History of TCP/IP and DoD Model
Brief History Of TCP/IP
The global system of interconnected computer networks — ‘The Internet’ makes use of TCP/IP to communicate across networks and devices.
Transmission Control Protocol / Internet Protocol (TCP/IP) as the name suggests are protocols i.e. system of rules. The protocols in this case are ‘Communication Protocols’ which define rules, system, semantics and synchronization of communication and possible error recovery methods.
The TCP/IP suite was introduced by United State’s Department of Defense (DoD) with a vision to ensure and preserve data integrity as well to maintain communication in event of major wars.
TCP/IP was first introduced in 1973; later in 1978 it was divided to two protocols TCP and IP. Finally in 1983 TCP/IP replaced Network Control Protocol (NCP) which was till the standard mechanism of communication used in ARPAnet.
TCP/IP and DoD Model:
The equivalent of OSI Model used in intitial days of TCP/IP is known as DoD Model. The DoD Model is infact a condensed OSI Model; having only four layers instead of seven as in OSI Model.
The layers being:
1. Process/Application Layer
2. Host to Host Layer
3. Internet Layer
4. Network Access Layer
The figure below shows the condensation of OSI to DoD Model and correspondence between these layers in both models
The Process / Application Layer is composite of OSI Model’s Application, Presentation and Session Layers. It deals with node to node application communication and also user-interface specification.
Host-to-Host Layer is similar to OSI Models’s Transport Layer. It deals primarily with transporting data i.e. packet sequencing and error-free delivery of data.
Internet Layer corresponds to OSI Model’s Network Layer. It is responsible for logical transmission of data. Internet layer give IP address to hosts and handle routing of packets.’
Network Access Layer at bottom of DoD Model is equivalent of Data Link and Physical Layers of OSI Model. This layer is responsible for exchange of data between host and network.
