-: We finally made it, 2 2
we've gotten to layer 7, the application layer. 3 3
We've gone through seven different layers of the OSI model, 4 4
starting all the way down with physical, 5 5
and then going up to data link, network, transport, 6 6
session, presentation, and now we're here at application. 7 7
The application layer is going to provide 8 8
all of your application-level services, 9 9
which makes sense since it's the application layer. 10 10
But I don't want you to think 11 11
about an application like Internet Explorer, or Chrome, 12 12
or Word, or PowerPoint, or Notepad. 13 13
That's not the kind of application we're talking about. 14 14
We're actually going to be talking 15 15
about more lower-level applications. 16 16
When we talk about applications in the OSI context, 17 17
we're really talking about things 18 18
like file transfer or network transfer. 19 19
This is the layer where the user 20 20
is going to communicate with the computer, 21 21
and the computer can then take that information 22 22
and pass it across the network. 23 23
These are functions like application services 24 24
and service advertisement, and we're going to talk about those 25 25
as we go through this short lecture. 26 26
Application services are the thing 27 27
that unites communicating components 28 28
from more than one network application. 29 29
If I have a file transfer and file sharing, email, 30 30
remote access, network management activities, 31 31
and client server processes, 32 32
these are all different types of application services. 33 33
Now, again, I want to caution you, when I talk about email, 34 34
I'm not talking about Microsoft Outlook. 35 35
Instead, I'm talking about 36 36
the low-level protocol that's used by email, 37 37
things like POP3 or Post Office Protocol 3, 38 38
or Internet Message Application Protocol, IMAP, 39 39
or something like SMTP, the Simple Mail Transfer Protocol, 40 40
things of this nature, and we're going to talk about these 41 41
as we go through our ports and protocols in a future lesson 42 42
when you have to memorize the different port numbers 43 43
for each of these three types of services. 44 44
Now, the other thing we want to talk about 45 45
is service advisement. 46 46
This is where applications can send out announcements 47 47
to other devices on the network, 48 48
and they can say these are 49 49
the different services that I offer. 50 50
If you have something like a printer 51 51
that is essentially managed by your active directory, 52 52
or a file server that's managed by an active directory, 53 53
it can do those advertisements for you. 54 54
If not though, your files and your printers 55 55
can actually advertise for themselves, 56 56
and that's the idea of a service advertisement. 57 57
For example, let's say you have 58 58
a nice wireless printer that's on your network. 59 59
Any time you connect to the wireless network, 60 60
it actually sits out there and the printer goes hey, 61 61
brand new device that I don't know 62 62
that just joined my network, I'm a printer. 63 63
And guess what? 64 64
You can use me to print things, cause I'm a printer! 65 65
That's what it does, it advertises itself. 66 66
And all of this is done under this concept 67 67
of service advertisement here in layer 7. 68 68
Now, when we talk about layer 7, 69 69
what are some examples of layer 7 things? 70 70
Well, these are email applications 71 71
like POP3, IMAP, and SMTP. 72 72
This would be web browsing applications like HTTP or HTTPS. 73 73
This could be things like DNS, the Domain Name Service, 74 74
which is going to translate 75 75
our names to numbers and our numbers to names. 76 76
It can be things like file transfer protocols 77 77
like FTP, and FTPS, and SFTP. 78 78
It could be things like remote access like TELNET and SSH, 79 79
and Simple Network Management Protocol, or SNMP. 80 80
All of these things are layer 7. 81 81
And if it sounds like I just dropped 82 82
a lot of acronyms to you, I know I did. 83 83
Don't worry about it, we're going to talk about 84 84
each and every one of those 85 85
as we go through the future lessons in this course. 86 86
So, just hang with me, and by the end of this, 87 87
you are going to know all of those like the back of your hand. 88 88
You're going to know what the acronyms are, 89 89
what they stand for, and what ports they operate on, 90 90
because that is going to be important for the exam, as well.