Hi Franco,

You can use either software or hardware hanshake. For software hanshake using only RX, TX and GND are enough. For hardware handshake you need additional 2 signals : RTS and CTS. Both ways are suitable for serial comunication.
"Why theese control lines are omitted?"
I don't think someone avoid to use hardware handshake.
"RX and TX alone are enough to estabilish a safe serial link?
"
The magic control characters XON and XOFF are enough for serial link. If you want to make it really safe you have to add check sum bytes.

Please search the Forum.

Regards,
Silviu