View source for Asterisk Feature Busy Lamp Field (BLF)

== Introduction ==

The busy lamb feature allows users to monitor the dialog state of another phone/user extension. This is indicated by the LEDs adjacent to an FPK. This feature is called "Busy Lamp Field" in the Asterisk community. Sometime the term 'Direct Station Selection' is used for the same functionality.

== For Users ==

The basic Busy Lamp field feature allows the user to monitor the dialog state of another phone/user extension. The dialog state is shown by a distinct LED behavior:

* LED off -> Watched extension is idle
* LED blinking -> Watched extension is ringing
* LED on -> Watched extension is busy/connected

In the basic configuration pressing the FPK will call the monitored persion in any call state

'''Example:'''

There are four users: Leo, Alice, Joe and Bob. Leo is watching the extensions of Alice, Bob and Joe. Each of the extensions are configured on an specific FPK. The example shows the three different extension status. Joe is talking to annother persion, Alice gets a call, her phone is ringing and Bob is in idle like Leo is. The following picture shows this example:


[[Image:FPKBLFStatus.gif|framed|center|Joe is in busy, Alice is in ringing and Bob is in idle state]]


== For Administrators ==

The FPK are administrated as '''Server Key'''. This is one option of the FPK programming options. The configuration can be found in

''Administrator Pages -> System -> Features -> Program Keys'':

The FPK function is ‘''Server Feature''’. Select this option and press ‘''Edit''’

[[Image:BLFBasicFPKConfig.png|framed|center|Basic BLF Configuration with Server Key]]

Within the server feature four options are given:

[[Image:BLFBasicFPKParam.jpg|framed|center|Basic BLF Configuration Parameters]]

'''Key label''' - This is the label of the selected FPK <br />
'''Feature Code''' - This code is sent within an INVITE message, if the key is pressed in idle status <br />
'''DTMF Digits''' - These Digits are sent as DTMF signals, if the key is pressed during a call <br />
'''LED control''' - A Subscribtion is sent to the given URL <br />

'''Example:'''

If Bob has the extension numer ''222'', the parameters will be:

'''Key label''' - ''Bob'' <br />
'''Feature Code''' - ''222'', pressing the FPK will always call Bob independant of his line status.. <br />
'''DTMF Digits''' - n.a..,  not neccessary in this feature <br />
'''LED control''' - ''222@192.168.6.10'', a subscription for the LED will be sent to the server at the IP address <span style="color: red;">192.168.6.10</span>. If no IP address is given, the request will be automatically sent to the configured SIP proxy server. <br />

== Technical Backround ==

The BLF features give the user the possiblity to watch one other users dialog state. To support the feature [http://www.ietf.org/rfc/rfc4235.txt RFC 4235] is used.

This document defines a dialog event package for the SIP Events architecture, along with a data format used in notifications for this package. The dialog package allows users to subscribe to another user and to receive notification of the changes in state of INVITE -initiated dialog usages in which the subscribed- to user is involved.

== See also ==
[[Preview:OpenStage and Asterisk]]