Layer 1 - Physical Layer
Video Activity
Layer 1 Physical Layer Overview Our first lesson of the Cybrary CCNA course focuses on Layer 1 of the OSI Model, the physical Layer. You'll learn what is met by physical layer, what is met by working at that specific layer, and what if any interrelationship or impact exists with other layers in the OSI model. Then you'll observe diagrams and demons...
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Time
27 hours 46 minutes
Difficulty
Intermediate
CEU/CPE
31
Video Description
Layer 1 Physical Layer Overview Our first lesson of the Cybrary CCNA course focuses on Layer 1 of the OSI Model, the physical Layer. You'll learn what is met by physical layer, what is met by working at that specific layer, and what if any interrelationship or impact exists with other layers in the OSI model. Then you'll observe diagrams and demonstrations of component process flows which explain this concept in action.
Video Transcription
00:04
Let's get started. The physical, they're the physical, their deals with it,
00:08
stuff then you can touch.
00:12
For example, cables,
00:16
hubs and repeaters
00:18
do the three things that work specifically at the physical layer.
00:23
Now, sometimes in classes, I get a question, and some people ask, Well, Jenny, you said that the physical layer deals with devices that you can touch. I can touch a router now when we get to layer three. I will tell you at that time that routers work at the network layer earlier, three.
00:40
And you can touched a router. So why does it not work at the physical layer?
00:44
The answer is when I see a router works at the network where I mean it works at the network layer and all lives below.
00:52
When a device works at the physical layer, there's nothing below that layer it on. Lee works at the physical wear. A router, for example, again will work at the network layer, the data link clear and the physical. The three device types that work on Lee at the physical layer Number one would be cabling. Your cabling number two
01:11
would be a repeaters,
01:12
and number three would be your hubs
01:17
now covering cable types.
01:19
The first cable type is your ex based T cabling.
01:23
Everybody commonly known that no this as your eternity cabling
01:27
the X in the X based T stands for the speed of the cable.
01:33
The base, The word base stands for bass band signaling,
01:37
and the letter T stands for twisted pair.
01:41
Now let's look at X.
01:42
If that first X X pasty is the number 10 that means the cable can transmit at 10 megabits per second.
01:51
If that number is 100 it can transmit at 100 megabits per second. And if it is 1000 that means the cable can transmit at 1000 megabits per second, also called a gigabit.
02:04
Now
02:06
the base in the X based T stands for based band Signaling
02:10
Base Man singling means that they can only be one signal on the wire at a time
02:17
as opposed to the opposite off that you guys all have. It at home is called broadband singling, where you have more than one signal
02:25
as you may have more than one channel at home, and your cable also carries your Internet so you can have more than one signal on the wire at one time.
02:35
The tea
02:37
in base X based E stands for twisted pair. That is simply mean. That simply means that eight wires or four pairs of wires have been twisted together to form that cable.
02:47
Now, for those of you that are wondering
02:50
why, sometimes when you go to Best Buy, you can buy a Category four cable or a Category five cable or a Category three cable
02:58
that's simply
03:00
Category three Category four, Category five. Different simply in the fact that Category five has more twists per meter of wire than a Category three andMe or twists means you have more copper. More copper means a cleaner signal.
03:15
That's the only difference.
03:16
No ex pasty candling
03:20
come in two flavors.
03:22
They can either be straight through or they can be cross over
03:25
for the purposes of C, C and A. All you need to remember is like device types or similar device types will use a crossover cable between them,
03:37
unlike device types, or two different device types will use a straight through cable between them.
03:44
So an end host, like a computer and a switch, will use a straight to cable
03:50
if do you have a connection between a router and a switch. You also use a straight through cable.
03:55
If you're connecting two switches together,
03:59
you're gonna have a crossover cable. If you're connecting to rounders together on the eating that porch again, you're gonna have a crossover cable. The last connection type is your connection between a PC, Ethernet and a router eternity that will use a crossover cable. Also
04:16
moving on
04:17
expense T cables also are. There are two types of ex pasty cables. One is your shield, a twisted pair, and the other one is your unshielded twisted pair.
