For devices specifically, you may need to enable "Meta Mode" by dialing *#0*# or using a special download mode key combination (Volume Down + Home + Power).
A handshake is a mutual agreement between two devices on how to communicate. The "modem handshake" here refers to the initial signal between your PC’s flashing tool and the phone’s modem processor. Without this handshake, the tool cannot verify that the modem is ready to receive data. it cannot find the meta usb com port for modem handshake