[jdev] check user online

Fri Oct 23 22:30:01 CDT 2009

SEND: <body rid='296594347' xmlns='http://jabber.org/protocol/httpbind' sid='6b52c7a7'><presence/><iq type='get' to='test at computer' id='os1'><onlinestatus xmlns='computer:contact'/></iq></body>

RECV: <body xmlns='http://jabber.org/protocol/httpbind'><iq type='error' id='os1' from='test at computer' to='6b52c7a7 at computer/6b52c7a7'><onlinestatus xmlns='computer:contact'/><error code='503' type='cancel'><service-unavailable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/></error></iq></body>

may i know is above the correct stanza ?  what does 503 means? i try to check whether user is online.. is the stanza that i sent correct?