comprising a collision detector operable to detect a collision between the packet-based communication and the packet-based traffic flow, the collision detector being further operable to output a collision detection signal to the phase shifter.

17. The system of claim 16, wherein the packet-based traffic flow and the packet-based communication occur via a contention-based network.

18. The system of claim 15, further comprising a collision avoidance detector operable to detect a delayed transmission of the packet-based communication with respect to the packet-based traffic flow, the collision avoidance detector being further operable to output a collision detection signal to the phase shifter.

19. The system of claim 18, wherein the packet-based traffic flow and the packet-based communication occur via an isochronous network.

20. The system of claim 14, wherein the clock is a high-speed clock that is local to the system.

21. The system of claim 14, wherein the clock is a packet generation clock operable to set a timing of the packet-based communication generated by the packet generator.

22. The system of claim 14, further comprising a sample threshold decision circuit operable to determine a length of time over which the packet detector monitors the packet-based traffic flow, the sample threshold decision circuit being further operable to output the length of time to the correlation determination circuit.

23. The system of claim 14, wherein the correlation determination circuit is further operable to calculate the transmission interval based on a correlation analysis based on the clock signal and the packet based traffic flow.

24. The system of claim 14, further comprising:

a transmission coordination circuit operable to communicate with one of a plurality of data sources to establish a virtual clock, the virtual clock thereafter maintained by each of the plurality of data sources and operable to govern a timing of packet transmission by the packet generator; and

a phase adjuster operable to adjust a phase of packets in the packet-based communication in accordance with instructions from the transmission coordination circuit.

25. A computer having a processor for executing instructions stored on an associated storage media, the instruction including:

a first code segment for monitoring a packet-based traffic flow;

a second code segment for calculating a transmission interval for transmitting a packet-based communication, the transmission interval providing a first reduction in a chance of collision between the packet-based communication and the packet-based traffic flow; and

a third code segment for transmitting the packet-based communications.

26. The computer of claim 25, further comprising a fourth code segment for detecting a collision between the packet-based communication and the packet-based traffic flow.

27. The computer of claim 26, further comprising a fifth code segment for selecting a modified transmission timing of the packet-based communication relative to the packet-based traffic flow, the modified transmission timing providing a second reduction in the chance of collision.

28. A system for transmitting data, the system comprising a plurality of data sources, the plurality of data sources each transmitting data via a common transport medium, each of the plurality of data sources comprising:

a packet generator operable to generate packets for transmission via the common transport medium;

a transmission coordination circuit operable to communicate with remaining ones of the plurality of data sources to establish a virtual clock, the virtual clock thereafter being maintained by each of the plurality of data sources and being operable to govern a timing of packet transmission by the packet generator; and

a phase adjuster operable to adjust a phase of the packets in accordance with instructions from the transmission coordination circuit.

29. The system of claim 28, wherein the data sources communicate in a peer-to-peer fashion to establish the virtual clock.

30. The system of claim 28, wherein the data source further comprises:

a high-speed clock local to the data source and operable to output a first clock signal that governs operations of the data source;

a packet-generation clock operable to receive the first clock signal and output a second clock signal that governs a timing of the packet generator.

31. The system of claim 30, wherein the transmission coordination circuit further comprises:

a packet-monitoring subsystem operable to monitor data traffic output by the packet generator and by remaining ones of the plurality of sources via the common transport medium.

32. The system of claim 31, wherein the transmission coordination circuit outputs a correlation analysis based on the first clock signal, the second clock signal, and a monitoring results signal output by the packet-monitoring subsystem.

33. The system of claim 32, wherein the phase adjuster adjusts a phase of the packets based on the correlation analysis.

34. The system of claim 33, wherein the phase adjuster inputs a collision detection signal from the packet-monitoring subsystem, the collision detection signal representing a collision between the packets and data traffic output by the remaining ones of the plurality of sources via the common transport medium, and further wherein the phase adjuster determines an adjustment in phase of the packets based on the collision detection signal.