Cable modem system with sample and packet synchronization

• US 8,718,091 B2
• Filed: 08/16/2010
• Issued: 05/06/2014
• Est. Priority Date: 02/12/1999
• Status: Expired due to Fees

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Rabenko, Theodore F., Thi, James C. H., Horton, John D. Jr.
• Primary Examiner(s): Ton, Dang
• Assistant Examiner(s): KAVLESKI, RYAN C
• Application Number:
  US12/857,088
• Publication Number:
  US 20100309935A1
• Time in Patent Office: 1,359 Days
• Field of Search: 370/503, 370/507, 370/508, 725/111
• US Class Current: 370/468
• CPC Class Codes: H04L 12/2801 Broadband local area networks
• CPC Class Codes: H04L 12/66 Arrangements for connecting between networks having differing types of switching systems, e.g. gateways

Abstract

A method and system of processing sampled voice packets from a voice packet sender for transmission over a bit-rate sampled data transmission system, such as by a cable modem over a cable modem termination system, to a voice packet recipient. Unsolicited grant arrivals in response to a request from the voice packet sender coupled to the cable modem are determined. The storing of sampled voice packets is synchronized with the unsolicited grant arrivals. Upon receipt of an unsolicited grant arrival, currently stored sampled voice packets are transmitted to the cable modem for further transmission to the voice packet recipient over the cable modem termination system.

Claims

1. An apparatus for synchronizing a data collection deadline time to a grant schedule, comprising:

a receiver configured to receive a downstream information flow including a time based message and a grant slot timing message that is indicative of the grant schedule;

a time based message detector configured to provide an absolute timing reference clock utilizing the time based message;

a tracking loop configured to converge a local time reference clock to the absolute timing reference clock;

a timing offset correction module configured to provide a sampling clock based upon the local time reference clock; and

a grant time calculator module configured to analyze a time between successive grants within the grant schedule utilizing the sampling clock, to compensate for processing time of data to be transmitted to set the data collection deadline time, and to ensure the data is ready for transmission when a grant subsequent to the successive grants is received in accordance with the grant schedule.

2. The apparatus of claim 1, wherein the absolute timing reference clock is representative of an oscillator frequency associated with a cable modem termination system (CMTS).

3. The apparatus of claim 1, wherein the tracking loop comprises:

a differencing circuit configured to determine a difference between the absolute timing reference clock and the local time reference clock;

a numerically controlled oscillator configured to provide an oscillator drive signal based upon the difference; and

a local time reference generator configured to provide the local time reference clock based upon the oscillator drive signal.

4. The apparatus of claim 3, wherein the difference between the absolute timing reference clock and the local time reference clock is representative of a frequency error.

5. The apparatus of claim 4, wherein the tracking loop further comprises:

a loop averaging filter configured to prevent substantial deviations in the frequency error.

6. The apparatus of claim 1, wherein the timing offset correction module is configured to adjust the local time reference clock by a timing offset to provide a reference for the sampling clock.

7. The apparatus of claim 6, wherein the timing offset is based upon predetermined values corresponding to delays caused by propagation of the downstream information flow.

8. The apparatus of claim 6, wherein the timing offset is based upon predetermined values corresponding to delays caused by the processing time.

9. An apparatus for synchronizing a data collection deadline time to a grant schedule, comprising:

a time based message detector configured to receive a downstream information flow, which includes a time based message and the grant schedule, from a headend of a communications system, and to utilize the time based message to provide an absolute timing reference clock;

a tracking loop configured to provide a sampling clock which tracks the absolute timing reference clock; and

a grant time calculator module configured to analyze a time between successive grants within the grant schedule utilizing the sampling clock, to set the data collection deadline time by compensating for processing time of data to be transmitted, and to ensure the data is ready for transmission when a grant subsequent to the successive grants is received in accordance with the grant schedule.

10. The apparatus of claim 9, wherein the absolute timing reference clock is representative of an oscillator frequency associated with the headend.

11. The apparatus of 9, wherein the tracking loop comprises:

a differencing circuit configured to determine a difference between the absolute timing reference clock and a local time reference clock;

a numerically controlled oscillator configured to provide an oscillator drive signal based upon the difference; and

a local time reference generator configured to provide the sampling clock based upon the oscillator drive signal.

12. The apparatus of claim 11, wherein the difference between the absolute timing reference clock and the local time reference dock is representative of a frequency error.

13. The apparatus of claim 12, wherein the tracking loop further comprises:

a loop averaging filter configured to prevent substantial deviations in the frequency error.

14. The apparatus of claim 11, further comprising:

a timing offset correction module configured to adjust the local time reference clock by a timing offset to provide a reference of the sampling clock.

15. In an apparatus for implementing synchronization between a data collection deadline time and a grant schedule, a method comprising:

processing a downstream information flow received from a cable modem termination system (CMTS) to extract a time based message and the grant schedule;

generating an absolute timing reference clock utilizing the time based message;

generating a sampling clock which tracks the absolute timing reference clock;

analyzing a time between successive grants within the grant schedule utilizing the sampling clock;

setting the data collection deadline time based on the time between the successive grants by compensating for processing time of data to be transmitted; and

storing the data to be transmitted prior to receiving a grant subsequent to the successive grants in accordance with the grant schedule.

16. The method of claim 15, wherein the absolute timing reference clock is representative of an oscillator frequency associated with the CMTS.

17. The method of claim 15, wherein generating the sampling clock comprises:

determining a difference between the absolute timing reference clock and a local time reference clock;

generating an oscillator drive signal based upon the difference; and

generating the sampling clock based upon the oscillator drive signal.

18. The method of claim 17, wherein the difference between the absolute timing reference clock and the local time reference clock is representative of a frequency error.

19. The method of claim 17, further comprising:

adjusting the local time reference clock by a timing offset to provide a reference for the sampling clock.