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at the other end it is very very similar in nature
except that it is going to happen in the reverse
in david d encapsulation which some people refer to as uncapped elation
the bits themselves are received at the physical layer
on the network medium
what happens at first
is that every system on the wire will actually view the layer to better to see
if the mac address matches their own
if the mac address does manage their own
then it indicates that the package
is in fact for them
any hosted is not match the local layer two header
will discard this frame will not examine any further
once the layer two header is verified by the receiver
indicating that this data packet was in fact destined for this particular
receiver
the receiver or actually performance own check of the information from the layer
two header
all the way through the user date
using the same type of mathematical computation
which is media specific it will come up with its only answer
will then look into the frame check sequence field and figure out what
answer of the sender
actually identified originally
if the two answers match
it indicates that the frame was received correctly
and us the frame check sequence has actually served its purpose
the frantic sequences sometimes referred to as the c_ r_c_
or cyclic redundancy check
once letter to has been verified the remaining data would be passed up
with the layer two header stripped off
at this point the network layer is going to death by any layer three information
such as the source and destination addresses
verifying this information will strip off the layer three header
and pass the remaining data two-layer four
now therefore which is the transport layer
we typically have something like a port for value
which is used to send the data to the right application
any information which needs to be executed at this point
can be executed and the remaining data would that be passed up to the
appropriate session level
and application level component
here at lair five session level information is stripped off
layer six information is applied and then stripped off
finally leaving us with nothing but the application later date
where authentication
or synchronization appears may have occurred
once layer seven has its job done
then playing user data is past up to the physical application or the actual
application
but there are a couple points about data and caps elation
and dvd encapsulation that are very important
not everything to the sender and receiver will do happen inside of
a single packet
so we will see that every one of our layers is required
certain things will happen in certain times
let's say that application requires authentication
before he did he can be sent
authentication has to happen at layer seven dust
everything else that occurs below layer seven
is all based upon supporting this authentication routine
so where the sender what actually send the data from layer seven
during the day encapsulation process the layer seven component will perform
authentication
everything below it is going to be in support
of that authentication request
that's when the date is received during the day in cancellation process anything
that is stripped off down below
is fully in support of that authentication itself in fact
when systems are communicating with each other
they both must be utilizing the exact same protocols
and information on both sides so that the processes that happened at the
functional layers
of the o_s_i_ model casually do their job
this is what is known as peer to peer
communications
can impair communications is actually the process of one sender
being able to communicate with the receiver
now of course this can be multiplied many many thousands of times on the same
network
but the fact is that every sender
never receiver that exist in a conversation
have to have the same protocol
and the same settings for the network
to be able to get it to work
when the networks tak itself is doing its job
different layers of the o_s_i_ model they're being emulated by the network
operating system are going to have different protocol data units for each
and every lawyer
for instance things that happened the session layer or above are known as true
data grams
a data graham for an application
is required for applications do its job whereas peer network communications
begin to occur
at the transport layer itself
were segments are physically sent
from the transport layer directly to the transport layer the other round
segments typically indicate anything required for guaranteed delivery of
packets
and to provide knowledge mince
wind data is in fact received
the network layer
is where our packets are actually formulated
packets are going to be routed through the network environment and the protocol
data unit or pes mou
which occurs a buyer three
is known as the packet
once we drop down into the layer two
we have now bill frame
so when we are dealing with
elements of layer two
we're typically talking about frames of that of course below the physical layers
we're always dealing with bits
the very important thing about all this
is that every letter of the o_s_i_ model is designed to functionally provide
some support for the communication of applications
across the network
whether it is something that has to happen at lair four
where we are dealing with segments or something has to happen layer three
where we're dealing with packets and packet based information
it doesn't really matter because
every single host in the network
has got to support the o_s_i_ model
the same protocol
and saying configuration for any of this to work together
now it's time to begin our learning of the t c_p_i_ p protocol
this is one of the most important
protocol suites that we utilize on our network
and it's essential we understand its history
and how it is utilized
and how i actually works at a low level
so we want to begin looking at it from a high level perspective and then dive
deeper into its relationship to the o_s_i_ model and all of the things that
it does
to allow us to communicate on the internet at our local network
what's amazing is that the idea for the internet and t c_p_i_ p
actually began with thirty five years ago
with the department of defense
department defense actually had a project that they were actively pursuing
which was designed to interconnect
all of their islands of automation
different mainframe computer systems that they had from different vendors
and which did not have any common connected he between
the ideal is what's known as the arpan at or d_o_d_ barber net the dark in that
this stands for the advanced research
projects agency network
this network was actually set up in design to interconnect the islands of
automation
at key strategic locations
by creating water known as alternate communication routes
kisi bhi i_d_ research actually began
three funding by the department of defense
and your stanford university
