code: public byte[] sendDataSmResp(OutputStream os, int sequenceNumber,
              String messageId, OptionalParameter... optionalParameters)
              throws PDUStringException, IOException {
          synchronized (os) {
              return pduSender.sendDataSmResp(os, sequenceNumber, messageId,
                      optionalParameters);
          }
      }
docs: /*
  (non-Javadoc)
  
  @see org.jsmpp.PDUSender#sendDataSmResp(java.io.OutputStream, int,
  java.lang.String, org.jsmpp.bean.OptionalParameter[])