CA2199647C

CA2199647C - Synchronization of communication devices connected over an asynchronous link

Info

Publication number: CA2199647C
Application number: CA 2199647
Authority: CA
Inventors: Robert Wood
Original assignee: Mitel Networks Corp
Current assignee: Mitel Networks Corp
Priority date: 1997-03-11
Filing date: 1997-03-11
Publication date: 2004-01-27
Anticipated expiration: 2017-03-11
Also published as: CA2199647A1

Abstract

In a method of establishing communication between synchronous devices over an asynchronous communications channel, each device samples a signal to be transmitted at a rate determined by a local clock. The rate of transmission of samples over the channel is determined by the local clock in each device. At least one of the devices is periodically adjusted to match the rates of transmission and arrival of samples over the channel, for example, by adjusting the frequency of the local clock or by dropping or duplicating samples. With this arrangement there is no need to exchange explicit timing information.

Claims

1. A method of establishing communication between synchronous devices over an asynchronous communications channel, wherein each device creates, at a rate determined by a local clock associated therewith, samples of a signal to be transmitted to the other device; transmits said samples over said channel at a rate determined by its local clock;
and receives samples from the other device at a rate determined by the local clock;
associated with the other device, and wherein at least one of said local clocks is periodically adjusted to match the rates of transmission and arrival of said samples over the channel at the device associated therewith.

2. A method of establishing communication between synchronous devices over an asynchronous communications channel, comprising at each device carrying out the steps of:
a) sampling a signal to be transmitted at a nominal rate determined by a local clock associated with the device;
b) storing successive samples of the signal to be transmitted in a transmit buffer until a predetermined number of samples have been stored and then transmitting the stored samples over the communications channel at a rate determined by the local clock of the device;
c) storing received samples in a receive buffer at a rate determined by the local clock of the other device until number of a predetermined number of received samples have been stored;
d) reconstructing a received signal from the received samples at said nominal rate determined by the local clock of the device; and e) periodically adjusting the local clock of the device to match rate of transmission and arrival of samples in the respective buffers.

3. A method as claimed in claim 2, wherein each buffer is associated with a counter that keeps track of the number of incoming and outgoing samples, a difference signal is derived for each buffer that represents the difference between these two values, and the local clock is adjusted to match the difference signal associated with each buffer.

4. A method as claimed in claim 3, wherein said difference signals are smoothed prior to adjusting said local clock.

5. A method as claimed in claim 3, wherein each buffer is associated with a counter that keeps track of the number of samples in the buffer, and the local clock is adjusted to match the samples in each buffer.

6. A method as claimed in claim 5, wherein the count in the counter associated with each buffer is passed through a smoothing circuit prior to adjusting the local clock.

7. A synchronous communication device capable of establishing communication with another synchronous communication device over an asynchronous communications channel, comprising means for sampling a signal to be transmitted at a rate determined by a local clock associated with said device, means for transmitting samples of said signal over said channel at a rate determined by said local clock, means for receiving samples of said signal at a rate determined by the local clock of the other device, and means for adjusting at least one of the local clocks periodically to match the rates of transmission and arrival of said samples over the channel.

8. A synchronous communication device capable of establishing communication with another synchronous communication device over an asynchronous communications channel, comprising:
a) means for sampling a signal to be transmitted at a nominal rate determined by a local clock associated with the device;
b) means for storing successive samples of the signal to be transmitted in a transmit buffer until a predetermined number of samples have been stored and then transmitting the stored samples over the communications channel at a rate determined by said local clock;
c) means for storing received samples in a receive buffer until number of a predetermined number of received samples have been stored at a rate determined by a local clock associated with said another synchronous communication device;
d) means for reconstructing a received signal from the received samples at said nominal rate determined by said local clock associated with said device; and e) means for periodically adjusting said local clock of said device to match rate of transmission and arrival of samples in the respective transmit and receive buffers.

9. A device as claimed in claim 9, further comprising a counter associated with each buffer that keeps track of the number of incoming and outgoing samples, and means for generating a difference signal for each buffer that represents the difference between these two values, said clock adjusting means adjusting the local clock to match the difference signal associated with each buffer.

10. A device as claimed in claim 9, wherein said difference signals are smoothed prior to adjusting said local clock.

11. A device as claimed in claim 10, wherein each buffer is associated with a counter that keeps track of the number of samples in the buffer, and said clock adjusting means adjusts the local clock to match the difference signal associated with each buffer.

12. A device as claimed in claim 11, wherein the count in the counter associated with each buffer is passed through a smoothing circuit prior to adjusting the local clock.