TCP/IP Model
The TCP/IP model was developed prior to the OSI model.The TCP/IP model is not exactly similar to the OSI model.It was designed and developed by Department of Defense in 1960. and is based on the standard protocols.
It stands for Transmission Control Protocol/Internet Protocol. TCP/IP model helps you to determine how a specific computer should be connected to the internet and how data should be transmitted between them.
The functionality of the TCP/IP model is divided into four layers, and each includes specific protocols.All these four TCP/IP layers work collaboratively to transmit the data from one layer to another.The layers are :-
1. Process/ Application layer
2. Host to Host/ Transport layer
3. Internet layer
4. Network Access/Link layer
Network Access Layer
A network Access layer is the lowest layer of the TCP/IP model. This layer corresponds to the combination of Data Link layer and Physical layer of the OSI model.
It defines how the data should be sent physically through the network.The functions carried out by this layer are encapsulating the IP datagram into frames transmitted by the network and mapping of IP addresses into physical addresses.
Internet Layer
An internet layer is the second layer of the TCP/IP model.An internet layer is also known as the network layer. This layers parallels the functions of OSI network layer.
The main responsibility of the internet layer is to send the packets from any network, and they arrive at the destination irrespective of the route they take.
It defines the protocols which are responsible for logical transmission of data over the entire network.The main protocols at this layer are-
IP : It stands for Internet Protocol. It is responsible for delivering packets from source Host to destination Host by looking at the IP addresses in the packet headers.
IP has two versions IPV4 and IPV6.
ARP : It stands for Address Resolution Protocol. ARP is a network layer protocol which is used to find the physical address from the IP address. ARP has several types like Reverse ARP, Proxy ARP, Inverse ARP etc.
ICMP : It stands for Internet Control Message Protocol.It is a mechanism used by the hosts or routers to send notifications regarding datagram problems back to the sender.
A datagram travels from router-to-router until it reaches its destination. If a router is unable to route the data because of some unusual conditions such as disabled links, a device is on fire or network congestion, then the ICMP protocol is used to inform the sender that the datagram is undeliverable.
The core responsibility of the ICMP protocol is to report the problems, not correct them. ICMP can send the messages only to the source, but not to the intermediate routers because the IP datagram carries the addresses of the source and destination but not of the router that it is passed to.
Transport Layer
This layer is analogous to the Transport layer of the OSI layer. It is also called The Host to Host Layer. IT is responsible for end to end communication and error free delivery of data.The transport layer is responsible for the reliability, flow control, and correction of data which is being sent over the network.
The two main protocols are presenting in this layer are :-
Transmission Control Protocol
TCP is a reliable protocol as it detects the error and retransmits the damaged frames.Therefore, it ensures all the segments must be received and acknowledged before the transmission is considered to be completed.
At the sending end, TCP divides the whole message into smaller units known as segment, and each segment contains a sequence number which is required for reordering the frames to form an original message.
At the receiving end, TCP collects all the segments and reorders them based on sequence numbers.
User Datagram Protocol
It provides connectionless service and end-to-end delivery of transmission.It is an unreliable protocol as it discovers the errors but not specify the error.
User Datagram Protocol discovers the error, and ICMP protocol reports the error to the sender that user datagram has been damaged.
Application Layer
An Application layer is the topmost layer in the TCP/IP model. This layer performs the functions of top three layers of the OSI model (Application, Presentation and Session layer) .
This layer allows the user to interact with the application.When one application layer protocol wants to communicate with another application layer, it forwards its data to the transport layer.There is an ambiguity occurs in the application layer. Every application cannot be placed inside the application layer except those who interact with the communication system.
For example: Text editor cannot be considered in application layer while web browser using HTTP protocol to interact with the network where HTTP protocol is an application layer protocol.
Some of the protocols used in this layer are :-
HTTP: HTTP stands for Hypertext Transfer Protocol. This protocol allows us to access the data over the world wide web. It transfers the data in the form of plain text, audio, video. It is known as a Hypertext Transfer Protocol as it has the efficiency to use in a hypertext environment where there are rapid jumps from one document to another.
SMTP: SMTP stands for Simple Mail Transfer Protocol. The TCP/IP protocol that supports the e-mail is known as a Simple mail transfer protocol. This protocol is used to send the data to another e-mail address. It is a combination of HTTP with SSL(Secure Socket layer).
DNS: DNS stands for Domain Name System. An IP address is used to identify the connection of a host to the internet uniquely. But, people prefer to use the names instead of addresses. Therefore, the system that maps the name to the address is known as Domain Name System.
TELNET: Telnet stands for Teletype Network.It establishes the connection between the local computer and remote computer in such a way that the local terminal appears to be a terminal at the remote system.
FTP: FTP stands for File Transfer Protocol. FTP is a standard internet protocol used for transmitting the files from one computer to another computer.
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