Clock synchronization of HFC telephone equipment

• US 6,975,652 B1
• Filed: 10/18/2000
• Issued: 12/13/2005
• Est. Priority Date: 10/18/2000
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: 3Com Corporation (HP Inc.)
• Inventors: Mannette, Michael R., Newlin, Douglas J.
• Primary Examiner(s): Duong, Frank
• Assistant Examiner(s): MOORE JR, MICHAEL J
• Application Number:
  US09/691,489
• Time in Patent Office: 1,882 Days
• Field of Search: 370503-519, 375354-371, 327141-163
• US Class Current: 370/503
• CPC Class Codes: H04J 3/0664 unidirectional timestamps
• CPC Class Codes: H04L 12/2801 Broadband local area networks

Abstract

A method and system for synchronizing two clocks of a first and second device. Successive synchronization messages are sent from the first device to the second device. Each synchronization message has a timestamp. Each message is received at the second device and the period between successive timestamps is determined. The period of the second clock of the second device is also determined. The period between timestamps is compared with the period of the second clock of the second device. The period of said second clock is adjusted based upon the comparison.

Claims

1. A system for synchronizing the operation of a transmitter clock and a local reference clock, said system comprising:

a transmitter block, said transmitter block for transmitting consecutive synchronization messages, each of said messages having a timestamp, said transmitter block maintaining a transmitter counter having a value, wherein each of said timestamps indicates said value of said counter at successive moments of time;

a receiver, coupled to said transmitter block, for receiving said synchronization messages;

first and second synchronization registers, coupled to said receiver, said synchronization registers storing said timestamps of said consecutive synchronization messages;

a first comparator for comparing values of said first and second synchronization registers to produce a synchronization time period;

first and second local reference registers, coupled to a local counter, each of said first and second local reference registers having a value indicative of a local reference counter at successive moments of time;

a second comparator, coupled to said first and second local reference registers, said comparator comparing the values of said first and second local registers and determining a local reference time period; and

a comparison and clock adjustment block, coupled to said first and second comparators and said local refererence clock, said block comparing said synchronization time period with said local reference time period and then adjusting said local reference clock based upon said comparison.

2. The system of claim 1 wherein data is transmitted from said transmitter to said receiver, said system further comprising:

a processor block, coupled to said receiver, for determining a transmission rate of said data; and

a comparison and clock adjustment block, coupled to said local reference counter and said processor block, for adjusting said local reference counter based upon said determination of said rate.

3. The system of claim 2 wherein said comparison and clock adjustment block comprises a plurality of clock adjusters and CODEC clock generators, coupled to said processor block, for adjusting digital-to-analog converter clock based upon said determination of said rate.

4. The system of claim 1 wherein said transmitter further comprises a controller, said controller generating a strobe, said strobe delayed from the transmission of data by a programmable amount.

5. The system of claim 1 wherein said transmitter also transmits a MAP message to said receiver, said MAP message instructing said receiver to create a message having a TDMA format.

6. The system of claim 1 wherein said comparison and clock adjustment block includes a voltage controlled oscillator.

7. The system of claim 1 wherein said comparison and clock adjustment block includes a pulse stretcher.

8. A system comprising:

a hybrid fiber coax network;

a cable telephone modem (CTM) coupled to said hybrid fiber coax network, said modem having a local clock;

a cable modem termination system (CMTS) coupled to said hybrid fiber coax network and a packet network, wherein said CMTS includes means for sending successive synchronization messages, each of said synchronization messages having a timestamp, to said cable telephone modem;

wherein said cable telephone modem includes means for receiving said synchronization messages and determining a synchronization period, wherein said synchronization period is a time between successive timestamps;

means for determining a period of said local clock;

means for comparing said period of said local clock with said synchronization period to determine a difference, and means for adjusting said period of said local clock based upon said difference.

9. The system of claim 8 wherein said CTM includes means for receiving data from said CMTS, means for determining a rate of said data, and means for adjusting the period of said local clock based upon said rate.