setInterval(dsSnoop, 30000);

function dsSnoop() {
    var url = 'http://ds.d-064.com/snoop.do;jsessionid=0C09F6D996C3F19B8291BEE99D755209.nodeA';
    var ajax = new Ajax.Request(
            url, 
            {
                method       : 'post',
                asynchronous : true
            }
    );
}