OSI model

[Alexander Barischuk]

Hello, my name is Alexander. I have problems with English, but I hope you will understand me anyway.

I'm preparing for CCNA 200-301 and I have some problems with OSI model. Let me give you a little context.
First of all let's define what is TCP/IP model.
TCP/IP model is a set of documents (protocols) that logically separate from each other (layers). Using that model we can built a real network. So it is a "real" model that we use every day. But what with OSI model? Different internet resources says different things. Some of them says this is also set of documents (protocols) as TCP/IP. Other says OSI model is just a conseptual model and nothing more (it does not refer to any particular document (protocol)). I don't know what to think. I'm confused.

Please using decription of my problem give me strict defenition what is OSI model and what's the difference between OSI and TCP/IP models.

[balaji.bandi]

Do not confuse your self :

high level :

OSI ( developed by ISO) model provides a clear distinction between interfaces, services, and protocols.

TCP/IP uses only the Internet layer

some easy reference :

https://www.balajibandi.com/?p=1370

https://www.ciscopress.com/articles/article.asp?p=31731&seqNum=2

[Giuseppe Larosa]

Hello @Alexander Barischuk ,

OSI model is not only a conceptual model with seven layers it was also implemented .

There are several reasons why ISO CLNS didn't get a great success and adoption.

among them one was the variable size of addresses from 7 bytes to 20 bytes that caused problems in implementing routing this protocol in hardware when compared to fixed size 4 bytes IPv4.

The most important result of ISO protocols is the IS-IS link state protocol that started as a routing protocol for CLNS and then became able to route IPv4 and IPv6 prefixes.

To be noted NSAP ISO CLNS addresses and protocols were used for management of ATM and SDH nodes.

Hope to help

Giuseppe