Data transmission over packet switched network

1. A method of transmitting data over a packet switched data network between time-synchronized communication modules, the method comprising:

receiving synchronous time division multiplex (TDM) data in a first communication module;

generating, by the first module, a time stamp indicative of a receive time of the synchronous TDM data at the first module;

transmitting, in a data packet, the received synchronous TDM data to a second communication module via the packet switched data network;

outputting, by the second module, the transmitted synchronous TDM data at an output time determined by adding a predefined delay time to the time stamp;

calculating, by the second communication module, a transmission time based on a difference between a packet receive time of the data packet at the second module and the time stamp;

calculating a wait time as a difference between the predefined delay time and the transmission time; and

delaying the outputting of the transmitted synchronous TDM data for the wait time.

2. The method of claim 1 , comprising:

storing the transmitted synchronous TDM data in a jitter buffer of the second communication module for the wait time.

3. A destination communication module configured to exchange data packets with a source communication module over a packet switched data network, wherein the communication modules are time-synchronized, the destination module having at least one hardware processor circuit configured to:

output, at an output time, synchronous TDM data transmitted in a data packet from the source module,

wherein the output time is determined by adding a predefined delay time to a time stamp generated by the source module and indicative of a receive time of synchronous TDM data at the source module, and

wherein the processor of the destination communication module is configured to

calculate a transmission time based on a difference between a packet receive time of the data packet at the destination module and the time stamp;

calculate a wait time as a difference between the predefined delay time and the transmission time; and

delay the outputting of the transmitted synchronous TDM data for the wait time.

4. The method of claim 1 , comprising:

determining, by the second module, the output time for the transmitted synchronous TDM data.

5. The method of claim 1 , comprising:

determining, by the first module, the output time, and transmitting the output time in the data packet to the second module.

6. The method of claim 1 , comprising:

transmitting the time stamp in the data packet to the second module.

7. The method of claim 1 , comprising:

synchronizing a first clock of the first communication module with a master clock, the first clock being used for time stamping the synchronous TDM data;

synchronizing a second clock of the second communication module with the master clock,

wherein the first clock and the second clock are synchronized via the packet switched data network with the master clock.

8. The method of claim 7 , wherein one of the first clock or the second clock acts as the master clock.

9. The method of claim 8 , wherein for synchronization the precision time protocol (PTP) according to time and frequency synchronization protocol IEEE 1588v2 is used.

10. The method of claim 1 , wherein the predefined delay time has a constant value in a period of time.

11. The method of claim 10 , wherein the constant value is adapted by an operator.

12. The method of claim 10 , wherein the constant value is adapted by an automated mechanism.

13. The method of claim 1 , wherein:

the communication modules are nodes of a communication network of an electric power system;

the synchronous TDM data include measurement data;

the predefined delay time is less than 10 ms; and

the method comprises providing, by the second communication module, the transmitted synchronous TDM data to a line differential protection relay configured to protect a power line of the power system.

14. The method of claim 13 , wherein a communication link for the synchronous TDM data including the two communication modules and the packet switched data network has a communication delay accuracy of better than 80 μs per direction.

15. The method of claim 13 , wherein the line differential protection relay is designed to receive synchronous TDM data with a constant time delay.

16. The method of claim 13 , wherein:

the line differential protection relay processes the measurement data and another measurement data from a second location on the power line, the line differential protection relay comparing measurements at equal time points, and

the line differential protection relay shifts the synchronous TDM data by the predefined delay time.

17. The method of claim 16 , wherein the line differential protection relay is designed to receive synchronous TDM data with a constant time delay.

18. The method of claim 17 , comprising:

transmitting the time stamp in the data packet to the second module;

synchronizing a first clock of the first communication module with a master clock, the first clock being used for time stamping the synchronous TDM data;

synchronizing a second clock of the second communication module with the master clock,

wherein the first clock and the second clock are synchronized via the packet switched data network with the master clock;

wherein the predefined delay time has a constant value in a period of time; and

wherein the constant value is adapted by an operator.