System and method for synchronizing between communication terminals of asynchronous packets networks

• US 20040076187A1
• Filed: 10/16/2002
• Published: 04/22/2004
• Est. Priority Date: 10/16/2002
• Status: Active Grant

• Current Assignee: Terasync Limited
• Original Assignee: Terasync Limited
• Inventors: Peled, Eran
• Granted Patent: US 7,079,554 B2
• Time in Patent Office: Days
• US Class Current: 370/514
• CPC Class Codes: H04J 3/0685 Clock or time synchronisation in a node; Intranode synchronisation
• CPC Class Codes: H04L 12/2852 Metropolitan area networks

Abstract

The present invention will allow the use of the asynchronous Ethernet MAN as if it was a regular fiber optic line, while eliminating the uncertainties of it'"'"'s cloud environment. The invention provides a new method for synchronizing transmissions of real time synchronous data packets over an asynchronous network between two terminal nodes. The synchronization procedure is implemented within intermediating communication devices, which connect between the terminal nodes TDM equipment and the asynchronous network. Each communication device comprises local clocks, which are activated by a Stratum 2/3/3e/4/4e pulse generator. The local clocks synchronization is based on the transmission of a reference timestamp packet through an asynchronous network. Based on this timestamp references, an internal digital PLL is used for attenuating the jitter/wander in data transmission signal in accordance to Stratum 2/3/3e/4/4e accuracy standards. The DPLL data result is then processed to be used by the local clock of the receiving terminal.

Claims

1. A method for synchronizing transmission of real time synchronous data packets over an asynchronous network between at least two terminal nodes using an intermediating communication device which connects between the terminal nodes TDM equipment and the asynchronous network wherein said communication devices comprise internal local clocks which are activated by a Stratum pulse generator wherein the clocks are synchronized by utilizing transmission of reference timestamp packets through the asynchronous network and using an internal digital PLL for attenuating jitter/wander in data transmission signal in accordance to Stratum accuracy standards.

2. The method of claim 1 wherein the stratum standard include stratum 2, 3, 3e, 4, and 4e.

3. The method of claim 1 wherein the synchronization procedure of the local clocks comprise the steps of:

A. Transmitting the timestamp, at a low layer through an asynchronous network;

B. Receiving incoming data packets from the asynchronous network at the receiver terminal node;

C. Identify the timestamp packet of the respective transmitting station;

D. Calculating the difference between the remote timestamp, which originated in the network and the local timestamp and using the result as an input data to the DPLL.

E. Attenuating jitter/wander in data transmission signal, in accordance to Stratum accuracy standards using a DPLL;

F. Using the DPLL output result as a new reference for generating the next timestamp.

4. The method according to claim 1 wherein the timestamp packets are broadcasted at periodic intervals to all active terminals in the network from each terminal node to all active terminal nodes connected to the asynchronous network.

5. The method according to claim 1, wherein the timestamps are transmitted within regular data packets;

6. The method according to claim 1, wherein the asynchronous network is an optical network

7. The method according to claim 1, wherein extremely high jitter/wander jitter is reduced to meet the various stratum standards.

8. A receiver/transmitter system that is implemented within intermediating communication devices which connect between TDM communication equipment and the asynchronous optical network for synchronizing transmissions of real time synchronous data packets over the asynchronous network between at least two user terminal nodes, said system comprising of:

A. At least one Stratum clock rate generator for providing classified clock pulse to each TDM switch terminal node;

B. Data transceiver unit for generating the timestamp packets according to stratum clock pulse and transmitting thereof through the asynchronous network;

C. Receiver unit for receiving incoming data packets from the asynchronous network;

D. Data packets detector for Identifying the relevant timestamp of the respective transmitting station;

E. Computing module for calculating the time difference between the local timestamp and the remote timestamp;

F. Advanced DPLL unit for attenuating the jitter and wander of the incoming signals, based on the calculator results for providing output signals in accordance to stratum standards, wherein the output of the DPLL provides the reference for the generation of the next local timestamp.

9. The system of claim 8 wherein the stratum standards include standard include stratum 2, 3, 3e, 4, and 4e.

10. The system of claim 8 further comprises a redundancy mechanism that supports simultaneous analyzing of two synchronization sources and enables hitless-switching between two references (according to the relevant standard;

GR-1244, GR-253, etc).

11. The system according to claim 8, wherein the timestamps packets are broadcasted at periodic intervals to all active terminals in the network from each terminal node to all active terminal nodes connected to the asynchronous network.

12. The system according to claim 8, wherein the timestamps are transmitted within regular data packets;

13. The system according to claim 8 wherein the asynchronous network is an optical network;

14. The system according to claim 8 wherein the jitter is reduced bellow the value of +−

250 microseconds.to a value of +−

1 nanoseconds, despite the large amplitude jitter/wander at the input.

15. A module for synchronizing transmission of real time synchronous data packets over an asynchronous network between at least two terminal nodes, said synchronization module implemented within intermediating communication devices connecting between the TDM equipment and the asynchronous optical network wherein each communication device has an internal digital PLL associated with a Stratum pulse generator, which is synchronized by utilizing the transmissions of low layer timestamp packets.