[Asterisk-Users] Possible to display which extensions are in use on the phone's display?

[Peter Svensson]

On Wed, 17 Nov 2004, Jason Becker wrote:

> > On our current phones (Iwatsu) we have a button on the
> > phones for each extension that lights up when that
> > extension is ringing or is in a call, so I can see at
> > a glance if one of my coworkers is on the phone before
> > I go barging into his office.  Also, if I am in a
> > coworker's office and my phone rings, I can hit my
> > extension button on his phone and answer the call.  
> >  
[snip]
> 
> This question was dealt with in a recent thread. What it comes down to 
> is a paradigm shift from a key system unit (which is what you describe) 
> to a PBX.

I don't think this is really a key system. AFAIK a traditional key system 
has a one-to-one mapping between lines and the buttons. Some pbx:es offer 
a mode where each *extension* is / can be represented by a button. This is 
called a Busy Light Field (BLF) for the status indications and also allows 
Directed Call Pickup. 

These systems exist on scale between a pure key systems and pure pbx. It 
is actually a very nice feature to have.

The use of SIP subscriptions for the BLF and (I think, not sure about this
one) SIP Replaces for the directed pickup allows a similar functionality.
In asterisk the sip subscription is implemented with the word "hint" in
the dialplan. Others have provided links to documentation.

With Asterisk it is also possible to implement the BLF / DCP on a 
computer. Asterisk provides the necessary hooks to the call handling.

Peter