Let's get started the physical layer, The physical layer deals with stuff that you can touch, For example, Cables, Hubs and repeaters. These are the three things that work specifically at the physical layer now sometimes in classes. I get a question and some people ask well Junaid. 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 after the network layer or layer 3 and you can touch a router. So why does it not work at the physical layer? The answer is: when I see a router works at the network layer, I mean it works at the network layer and all layers below when a device works at the physical layer. There's nothing below that layer. It only works at the physical layer.

A router, For example, Again will work at the network layer, The data link layer and the physical layer. The 3 device types that work only at the physical layer number one would be cabling. Your cabling number two would be a repeaters and number three would be your hubs now covering cable types. The first cable type is your X base. T cabling everybody commonly known that.

I know this as your Ethernet cabling, The X in the X base. T stands for the speed of the cable the base. The word base stands for baseband signaling and the letter T stands for twisted pair now.

Let's look at X. If that first X in X base T is the number 10 that means the cable can transmit at 10 megabits per second. If that number is a hundred, It can transmit at 100 megabits per second, And if it is a thousand, That means the cable can transmit at a thousand megabits per second also called a gigabit. Now the base in the X base T stands for baseband signaling, Baseband signaling means that t can only be one signal on the wire at a time, As opposed to the opposite of that. You all have it at home.

It's called broadband signaling, Where you have more than one signal, 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. The T in base X base T stands for twisted pair. That is simply me that simply means that eight wires or four pairs of wires have been twisted together to form that cable. Now, For those of you that are wondering why sometimes when you go to Best Buy, You can buy a category four cable or a category 5 cable or a category 3 cable. That's simply! Category 3! Category 4 category 5 differs in the fact that category 5 has more twists per meter of wire than a category 3 and more twists means you have more copper, More copper means a cleaner signal.

That's the only difference now X base T cabling come in two flavors. T can either be straight through or t can be crossover for the purposes of CCNA. All you need to remember is like device types or similar device types will use a crossover cable between them, Unlike device types or two different device types will use a straight through cable between them, So an end host like a computer and a switch will use a Straight to cable, If do you have a connection between a router and a switch? You will also use a straight through cable if you're connecting two switches together, You're going to have a crossover cable if you are connecting two routers together on the ethernet port again, You're gonna have a crossover, Cable. The last connection type is your connection between a PC, Ethernet and a router Ethernet that will use a crossover, Cable. Also moving on X means T cables.

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Also, Are there are two types of X based T cables? One is your shielded twisted-pair and the other one. Is your unshielded twisted-pair, The unshielded twisted-pair are the ones that you are familiar with, That you use at home for your Ethernet connections. The shielded twisted-pair is only used in places where there might be electromagnetic interference 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, So the signal might not be clean and pure to Prevent against that there are 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 shielded, Twisted-pair, Cable, The other tip, Cable types that you need to remember are your serial, Cable or the V: dot. 35.

Cable. The serial cable is connected to a serial port on a router, So between a router and another router, You will run a serial cable. The last cable type that I'm going to cover are your rollover cables or your console cables. So from the console port of a Cisco device which is located in the rear of the device - and it actually says, Console to the comm port or the communications port of your PC, You will run a rollover cable. This cable is actually the cable that enables you to directly connect to a router.

So you would run a console cable from the console port of a router to the comm port of your PC. And then you will open up a terminal emulation program such as teraterm or putty, And then, As soon as you open up that program and you power on the device immediately, You will see that your on console that you are logged into the router or the PC That concludes the cable types that we're supposed to cover for CCNA the next device that I'm going to cover that works only at the physical layer is your repeater. So a very rudimentary diagram about our repeater. Let's say this box is a repeater.

Now a repeater does exactly what the name an X based E cable is capable of carrying a signal for a total of 100 meters after 100 meters, No guarantees are made that the signal will not degrade. So what a repeater does is if a signal is coming inbound on a cable. This way, It will repeat it out and amplify it for another 100 meters. Usually, If repeaters are being used in a network, The network wasn't properly designed - or at least that's my opinion. Now, What is a hub, A hub, Is nothing more than a multi-port repeater.

We change the name of this device over from a repeater to a hub and we go ahead and connect 3, Pcs to it or 4 pcs to it. These little boxes represent pcs, And let's say this is pc-1 pc2, Pc, 3 and pc 4 and PC 1 sends a transmission. The hub will flood the signal out every other port to all of the devices except the port. That originated the signal, So it makes sense.

Pc once sent the signal. You don't want PC one receiving the same signal back, So a hub will repeat the signal out or flood the signal out, All other port except the one that originated the signal. Remember that, Because, On the CCNA exam there is a question, What does a hub do and the first answer that you will see it will say: a hub floods out 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 say a 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 and answer F is more correct than just saying: aha takes a signal in one port and floods: it out all of the ports.

You need those words except the port. That originated the signal. At this point, We have concluded our physical layer for the CC. The CCNA physical, Their questions aren't very extensive, T're, Pretty simple. For the most part, You might get asked what a hub does and as long as you remember that a hub takes a signal in one port, And I know I'm repeating myself and that's for a reason.

Hub takes a signal in one port, Repeats it out of all of the ports except the port. That originated the signal as long as you remember that you knew the physical layer stuff on your CCNA exam,

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