TCP/IP

TCP/IP is an industry standard suite of protocols designed for local and wide area networks (LAN – WAN). It was developed by the United States Department of Defense Advanced Research Projects Agency (ARPA) in 1969 for a research sharing project called ARPANET. Their purpose in creating TCP/IP was to provide high-speed communication links. The Internet was built on the foundation of the original ARPANET project.

The TCP/IP protocol suite can be mapped directly to the seven-layer Open Systems Interconnection (OSI) model.

Network Interface – responsible for putting frames on and pulling frames off the network wire.
Internet – responsible for addressing, packaging, and routing. Three protocols make up this layer:

• IP – responsible for addressing and routing packets between networks and hosts.
• ARP – responsible for obtaining hardware (NIC) addresses of hosts located on the same physical network.
• ICMP – responsible for messages and reporting errors regarding the delivery of packet(s).
  

Transport – responsible for providing communications between two hosts. Two protocols make up this layer:

• TCP – provides connection-oriented, reliable communications for applications that transfer large amounts of data at one time or that requires an acknowledgement of data received.
• UDP – provides connectionless communications and does not guarantee a packet will be delivered. Applications that use UDP transfer small amounts of data at one time, and pass responsibility of the reliable delivery of packet(s) to the application.
  

Application – responsible for allowing applications to gain access to the physical network.

When an application sends data to another host on the network, a data packet is assembled by combining the output of each of the TCP/IP protocol layers. The protocol layers adds their own information to a header that is encapsulated as data by the protocol in the layer below.

When the destination host receives the packet, the corresponding layer(s) strips off the header(s) and treat the remainder of the packet as data for the protocol that is above it.