which actually develop the original d_o_d_ model
or the four layer
t c_p_i_ ke model but we know today
the protocol system that involved and became the protocol choice for use in
the arkin et
or dark in that as its referred to
we also begin to see the national science foundation m_s_f_
take hold of this protocol
and based upon the architect standard actually created
or evolved into the internet as we know it today
all of this began back in nineteen sixty nine when this first research towards
consolidating this type of difference in networking activity started
and that's really weird he c_p_i_ peeking from
ccp ideas the primary protocol for the internet
and it has just simply grown by leaps and bounds unpopular in fact
its popularity is based upon the ability for to be rowlett over a large networks
and to be used by virtually everyone
on the planet
as a large number of built-in utilities
applications
tools and capabilities
and is required for connected me to the internet
more than ninety eight point five percent of all corporate bandwidth in
the world utilizes
t cpa p protocol transmissions
which means that it is something that we definitely need to know
one of the biggest problems that we have with t c_p_i_ p at this time is the
depletion of the dresses public addresses
and those were starting to see a new version of t c_p_i_ p being invented and
implemented right now i_d_ version four is what we're currently using in most
implementations
but we will soon be seeing i_p_ version six being used and were already
beginning to see it somewhat in much of our computing environments
let's start off by looking at i p version four
and kinda map it to information that we already have about the o_s_i_ model
mapping the t_c_k_ p model to the o_s_i_ includes what is known as the d_o_d_
ortiz cpa p four layer model
this four layer model includes the process application area
were all applications that run the t c_p_i_ p protocol suite actually
encompass layers five percent
the host of host layer
as it's known in the original deal the model
is the functional equivalent of the transport layer
there are two protocols that existed layer four in this case
at the host of host layer
the t_e_c_ people call
or transmission control protocol and the uti p or user datagram protocol
these to transport will give us an option
of either connection with transmission or connection or unit transmission
now the idea here is that connection was transmission can be sent
best effort delivery
with no acknowledgement date of receipt
whereas connection oriented transmission is actually an established connection or
session between two systems
were all data that is sent from one system to the other
is going to be acknowledged upon receipt
this guarantees the delivery and that's why it's called a guarantee
acknowledgement type of protocol
this allows us to use applications that have a higher level
of criticality
and to use them with a lot more confidence
at the internet layer which is the functional equivalent of layer three of
the o_s_i_ model
we see the primary protocol natty c_p_i_ peas sweet
which is known as the are eight people were internet protocol
photocall
the i_d_ protocols job is to handle all of the routing
the addressing
and all the functional aspect of t c_p_i_ p conversations
it utilizes three different main protocols to assist in its
communications
icn p
or internet control message or messaging protocol
and this is a protocol that is used by the i_p_ protocol for assistance with t
c_p_i_ p conversations
the icn p protocol is also used for testing
via what is known as paying or
package internet grow per which gives us the ability to identify
if the target system as a wide or on and connected to the network
in addition
at layer three of the o_s_i_ model and on the internet layer of the t c_p_i_ p
d_o_d_ model
we must have a protocol the allows us to map the native ait p addressing
which is used by the i_p_ protocol
to back to the burned in address b_i_a_ the mac address
of the target systems
what we use here is the address
resolution
protocol
and the reverse address resolution protocol
address resolution protocol or are as it's known is responsible for mapping
hiking addresses
to layer two back addresses
whereas the reverse address resolution protocol
or rourke is responsible for mapping
and later to mac address to a layer three i'd p address
so one uses forward addressing
and the other uses reverse addressing
at dusk it is called the reverse
address
resolution protocol or
however the three main protocols of the key c_p_i_ p protocol suite
are alright p
you d p
anti cd
it is very important that we understand the characteristics of each one of these
in greater detail
so we've learned about the fundamentals of the o_s_i_ model
and the basics of t c_p_i_ p
we've also learned
how picky c_p_i_ p protocol suite
relates to the o_s_i_ model
this is all very important
as a foundation for you
as you begin to learn about the in-depth knowledge and how to c_p_i_ p actually
works on a network that'll be the next step
as we began to dig deeper into the key c_p_i_ p protocol
will need to understand some of the fundamental protocols used in this week
this includes of course p_c_p_ the transmission control protocol
and you deeply as well as icy and he and others so will begin looking at those
now
the first protocol the internet protocol
has specific characteristics that you need to be familiar with
obviously working at the network layer of the o_s_i_
is one of its most important features
it handles all activities a layer three the logical addressing
path determination
being able to route packets properly and so forth
it is connections and does not have any capabilities for data recovery
it actually relies upon upper layer protocols for this function
packets are always treated independently as well
by i i p standard
it has no capability or intelligence to identify a full session level activity
so each packet is treated as an individual conversation
moreover the internet protocol
does not have the same types of the damage is that the t_e_c_ people called
us
that ccp protocol can actually establishes session and has no
connection with haitians
idea also implements a hierarchical addressing scheme giving us the ability
to addresses many systems as would be required in a hierarchical fashion
this makes it easier to understand administer once we decide exactly what
the addressing schemes look like
one of the things that we're going to explore in greater detail in this course
is to understand how these addresses actually look and how they're going to
be applied to our networks and our hosts to make i p function
in addition hype uses a best effort delivery very much like you deeply
it does not require an acknowledgement for packets better sent
it relies upon it upper layer protocol to do this it also does not have any
data recovery features you'll actually find that the internet protocol or i_p_
protocol
is very much the same in basic function as you d p