function sessionKeepAlive() {
    var wRequest = new Sys.Net.WebRequest();
    wRequest.set_url("/Library/Javascript/SessionKeepAlive.aspx");

    wRequest.set_httpVerb("POST");
    wRequest.add_completed(sessionKeepAlive_Callback);
    wRequest.set_body();
    wRequest.get_headers()["Content-Length"] = 0;
    wRequest.invoke();
}

function sessionKeepAlive_Callback(executor, eventArgs) {

}

window.setInterval("sessionKeepAlive()", 1 * 60 * 1000);