[Asterisk-Dev] SUBSCRIBE support

[Olle E. Johansson]

Thanks to pointers on the mailing list, I fired up Windows Messenger and added contacts.
First everything was online, since my default sip users context matched everything, in order
to be able to call anyone everwhere on the net. So I added a special context for subscriptions,
and now I see the extensions.

However, the Asterisk sip channel, check IF THE EXTENSION EXISTS and then delivers information
on telephone state - BUSY, Available etc.

If a SIP user isn't registred, he's still available on an extension level since his voice messages
is transferred to voice mail. The PBX doesn't know he's not there, really. The extension still exists.

With a Windows Messenger, I would like to know if he's not there. Still available to call to
for voicemail, but not on line....

Anyway, obviously the SUBSCRIBE support wasn't written for Messenger. Someone else can't check
the status of my connection with SUBSCRIBE, since he or she can't authorize himself.

So I still wonder what device this was made for? Any idea? Sounds like a device that checks
if someone's on the phone or not - if the line is busy. And if you're one SIP peer, you have
the right to check anyone else within the context.

The subscribe-context fix will be in the next upload of chan_sip2.c if you want to play with it.
/Olle