[Asterisk-Dev] SUBSCRIBE support

Clif Jones ctjones at earthlink.net
Sun Feb 1 12:17:49 MST 2004

Maybe this is just the beginning efforts of this feature.  It really 
needs to be tied into:
registration state, busy/idle state, and DND state to be really useful. 
See more below...

Olle E. Johansson wrote:

> 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.

Actually it does.  Windows Messenger 5.0, MSN Messenger 4.6/4.7 support 
SIP and partially support SIMPLE.
We use the SIP Messenger versions where I work on our own SIP products 
to do: Caller-ID of incoming calls with
the option to answer (multiple-contact per account supported required), 
phone presence (Messenger has limited
enumerations for states and is sort of proprietary) and SIP instant 

During my prototyping phase of a SIMPLE presence and messaging server, I 
reversed engineered MSN Messenger and
added support for this client until we could write our own fully 
compliant client apps ourself.  Take a look at this message
flow for some hints.  http://www.cs.columbia.edu/sip/drafts/messenger.txt

> 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
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