Why ISO-OSI model is considered as a reference model?
The OSI model these days is primarily an educational tool. Originally, OSI was the base for a number of protocols that were used in networks but the rise of TCP/IP and the internet spelled the end for it. However, the OSI model still provided an excellent means for explaining networking and how networks operate in general terms, how the layers fit in together, etc.
It's called a reference model for this reason, it's not actually how stuff works but it's close enough and a really good way to teach people the general principles involved in how current networking protocols work.
The ISO OSI model provides a good glossary (word definitions) of reference points that really help in communicating (as in speaking) with other designers.
Breaking things down into physical, link, network, etc reflects the layering that naturally occurs in real designs. The boundaries are gray, and many times layers are combined, but at least you have a reference definition to compare to. Being a hardware designer, I relate best to phy, link and network levels. Network and above is "just software"
Yes, it is.
No I don't think so. TCP/IP is only part of the model, in particular from the network up to application layer.
Yes, but each layer act like a assembly machine in a factory where each packet is produced then framed then transfered etc. They don't simply "fit" together. Each has its own function to perform its solely designed task.
No, it's reference because its useable components are public. Each layer provides a public interface for the next one to use and be used.
This model is standardized, reused and can certainly be reformed (i.e Cisco suggests only 4 layers instead of 7).
No. TCP/IP was never part of the OSI model. OSI had it's own network protocols like CLNP and CONP. TCP/IP and OSI were competing protocol suites.
OSI was an initiative started by the International Organization for Standardization (ISO) while TCP/IP was started by the US Department of Defence.
TCP/IP won out in the 90s after it was commercially adopted and became what we now call the internet. OSI all but disappeared.
We still use the OSI reference model as a teaching apparatus instead of the TCP/IP reference model because OSI is more instructive, but with an important distinction. We replace the OSI network & transport protocols with protocols from the TCP/IP suite. We place the Internet Protocol at the network layer and TCP/UDP at the transport layer.
Unfortunately, this has resulted in people thinking TCP/IP is part of the OSI model. It isn't.
In the context of the OP's question, my meaning with "fit in" was how data is encapsulated. I intentionally left out specific details as it provides an opportunity for the OP to do a little research.
Technically, a reference model is a concept. A set of interconnected/interdependent ideas or functions that are defined by some accepted relevant body of experts with the goal of establishing or encouraging clear communication.
But such a definition is not very helpful for someone new to the field who's looking to understand what the OSI reference model means. It's much better to instead position it as a "good way to teach people the general principles involved in how current networking protocols work."
It's not very accurate, but it is much more useful.
Cisco isn't suggesting nor has it reformed the OSI model, when they say 4 layers. They are simply making a reference to the TCP/IP model which contains only 4 layers.
OK cool, I misunderstood about concepts of TCP/IP in programming and the model itself at that time.
But the TCP/IP model is not much different from the OSI. It's like a GMO product of OSI.
Yes, they apply the TCP/IP model and they never say anything about 7 layers while These two models are not totally different at all (one layer of one already encapsulates 2-3 layers of another).
BTW thank you for your reply.
Back in the 1980's, the European companies proposed the 7-layer model for use in the internet. I was writing lightwave transmission software at Bell Labs at the time, and it was a big controversy. Many American companies had already pretty much standardized everything to use TCP/IP (3 layers), and so eventually, people gave up trying to force there to be 7 layers when it wasn't actually necessary. The analysis of networking into 7 layers is still useful, but networking is seldom implemented that way.
Cisco talk about layer 7 as much as any vendor at the moment; L7 (application layer) security tools are massive business and Cisco has it's own slice of the very lucrative pie!
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