The TCP/IP Reference Model will be having 4 layers which are:
- Internet Layer.
- Transport layer.
- Application Layer.
- Host-to-Network layer.
The Internet Layer: Internet layer acts like the linchpin which holds the complete architecture together. Its task is to permit hosts to inject packets into any of the network and allow them travel independently to the destination (on a different network). They may not arrive in the order in which they were sent, in which case higher layers perform the rearrangement of them. “Internet” is used in this section is a generic sense, even though this layer is present in the Internet.
The internet layer gives the definition of an official packet format and protocol called IP (Internet Protocol). The task of the internet layer is to deliver IP packets to respective destination. Avoiding congestion is the main issue here. For these reasons, it is reasonable to say that the TCP/IP internet layer is similar in functionality to the OSI network layer.
Transport Layer: The layer above the internet layer in the TCP/IP model is called the transport layer. Its task is to allow peer entities to carry message from source to destination, just like the way it happens in OSI transport layer. Two end-to-end transport protocols have been defined here. Two end to end transport protocol are explained in this article. The first one, TCP (Transmission Control Protocol), is reliable connection-oriented protocol which allows byte stream coming from one system to be delivered without any flaw on another other system in the internet. It breaks the incoming byte stream into discrete messages and passes every message on to the internet layer. On destination, the receiving TCP process and reassembles the received messages to the output stream. TCP handles flow control to ensure that a fast sender cannot over burden a slow receiver with messages than can be handled.
The second protocol in this layer, UDP (User Datagram Protocol), is unreliable, connectionless protocols that does not need TCP’s sequencing or flow control and wish to provide their own. This type of transport protocol is used where delivery of message is more important than proper or accurate delivery.
The Application Layer: The TCP/IP model does not have either or presentation layers. OSI model is of little use to most applications. Above the transport layer is the application layer and contains all the higher-level protocols. Earlier layers included virtual terminal (TELNET), file transfer (FTP), and electronic mail (SMTP), which are mentioned. The virtual system protocol allows a user on one system to log onto a faraway system and perform task on it. File transfer protocol provides a way to move data efficiently from one system to another. A specialized protocol (SMTP) was developed for it Electronic mail. Several protocols have been added over the due course of time, Domain Name System (DNS) for mapping host names onto their network addresses, NNTP, the protocol for moving USENET news articles around, and HTTP, the protocol for getting pages on World Wide Web, and many more.
The Host-to-Network Layer: Down to internet layer is a great space. TCP/IP reference does not give much information whats going on here.Host connects to network using some protocol which is not mentioned for sending IP packets to it. Protocol used in Host to Network Layer is not defined and varies from host to host and network to network.