Okay, so we talked about how the OS I model is a top down model. So the sending computer, the data starts out at the application layer and travels down through the OS on. That's very much true. However, I've found that the S I model is easier to understand from the bottom up, because at the lower levels,
you really have less sophisticated technology.
And as we go up through the S, I model, things get more complex. So let's go ahead and look at it from the physical layer up layer one. So at the physical layer, honestly, these air really are dumb devices and by dumb devices, what I mean is those devices that don't have a lot of decision making capability, they don't really have a lot of intelligence to the,
you know, think about cable
this cable know where your dad is going. Cable doesn't care where your dad is going. Cables just there.
Ah, hub. Ah, Hub doesn't care where your dad is going either. Hub doesn't address, doesn't really add anything, doesn't do anything. But in fact, it's just really a place for the signal to travel across hubs back in the day. passive hubs
used to just be a metal rack that provided a conduit for the signal. And now, of course, you know. And then that didn't take long before we had active hubs. That would boost the signal. They're still layer one devices they still don't do addressing or any other real intelligence
layer. One stuff is about the cable and sending signal just across the wire. Now there's a portion of the network Cartoon Network interface card, the nick that does. You know, that's just physical layer stuff. It gives me a place to plug in to the cable, and Nick is one of those devices that operates it both
at two different layers.
Both the physical layer and the data link layer, which is next. So it later one. We've got hubs. We've got cable, we've got connectors. We get all of those elements that are really just about
signal on the wire conversion of signal from analog to digital, like a modem. Does
connective ity that sort of thing? All right, so cable.
The question is, do you have to know cable lengths and Cat three versus Cat five or Step Daddy, Here's the way I look at that. If you are a network person from way back, refreshed this in your memory,
I would expect you for network person to spend some time and say, OK, 10 base five stick net cable that used vampire tap. It could get 500 meters without attenuation.
If you're not a network person, please do not spend your time here. You have far bigger fish to fry than memorizing cable lates. Okay, if I were to pick out what I really thought was testable from here, twisted pair cabling is the least secure. It's susceptible to eavesdropping.
It's susceptible to interference, like electromagnetic interference,
radio frequency interference. Ah, easy to eavesdrop, easy to tap into. So naturally, that would be our first choice for networks. And it's true. And the reason for that is in networks. Many decisions are made on two words. We like cheap that we like easy,
and if I could get the two of those together
score many times, those two words supersedes secure, and that has the case and go into most networks today, UNC Twisted payer.
Now the more secure option would be fiber optic cable or fiber fiber goes much greater distances sends signals of lighter pulses of light, so it's not as susceptible nowhere near susceptible to eavesdropping. It's not susceptible to enter, uh, interference,
but again it it's more expensive and it's harder to work with.
And that's very true. So you know, many times we make our choices once again cost benefit analysis. Will I trade some security for ease of use and cost? A lot of times, the answer is yes.
Watch for a question like this.
You're you've been asked to conduct a side assessment for your new data center and to recommend specifically the type of cabling that should be used. What cable do you recommend keeping in mind? Your boss has asked you to keep costs low.
The answer is, you recommend fiber optic. Now I know that part about keeping call slow. Makes you want to say, Oh, twisted pair. But here's the thing.
People will always tell you to keep costs low. I have never had a manager just throw money at me and say you spend the most money you can't write. That doesn't happen. So the fact that he said keep costs low,
find a good deal on fiber
now in the reality. The fiber runs to the data center and in the data center, we usually have twist appear. Don't go down that trail. They didn't really specify what they meant.
If they say you're in a secure data center, they want fiber optic cable. OK, so make sure you get that also physical layer stuff. How doe I connect the computers. What sort of wiring arrangement? Now, honestly, this is kind of network plus stuff.
You know, this isn't really something that I think coming would would show up on the C I s SP exam.
This is some pretty basic stuff, but I leave it on here just for the fact that I know some of you are new to networking. And the configuration that we're using today is the star configuration. We connect our systems into a switch, and a lot of times we have switched to switch connections.
Ah, switch to router connections, whatever that might be switched
whatever. But the bottom line is traditionally like back in the old days. If you've heard of 10 based T networks 10 based to 10 base five, we were using co ax cable in the tin base. Two and 10 base five networks, and we have them arranged in a bus and you could tell a bus by a central trunk of cable.
And then the systems would connect into that central trunk.
If you've heard of token ring technology, which was popular at the times of the early Ethernet networks, but it's really gone away. Ah, for the most part
and the token ring networks, hence the name token rain, were connected in a ring. And you know the problem with this true ring configuration is that it? If there's a break in the cable or one computer goes down, nobody else can communicate so later. What they did is they brought something called a multi station access unit amount
into the center and rather having
than having all the computers connected, uh, in in a giant ring. They actually connected into the mouth, and the ring passing happened in the middle. In the multi station access, you know,
are switched Network star. Everybody's connected in Ah, if a computer goes down, it doesn't matter. But if the switch goes down, we have a problem. Mesh environments. Uhm, you can either have a full match, your partial mess.
So the idea behind the mash is Let's get redundancy in there, every computers connected to every other computer in every possible way.
So that would be a full mash. Partial mash means we have more than one route from pathway to pet be. And usually you don't see this with computers. You might see this with ran connections. You know, Branch Office A's connected branch off speak. You might see a partial match back in the server room,
you know, to allow redundancy from switch to switch around round or switched around her.
Um, but you certainly don't see this out on the floor from computer to computer. So those air physical apologies again. Um, you know the basic devices Hub modem, wireless access points bridge the gap between the wireless medium and the wired connective wired medium. Those are all layer one devices.
And then, if I were to look it, threats associated with layer one.
In a lot of ways, we're thinking about physical threats like vandalism, theft,
unauthorized access to a system, um, tapping into a networks of sniffing the Network Data Emanation, which we'll talk about in Chapter five. But all electronic devices admit some form of radiation. So can I analyze that information? Learned anything meaningful?
Ah, so those would all be attacks at layer one
so later won the bottom layer of the O. S. I modeled layer one physically.