Difference between RawTCP and RFC2217 (Telnet)

• RAWTCP is an simple encapsulation of the Serial communication data inside TCP frame.
    Only the Rx and Tx lines are transmitted.

• RFC2217 is a complete handling of a serial port through a TCP stream.
    All the data and control lines are transmitted.
 

Then, if you use a Serial device using some control lines, you must use RFC2217 as VCOM protocol.
If your Serial device only read and write data, you may use RawTCP.