int code = (subscription.getState() != Subscription.State.PENDING) ?
SipServletResponse.SC_OK : SipServletResponse.SC_ACCEPTED;
SipServletResponse response = subscribe.createResponse(code);
response.setExpires(expires);
response.send();
// Ensure 200/SUBSCRIBE is received before NOTIFY
try { Thread.sleep(50); } catch (Exception e) {}
_presence.notify(subscription);
}