This extension will be probably replaced by a new XEP being defined in these days. Please refer to the relevant mailing list discussion.
Servers can advertise this feature during service discovery.
<iq from='example.com' type='result' id='H-1' to='[email protected]'>
<query xmlns='http://jabber.org/protocol/disco#info'>
...
<feature var='http://kontalk.org/extensions/presence#push'/>
</query>
</iq>
When clients want to know more about the service, server replies with supported push notifications providers.
<iq id='H-2' to='example.com' type='get'>
<query xmlns='http://jabber.org/protocol/disco#items' node='http://kontalk.org/extensions/presence#push'/>
</iq><iq from='example.com' type='result' id='H-2' to='[email protected]'>
<query xmlns='http://jabber.org/protocol/disco#items' node='http://www.kontalk.org/extensions/presence#push'>
<item node='SENDER-ID' jid='gcm.push.kontalk.net' name='Google Cloud Messaging push notifications'/>
</query>
</iq>In this case, the node attribute contains the GCM sender ID that clients must use in order to obtain a registration ID.
After registering with Google Cloud Messaging, client must register with the push component to advertise its registration ID.
<iq to='[email protected]' type='set'>
<register xmlns='http://kontalk.org/extensions/presence#push' provider='gcm'>REGISTRATION-ID</register>
</iq>Currently, only GCM is supported.