We've finally made it.
We've gotten to layer 7, the application layer.
We've gone through seven different layers of the OSI model,
starting all the way down with physical, then going up
to data link, network, transport, session, presentation,
and now we're here at application.
The application layer is going to provide
all of your application-level services,
which makes sense since it's the application layer.
But I don't want you to think about an application like
Internet Explorer or Chrome or Word
or PowerPoint or Notepad.
That's not the kind of application we're talking about.
We're actually going to be talking about
more lower-level applications.
When we talk about applications in the OSI context,
we're really talking about things like file transfer
or network transfer.
This is the layer where the user is going to communicate
with the computer and the computer can then take
that information and pass it across the network.
These are functions like application services
and service advertisement, and we're going to talk about those
as we go through this short lecture.
Application services are the thing
that unites communicating components
for more than one network application.
If I have a file transfer and file sharing, email,
remote access, network management activities,
and client server processes,
these are all different types of application services.
Now, again, I want to caution you.
When I talk about email,
I'm not talking about Microsoft Outlook.
Instead, I'm talking about the low-level protocol
that's used by email.
Things like POP3 or Post Office Protocol 3,
or Internet Message Access Protocol, an IMAP,
or something like SMTP, the Simple Mail Transfer Protocol,
things of this nature.
And we're going to talk about these as we go through our ports
and protocols in a future lesson when you have to memorize
the different port numbers for each
of these three types of services.
Now, the other thing we want to talk about
is service advertisement.
This is where applications can send out announcements
to other devices on the network, and they can say,
"These are the different services that I offer."
If you have something like a printer
that is essentially managed by your active directory
or a file server that's managed by active directory,
it can do those advertisements for you.
If not though, your files and your printers
can actually advertise for themselves.
And that's the idea of a service advertisement.
For example, let's say you have a nice wireless printer
that's on your network.
Anytime you connect to the wireless network,
it actually sits out there and the printer goes,
"Hey, brand new device that I don't know
that just joined my network, I'm a printer.
And guess what?
You can use me to print things because I'm a printer."
And that's what it does, it advertises itself.
And all this is done under this concept
of service advertisement here in layer 7.
Now, when we talk about layer 7, what are some examples
of layer 7 things?
Well, these are email applications like POP3,
IMAP, and SMTP.
This would be web browsing applications like HTTP or HTTPS.
This could be things like DNS, the Domain Name Service,
which is going to translate our names to numbers
and our numbers to names.
It can be things like File Transfer Protocols like FTP
and FTPS and SFTP.
It could be things like remote access like Telnet and SSH
and Simple Network Management Protocol or SNMP.
All of these things are layer 7.
And if it sounds like I just threw out
a lot of acronyms to you, I know I did.
Don't worry about it.
We are going to talk about each and every one of those
as we go through the future lessons in this course.
So just hang with me, and by the end of this,
you are going to know all of those like the back of your hand.
You're going to know what the acronyms are,
what they stand for, and what ports they operate on,
because that is going to be important for the exam as well.