04:28
The unshielded twisted pair are the ones that you're familiar with that you
04:32
use at home for you. Lieutenant Connections.
04:34
The Shield of twisted pair is only used in places where they might be electromagnetic interference.
04:42
Now, every device that runs an electric current through them, like a refrigerator or an air conditioning unit, produces an electromagnetic field. If you run a regular cable or an unshielded twisted pair cable behind that device behind a refrigerator or an air conditioning unit, you might have signal degradation,
05:00
so the signal might not be clean and pure
05:02
to prevent against that, their cables made with a special shielding around them. And when you run a cable behind the device that produces an electromagnetic field, you run a shield. It twisted pair cable
05:15
the other 10 cable types that you need to remember our your
05:19
serial cable or the V 0.35 cable.
05:24
The serial cable is connected to a serial port on a router.
05:29
So between the router and another router, you will run a serial cable,
05:34
the last cable tied that I'm going to cover our your rollover cables
05:40
or your consul cables.
05:42
So from the console port off Cisco device, which is located in the rear of the device, and it actually saves console to the com port or the communications port off your PC,
05:53
you will run.
05:54
I roll over cable.
05:56
This cable is actually the cable that enables you to directly connect to a router so you would run
06:02
a council cable from the council porter for outer to the com port of your PC, and then you will open up a terminal emulation program such as terror term or Putty. And then, as soon as you open up that program and your power on the device immediately, you will see that your own counsel that you logged into the router or the PC
06:21
that concludes
06:24
the cable types that were supposed to cover for CCNET.
06:27
The next device that I'm going to cover that works on Lee at the physical layer is your repeater.
06:32
So a very rudimentary diagram about offer repeater. Let's say this box is a repeater.
06:41
Now a repeater does exactly what the name says it does.
06:45
An ex pasty cable is capable of carrying a signal for a total of 100 meters after 100 meters. No guarantees air made that the signal will not degrade.
06:56
So whatever Peter does
06:58
is if the signal is coming inbound on a cable this way,
07:01
it will repeat it out and amplify it for another 100 meters.
07:08
Usually, if repeaters are being used in a network, the network wasn't properly designed. Or at least that's my opinion.
07:16
Now what is a hub?
07:18
Ah, Hub is nothing more than a multi port repeater. We change the name of this device over from a repeater to ah hub and we go ahead and connect three PCs to it or four pieces to it. These little boxes represent PCs. And let's say this is PC one
07:38
pc to
07:40
PC three and P C four and PC one sends a transmission.
07:46
The hub will flood the signal out every other port
07:51
to all other devices
07:54
except the port that originated the signal. So it makes sense. PC one sent the signal You don't want PC one receiving the same signal back so hard will repeat
08:03
the signal out or flood the signal out all other ports except the one that originated the signal.
08:11
Remember that Because on the CCN exam there is a question.
08:16
What does the hub do? And the first answer that you will see it will say a hub floods out
08:22
a signal received on one port out of all other ports. And if you pick that answer and move on, you probably got the question wrong because answer f might see Hub takes a signal in one port and floods it out. All other ports except the one that originated the signal. You just got that question wrong because you didn't read far enough
08:41
and answer f is more correct.
08:43
Then just saying Hub takes a signal in one port and floods it out all of the porch. You need those words except the poor that originated the signal.
08:52
At this point, we have concluded
08:54
our physical Lear
08:56
for the CCN A CC and their physical. Their questions aren't very extensive. They're pretty simple.
09:03
For the most part, you might get asked what a hub does. And as long as you remember that Ah ha takes a signal in one port. And I know I'm repeating myself, and that's for a reason. Takes a signal in one port, repeats it out off all of the ports except the port that originated the signal.
09:18
As long as you remember that you, Neil
09:22
the physical layer stuff on your CCN exam.
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