Transmission Control Protocol/Internet Protocol (TCP/IP) is a communications architecture used for networking computers and to communicate across the Internet.
TCP and IP were originally developed by the Department of Defense (DOD) to connect a number of different networks from various vendors into a network of networks called the Internet. Its success was based on providing services such as file transfer, electronic mail, and remote logon across a large number of client and server systems. Several computers in a small department could use TCP/IP, along with other protocols, on a single Local Area Network (LAN). The IP component provides routing from a department to the enterprise network, then to regional networks, and finally to the global Internet. TCP/IP is very robust and will automatically recover from a node or phone line failure. Because of the automatic recovery, large networks are created with minimal amounts of management which can lead to problems going undiagnosed and uncorrected for long periods of time.
IP - is responsible for moving packet of data from node to node. IP forwards each packet based on a four byte destination address, or the IP number. The Internet authorities assign ranges of numbers to different organizations. The organizations assign groups of their numbers to departments. IP operates on gateway machines that move data from department to organization to region and then around the world.
TCP - is responsible for verifying the correct delivery of data from client to server. Data can be lost in the intermediate network. TCP adds support to detect errors or lost data and to trigger retransmission until the data is correctly and completely received.
Level 1: TCP/IP was standardized by DOD on LAN to make sure all types of systems can communicate on the Internet. Experts who administer a regional or national network must design a system of long distance phone lines, dedicated routing devices, and large configuration files. They must know the IP numbers and physical locations of thousands of subscriber networks. Network administrators must have a good strategy for detecting problems and being able to respond quickly.
Level 2: Each company or university that subscribes to the Internet must have an intermediate level of network organization and expertise. Routers might be configured to connect to several dozen department LANs in several buildings. All traffic outside the company would be routed to a single connection and thru a regional network provider.
Level 3: The end user however, can install TCP/IP on a personal computer without any knowledge of either the corporate or regional network. Three pieces of information are required:
The IP address assigned to this personal computer
The part of the IP address (the subnet mask) that distinguishes other machines on the same LAN (messages can be sent to them directly) from machines in other departments or elsewhere in the world (which are sent to a router machine)
The IP address of the router machine that connects this LAN to the rest of the world.