This video will cover chapter 2 and is the 2nd
part of two videos for the
CCNA course on
There is a link at the end of this video or
if you look down at the description i
should have a link down there as well to
part one
so my name is Jason Johnson thank you
for watching this video if you find it
helpful and you want to be updated on
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any questions you can also leave a
comment i'll try to get back with you as
quick as possible so let's continue on
with chapter 4 chapter part two of two
for chapter four is going to cover the
data link layer protocols and the media
access control so what are the data link
layer protocols as you remember we have
protocols set for when we do networking
and those protocols allow media to be
able to talk with each other or no to be
able to talk with each other properly so
we have to speak the same language so
the data link layer is the next layer in
this OSI layer here that we're dealing
with and and so this is the next layer
we have our physical layer that we
looked at and part 1 of this video and
now we're going to talk about the data
link layer and the data link layer
prepares network data for the physical
network if so when we look at this up
screen here where the data link layer
this is a continuation of the slide and
if we're in a local area network it's
going to use just a layer 2 but if we
need to have routing it will go to the
layer 3 so the layer to header has the
destination Nick and the source Nick
that mac address and then the layer 3 is
going to have the IP packet or IP
address your internet protocol address
so that is so it's able to route that
from both the source and the destination
so if we look at it this way as well we
have our physical layer and that's
governed by the either the 8023 ethernet
they do 21 you know that this is our
wireless was here or and we have our mac
sublayer when we get up to the data link
layer here so we have our layer to
overlay layer one layer to internet
layer 3 and at the data link layer we
have two sublayers here we have a Mac
sub-layer an LLC sub-layer so when
you're looking at this visually from an
OSI standpoint or a layer standpoint you
get your physical then when you get your
data link is broken into two separate
sections and the governing bodies are
the governor up they govern this part
right here the mac sub-layer an
immediate media access control it can be
represented this way as well we have may
have from Paris to Japan here and at
each hop along the way the media access
control says how am i communicating with
the next device so for example if my pc
here is connecting with the router and
i'm using ethernet here i'm using an
ethernet cable and it says I'm going to
connect using ethernet and so it's going
to send that frame or that packet of
information in a certain in a certain
way it's going to send it a certain up
certain language certain bits and then
we get from the router maybe to the
upload it may be going into fiber optics
and so it changes the media access or
how it's communicating and then when it
goes from the let's say our dish up to
the satellite it goes in a different
medium and then it comes back down it
converts it again and then went down
here it may be using wireless so it
converts it again and it's converting
those frames that media access control
layer or that first layer we're looking
back here that media access controller
sub-layer here and this this whole data
link layer is saying how are we
communicating its setting the standard
for how that information gets forwarded
so it also provides access to media so
whether we're using a serial connector
or an ethernet connection
the packet of information of the data
link layer is responsible for
controlling the transfer frames across
the media so that's it is to say how are
we being transferred
what's the medium and how's it going to
talk to each other the standards are set
by these governing bodies here is so
gently and see and I tu and you can look
those up if you want to just google
those now on media access control the
section 44 we're going to talk about
next is logical topology and physical
topology when we're dealing with
networks you need to understand that
there is a difference between the
logical topology and physical topology
and when you're talking in the field of
networking you need to understand those
so you do need to have a good
understanding of when you're looking at
a topology whether it's a logical or
physical because it doesn't matter
so let's take a look here at top
apologies when we control access to the
media we need rules to govern how we're
sharing those and those frames are going
across and how we represent those in the
topology on how those are gonna get
through this is a physical topology here
this is gonna show what type of
equipment we have you may not have the
exact server on there so you're not
gonna say that this is a you know the
actual brand name of the server and how
much RAM you have on all that but you
are going to say that that's a file
server so it gives your function of what
it's doing and also going to tell you
what rackets on one shelf its own so
it's going to be a rack to shell three
so server act to ensure all three so
you'll be able to find that web server
is setting on Iraq to shelf one so you
know you can go find out the the rack
too and look on shelf one that's gonna
be your web server and then your switch
may be on track one shelf to track one
shelf too so it's gonna be a different
server rack and your router may be right
above that rac1 shelf one track one
shelf the reason that same rack so even
though you are physically located right
above each other on this topology here
they are represented kind of on a map
kinda like what you would do if you were
up mapping out who reports to who this
is just telling you which piece of
equipment talk to which piece of
equipment and that's really what we're
doing here so we're saying these are
local area networks here see
the local area network that's a local
area network actually let me delete this
that's a local area network there
here's one here here's one here and this
is our wide area network our way in our
when going out so that's how you can
just quickly look at this and say that's
how that's kind of broken out but i can
look and I can say okay I've got no one
to three computers here what room are
they in and i'm not even listening out
the number what you would do is you
would say classroom a classroom one room
225 and you may put a 5 there that
you've got five notes in there you may
put a 10 there that you've got ten in
there maybe five here and that lets you
just know how many did you have in each
one
now are logical topology is going to
show us are just showed you on the
previous slide where you have your land
second it out I kind of Drew those well
this is what we're gonna do here we're
going to segment out our lands and you
don't always put the color bubbles
around these but this it's done here on
this slide just so you can see it much
easier you just kind of you as you get
used to working in networks and looking
at physical and logical topologies
you'll just immediately look at him and
say okay I know which ones are segmented
off based upon IP addressing and based
upon routers and switches and where
everything is located so you just know
naturally that this the router here is
segmented your network and then over
here your segment in your network based
upon IP addressing and this is most
likely going to have your subnet so
you're probably gonna have a slash
something out here for your side okay
take notation cidr and we're gonna get
the baton later up chapters so this is a
logical topology and your physical
topology just be real familiar that when
you look at one of these from a visual
