1.1.e Explain TCP operations - 1.1.e (ii) MSS

https://en.wikipedia.org/wiki/Maximum_segment_size

The maximum segment size (MSS) is a parameter of the options field of the TCP header that specifies the largest amount of data, specified in bytes, that a computer or communications device can receive in a single TCP segment. It does not count the TCP header or the IP header (unlike, for example, the MTU for IP datagrams).^[1] The IP datagram containing a TCP segment may be self-contained within a single packet, or it may be reconstructed from several fragmented pieces; either way, the MSS limit applies to the total amount of data contained in the final, reconstructed TCP segment.

To avoid fragmentation in the IP layer, a host must specify the maximum segment size as equal to the largest IP datagram that the host can handle minus the IP header size and TCP header sizes.^[2] Therefore, IPv4 hosts are required to be able to handle an MSS of 536 octets (= 576^[3] - 20 - 20) and IPv6 hosts are required to be able to handle an MSS of 1220 octets (= 1280^[4] - 40 - 20).

Small MSS values will reduce or eliminate IP fragmentation, but will result in higher overhead.^[5]

Each direction of data flow can use a different MSS.

For most computer users, the MSS option is established by the operating system.