Earlier internet was used for military purposes, for setting the trajectory of the missiles.ARPANET was first used for military purpose but later on the same was been used for basic purposes.INTERNET had become the basic need for every business and school or college, it has spread his web every where.You have come across so many times with this word “PROTOCOL”, but have you ever thought what is it and what is the use of it?
Well, PROTOCOLs are set of rules to be followed for completing a particular connection.Rules make any two computers to work and share data among each other.Now it comes to the question what will happen if protocols will not be there?The answer will be clear when history of the internet will be told.Earlier every company was using his own internet facilities given by different vendors.This was helpful for the particular company who does share data with any other company, when the issue came for sharing of data companies lacked behind.Then an ISO (International Standard Organization) came up with a superb idea, and that was internet with protocols which are going to be common for every company.This helped a-lot in making the sharing business more reliable as the data was directly transferred from one organization to another.
After this ISO introduced OSI REFERENCE MODEL, which stands for Open System Interconnection.This model consisted of seven layer, that is why it is also known as seven layered architecture model.The layers are as follows:-
(ii).Data Link Layer
Physical Layer is the first layer of OSI REFERENCE MODEL.It accepts the data from the other host(computer).It is the only layer which transfers the data to other subsequent layers.
Data Link Layer is the second layer of OSI REFERENCE MODEL.It accepts the data from the physical layer and it makes the data in frames(small parts of the huge data so that it will be transferred to the destination with out any error.Moreover the data transferred has a CRC code for checking the small parts of the data whether they are received at the destination with accuracy or not.
Network Layer is the third layer of OSI REFERENCE MODEL.It is important layer which helps in communication between two host.It actually makes a connection between the two host and helps in data transfer from source to the destination.
Transport Layer is the fourth layer of OSI REFERENCE MODEL.It is responsible for delivering data to the appropriate application process on the host computers. This involves formation of data packets, and adding source and destination port numbers in the header of each Transport Layer data packet.
Session Layer is the fifth layer of OSI REFERENCE MODEL.It provides the mechanism for opening, closing and managing a session(time period) between end-user application processes.
Presentation Layer is the sixth layer of OSI REFERENCE MODEL.This layer is responsible for the delivery and formatting of information to the application layer for further processing or display.
Application Layer is the last, seventh layer of OSI REFERENCE MODEL.This layer is users layer where the application is seen by the user.
After OSI REFERENCE MODEL, TCP/IP was introduced.It was a greater achievement as OSI REFERENCE MODEL is a connection oriented model and TCP/IP is connectionless model.Moreover, the layers introduced were only four in comparison with OSI MODEL.These layers are:-
(iii).Transport Layer(host to host Layer)
Link Layer is the lowest layer of TCP/IP and it results in end to end data transmission without the intervention of the router.
Internet Layer is the second layer after link layer.It helps in transforming the datagrams across the network.It has protocols TCP/IP for making the data reach the destination end, it consists of the IP address of the destination and it also has addressing and routing structures.These structures help in making the data route without any error.
Transport Layer is also called as HOST-TO-HOST Layer.It provides a uniform networking interface for hiding the topology layout of the network connection.It checks out data flow, error correction and congestion control.It helps in maintaining the connection between the host.It has UDP (user datagram protocol) for providing connectionless service.It is not reliable than a connection oriented one’s.It the channel is not dedicated then its obvious that the loss of data can be there.
Application Layer as usual is the users layer and provides the output to the user.It helps in making the user to get communicated to the other host.Here, we have higher level protocols like HTTP(hyper text transfer protocol), FTP(file transfer protocol), SMTP(simple mail transfer protocol).
TCP/IP works on the principle of ACK (acknowledgment), where the data is transferred form source to destination, after data reaches the destination then acknowledgment is send back that the is received