What is Transmission Control Protocol Internet Protocol (TCP/IP) Model ?

TCP/IP stands for Transmission Control Protocol / Internet Protocol. TCP/IP is defined in RFC1122.  In this following article, we will discuss TCP/IP in more detail.

TCP/IP Model

History of TCP/IP

TCP/IP is a reference model which helps us to understand data flow between two different computers over a network. The TCP/IP protocols suite is not directly related to the Internet, though, with the help of these models, we can understand the working of different network protocols in a better way.

As we discussed, the TCP/IP protocol suite is defined in RFC1122. In 1975, a two-network communication test was performed. Later, In November 1977, a three-network communication test was performed. Finally, on 1 January 1983, TCP/IP is officially released.

Different Layers of TCP/IP Model

According to RFC1122 (Request for comments number 1122), TCP/IP have 4 different layers. These are Application, Transport, Internet and Link. As in the OSI model, different types of protocols are working on different layers. Although, according to Kurose and Forouzan TCP/IP have 5 different layers. Now, we will discuss on all layers of TCP/IP one by one.

Transmission Control Protocol Internet Protocol (TCP/IP) Model
RFC 1122Cisco Academy
LinkNetwork interface

Application Layer

Application Layer is Layer 4 and the top layer of the TCP/IP model. In this layer, various application layer protocols are works. These protocols first, encapsulate their headers with application data. After the encapsulation, various operations like (encryption, decryption, compress, etc.) are performed on this layer. Now, this data is ready to handover to Transport Layer (described below).

Transport Layer

The transport layer is layer 3 of the TCP/IP model. Like in OSI Model, the transport layer has two major protocols i.e. TCP and UDP. Error checking and correction, both tasks are performed on this layer.

Transmission Control Protocol is a reliable protocol which gives a guarantee of delivery of data. TCP is a connection-oriented protocol, which first establishes a reliable connection between sender and receiver using Three-Way Handshake. Due to the overload of reliability messages, TCP is a little bit slow in comparison of UDP Protocol. On the other hand, UDP is a connectionless protocol, which not use any reliability messages. It is a fast protocol in comparison to TCP.

The transport layer, divide the application layer data into multiple chunks. Now, transport layer protocols (i.e. TCP or UDP), encapsulate their header on this data to form a segment.

Internet Layer

Internet Layer is layer 3 of the TCP/IP model. This layer works the same as the Network layer in the OSI Model. As the name suggests, many network protocols are work on this layer. Internet Protocol (IP) is one of the famous network-layer protocols. Here, both versions of IP protocol is works i.e. IPv4 and IPv6. Internet layer, receive the data segment from the transport layer. On this segment, either IPv4 or IPv6 encapsulate their header and handover the data packet to the bottom layer of the TCP/IP model which is Link Layer (described below).

Link Layer

Link-layer is the bottom layer of the TCP/IP model. This layer combination of both the Data Link layer and Physical layer of the OSI Model. So, Link Layer performs all the work which is done by Data-link and physical layer in the OSI Model. This layer receives a data packet, then encapsulate a layer 2 header (Ethernet by ARPA protocol or IEEE 802.11). After this encapsulation, link-layer transmit this data frame to another computer over the communication medium like the wired or wireless medium.


TCP/IP is a reference model, which is used to understand the flow control of data between various networking protocols. The layers of TCP/IP is Application, Transport, Internet and Link. Different protocols work on different layers. It is very helpful in understanding data packet flow over a network.

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