Dialogic 6.2 manual Actions During a Two-Channel Call Transfer, Performing Echo Cancellation

Making Two-Channel Call Transfers (Tromboning)

The application created a new connection from the output of network timeslot 0 to the input of network timeslot 1 and another new connection from the output of network timeslot 1 to the input of network timeslot 0 (see Figure 13 on page 193).

Using this model, Channel 0 can record the data that is being transmitted from the network timeslot 0 and Channel 1 can record the data that is being transmitted from network timeslot 1.

Because of firmware requirements, when disconnecting resources, you have to invert the source and destination resources. For example, if you made a transmit connection from the output slot of Channel 0 to the input slot of network timeslot 0, where Channel 0 is the source, then you must disconnect from the input slot of network timeslot 0 to the output slot of Channel 0.

Actions During a Two-Channel Call Transfer

After the application establishes a two-channel call transfer, it can then perform voice playback and voice recognition. In addition to these voice actions, the application must provide secondary functionality. For example, when performing voice recognition during a two-channel call transfer, the application must configure echo cancellation in the channel correctly. Also, when performing voice playback to a caller, the application must place the other caller on hold to avoid providing the original caller with two source inputs.

Performing Echo Cancellation

When a caller sends voice data over the telephone network, the network reflects some of that data back as input data. The reflected data is then mixed in with valid input voice data from the remote end. The channel that is connected to the telephone network must be able to remove the reflected data from the valid input data. This technique is called echo cancellation.

When a channel performs echo cancellation, it analyzes the voice data that is being sent out into the telephone network. When this voice data reappears as input voice data (the echo), the channel removes the data from the input data stream. What is left is the actual voice data from the remote end.

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