standpoint you just immediately be able
to say okay i know that's a physical
topology because that's showing me all
about physical devices and this is
showing me all of biological how how I'm
connecting those devices i'm actually
connecting so see here we wouldn't say
how many computers we have we would just
say what's our connection point from
those devices into our switches and
what's our IP addressing
on way and topology this is our wide
area network topologies we have a
representative of different ways up
there's a you have point-to-point
topology hub-and-spoke or a star cluster
you have been having spoken one way to
do it or it's called a star topology and
this is a full mesh topology this is a
topology that the reason it's called
mesh is because if one device goes down
so instead of sending my signal here at
this device and I'm sending my signal
here to here if this device goes down i
can just go directly or if this device
goes down and I was riding through here
to here then I could route directly over
to here but you get the point on that it
up its to allow better functionality or
better at fault tolerance now with
physical point-to-point topology we have
two devices connected through some type
of medium whether it's do you know up of
cloud but you've got your limited to two
notes when we're doing point-to-point we
connect those two together and they talk
to each other on local point-to-point
connection we cannot connect those two
and those frames just go through this
another expanded view of that and on
land topology there sometimes there are
some terms that you need to know that
when somebody says star topology you're
looking at this type of star because all
of them come to a point you're probably
going to have either a switch here or
router but most likely a switch i have
extended star topology where you might
have a switch here and you might have a
switch here that's managing and those
are connected into that Hardware you're
not going to put the switch on there but
you're just going to know that you've
got some kind of device that ties us
together bus topology is more what you
would see on a backbone you might have a
router here and so you would you might
have a switch here and so you would
switch in and you would have start our
polity connected into a bus topology
onto a backbone and then ring topology
we don't see a lot anymore with our
networking but you do need to understand
what it looks like and how it functions
and you'll get more of that material
inside the class
inside the Attic at course now some
terms that you need to understand as
well as half and full duplex so when you
hear someone or you read read somewhere
about half and full duplex we're talking
about the way we send the signal so a
half duplex is you can only be send and
receive it at one time so if i'm
receiving data the service receiving
data it cannot send so it has to wait to
send so it's half duplex so it's slower
so what you know we receive a signal and
then we were sent a signal back out with
full duplex we're sending and receiving
at the same time you have more chance of
collisions there's more bandwidth is
going to be used but you're going to get
information faster using that type of
for full duplex now when we have
contention based access that's where a
media is trying to fight with each other
and that used to happen when you would
have a hub in place and not many places
have hubs anymore but you will still see
them sometime and some of up some
companies still have the older
technology out there they still have
hubs hubs are do not regulate the
traffic they just send it on through
it's basically a rock a repeater I just
repeats the signal so when you have
contention based access they're all
trying to send so it's trying to send
when it's ready so it's looking to say
okay can i send this yet but there's
frames coming in and hitting each other
and colliding and then this one saying
okay as soon as I can get in there else
in my signal but that's a contention
based controlled access on a real ring
topology and on the token ring it would
wait for its turn and it would say okay
it
no it's my turn to send also else in my
packet and then the next one in line
i'll send his packet and then those
packets and then go around the ring
until they get to the proper destination
and then they will love drop off after
that and when you hear csma / CD that's
contention based access as well it will
send and it will have to wait because
it's receiving a framed it won't send it
won't send something out so you need to
you read more about you learn more about
csma / CD later in the course
another slide on that but I'm gonna go
passes you can pause the video if you
want to look at that and this is
Wireless csma and so if it's trying to
send and receive and so if it's trying
to if it's receiving the wireless frame
and this one sees the frame the channel
is going to be unavailable first picture
specific amount of time so it cannot
send you know the router and this device
might be connected and talking and so
they have to wait their turn and this is
all happening in split seconds I mean
it's all happening subseconds I mean
it's happening so fast that you don't
see this really anymore with the
bandwidth that we have
ok let's take a look at the data link
frame the frame when we when we frame
that data like frame it has a different
components to it it's got a header it's
got its data in there and it's got the
trailer and it sends that frame through
and it looks up like this as well you
would have your rob your header your
packet your dad in your trailer and
inside your head or you're going to have
your frame start you're going to have
you're addressing what type of frame
your control your data is built into
their your ones and zeros in there then
you would have error detection and frame
stop so basically what you're saying is
ok i'm sending a frame
here's my address information here's my
type here's my control error detection
is saying did I get all the ones and
zeros that were supposed to and here's
where I'm supposed to stop so when it
gets to this point it says that i drop
any packets and do i need to read
request that frame again or is it can
read that is it good information so a
layer to address looks very similar to
what we looked at earlier you're going
to up send it on so you have a layer to
your destination dick in your shorts
Nick but if it needs to go through
routing it's gonna have to add the layer
3 or it's going to use later three
so a switch is just going to use this
part here a router is going to use this
part here
and i'm just going to move this so you
have it going there later to heading is
still built in there so even though
you're sitting layer 2 and layer 3 the
layer 2 is getting red as well and
examples of layer two protocols or 802
11 wireless frame frame relay ethernet
frame
ok so this second video we recovered in
both videos for chapter four part 1 and
2 we covered how physical layer
protocols and service support
communications are in services support
communications across the network's you
how you can build a simple network using
appropriate media whether it's a copper
or wireless or some type of other medium
and we look to have data link layer
support communications across data
networks and compare media access
control techniques
ok thank you for watching again my name
is jason johnson and if you have found
this information helpful on any of these
videos just go ahead subscribe to see
new videos when they get posted and if
you have any questions you can leave a
comment below and I'll try to get back
with you as quick as possible and i hope
you have a great day and I should have
links in the upper upper right-hand
lower left-hand here that leads back to
part one and leads to a chapter 5