About the TCP/IP Protocol Suite

Initially, TCP/IP was designed for the U.S. Department of Defense’s data communication. After the 1960s, the ARPA (Advanced Research Projects Agency) built a partnership with universities to design an open, standard protocol suite, aiming to help develop a multi-vendor network.

In 1969, ARPANET emerged as an experimental project. Four nodes were created here using the NCP (Network Control Protocol), and a circuit with a speed of 56 kbps was established. The experiment was successful, and later this came to be known as the ARPA Internet. In 1974, Vinton G. Cerf and Robert E. Kahn proposed the main protocol for ARPANET. The official name of this protocol became the TCP/IP Internet Protocol Suite, which we now know simply as TCP/IP. The primary responsibilities of the TCP/IP layer are to transfer information from the source to the destination reliably and precisely (reliability) and to control the flow (Flow Control). TCP performs end-to-end control and precise transport using sliding windows, sequence numbers, and acknowledgments.

Figure-1: The process of establishing a connection and controlling the precise transport and flow of information can be imagined like this: suppose someone has learned a foreign language over a year and now travels to a country where that language is spoken. In conversation, for the sake of reliability, they must repeat the words they know. Another thing to note is that to ensure others can understand them easily, they have to speak slowly—this is flow control.

Figure-2: Flow control 1

Figure-3: Flow control 2
The transport layer mainly creates a logical connection between the ends of two networks. Transport layer protocols divide the data received from upper-layer applications and then reassemble the segmented data.

Figure-8: TCP in OSI layer

The main functions of the layer are:

• Dividing application data from the upper layer.
• Establishing end-to-end connections.
• Sending segments from one host to another.
• Flow control using sliding windows.
• Reliability using sequence numbers and acknowledgments.

TCP/IP is a combination of two special protocols. IP operates at the third layer of the OSI model and is a connectionless protocol, aiming to provide maximum delivery within a network. TCP, on the other hand, works at the transport layer and provides a connection-oriented service, ensuring flow control and reliability. When these protocols are combined, they can offer much larger-scale services. This combined protocol is known as the TCP/IP protocol suite. The Internet itself is built based on this TCP/IP protocol suite.