TCP/IP: TCP transport-1
TCP provides a reliable bi-directional data flow
As a transport layer, it multiplexes data between applications
To identify an application, it uses a 16 bits port number
Standard application has well-known port number, e.g. 25 for the mail, 80 for the Web
The set: src port, src address, dest port, dest address is named a socket and is unique in all the Internet at a giving time