[SIPForum-discussion] Knowing a SIP phone status

[M. Ranganathan]

On Mon, Dec 14, 2009 at 11:41 AM, M. Ranganathan <mranga at gmail.com> wrote:
> On Mon, Dec 14, 2009 at 9:28 AM, Junaid Abid <junaid.abid at gmail.com> wrote:
>> Hi Guys
>>
>> Is there a way to MONITOR SIP extensions using SIP or something?
>
>
> That is an ill posed question.
>
> You can do this provided your PBX supports a dialog package that
> allows you to subscribe for Dialog events.


To elaborate ( sorry for the short answer), you can do it in one of two ways:

1. Most  phones allow you to subscribe for Dialog Events if they have
been configured to allow it. If this is the case you can write a
daemon to send SUBSCRIBE to the phone. Each time a Dialog is created
or a dialog state changes, you will get NOTIFY. You can thus infer the
state of the phone. When an INVITE Dialog is Created that corresponds
to  a call. When it is destroyed it corresponds to a hangup etc.
However, this can get unscalable.

2. The PBX can support a Dialog Event package. For example, if the PBX
is structured using a proxy server or a B2BUA where all signaling
passes, that proxy server or B2BUA can keep call state. This method is
more efficient as you can subscribe to events from a single entity as
opposed to multiple phones.

Ranga






-- 
M. Ranganathan