Introduction to TCP/IP Model Layers for absolute Beginners

The Complete name of TCP/IP model is “TRANSMISSION CONTROL PROTOCOL/INTERNET PROTOCOL MODEL”. This model was designed in 1970 by DARPA (Defense Advanced Research Projects Agency), an agency of United States Department of Defense. Arpanet, which is the predecessor of internet is created based on this model. This protocol is widely used for interconnecting computers and it is the protocol of the internet. TCP/IP model has 5 layers as Physical layer, Data link layer, Transport layer, Network layer and Application layer.


The top layer of the TCP/IP model is Application layer. Here, the data in the application specific format is transferred from program to transport layer. It does the work of session layer, application layer and presentation layer in the OSI 7 layers.

Examples of Application layer protocols are TCP, FTP (File Transfer Protocol) and TELNET (which uses a thin client to get connected to the server).


The layer next to application layer in TCP/IP model is transport layer. It is responsible for end-to-end message transfer capabilities autonomous to the underlying network with error control, flow control and fragmentation. This layer breaks the message (data) into small chunks. Which helps network layer to work more efficiently. This can be of two types.

Connection oriented – In a connection oriented type, connection between end points should be established before transferring any data. TCP is an example of connection oriented protocol.

Connectionless – In a connectionless type data can be sent between end points without even establishing a connection. UDP (User Datagram Protocol) is an example of connectionless protocol. UDP allows computers to send datagram between each other. Datagram is similar to a packet of information.

There are many advantages by using a connection oriented TCP protocol. They are:

  • Data arrives in-order
  • Data has minimum errors (i.e. correctness)
  • Data duplicated is discarded
  • Lost/discarded packets are resent
  • Includes traffic congestion control

The major drawbacks of Transport Layer is it does not gives guarantee about delivery of data packets.


Network layer forms the third layer from top in the TCP/IP model. It does the functionality of transferring packets between networks. Internet protocol (IP) is an example of network layer protocol. IP performs the basic task of sending packets of data from source to target.


The data link layer is the second layer. This layer has the functionality of adding the header information to the packet and also to transfer packets to the physical layer. The layer where packets are intercepted and sent over a virtual private network.


The first layer in TCP/IP model is Physical layer. It is accountable for encoding and spread of data through network communications media. It sends the data in the form of bits from the Physical layer of the source device and is received at the destination device. It also contains many hardware-related network design issues. For example, LAN, WAN and wireless technology.