Chapter 9. Transmission Control Protocol

Transmission Control Protocol (TCP) is an upper-layer protocol from the IP point of view. The first question that always occurs to a beginner is "Why do we need two protocols, IP and TCP?"

While IP transmits data between individual computers on the Internet, TCP transfers data between two actual applications running on these two computers. IP is used for data transfers between computers. An IP address is the address only of a computer's network interface, while TCP uses a port number as its address. If we were to compare this to a standard postal system, the IP address would be the building address and the port number (the address in TCP) would be the name of an actual resident in the building.

TCP is connection oriented. In other words, this is a service that establishes a connection between two applications, i.e., creates a virtual circuit for the time of connection. This is a full duplex circuit; data is simultaneously...