code: public byte[] sendHeader(OutputStream os, int commandId, int commandStatus,
              int sequenceNumber) throws IOException {
  
          byte[] b = pduComposer.composeHeader(commandId, commandStatus,
                  sequenceNumber);
          writeAndFlush(os, b);
          return b;
      }
docs: /*
  (non-Javadoc)
  
  @see org.jsmpp.PDUSender#sendHeader(java.io.OutputStream, int, int, int)