Everybody welcome to the next video.
So in this video going to be going over the OSA model.
Now the OSA or open systems in our communication model is commonly used to identify the flow of communications
between two devices.
So this is everything from you go into Google dot com or read termination no common hitting enter all
the way down to where the data gets sent and back.
This is commonly used for troubleshooting.
However some people refer to things as a layer two or three switch which we'll talk about a little bit.
But outside of that from a red team's perspective it's not as important of information to know.
But I want you to understand and be aware of what it is and what it looks like and what the components
are.
Just so you have that extra little bit of knowledge when somebody refers to it layer three switch as
an example.
Now the model consists of seven layers.
So from top starting at the highest number to the to the bottom with the lowest.
So the first is application layer then presentation session transport network data link and physical.
Now first one is the application layer.
So this is closest to the end user which is what you're normally going to see.
This is how this.
This is the software itself that interacts.
So let's say the browser wants to go to automation dot com.
In that case high level API is that it's interacting with the browser itself to be able to start the
process of transferring the data.
So this is this is the application layer or Layer 7.
Now the presentation layer this is where the protocol starts to take over where if it needs to be encoded
into a specific way or it needs to be compressed or encrypted or decrypted.
This is where the layer where all of that type of process happens.
Now the reverse happens when you send the data across the network and it goes back up from layer one
to layer six which is the presentation layer.
It's going to on encode or decompress or decrypt whatever the data was now.
Next layer is the session layer.
So this is starting to get more into the protocol on how the protocol itself is being used.
So it could be TI CPI PPI could be tell us this is on top of that or SSL it makes sure that all of the
sessions between the two devices are in sync so it knows what was sent what wasn't.
It also knows whether there's something active or not.
So the sessions hasn't been used in a while and it can kill off the session next layer is the transport
layer.
Now this layer handles the actual transferring and data the segmentation of packets to making sure that
they get the packet can only hold so much data.
So what you want to do is you want to segment that a little bit further into five 10 20 100 different
packets that all get sent across.
So this is where that layer tends to happen in the acknowledgements that we receive the data happens
at the transport layer next layer is the networking layer.
So the networking layer manages the eyepiece the routing and the IP layer of the packet.
So the IP header.
Now this is an important layer because this is how things get from one set to another the data link
layer so this handles the data frames so there's something called in most cases you're gonna be looking
at something called an Ethernet frame.
Now an Ethernet frame is the top most level of a packet or the type of frame.
So in this game for example wireless will have beacon frames so the frame is what the physical medium
or the wires the fiber whatever the case might be is able to transmit it under the the core circuitry
understands what that frame looks like.
So it can start transferring the data.
So an Ethernet frame can only travel over an Ethernet based cable which is the twisted twisted pair.
So it's important I understand that go ahead and look a little bit more into data frames or Ethernet
frames just so you can kind of get a better understanding this layer also corrects any errors that that
happen during transfer.
So if something's out of sequence we haven't acknowledged something any errors in transit occur here
and this is also again the protocol this defines the protocol used to actually transfer the data itself
at the lowest level.
Now we have the physical layer the physical layer is the where the wire sits the radio waves the wireless
all of that it sits at this layer.
This is the lowest layer you're gonna get to this is where the signals themselves the on off gets sent
across the network medium.
This is that's all that's really important about this layer is that it's the actual physical hardware
sending raw signals out.
Now this is a high level Rubio aside the OS model it's it's important to understand the model and what
that it exists in sort of what the layers are.
Now we don't have to go into every detail and you're not going to have to know this off the top of your
head but it's good information to just keep in the back of your mind whenever it might present itself.