In this section, let us understand the TCP/IP protocol suite and various protocols used in its different layers.
Introduction to TCP/IP Protocol Suite
TCP/IP is the acronym for Transmission Control Protocol / Internet Protocol. The TCP/IP is a suite of various network protocols that are used to interconnect various network devices and exchange information on the Internet. It is also used in private communication networks like Intranet or Extranet.
TCP and IP are in fact two different protocols. TCP is responsible for end to end communication between the two devices. It is a connection-oriented and reliable protocol defined at the transport layer of the TCP/IP model.
Whereas, IP is a connection-less protocol responsible for the delivery of data packets from source to destination. IP defines the addressing scheme and labels the datagram packet with source and destination address.
TCP and IP work together along with some other protocols to form TCP/IP suite and defines how data are broken down into small packets, addressed, routed and error-free reception at the destination.
The TCP/IP protocol suite was initially developed by the United States Defence Advanced Research Projects Agency Network ( ARPANET) during the 1970s. It was a part of a research project sponsored by the US Department of Defence for data communication. This model, later on, became the basis for the Internet.
Layers of the TCP/IP model
The TCP/IP model is divided into four distinct layers to understand the functionalities of different protocols implemented in each layer.
Application layer
Application layer resides on top of the TCP/IP model. It provides the interface between the end-user and the network services such as email, web browsing, file transfer, DNS, telnet etc. Application layer helps the end-user and the application software to get access to the network.
Various protocols are used by application layer that is defined in TCP/IP Suite are: HTTP, DNS, DHCP, FTP, TELNET, SMTP, IMAP, etc.
Transport layer
Transport layer deals with the process to process communication between the two hosts.
It receives data from the application layer, breaks them into smaller units called segments and then passed to the layer below it i.e. Internet layer.
The transport layer of TCP/IP model does the following functionalities :
- Segmentation and reassembly
- Service point addressing
- Connection control
The transport layer uses two very popular protocols: TCP and UDP.
TCP stands for transmission control protocol and is considered to be a reliable protocol. It establishes the TCP session between the source and destination, before exchanging the data between them. Hence, it is also called the connection-oriented protocol. TCP always asks for acknowledgement from the receiver for every segment it transmits. The segment is re-transmitted repeatedly until the receiver does not respond. TCP is used in network services like email, FTP, etc.
Another protocol used in the transport layer is UDP. UDP stands for User Datagram Protocol. In contrast to TCP, UDP is considered to be connectionless and unreliable protocol. Because UDP does not establish any session before transmitting any segment from source to destination. It does not wait for acknowledgement from the receiver. Hence, it is a very fast protocol and is mostly used in real-time communication like live tv broadcast, video conferencing, etc.
Internet layer
Internet layer is also referred to as the internetwork layer or network layer and is responsible for the delivery of packet from source to destination across the communication network. IP (Internet Protocol) is the major protocol in this layer that provides a logical addressing scheme for data packets from source to destination. Every node in a network is uniquely identified by their respective IP address.
The other important protocols used in this layer are ICMP, IGMP, ARP, RARP etc.
Network Interface Layer
The network interface layer is the lowest layer of the TCP/IP model and is also sometimes called a network access layer. This layer is responsible for encapsulating IP packets received from the internet layer to data frames. The data framing is done by adding a physical address of the host. The frame is further transmitted over the physical link on the same network.
The network interface layer provides interface with the physical media like coaxial cable, twisted pair cable, optical fibre cable or wireless media.
The different protocol is used in this layer such as Ethernet, Token Ring, FDDI, Frame Relay, ATM, X.25, etc.
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