File transfers are performed using an 8-bit binary transparent protocol. A transparent channel is a communication method and medium that does not use any of the byte values for control of the channel itself. An 8-bit channel does not use any of the bits in an 8-bit character set for control of the channel (for parity, for example) and can transmit all 256 codes in the character set. This is important when transferring data that contains anything that is not printable text in the data stream.
If the channel you are using is not transparent, the Kermit protocol performs the most reliable file transfer.
Channels less than 8-bits wide are not supported.