>> After the network and the transport layer,
coming of the OSI model,
we're now at Layer 5, which is the session layer.
The session layer is all about the setup,
maintenance and tear-down of the connection.
Quite honestly, it's about the setup,
maintenance and tear down of a session,
that seems a little redundant.
When I see a session is
about when your web browser or client
system uses a web browser to connect to a web server.
That's an application to application session.
You communicate throughout that session,
you close out the session.
You connect again ten minutes
later and you have a new session.
That session layer is the setup,
maintenance and tear-down of the session
between one application and another.
It is a client piece and server piece.
There are a couple of protocols that work there.
RPC is referred to as Remote Procedure Call.
When you're performing an operation that's
actually happening on another system,
that's a remote procedure call.
SIP stands for Session Initiation Protocol.
This is used with VoIP,
and as a matter of fact,
it's this protocol that makes the VoIP phones ring.
If it makes sense, you dial a
number and that session has to be setup.
The receiving end has to have that ringing say,
"Okay, we're connecting."
That's set. SQL, which is database language,
but it's also is a protocol.
It's layer 5 base from
the database client to the database server.
As we continue to head them up,
when we go to Layer 6, which is the presentation layer,
three big things happen at the presentation layer;
formatting, compression and encryption.
When we talk about formatting,
we're talking about presenting
the data in a universal format.
That's why you can sit at Mac and I can be in
a Windows PC and you send
me a message that I can read perfectly.
That's because at some point in time,
that message has to be translated to
a universal format set
regardless of where the message is going,
it will present correctly when it arrives.
Formatting happens here at Layer 6.
What compression does is remove redundancy from files.
That allows the file to be smaller as
it's being transported across the network,
so it doesn't take as long.
It doesn't take as much space in order to transmit.
Of course, we have encryption.
I'll mention encryption happens in
many places on the OSI model.
At Layer 1, there's hardware-based encryption.
At Layer 3, we have IPsec,
which secures IP traffic,
which we can use encryption.
At Layer 4 through seven,
we have SSL and TLS,
which we haven't talked about yet,
but that secures web traffic.
Here at Layer 6, the encryption that
happens at this level is within the filing system.
If you're using EFS and you're
going to send a file that's encrypted,
that happens at this layer,
or if you're going to store
the file encrypted format
somewhere within the filing system,
that also happens here.
For multimedia formatting,
whether you have a GIF, a JPG,
or an MP4, or really any type of multimedia,
that formatting happens at this layer.
Interestingly enough, this is the only layer the
entire OSI model that has no protocols.
That's probably worth a look
from a test-taking perspective.
Man, if you want to get to the layer where you
get the most intelligence, it's here.
Remember, down at Layer 1,
we said that those were the devices
that don't really know much.
They don't know what data is traversing.
A cable doesn't know what data is going across it,
and a cable doesn't care.
But if you really want intelligence with your devices,
you go all the way up to the top,
which is the application layer. Layer 7.
These are the protocols that drive
the applications users are using.
These protocols have to be really
smart because they have direct access to your data.
When we're thinking about
the things that we can do at Layer 7,
this is where you'll see certificate services.
To tell you the truth, a lot of
these things we haven't talked about.
What I'm going to encourage you to do is
later on come back and review
this session on the OSI model
>> after we talked about what
>> a web application firewall is
and what certificate services are.
For now we're just going to suffice to say
that certificate services happen at this layer.
Certificates are used in order to provide
authentication for individuals or for systems.
That's going to be important.
Proxy servers, which are
high-end deep packet inspection devices give
us a really good understanding and inspection of
the content of traffic and other information.
A web application firewall is specific to web traffic,
but provides a good degree of protection,
specifically focusing in on HTTP and HTTPS.
When it comes to any attacks that are
specifically geared towards web servers,
a WAF is a really good defensive mechanism.
Your email applications are
going to use digital signatures.
Digital signing happens up at Layer 7.
There's a lot of really good,
very important stuff that happens here
in just a ton of protocols.
SNMP, Simple Network Management Protocol, FTP,
TFTP, by the way,
let me just mention you see FTP
>> and TFTP mentioned here.
>> Most people have heard of File Transfer Protocol,
but there's also Trivial File Transfer Protocol.
The only difference between the two,
if you remember earlier,
we talked about TCP and
UDP and that upper layer services, piggyback.
FTP piggybacks on TCP,
TFTP, piggybacks on UDP.
Which one do you think is
going to provide better performance?
TFTP, because UDP is fast,
FTP is going to provide more reliable delivery.
What are our key takeaways from the OSI model?
The OSI model is conceptual model
>> that was brought to us
>> from the International Organization
>> for Standardization.
>> It essentially breaks down networking
into seven categories called layers.
You see the layers in front of us here.
This is a really good chart and I would
certainly recommend screenshotting it
and printing it out.
Because this hits the gist of
what's going on with the OSI model.
Gives you a look at network processes
to the application Layer 7,
data representation,
inter-host communication,
>> end-to-end path determination.
>> Down layer by layer gives
you a quick view of what happens at each layer.
It also gives you some of the more important protocols.
But you can go back and add to this,
you know that cable is at Layer 1.
Switches and MAC addresses are at Layer 2,
at Layer 3 we have routers and Layer 3 switches.
If there's anything missing,
you can go back and re-listen.
But know your layers,
know the gist of what happens at each layer and know
any protocols or any specific hardware devices,
because you can bet this is going to be on your exam.