DoD Model - Department of Defense Model

DoD model of Networking was the first layered protocol model designed way back in the 1970s. At that time there was no common architecture on which operating systems or hardware devices are based. So, a computer system running a particular operating system can't communicate with a system running some other OS or other proprietary software.

To overcome this problem, and to make different vendor's system interrelate each other, Defense Advanced Research Projects Agency (DARPA)  started a project which slowly and gradually grew into what we call today, the 'Internet'. The architecture model which was designed by the DARPA  is known as the DoD model.

DoD model is also known as the TCP/IP model due to the presence of the two most important protocols - TCP and IP. DoD model has 4 layers that  resemble the 7 layers of the OSI model:-

1. Network Access Layer - This layer acts as an interface between the system and the network medium in use. The layer has different protocols  which are used according to the physical network.
2. Internet Layer - The most basic protocol of the Internet, the IP protocol resides at this layer. This layer is responsible for transferring data across different physical networks.
3. Host-to-Host Layer - The host-to-host layer is responsible for flow control and error control, and handles process-to-process communication.
4. Process Layer - The top most layer of the DoD model is the process layer that interfaces directly with the end user. Protocols belonging to mail delivery, remote login, and file transfer resides at this layer.