BLF

From Taridium

ipbx supports extension presence/status indication on wide variety of SIP devices. This feature is quite often referred to as busy lamp field (BLF). Not all phones do support BLF, some only do partially or using a non-SIP firmware (e.g. Cisco 79XX series phones).

SIP General Settings

In order for BLF to work correctly you will need to make sure the following settings in your general SIP configuration are enabled. Go to System → SIP Channels → General Settings or using the Manual Editor and enable:

 allowsubscribe = yes
 notifyringing = yes
 limitonpeers = yes

SIP Channel Settings

Go to System → SIP Channels → General Settings and make sure each phone you want to monitor has a call-limit set.