System information

SIP Presence
Asterisk provides the ability for devices to subscribe to extension state using the SIP
protocol. This functionality is often referred to as BLF (Busy Lamp Field).
*
Asterisk Configuration
To get this working, hints must be defined in /etc/asterisk/extensions.conf (see
“Hints” on page 303 for more information on configuring hints in the dialplan). Ad-
ditionally, there are some important options that must be set in the configuration file
for the SIP channel driver, which is /etc/asterisk/sip.conf. The following list discusses
these options:
callcounter
Enables/disables call counters. This must be enabled for Asterisk to be able to
provide state information for SIP devices. This option may be set either in the
[general] section or in peer-specific sections of sip.conf.
If you would like device states to work for SIP devices, you must at
least set the callcounter option to yes. Otherwise, the SIP channel
driver will not bother tracking calls to and from devices and will
provide no state information about them.
busylevel
Sets the number of calls that must be in progress for Asterisk to report that a device
is busy. This option may only be set in peer-specific sections of sip.conf. By default,
this option is not set. This means that Asterisk will report that a device is in use,
but never busy.
call-limit
This option has been deprecated in favor of using the GROUP() and GROUP_COUNT()
functions in the Asterisk dialplan. You may find older documentation that suggests
that this option is required for SIP presence to work. That used to be the case, but
this option has been replaced by the callcounter option for that purpose.
allowsubscribe
Allows you to disable support for subscriptions. If this option has not been set,
subscriptions will be enabled. To disable subscription support completely, set
allowsubscribe to no in the [general] section of sip.conf.
* Some also like to call these “blinky lamps” or “blinky lights” for their phones. Geeks and their LEDs…
306 | Chapter 14: Device States