XMPP Subscription Stanza for Google Cloud Print XMPP Print Job Service Using XMPPHP
<iq from='{Full JID}' to='{Bare JID}' type='set' id='1'>
<subscribe xmlns='google:push'>
<item channel='cloudprint.google.com/proxy/b{Proxy ID}' from='cloudprint.google.com'/>
</subscribe>
</iq>