Method for the clock synchronization of a plurality of modules

• US 9,276,688 B2
• Filed: 01/28/2011
• Issued: 03/01/2016
• Est. Priority Date: 01/11/2011
• Status: Active Grant

• Current Assignee: Unify Patente GmbH & Co. KG (Atos Se)
• Original Assignee: Unify GmbH & Co. KG (Atos SE)
• Inventors: Lindner, Thomas
• Primary Examiner(s): Skripnikov, Alex
• Application Number:
  US13/990,919
• Publication Number:
  US 20130250976A1
• Time in Patent Office: 1,859 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: H04J 3/0602 Systems characterised by the synchronising information used
• CPC Class Codes: H04J 3/0638 Clock or time synchronisation among nodes; Internode synchronisation synchronization for ring networks H04L12/422; data switching networks with synchronous transmission H04L12/43
• CPC Class Codes: H04J 3/0644 External master-clock
• CPC Class Codes: H04J 3/1688 the demands of the users being taken into account after redundancy removal, e.g. by predictive coding, by variable sampling reducing bandwidth of signals in general H04B1/66; in PCM-systems H04B14/046; removal of redundancy in telegraph communication H03M7/30
• CPC Class Codes: H04L 7/08 the synchronisation signals recurring cyclically

Abstract

The invention relates to a method or an arrangement for the clock synchronization of a plurality of distributed modules of an information or communication system, said modules being coupled via a packet-switched network. At least two of said modules are controlled by a local clock generator of the modules using an adjustable frequency, and a clock signal is transmitted via the network in the form of clock signal packets in a synchronous minter with respect to the local clock of the modules. One of said at least two modules takes over the function of a master module, and all remaining said at least two modules, the slave module(s), synchronize the local clock of the modules with the clock of the master module, wherein said slave modules ascertain a measurement for the deviation of the local clock generator of the modules relative to the clock generator of the master module by comparing the clock signal transmitted by the master module with the clock signal of the modules and use said measurement in order to regulate the local clock generator of the modules.

Claims

1. A method for clock synchronization of a plurality of distributed modules in an information system or a communications system, said modules being coupled via a packet-switched network, comprising:

controlling a plurality of modules comprising a first module, a second module, and a third module, each of the modules having a local clock generator, each of the modules being configured to transmit a clock signal of the local clock generator of that module over the network as at least one clock signal packet synchronous to a local clock rate of the local clock generator, the controlling of each of the modules comprising;

causing the first module to assume a master module role for synchronization of clock rates for the modules;

sending, by the first module, at least one first clock signal via the network;

transmitting, by the second module, at least one second clock signal during a first time window via the network;

transmitting, by the third module, at least one third clock signal during a second time window via the network, the second time window being different from the first time window such that the at least one third clock signal of the third module is not transmitted during the first time window;

determining a first measurement for a deviation of the local clock generator of the second module relative to the local clock generator of the first module by comparing the at least one first clock signal transmitted by the first module to the at least one second clock signal transmitted by the second module and using the first measurement to control the local clock generator of the second module;

determining a second measurement for a deviation of the local clock generator of the third module relative to the local clock generator of the first module by comparing the at least one first clock signal transmitted by the first module to the at least one third clock signal transmitted by the third module and using the second measurement to control the local clock generator of the third module.

2. The method of claim 1, comprising assigning a local control unit to each module and connecting each local control unit to a central control computer via the network.

3. The method of claim 2, where each local control unit has a quartz oscillator with an adjustable frequency, said quartz oscillator controlled by a program via a digital-to-analog converter.

4. The method of claim 1, wherein each of the at least one first clock signal, at least one second clock signal, and at least one third clock signal comprises at least one pulse code modulation signal, and wherein the pulse code modulation signal is transmitted over the network in data packets formed in accordance with real time transport protocol.

5. The method of claim 1, comprising determining a frequency difference and a phase difference between a packet stream transmitted from a slave module and a packet stream of the master module for each slave module.

