code: public byte[] sendEnquireLink(OutputStream out, int sequenceNumber)
              throws IOException {
          synchronized (out) {
              return pduSender.sendEnquireLink(out, sequenceNumber);
          }
      }
docs: /*
  (non-Javadoc)
  
  @see org.jsmpp.PDUSender#sendEnquireLink(java.io.OutputStream, int)