If the IP header is 20 bytes how big is the TCP segment encapsulated by this header?

The size of a TCP segment encapsulated by an IP header does not have a fixed size and can vary based on the data being transmitted. However, the maximum size of a TCP segment is typically constrained by the Maximum Transmission Unit (MTU) of the network, which is commonly around 1500 bytes for Ethernet. Given that the IP header is 20 bytes, the maximum TCP segment size would be approximately 1480 bytes if there are no additional headers or options. In practice, the exact size would depend on the TCP header size and any options included.