TCP/IP consists of various protocols. The two defining protocols are the layer 3, IP (Internet Protocol) and layer 4, Transmission Control Protocol. Hence the name, TCP/IP. Both TCP/IP and the internet were developed at the same time by DARPA with the purpose of creating a research network. At the beginning, there was only TCP but upon realizing its limitations its developers split it into TCP for transmission and IP for end-to-end communication. This change was introduced in version 4 hence the first real version of IP is 4.
TCP/IP isn’t the only internetworking protocol but the universally accepted standard. It’s open standard, route friendly design and scalability gave it a low entry barrier and wide success.
TCP/IP provides many services to other protocols and end users. Those services operate primarily in a client/server structural model. This is different from a peer network in that clients create requests and servers respond to those requests with data.
The client/server role is a recurring theme in TCP/IP as it is used to describe a hardware role that functions as a server or client, as a software role it tells whether a software component functions as a client or server and as a transactional role when servers communicate with each other in certain protocols.
The TCP/IP model actually describes the architecture without using the OSI model. It essentially compresses the OSI model’s top 6 layers down into 4 layers. At the bottom we have the network interface layer and it is the place that allows TCP/IP to run on. Next comes the internet layer, which is responsible for logical devise addressing, routing and data packaging. Then comes the host-to-host transport layer which handles the internetwork communication. Finally there is the application layer, which compresses layer 5-7 of the OSI model and describes the blurriness of these layers in the OSI model well. In summary the TCP/IP model looks as follows compared to the OSI model.
- Network Interface (layer 2)
- Internet (layer 3)
- Host-to-Host Transport (layer 4)
- Application (layer 5-7)