Using BLF on Escene Phones

The BLF ( Busy Lamp Field ) feature allows you to monitor the current status of other subscriber lines in real time, as well as intercept calls destined for other subscribers. It is necessary that the BLF function is supported by both the PBX and the telephone on which the state of the lines will be monitored.

The following line conditions are available: free ( Idle ), ringing , line in use ( Connected / Busy ). It should be mentioned that the registration status of the line is not monitored: even if the line is not registered, its status will be indicated as “free”.
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If you press the BLF button for a free line, the call will be made there. If you press the BLF button for the line to which the call is going, it will be intercepted.

The BLF function is necessary first of all for secretaries who redirect calls. It allows you to determine whether the subscriber can accept the call at the moment and, in case of impossibility, switch to another responsible employee or voice mail.

The function is also useful for employees who constantly make a large number of calls to a limited number of people, since it allows them to significantly save working time on dialing numbers .

How it works

First, the phone sends to the PBX a SUBSCRIBE SIP message with the line number, whose status it wants to monitor. After that, when the state of the line changes, the PBX sends a NOTIFY SIP message to the phone, which indicates the current state.

To intercept a call, the phone sends an SIP INVITE message to the PBX, which contains a special prefix and the number of the intercepted line. This prefix is ​​determined by the PBX settings and is specified in the phone settings.

Configure Asterisk

In order for Asterisk to start supporting BLF, the following settings must be made:

In the sip.conf file in the section with settings for extensions:

allowsubscribe = yes
call-limit = 4
limitonpeers = yes
notifyringing = yes
notifyhold = yes
context = phones
subscribecontext = BLF

In the extensions.conf file:

[BLF]
exten => _., hint, SIP / $ {EXTEN}
[phones]
exten => _ **., 1, Pickup ($ {EXTEN: 2})

In the BLF group, you must specify all the lines whose status is to be monitored.

When using Asterisk-based distributions, BLF support can be enabled initially. In the case of FreePBX, the settings did not need to be changed. No additional configuration is required when working with IP-ATC 3CX.

To support the BLF distribution, Thirdlane needed to make the following changes:

notifyringing = yes
notifyhold = yes

Phone setup

The presence of a built-in expansion panel with function buttons that support BLF is an important feature of Escene corporate IP phones . The built-in panel is available for models ES320-N, ES320-PN, ES330-PE, ES410-PE, gigabit model GS320-P and Wi-Fi model WS320-N. Starting with the ES330-PE model and above, all corporate phones also support an additional extension panel with 32 buttons. In total, the phone can support up to 6 expansion panels with a total capacity of up to 192 buttons.



On Escene phones, the BLF function is implemented using the softkey settings: you must specify in the web interface:

• BLF mode
• account number
• name
• line number

If your PBX is configured correctly and the phone is registered on it, then it will display the status of the lines as follows:

• The indicator is highlighted in green - the line is free.
• LED blinks red - call in progress
• The indicator is highlighted in red - the line is used

Call Pickup

In accordance with the settings of the PBX in the phone settings, you must specify the prefix used to pick up the call. In our case, the prefix “**” is used.



Thus, BLF support is one of the most important advantages of corporate phones over universal ones. By simple settings, the phone becomes part of a unified system of unified communications, allowing you to control the telephone lines of employees, simplify communications and, as a result, significantly save working time.