Now in the past they were older models that were proprietary and were typically controlled by a single
vendor.
This caused multiple issues especially in networking where we have many different devices that need
to communicate with each other.
Issues resulting from a proprietary model included slow development and no interoperability between
vendors.
For many years there's been a major drive to standardize protocols enhance interoperability and use
open standards.
The OS on Model was developed by the International Organization for Standardization or the ISO and it
provides a layered approach to development and interoperability.
It allows for multi vendor interoperability and rapid development.
Thus for example a web browser like Chrome from Google can run on an HP computer or Dell a laptop and
connect to a Cisco network traverse the Internet and connect it to a web server running Apache on top
of Linux.
So your web browser is running perhaps in Windows or it could be a Safari browser running on a Macbook
connecting across a Cisco network in your corporate environment traversing multiple devices on the internet
and communicating with a Apache server running on linux.
That kind of interoperability and communication is made a lot simpler because of the OS on model.
We have seamless interoperability where traffic is sent between multiple vendors and multiple applications.
Now the OS on model consists of seven layers with the advantage that each layer is independent of other
layers.
The layers of the OS on models starting from the top or Layer 7 are application presentation session
transport network data link and physical the physical layer is Layer 1.
When discussing the OS model we typically explain and reference it from the bottom up.
So we started Layer 1 2 3 4 5 6 and end up at 7.
There are many different ways to remember the different layers of the OS model.
So for example all people sleeping through networking don't pass.
So you're not gonna pass your exam if you sleep through networking presentations old people sleeping
through networking don't pass.
There are many other examples and you'll probably encounter some really funny ones and some which I
can't repeat here.
I'm gonna go through each of these layers and a lot of detail in the upcoming videos.
Please bear with me because I know this can get a bit tedious and a bit boring but it's important that
you work through these videos to make sure that you have an understanding of the ISI model and the different
layers.
It's really important to know this and it's going to help you immensely as a network engineer.
If you have a good understanding of the ISI model and you'll find this will help you a lot when troubleshooting
networks.
There are multiple advantages to the Western model as mentioned including interoperability and standards.
Another big advantage of the OS model is split development or split areas of concern and application
developer.
As an example writing an application like Microsoft Word doesn't need to understand the details of IP
routing.
So if you were writing an application and you were for instance writing in Python or another high level
programming language you don't have to understand a SPF or BGP or spanning tree or any one of the many
other protocols used at lower layers of the OS ie model because the different layers are separated from
each other a developer working at least 7 doesn't need to know what's happening at layer to or layer
3.