public void sendServerAcknowledgement() {
        if(isEnabled()) {
            if (session.isDetached()) {
                Log.debug("Session is detached, won't request an ack.");
                return;
            }
            String ack = String.format("<a xmlns='%s' h='%s' />", namespace, serverProcessedStanzas.get() & MASK );
            session.deliverRawText( ack );
        }
    }
Sends XEP-0198 acknowledgement &lt;a /&gt; to client from server
xmppserver/src/main/java/org/jivesoftware/openfire/streammanagement/StreamManager.java