Synchronization of asynchronous networks using media access control (MAC) layer synchronization symbols

• US 7,251,256 B1
• Filed: 05/18/2000
• Issued: 07/31/2007
• Est. Priority Date: 05/18/2000
• Status: Expired due to Term

• Current Assignee: ADTRAN Incorporated (ADTRAN Holdings, Inc.)
• Original Assignee: Luminous Networks, Inc (ADTRAN Holdings, Inc.)
• Inventors: Choi, Inwhan, Watson, David, Stillman, Robert, Fan, Jason, Barry, Charles
• Primary Examiner(s): Pham; Chi
• Assistant Examiner(s): LY, ANH VU H
• Application Number:
  US09/574,745
• Time in Patent Office: 2,630 Days
• Field of Search: 370/401, 370/445, 370/503, 370/254, 370/351, 370/400
• US Class Current: 370/503
• CPC Class Codes: H04J 3/0641 Change of the master or reference, e.g. take-over or failure of the master
• CPC Class Codes: H04J 3/0647 Synchronisation among TDM nodes
• CPC Class Codes: H04J 3/0658 Clock or time synchronisation among packet nodes
• CPC Class Codes: H04L 7/08 the synchronisation signals recurring cyclically

Abstract

A method and structure for the distribution and utilization of synchronization within an asynchronous network is described herein. Synchronization is distributed through an asynchronous network via a synchronization symbol periodically inserted on the MAC layer. The priority of this symbol ensures that this symbol is inserted in the MAC layer data stream ahead of all other types of symbols. The insertion of the synchronization symbol in the middle of an ongoing data frame is supported. In addition, a method for synchronization symbol distribution throughout an asynchronous network is presented, along with a method for switching to a new synchronization path (in the event of loss of original synchronization path) based on minimum number of hops from the synchronization source. In addition, a method is described for utilization of the count and interval of received synchronization symbols and the count and interval of transmitted synchronization symbols to generate an error correction signal used in the process of frequency locking of a device'"'"'s internal hardware to received synchronization symbols from another device. Using the prioritized insertion capability required for synchronization symbols, a variety of other MAC layer control symbols are defined to perform other functions, such as propagation time measurement between adjacent nodes.

Claims

1. A method performed in a communications network, said communications network comprising nodes, at least one of said nodes transmitting a data frame on said network, said method comprising:

generating a control signal by a first one of said nodes;

inserting and transmitting said control signal on said network to at least a second one of said nodes during a transmission of said data frame on said network, wherein said control signal is prioritized to be inserted before any other queued data or control codes;

receiving, by said second one of said nodes, said control signal after receiving only a portion of said data frame, wherein said control signal was inserted in said data frame outside of a payload field of said data frame; and

performing, by said second one of said nodes, an action required by said control signal prior to waiting until data frame has been fully received.

2. The method of claim 1 wherein said transmitting said control signal comprises transmitting a master clock signal, said method further comprising:

generating local clock signals by a local clock in said second one of said nodes, wherein said performing an action comprises;

correcting any timing error in said local clock based on the time that said master clock signal was received by said second node after receiving only a portion of said data frame so that timing jitter is limited to less than a data frame period.

3. The method of claim 2 wherein said master clock signal is an 8 KHz clock.

4. The method of claim 3 wherein said 8 KHz clock is a Global Positioning System (GPS) clock.

5. The method of claim 1 wherein said data frame is transmitted in accordance with an Ethernet protocol.

6. The method of claim 1 wherein said control signal is an 8B/10B encoded control character.

7. The method of claim 1 wherein said data frame is a packet.

8. The method of claim 1 wherein said control signal is a master clock signal.

9. The method of claim 1 wherein said performing an action comprises performing in action by media access controller (MAC).

10. The method of claim 1 wherein said control signal is a master clock signal, and wherein said performing an action comprises taking steps to correct a timing error between a local clock in said second one of said nodes and said master clock signal.

11. The method of claim 1 wherein said performing an action comprise synchronizing a local clock in said second one of said nodes with said control signal.

12. A method performed in a communications network, said communications network comprising nodes, at least one of said nodes transmitting a data frame on said network, a first one of said nodes generating a control signal and transmitting said control signal on said network to at least a second one of said nodes during a transmission of said data frame on said network, said method comprising:

receiving, by said second one of said nodes, said control signal after receiving only a portion of said data frame; and

performing, by said second one of said nodes, an action required by said control signal prior to waiting until said data frame has been fully received,

wherein said control signal is a master clock signal, and wherein said performing an action comprises taking steps to correct a timing error between a local clock in said second one of said nodes and said master clock signal, wherein said control signal is an 8B/10B encoded character, and wherein said timing error is corrected so that a clock jitter in said second one of said nodes is approximately the period of said 8B/10B encoded character.

13. A method performed in a communications network, said communications network comprising nodes, at least one of said nodes transmitting a data frame on said network, said method comprising:

generating a control signal by a first one of said nodes;

inserting and transmitting said control signal on said network to at least a second one of said nodes during a transmission of said data frame on said network, wherein said control signal is prioritized to be inserted before any other queued data or control codes;

receiving, by said second one of said nodes, said control signal after receiving only a portion of said data frame; and

performing, by said second one of said nodes, an action required by said control signal prior to waiting until said data frame has been fully received,

wherein said control signal is a master clock signal, and wherein said performing an action comprises taking steps to correct a timing error between a local clock in said second one of said nodes and said master clock signal,

wherein said control signal is a MAC layer encoded character, and wherein said timing error is corrected so that a clock jitter in said second one of said nodes is approximately the period of said MAC layer encoded character.