Another example would be a web developer writing a web application in P HP or some other high level
language that developer doesn't need to understand the details of copper or fibre cabling which resided
Layer 1 in the OS model.
The layers are separated and are independent of one another.
So the areas of concern and responsibility are split which makes things a lot less complex when saving
a file in Microsoft Word.
As an example to the local hard drive or to a remote network share the developer doesn't need to understand
the finer details of ice scuzzy or storage area networks Sands or some other low level disk management
software.
The developer doesn't need to be concerned about whether a local high drive is used which could be IDC
or scuzzy on the local machine or a remote network drive using some type of attached storage.
From the viewpoint of the developer his application is only talking to the layer directly below the
layer he's working at.
So the operating system for example such as Microsoft Windows or Mac OS will hide or abstract the developer
from the lower layers thus making development a lot easier.
Now as I've mentioned from a troubleshooting point of view the OS model is going to make your life a
lot easier especially when discussing network issues with other engineers.
We'll be able to determine as an example if a problem is a layer one problem.
So a cable is unplugged or it's a layer 3 issue let's say 0 SPF is not advertising rights or if it's
a layer 7 issue your FTB service may have stopped.
While there may be a bug in the application once I go through each of the layers you'll hopefully have
a good understanding of each of those layers what they do and hopefully it'll help you with troubleshooting
the OS on model has also helped accelerate development of new applications and technologies.
In the last few years there's been massive development in technologies that rely on networks think of
the fact that not many years ago sites such as Twitter Facebook LinkedIn and other social media sites
didn't exist today.
Developers for example working on Facebook don't need to understand what an ISP or Internet service
provider is doing in the UK.
All they concentrate on is the development of their Web site and the ISP will route traffic to those
Web sites using protocols such as BGP or SPF.
So it's not necessary for an application developer to understand the details of networking by the same
token a network engineer troubleshooting a network doesn't have to understand how Facebook works.
In other words he doesn't need to understand the details of P P programming or Apache services.
Network engineers can concentrate on network protocols rather than programming languages.
Now that may change and it probably will do with technologies such as software defined networking or
SDM and additionally you may be the only person who does all the network and service support in your
organization.
So you have to understand all the layers.
But that being said it still helps simplify teaching and learning as well as troubleshooting in the
real world.
Please ensure that you have a good understanding of the OS model because it will give you a much better
understanding of networking.
That's what these videos are hopefully going to give you.
We as network engineers will use names and numbers interchangeably so we'll often talk about Layer 2
or data link layer or Layer 3 or the network layer.
So remember your numbers and your layers layer 1 is physical.
As data link.
3 is network 4 is transport.
5 A session 6 is presentation and 7 is application.
Remember both the name and the number now in the past they used to be a major split of concentration
in the US model.
The top three layers were the focus of developers and server administrators.
The lower four layers were the domain of the network engineer these days because of the growth of technology
such as VM where this divide is blurring away.
This divide is often not they and these roles are blurred.
Often today network engineers need to troubleshoot servers and server administrators need to troubleshoot
virtual switches within a VM web server.
But traditionally developers focused on the development of applications such as Firefox or Chrome which
resides at the application layer.
Developers would need to understand how to present data in specific formats.
Server administrators would have to understand operating systems and how they manage sessions and interact
with applications and thus they tended to concentrate their effort on the top three layers.
Network Engineers concentrate in most cases on the lower four layers of the OS model and hence that
is the focus of this course.
We're going to concentrate mainly on the transport network data link and physical layers.
In other words layers 1 2 3 and 4.
It's a well-known joke in networking circles that developers will blame the network when applications
are running slow.
In some cases developers don't understand networking and that's perhaps a byproduct of the OS model.
They don't need to understand networking because of the split roles and the split layers.
Developers may blame the network for performance of the applications whereas as in actual fact the reason
could be something else such as the server being overloaded or a memory leak because of bad code in
their development.
But in brief network engineers concentrate on the lower layers server administrators tend to concentrate
on the upper layers even though those lines are now blurring.
So I'm going to start off with a brief overview of Layer 7 6 and 5 and then we'll look at the transport
network data link and physical layers in a lot more detail.