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

• US 7,079,554 B2
• Filed: 10/16/2002
• Issued: 07/18/2006
• Est. Priority Date: 10/16/2002
• Status: Expired due to Fees

• Current Assignee: Terasync Limited
• Original Assignee: Terasync Limited
• Inventors: Peled, Eran
• Primary Examiner(s): SHAH, CHIRAG G
• Application Number:
  US10/271,927
• Publication Number:
  US 20040076187A1
• Time in Patent Office: 1,371 Days
• Field of Search: 370/514, 370/503, 370/280, 370/314, 370/324, 370/350, 370/516
• 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

A new method for synchronizing transmissions of real time synchronous data packets over an asynchronous network between two terminal nodes is disclosed. 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 communication devices comprise internal local clocks which are each activated by a stratum pulse generator, wherein local clocks are synchronized by utilizing transmission or reference timestamp packets through the asynchronous network and using an internal digital phase locked loop (DPLL) for attenuating jitter and wander in a data transmission signal in accordance to stratum accuracy standards,

wherein the synchronization procedure of the local clocks comprises the steps of:

a. transmitting a timestamp, at a low layer through the asynchronous network;

b. receiving incoming data packets from the asynchronous network at the receiver terminal node;

c. identifying a timestamp packet of a transmitting station among the incoming data packets, and extracting a remote timestamp of the timestamp packet;

d. calculating a difference between the remote timestamp, which originated in the network, and a local timestamp, and using the calculated difference as an input to the DPLL;

e. attenuating jitter and wander in data transmission signal by the DPLL, in accordance to the stratum accuracy standards; and

f. outputting a DPLL output result as a new reference for generating a next timestamp.

2. The method according to claim 1, wherein the local timestamps are broadcast at periodic intervals to all active terminals in the network from each terminal node to all active terminal nodes connected to the asynchronous network.

3. The method according to claim 2, wherein the timestamps are transmitted within regular data packets.

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

5. The method according to claim 1, wherein jitter and wander are reduced to meet the various stratum standards.

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

6. A receiver/transceiver system that is implemented within intermediating communication devices which connect between TDM communications equipment and an 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. a data transceiver unit for generating the timestamp packets according to stratum clock pulse and transmitting thereof through the asynchronous network;

c. a receiver unit for receiving incoming data packets from the asynchronous network;

d. a data packet detector for identifying the relevant timestamp of the respective transmitting station;

e. a computing module for calculating the time difference between the local timestamp and the remote timestamp; and

f. a digital phase locked loop (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.

7. The system of claim 6 wherein the stratum standards include stratum 2, 3, 3e, 4, and 4e.

8. The system of claim 6 further comprising a redundancy mechanism that supports simultaneous analyzing of two synchronization sources and enables hitless-switching between two references.

9. The system according to claim 6, wherein the timestamps are broadcast at periodic intervals to all active terminals in the network from each terminal node to all active terminal nodes connected to the asynchronous network.

10. The system according to claim 6, wherein the timestamps are transmitted within regular data packets.

11. The system according to claim 6 wherein the asynchronous network is an optical network.

12. The system according to claim 6 wherein the jitter is reduced below the value of +250 microseconds to a value of +/−

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

13. A module for synchronizing transmission of real time synchronous data packets over an asynchronous network between at least two terminal nodes, said module for synchronizing transmission implemented within intermediating communication devices connecting between TDM equipment and an asynchronous optical network, wherein each communication device comprises:

a. a data packets detector for receiving incoming data packets from the asynchronous network at a receiver terminal node;

b. a timestamp detector for identifying a timestamp packet of a transmitting station among the incoming data packets, and extracting a remote timestamp of the timestamp packet;

c. a computing module for calculating a difference between the remote timestamp, which originated in the network, and a local timestamp;

d. an internal digital phase locked loop (DPLL) associated with a stratum pulse generator, attenuates jitter and wander interferences in accordance with stratum accuracy standards; and

e. a local timestamp generator, which receives an output from the DPLL for generating a next local timestamp.