var Timer;

function StartTimer() {
    if (Timer == null)
        Timer = setInterval("KeepSession();", 1000 * 60 *15);
}

function KeepSession() {
    KeepSessionWebService.KeepSession(onsuccess);
}

function onsuccess(result) {
    Sys.Debug.trace("KeepSession Success!");
}