write header:
		[8bit][16bit]
		[protocol_version][msg_length]

def writeHeader(self, msg):
		"""write header:
		[8bit][16bit]
		[protocol_version][msg_length]
		"""

		header = bytearray([self.protocol_version]) #protocol version 1.0
		header.extend(struct.pack('<H', len(msg)))

		msg = header + msg

		return msg