TCP MSS and window size
MSS is found in the options fields of the TCP header in the SYN packet and is defined during the 3-way handshake. It cannot be changed during a session. It has a maximum value of 65535 (2 byte field).
The MSS can be adjusted at the beginning of a session using the TCP MSS feature on Cisco devices.
Window size has a maximum value of 65535 (2 byte field) and is found in the main TCP header. It can be renegotiated during a session.