The English used in this article or section may not be easy for everybody to understand. (April 2012)
The TCP/IP model (Transmission Control Protocol/Internet Protocol) is a model with four layers which is for both modelling current Internet architecture, as well as providing a set a rules that govern all forms of transmission over a network. DARPA, an agency of the United States Department of Defense,created it in the 1970s. It evolved from ARPANET, which was an early wide area network and a predecessor of the Internet. The TCP/IP Model is sometimes called the Internet Model or less often the DoD Model.
This model was being made at the same time as the OSI Model was created. The TCP/IP model is not the same as the OSI Model, however it was influenced by the model, which is why many names of the different layers are the same.
The TCP/IP model describes a set of general design guidelines and implementations of specific networking protocols to enable computers to communicate over a network. TCP/IP provides end-to-end connectivity specifying how data should be formatted, addressed, transmitted, routed and received at the destination. Protocols exist for a variety of different types of communication services between computers.
TCP/IP has four abstraction layers as defined in RFC 1122. People often compare this layer architecture with the seven-layer OSI Reference Model; using terms such as Internet reference model. This is incorrect, however, because it is descriptive while the OSI Reference Model was intended to be prescriptive, hence being a reference model.
The TCP/IP model and related protocols are maintained by the Internet Engineering Task Force (IETF).
1. Physical and data link layer
At the physical and data link layer, TCP/IP does not define any specific protocol. It support all the standard and proprietary protocols. A network in TCP/IP internetwork can be local-area network or wide-area network.
2. Network layer
At the network layer (or, more accurately, the internetwork layer), TCP/IP supports the Internetworking Protocol. IP, in turn, uses four supporting protocols: ARP, RARP, ICMP, and IGMP.
a. Internetworking Protocol (IP)
The Internetworking Protocol (IP) is the transmission mechanism used by the TCP/IP protocols. It is an unreliable and connectionless protocol-a best-effort delivery service. The term best effort means that IP provides no error checking or tracking.
b. Address Resolution Protocol
The Address Resolution Protocol (ARP) is used to associate a logical address with a physical address. On a typical physical network, such as a LAN, each device on a link is identified by a physical or station address, usually imprinted on the network interface card (NIC). ARP is used to find the physical address of the node when its Internet address is known.
c. Reverse Address Resolution Protocol
The Reverse Address Resolution Protocol (RARP) allows a host to discover its Internet address when it knows only its physical address. It is used when a computer is connected to a network for the first time or when a diskless computer is booted.
d. Internet Control Message Protocol
The Internet Control Message Protocol (ICMP) is a mechanism used by hosts and gateways to send notification of datagram problems back to the sender. ICMP sends query and error reporting messages.
e. Internet Group Message Protocol
The Internet Group Message Protocol (IGMP) is used to facilitate the simultaneous transmission of a message to a group of recipients.
3. Transport Layer:
Traditionally the transport layer was represented in TCP/IP by two protocols: TCP and UDP. IP is a host-to-host protocol, meaning that it can deliver a packet from one physical device to another. UDP and TCP are transport level protocols responsible for delivery of a message from a process (running program) to another process. A new transport layer protocol, SCTP, has been devised to meet the needs of some newer applications.
a. User Datagram Protocol The User Datagram Protocol (UDP) is the simpler of the two standard TCP/IP transport protocols. It is a process-to-process protocol that adds only port addresses, checksum error control, and length information to the data from the upper layer.
b. Transmission Control Protocol The Transmission Control Protocol (TCP) provides full transport-layer services to applications. TCP is a reliable stream transport protocol. The term stream, in this context, means connection-oriented: A connection must be established between both ends of a transmission before either can transmit data.
c. Stream Control Transmission Protocol The Stream Control Transmission Protocol (SCTP) provides support for newer applications such as voice over the Internet. It is a transport layer protocol that combines the best features of UDP and TCP.
4. Application Layer: The application layer in TCP/IP is equivalent to the combined session, presentation and application layers in the OSI model. Many protocols are defined at this layer.
TCP is a language by using this we can communicate with others