private void SendWithChecksum(byte [] data, int length)
        {
            // add a CRC64 checksum in the reserved space
            ulong crc     = Crc64.Compute(data, RESERVED, length - RESERVED);
            var   encoder = new Encoder(data, 0);

            encoder.Encode64U(crc);
            RawSend(data, length);

            if (kcp.WaitSnd > 1000)
            {
                Debug.LogWarningFormat("Too many packets waiting in the send queue {0}, you are sending too much data,  the transport can't keep up", kcp.WaitSnd);
            }
        }