wrtc.setSIPSubscribe() is used to subscribe to someones SIP presence status.
wrtc.setSIPSubscribe(address,expires)
If no expires argument is specified timeout is set to 5 minutes.
You do not need to call wrtc.setSIPSubscribe() again after the timeout - all subsequent refreshes are taken care of by wrtc_kit. Therefore you do not need to specify any expires argument unless the SIP server used refuse to use the default 5 minute expire time.
Nothing.
Event wrtc.onSIPPresence() will occur each time monitored user's SIP presence status changes.
wrtc.setSIPSubscribe("adam@foo.com") will monitor Adam's SIP presence status and calls event function wrtc.onSIPPresence() each time his online status changes.
To receive a list of all persons subscribing to your online status call wrtc.setSIPSubscribe() with your own SIP address as argument. It will trigger a special wrtc.onSIPPresence() event function call containing the list.