Configuring busy tone detection

PBX switches might use different busy tone standards. If a user on the PBX side hangs up, the router knows the on-hook operation by detecting a busy tone. If the router cannot correctly identify the played busy tones, the FXO interface on the router will remain seized or goes on-hook prematurely.

As shown in Figure 1, Telephone A establishes a call to Telephone B, and then Telephone A goes on-hook. The PBX plays busy tones to Router A after detecting the on-hook condition of Telephone A. If Router A cannot detect the played busy tones, the FXO interface on Router A will remain seized. To solve this problem, you can configure busy tone detection for the FXO interface.

Figure 1: Busy tone detection

You can configure busy tone detection by customizing busy tone parameters or configuring automatic busy tone detection. If the tone that the router receives from the PBX matches the busy tone parameters, the router considers the tone as a busy tone and renders the FXO interface on-hook.

Configuring a busy tone standard

Two busy tone standards are available: European and North American. After you specify a standard, the device uses a set of parameters compliant with that standard for busy tone detection. If the actual busy tone data do not completely match the set of parameters, the device can use customized busy tone parameters or automatic busy tone detection to accurately detect busy tones.

To configure a busy tone standard:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter voice view.	voice-setup	N/A
3. Specify a busy tone standard.	area { europe \| north-america }	By default, the European standard is used.

Customizing busy tone parameters

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter voice view.	voice-setup	N/A
3. Customize busy tone parameters.	busytone-detect custom area-number index argu f1 f2 p1 p2 p3 p4 p5 p6 p7	By default, no custom busy tone parameters exist. The standard of busy tones depends on the area command.
4. Enable using customized busy tone parameters.	area custom	By default, the European standard is used. This command takes effect on all FXO interfaces on the device. The customized busy tone parameters take effect only after you configure this command.

Configuring automatic busy tone detection

Figure 2: Automatic busy tone detection

As shown in Figure 2, the procedure for automatic busy tone detection is as follows:

Place a call from Telephone A to Telephone B.
Hang up Telephone A first.
The PBX plays a busy tone to Router A after detecting the on-hook condition.
Execute the busytone-detect auto command on Router A to detect busy tones.
As a best practice, execute this command two seconds after Telephone A goes on-hook to make sure the FXO interface can capture the busy tones sent by the PBX.
The console prompts that busy tone detection is in progress and prompts detection success when the detection is complete.
Check whether the detected busy tone parameters are valid by repeating steps 1 and 2.
After Telephone A goes on-hook, the PBX plays a busy tone to Router A. If Router A detects the busy tone, it shuts down the FXO interface.

To configure automatic busy tone detection:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter voice view.	voice-setup	N/A
3. Configure automatic busy tone detection.	busytone-detect auto index line-number	N/A
4. Return to system view.	quit	N/A
5. Enter FXO interface view.	subscriber-line line-number	N/A
6. Set the number of busy tone detection periods.	busytone-detect period value	The default is 2. Test multiple values to select the value that can ensure normal on-hook.

Configuring busy tone sending

If the PBX does not play busy tones, configure the FXO interface to send busy tones.

To configure busy tone sending:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter FXO interface view.	subscriber-line line-number	N/A
3. Enable busy tone sending.	send-busytone enable	By default, this feature is disabled.
4. Set the busy tone duration.	send-busytone time seconds	The default is 3 seconds.

Configuring silence detection-based automatic on-hook

CAUTION:

Improper configuration of this feature can lead to false on-hook. To avoid false on-hook, configure multiple sets of parameters and select the set of parameters that will quickly release the FXO interface.

If the device fails to detect busy tones or the PBX does not play busy tones, you can configure this feature to implement automatic on-hook.

When the duration of silence (whose volume is smaller than the configured threshold) exceeds the configured silence duration, the FXO interface automatically disconnects the call.

To configure silence detection-based automatic on-hook:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter FXO interface view.	subscriber-line line-number	N/A
3. Configure silence detection-based automatic on-hook.	silence-detect threshold threshold time time-length	By default, the silence threshold is 20, and the silence duration is 7200 seconds (2 hours).

Configuring forced on-hook

In some countries, PBXs do not play busy tones, or the busy tones only last for a short period of time. When noise is present on a link, even the silence detection-based automatic on-hook feature (configured with silence-detect threshold) cannot detect the busy tones and fails to release a call after on-hook. To solve this problem, configure the forced on-hook feature. Forced on-hook disconnects a call when the specified time expires, even if the call is ongoing.

To configure forced on-hook:

Step

Command

Remarks

1. Enter system view.

system-view

N/A

2. Enter FXO interface view.

subscriber-line line-number

N/A

3. Configure forced on-hook.

hookoff-time time

By default, forced on-hook is disabled.

If you configure this command on an FXO interface of a card, the configuration takes effect on all FXO subscriber lines of the card.

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