APPARATUS AND METHOD FOR CONTROLLING INDEPENDENT CLOCK DOMAINS TO PERFORM SYNCHRONOUS OPERATIONS IN AN ASYNCHRONOUS NETWORK

• US 20100067531A1
• Filed: 09/17/2008
• Published: 03/18/2010
• Est. Priority Date: 09/17/2008
• Status: Abandoned Application

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Thiems, Michael Stephen, Augustine, Bruce A.
• Application Number:
  US12/212,355
• Publication Number:
  US 20100067531A1
• Time in Patent Office: Days
• US Class Current: 370/395.620
• CPC Class Codes: H04J 3/0632 Synchronisation of packets and cells, e.g. transmission of voice via a packet network, circuit emulation service [CES] queuing arrangements in packet switching elements H04L49/90; synchronising systems for the synchronous transmission of a pulse code modulated video signal with one or more other pulse code modulated signals H04N7/56
• CPC Class Codes: H04J 3/0664 unidirectional timestamps
• CPC Class Codes: H04J 3/0697 Synchronisation in a packet node
• CPC Class Codes: H04L 65/80 Responding to QoS
• CPC Class Codes: H04L 69/28 Timers or timing mechanisms used in protocols

Abstract

Method and apparatus are disclosed for synchronizing multimedia in asynchronous networks. In this invention, clock domains are first reduced to separate hardware clock correction circuits at the separate endpoints of an asynchronous network. At each end of the network node, the controllable input device such as a video device is synchronized to the non-controllable output device such as a set top box to prevent unknown or poor-quality alterations by the output device. Output device timestamp packets are regularly sent to the input device, which then adjusts its clock accordingly. The exchange of packets between input devices over the asynchronous network is then subjected to a software-based scheme to effectively synchronize these devices.

Claims

1. A method to synchronize multimedia in asynchronous network nodes, each asynchronous network node having at least two independent clocks and transmitting and receiving packets to and from the asynchronous network nodes according to an asynchronous network media access protocol, comprising:

adjusting the at least two independent clocks at each asynchronous network node to synchronize local traffic;

determining at each asynchronous network node a clock mismatch from the reception by the asynchronous network node of packets transmitted by another asynchronous network node; and

controlling data sampling or timestamps at the receiving asynchronous network node based on the determined clock mismatch of the packets transmitted by another asynchronous network node.

2. The method of claim 1, the method further comprising:

determining from a transmit timestamp field a best arrival time for the local traffic at each asynchronous network node.

3. The method of claim 2, wherein adjusting is nominal frequency adjustment of the local clock based on the best arrival time for the local traffic.

4. The method of claim 2, wherein adjusting is adjustment of a scaling factor based on the best arrival time for the local traffic.

5. The method of claim 1, wherein determining clock mismatch at each asynchronous network node is based on buffer estimation or timestamp-based estimation.

6. The method of claim 5, wherein controlling is changing data sampling rate at the receiving asynchronous network node.

7. The method of claim 1, wherein changing data sampling at the receiving asynchronous network node is a software-based correction on a first type of samples and a software-based correction on a second type of samples that is coordinated to the software-based correction on the first type of samples.

8. Communication apparatus, comprising:

a plurality of media production devices each with an adjustable clock, which are connected to communicate over an asynchronous network and are configured to capture data and to transmit the captured data;

a plurality of media reproduction devices electrically coupled to one of the plurality of media production devices and configured to reproduce at least a first type of signal and a second type of signal and to transmit back to the coupled one of the plurality of media production devices timing information; and

a processor in each of the plurality of media production devices, the processor capable of executing a set of instructions to perform actions that include;

fine-tuning the adjustable clock based on the timing information from the media reproduction device;

determining at each media production device a clock mismatch from the reception of packets transmitted over the asynchronous network by another media production device;

controlling data sampling or timestamps at the receiving media production device based on the determined clock mismatch of the packets transmitted by another media production device.

9. The apparatus of claim 8, wherein when fine-tuning the adjustable clock based on the timing information the processor executes the set of instructions to perform additional actions that include:

determining from the timing information a received time for packets transmitted from the media production device to the media reproduction device.

10. The apparatus of claim 9, wherein adjusting is nominal frequency adjustment of the adjustable clock based on the received time for packets transmitted from the media reproduction device to the media production device.

11. The apparatus of claim 9, wherein fine-tuning the adjustable clock is adjusting a multiply/divide ratio based on the received time for packets transmitted from the media reproduction device to the media production device.

12. The apparatus of claim 8, wherein determining clock mismatch at each media production device is based on buffer estimation or timestamp-based estimation.

13. The apparatus of claim 12, wherein controlling is changing data sampling at the receiving media production device.

14. The apparatus of claim 8, wherein changing data sampling at the receiving media production device is a software-based correction on a first type of samples and a software-based correction on a second type of samples that is coordinated to the software-based correction on the first type of samples.

15. A method to synchronize the exchange of multimedia between a plurality of capture devices with capture clock and a plurality set top boxes through an asynchronous network, the method comprising:

performing hardware synchronization at each capture device for controlling intra-node communication, wherein intra-node communication occurs between a capture device and a set top box; and

performing software synchronization at each capture device for controlling inter-node communication, wherein inter-node communication occurs between capture devices through the asynchronous network.

16. The method of claim 15, wherein performing hardware synchronization is adjusting the capture clock to synchronize the intra-node communication.

17. The method of claim 16, wherein adjusting is nominal frequency adjustment of the capture clock based on the best arrival time of a first type of packets and a second type of packets at the set top box.

18. The method of claim 16, wherein adjusting is adjustment of a scaling factor based on the best arrival time of a first type of packets and a second type of packets at the set top box.

19. The method of claim 15, the method further comprising:

estimating at each capture device a best arrival time for packets transmitted by another capture device, wherein estimating is based on buffer estimation or timestamp-based estimation;

wherein performing software synchronization is changing data sampling at the receiving capture device based on the estimation of best arrival time.

20. The method of claim 19, wherein changing data sampling at the receiving capture device is a software-based correction on the first type of samples and a software-based correction on the second type of samples that is coordinated to the software-based correction on the first type of samples.