6. The method of claim 1, comprising setting priority for clock signal packets in the network so that the clock signal packets have a higher priority as compared to other signaling packets.

7. The method of claim 1, wherein the determining of the first measurement comprises:

determining a frequency difference and a phase difference between the at least one second clock signal and the at least one first clock signal.

8. The method of claim 1, comprising:

a switch device receiving the at least one first clock signal, the at least one second clock signal, and the at least one third clock signal at different times such that stochastic delays associated with transmission of clock signals is avoided.

9. The method of claim 1, wherein the at least one first clock signal, the at least one second clock signal, and the at least one third clock signal are each transmitted to a control computer, and wherein the control computer performs the determining of the first measurement and performs the determining of the second measurement.

10. The method of claim 9, comprising:

receiving, by a switch device of the network, the at least one first clock signal, the at least one second clock signal, and the at least one third clock signal at different times such that stochastic delays associated with transmission of clock signals is avoided; and

forwarding, by the switch device, the at least one first clock signal, the at least one second clock signal, and the at least one third clock signal to the control computer.

11. The method of claim 1, wherein the at least one first clock signal is sent via the network during a third time window, the third time window being different than the second time window and the third time window being different than the first time window such that the at least one first clock signal is not transmitted during the first time window and is not transmitted during the second time window.

12. An apparatus comprising:

a plurality of modules in an information system or a communications system, the modules being connected via a packet-switched network, the modules comprising a first module, a second module, and a third module, each of the modules having a local clock generator, each of the modules being configured to transmit a clock signal of the local clock generator of that module over the network as at least one clock signal packet synchronous to a local clock rate of the local clock generator;

a control computer connected to the modules via the network;

the first module configured to send at least one first clock signal to the control computer via the network;

the second module configured to send at least one second clock signal to the control computer during a first time window via the network;

the third module configured to send at least one third clock signal to the control computer during a second time window via the network, the second time window being different from the first time window such that the at least one third clock signal of the third module is not transmitted during the first time window;

the control computer configured to determine;

a first measurement for a deviation of the local clock generator of the second module relative to the local clock generator of the first module by comparing the at least one first clock signal transmitted by the first module to the at least one second clock signal transmitted by the second module and using the first measurement to control the local clock generator of the second module, and

a second measurement for a deviation of the local clock generator of the third module relative to the local clock generator of the first module by comparing the at least one first clock signal transmitted by the first module to the at least one third clock signal transmitted by the third module and using the second measurement to control the local clock generator of the third module.

13. The apparatus of claim 12, wherein a local control unit is assigned to each module and is connected to the control computer via the network.

14. The apparatus of claim 13, wherein each local control unit has a quartz oscillator with an adjustable frequency, said quartz oscillator being controlled by a program via a digital-to-analog converter.

15. The apparatus of claim 12, wherein each clock signal comprises at least one pulse code modulation signal, which is transmitted across the network via data packets formed in accordance with real time transport protocol, synchronous to a clock rate of a pulse code modulation signal.

16. The apparatus of claim 12, wherein a frequency difference and a phase difference between the at least one second clock signal and the at least one first clock signal are determined by the control computer.

17. The apparatus of claim 12, comprising:

a switch device connected between the control computer and the modules, the switch device configured to receive the at least one first clock signal, at least one second clock signal and at least one third clock signal at different times and also configured to forward the at least one first clock signal, at least one second clock signal, and at least one third clock signal to the control computer at different times.

18. The apparatus of claim 17, wherein the control computer is a central control computer.

19. The apparatus of claim 17, wherein the at least one first clock signal is transmitted as at least one clock signal data packet, the at least one second clock signal is transmitted as at least one clock signal data packet, and the at least one third clock signal is transmitted as at least one clock signal data packet.

20. The apparatus of claim 12, wherein the at least one first clock signal is sent via the network during a third time window, the third time window being different than the second time window and the third time window being different than the first time window such that the at least one first clock signal is not transmitted during the first time window and is not transmitted during the second time window.