====== sip_presence_subscribe ======
**C → S {type:'sip_presence_subscribe', to:..., expires:...}**

Subscribe to SIP presence information. Server will send [[ixnx:wrtc:rtcgate:sip_presence_notify|sip_presence_notify]] messages every time requested client's presence status changes.

arguments:
  * to - SIP address of client you are interested to know status of
  * expires - time in seconds before subscription expires

====== subscribers ======
If you subscribe to your own status (to is set to your own SIP address) you will receive a [[ixnx:wrtc:rtcgate:sip_presence_notify|sip_presence_notify]] message containing a list of everyone currently subscribing to your status.

====== error ======
**S → C {type:'sip_presence_subscribe', from:..., error:'404', msg:'Not found'}**

If you attempted to subscribe to an unused SIP address (noone registered) a 404 error is returned.