TCP/IP Model

Because TCP/IP is so central to working with the Internet and intranets, you should understand it in details. TCP/IP uses the Department of Defense (DoD) model, which describes communications in only four layers.

DoD model:

In late 1960s, Advanced Research Projects Agency (ARPA) carried out a research project to connect a number different networks designed by different vendors into a network of networks (the "Internet"). And the model proposed for transmission of data was known as DoD model, it describes the communication in four layers: 

• The Network Access Layer is responsible for delivering data over the particular hardware media in use. Different protocols are selected from this layer, depending on the type of physical network.
• The Internet Layer is responsible for delivering data across a series of different physical networks that interconnect a source and destination machine. Routing protocols are most closely associated with this layer, as is the IP Protocol, the Internet's fundamental protocol. 
• The Host-to-Host Layer handles connection rendezvous, flow control, retransmission of lost data, and other generic data flow management. The mutually exclusive TCP and UDP protocols are this layer's most important members.
• The Process Layer contains protocols that implement user-level functions, such as mail delivery, file transfer and remote login.

TCP/IP was first proposed in 1973 and was split into separate protocols, TCP and IP, in 1978. In 1983, TCP/IP became the official transfer mechanism for all connections tp ARPAnet, replacing the earlier Network Control Protocol. We will study different protocols of TCP/IP model in details in later posts.

DoD model is theoretically comparable with OSI model :