TCP/IP was developed when all network nodes were stationary, and connection to a network is through cable,therefore it is unthinkable that a node will move to another subnet while accessing to the Internet, and the IP address of an end host is assumed to stay unchanged while a computer is running. As a result, IP address (together with IP port) is
used as identifiers for TCP session, and the TCP layer at the end host maintains TCP control blocks (TCBs), which hold
the IP addresses and IP ports of both ends for each TCP connection to fmd the right socket for each datagram it
receives from the IP layer.