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Voice Over IP (VOIP)

This example illustrates using the UDP Send and UDP Receive blocks to transmit audio data over a network.

User Datagram Protocol (UDP)

User Datagram Protocol (UDP) is part of the Internet Protocol (IP) suite. UDP provides efficient transmission of data, but does not guarantee reliability, data order, or data integrity. These characteristics make UDP suitable for streaming audio and video data, but not for binary files and similar situations where data loss is unacceptable.

Exploring the Example

You can run this example entirely on one system. However, to demonstrate UDP on a network, it is best to run the example on two networked computers. If the second computer has Simulink software installed, you can run the example on it directly. Otherwise, use Simulink® Coder™ to generate a stand-alone executable that can run on the second computer.

First, run both the dspUDPEcho model and the dspUDPVoip model on a single computer. The models pass audio data to each other via the localhost port, 127.0.0.1.

The dspUDPVoip model transmits the audio data to dspUDPEcho. The dspUDPEcho model echoes the data back to dspUDPVoip, which outputs the signal on your audio speakers.

If you have a microphone, you can use the Manual Switch in the dspUDPVoip model to transmit live audio instead of the sine wave.

Having run the models on a single computer, copy dspUDPEcho to the second computer. In both models, update the IP address in UDP Send from 127.0.0.1 to the IP address of the opposite computer. When you run both models, they transmit audio signals to each other across the network.

% Open both models and run simulatneously
open_system('dspUDPEcho');
open_system('dspUDPVoip');
set_param('dspUDPEcho', 'SimulationCommand', 'Start');
set_param('dspUDPVoip', 'SimulationCommand', 'Start');

% Let the models run for five seconds
pause(5);

% Stop the simulation
set_param('dspUDPVoip', 'SimulationCommand', 'Stop');
set_param('dspUDPEcho', 'SimulationCommand', 'Stop');

Close the models

bdclose dspUDPEcho
bdclose dspUDPVoip

Debugging your Network Connection

If you are unable to transmit the signal over the network, check the following items:

  • That your firewall is not blocking the IP port numbers you are using. If needed, consult your system administrator or operating system documentation.

  • That you are using a free IP port number. One not being in use by another application.

  • That the operating system is not restricting the port number to a privileged user. For example, Linux typically restricts ports below 1024 for use by root user.

If needed, please consult your system administrator or operating system for more information.

References

The Wikipedia entry on UDP

Postel, J., User Datagram Protocol, http://tools.ietf.org/html/rfc768

Available Example Versions

Audio Transmiter and Receiver: dspUDPVoip.mdldspUDPVoip.mdl

UDP Echo Subsystem: dspUDPEcho.mdldspUDPEcho.mdl

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