Controlling the B-Channels• 9-8 •
The H.110 Basic Rate ISDN Board
9.4.5 Detecting Energy
Each B-channel is equipped with an energy detection function. The energy
detector can be set to look for audio energy with a minimum duration time.
When a continuous audio signal has been detected for that time, a message
is sent. Another message is sent when the audio signal stops. This feature
can be used to monitor for dial tone restoration or call progress tones.
Energy detection does not affect existing connections and can be used in
conjunction with DTMF detection.
To enable energy detection on a B-channel the energy command “CE” is
used. This command takes the form CExxdd where xx is the B-channel
number and dd is the duration in steps of 100 msec. The range is from .1
to 22.3 seconds or from 01 to DF. For example, the command CE0714
would enable energy detection on B-channel 7 with a duration of 14h or 2
seconds. When a signal is detected the message would take the form
SP071 in this example where the “1” indicates detection. A “0” would
indicate that the signal has stopped.
Energy detection will be disabled when the B-channel changes state due to
a command. It can also be disabled without affecting the B-channel state
by sending a command where the duration is replaced by a single character
“F”. In the example above, this would be CE07F.
9.4.6 An Example of Originating a Call
The following is an example of the steps involved in a terminal originating
a call. Both the “C” commands and state change messages will be shown.
The “D” messages will also be shown to show the relative timing. The
dialed digits will be detected, ringback played, and finally a connection
made and broken when the phone hangs up.
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