Constant CEILING_16 

const CEILING_16: &str = "If a Request ID equal to or larger than this is received by the endpoint \
                          that sent the MAX_REQUEST_ID in any request message (PUBLISH_NAMESPACE, \
                          FETCH, SUBSCRIBE, SUBSCRIBE_NAMESPACE, REQUEST_UPDATE or TRACK_STATUS), \
                          the endpoint MUST close the session with an error of TOO_MANY_REQUESTS.";