code: protected String generateNOnce(MobicentsSipServletRequest request) {
  
          long currentTime = System.currentTimeMillis();
  
          String nOnceValue = request.getRemoteAddr() + ":" +
              currentTime + ":" + key;
  
          byte[] buffer = null;
          synchronized (md5Helper) {
              buffer = md5Helper.digest(nOnceValue.getBytes());
          }
          nOnceValue = MD5_ENCODER.encode(buffer);
  
          return nOnceValue;
      }
docs: Generate a unique token. The token is generated according to the
  following pattern. NOnceToken = Base64 ( MD5 ( client-IP ":"
  time-stamp ":" private-key ) ).
  
  @param request HTTP Servlet request