Introduction To OSI Layer Model – The Internetworking Tutorial Part1

Introduction to OSI layer model – The inter networking.

Why we need a model for inter networking . If a model has a flaw why cant we just change the model according to our needs and then use it . This is what WE do while coding but this is not in case of networking.

Imagine you being an English reader and I am writing this article in French. Will you be able to understand it . Probably not .This is the same case with networks they need to work on the same architecture through.

In the earlier days of internet there was no defined model for networking which was a pain in the neck (I wanted to use something else in place of neck but :) ) So OSI (Open System Interconnect came up with A layered approach .Which was consistent for all and it divided the network architecture into 7 layers .Why we needed a division . Hmmm consider a post office . The post office is divided into several departments one receives the parcel and add some info to it . The next department parses the parcel based on the info from previous department and send it to the higher department. If the parcel reaches directly to second department it cannot process as it needs some information which can only be present if it comes visa department1. All the work can be done by a single department also but it will lead to a disastrous situation. It is just like a man who is working as a peon , clerk, manager accountant etc a one man army example

Similarly this division was necessary for networking . The 7 layers were Application, Presentation, Session, Transport, Network, Data Link, and Physical . CHEAT SHEET( Please Do Not Take Sausage Pizza Away ) .The first letter of each word is the starting character of a layers name but in opposite order .Each OSI Layerprovide services to the layer above it and receives service from the layer below it.Same as I mentioned in the above example.

Continue reading…