Method and system for synchronizing separated edge QAM devices located remotely from a CMTS

1. A method for synchronizing the downstream clock of each of one or more corresponding edge QAM devices with the master clock of a remotely located CMTS, comprising:

driving a first counter located at the CMTS with a first temperature compensated crystal oscillator; latching the first counter contents when a media interface transmits a time synchronization message packet;

reporting the latched contents of the first counter to a first processor;

generating a next time synchronization message from the latched first counter contents;

transmitting the next time synchronization message from the gigabit Ethernet output of the CMTS;

receiving the next time synchronization message at each of the one or more edgeQAM devices from a means for communicating clock synchronization information between the CMTS and each of the one or more edgeQAM device(s), the communicating means being coupled with the CMTS;

driving a second counter located at each of the one or more edgeQAM devices with a second temperature compensated crystal oscillator;

driving a third counter located at each of the one or more edgeQAM devices with a voltage controlled crystal oscillator, which is controlled with a digital to analog converter, which is in turn controlled by a second processor located at the edge QAM device, wherein the third counter is locked to the second counter;

latching the contents of the second counter and the third counter when the next time synchronization message is received;

reporting the latched contents of the second and third counters to the second processor;

comparing the reported contents of the third counter with the contents of the received next time synchronization message packet to generate a phase error difference;

adjusting the digital to analog converter by the phase error difference to cause a corresponding change in the frequency of the voltage controlled crystal oscillator; and

outputting the frequency of the voltage controlled crystal oscillator to the local clock of the corresponding one or more edgeQAM devices.

2. The method of claim 1 wherein time synchronization messages are sent from the CMTS at a rate of 100,000 messages per second.

3. The method of claim 1 wherein an Ethernet switch is used to distribute time synchronization messages from the CMTS to more than one edgeQAM device.

4. The method of claim 3 wherein time synchronization messages are sent from the CMTS at a rate of 31,000 messages per second.

5. The method of claim 1 wherein the first counter is implemented with a field programmable gate array.

6. The method of claim 1 wherein the media interface is a gigabit media-independent interface.

7. A method for synchronizing the downstream clock of each of one or more corresponding edge QAM devices with the master clock of a remotely located CMTS, comprising:

locking a downstream symbol rate and a digital to analog converter at each of the one or more edgeQAM devices to a voltage controlled crystal oscillator at the corresponding edgeQAM device;

inserting a DOCSIS SYNC MAC message at a MPEG multiplexing input at each of the one or more edgeQAM devices;

locking a device clock at each of one or more user devices coupled with each of the one or more edgeQAM devices to the downstream symbol rate of the corresponding edgeQAM device serving said user device or devices;

locking the upstream burst symbol rate of each of the one or more user devices to the device's corresponding device clock;

locking a canary clock of one or more canary devices located at the CMTS to the downstream traffic stream of one of the one or more edgeQAM devices corresponding to the canary device;

comparing the canary clock frequency to the frequency of the CMTS master clock;

estimating a phase error of the canary clock based on the comparison of the canary clock frequency and the CMTS master clock frequency;

transmitting the phase error to the edgeQAM device corresponding to the canary device; and

adjusting the voltage controlled crystal oscillator of the edgeQAM device corresponding to the canary device based on the estimated phase error.

8. A method for synchronizing the downstream clock of each of one or more corresponding edge QAM devices with the master clock of a remotely located CMTS, wherein the CMTS master clock is locked to a temperature compensated crystal oscillator and the downstream clock of each edgeQAM device is locked to a corresponding local voltage controlled crystal oscillator, comprising:

initiating TDMA-only operation by periodically sending counter re-synchronization messages from the CMTS to each of the edgeQAM devices;

collecting at the CMTS timing information received from bursts sent by a predetermined number of user devices served by a given edgeQAM device;

averaging the collected timing information of the bursts over a predetermined period for each of the one or more edgeQAM devices;

estimating a clock error for each of the given edgeQAM devices based on the averaged timing information corresponding to said given edgeQAM device;

transmitting the estimated clock error to the corresponding edgeQAM device; and

adjusting the voltage controlled crystal oscillator of each edgeQAM device based on its corresponding estimated clock error.