Welcome back to Foundations of Computer Science. This is the first of four courses in the Introduction to Computer Programming with Visual Basic Specialization. In this module, we're going to focus on computer networks, Cloud Computing and Information Security. Remember, in this first course, we're not actually rolling up our sleeves and writing any visual basic code. We're trying to give ourselves a solid foundation on the kinds of things our application needs to understand. So in this module we're going to think about specifically how communicating across computers connecting them together offers both opportunities and challenges. When you're done with this module, there's many things I hope you'll be able to do. You should be able to list common network topologies things like Boston star, and ring network topologies. You should be able to list some common network protocols things like HTTP and UDP and TCP. You should be able to list some common network services like SMTP for mail services, and HTTP for web services. You should be able to describe the three primary types of cloud computing infrastructure as a service, platform as a service and software as a service. You should be able to differentiate between the internet which is the set of protocols, the TCP IP protocols, and the World Wide Web, which is the HTML hyperlinking of documents. Those two terms are interchanged in society. I don't want you to do that after you've done this module, you should be able to explain the use of a hash function to encrypt passwords. We're going to use this in our information security so that we can keep our passwords protected. And lastly, I would like you to be able to describe different cybersecurity attacks including viruses, worms, Trojan horses, denial of service attacks and phishing attacks. All right, so lesson 1 here we're going to focus on networking. So let's define a computer network as a bunch of computing devices or nodes that are interconnected. We can wire together networks or they can be wireless and we're going to have different types of protocols or links to allow them to communicate. We'll first start talking about wired networks. This includes dial up broadband, which is cable modems and DSL We'll also talk about wireless networks where we'll have wireless lands, wireless wide area networks, municipal area networks, local area networks, and personal area networks. So let's start talking about a little bit of history. So it used to be that every household had a plain old telephone service coming to their home. It was a set of wires that came into the house that ran an analog signal. In the beginning of networking computers we used that Network and that network was switched, meaning there was some sort of operator or mechanical switch that connected it so each person on each side of the phone had a direct connection. If you ever watched Sesame Street you saw Lily Tomlin as a telephone operator and she plugged together and patch cable on the wall so that the two people talking had a direct connection. Same idea with the switches the switches would close to close up a connection. Okay. These used analog lines meaning we would send an analog signal across the lines, which was the sound wave. And that sound wave cannot be represented in a computer we use digital signals So we want to transmit digital data and so you in front of you, essentially what we're trying to do in the image is we marry up a digital signal that's drift from frequencies to be the level of the analog signal. And we would add a modem which is going essentially convert between the analog and digital signal on each side of the connection. These early ideas over the Pots over the plain old telephone system network gave us speeds up to 56 kbps. Here we're thinking of bandwidth as the capacity of data we can pass in a certain amount of time. We then moved into broadband networking and broadband network gain gave us transmission rates around 25 megabits per second or greater. This is what we use in our home internet connections. And often in the early days, we would have asymmetric download versus upload speeds. What that means is we would download quicker and upload slower and that's because the use cases we would tend to be downloading things like movies or songs or images and we'd upload text. We had what are called DSL lines digital subscriber lines, and these use phone lines but send digital signals on different frequencies in the voice connection. This gave us a download rate someplace between 5 and 50 megabits per second and upload rate someplace between 1 and 5 megabits per second. We also had cable modems. Cable modems used the cable that was designed to send the analog video for TV bites. They said data rates that were greater someplace around 100 megabits per second upload or sorry download, with upload speeds averaging between 3 and 5 megabits per second. We also have what we call local networking. Local networking started out in the 1970s with Ethernet. This was a dedicated coaxial cable that connected computers and we talked about topologies. We'll talk about, this a little bit more. This operated at speeds around 10 megabits per second. In the early 90s, we got what we, see a lot today which is Fast Ethernet. This is these coaxial four fiber optic or twisted pair cables. This gave us speeds around 100 megabits per second. And then in the late 90s we got to Gigabit Ethernet standards which are still really being rolled out in the local networks. This gave us speeds up to 1000 megabits per second. And this was an I triple E standard that came out of the gigabit networking research project. So I've thrown a lot of numbers at you. But to give you a sense of comparison of these wired connections, I have a table in front of you that shows how long it takes over the different line types to transmit 8 million bits. That's about one compressed image. So like a photograph on the internet. So on a dial up phone line, that's about 2.4 minutes, versus that 100 Gigabit Ethernet, it's very small amount of time, right 0.00008 seconds. So we'll take a little break here, we'll come back and we'll talk about wireless.
