 A quick welcome to ITS 323, Introduction to Data Communications. My name is Stephen Gordon, I'm your lecturer for this course. The first time I've taught you as a group of students, I'll teach you again in some courses next semester too. This is, as the title suggests, your first coverage of communications, computer communications and computer networking. The internet, mobile communications, mobile phones and the technologies behind them. In fact, next semester I teach a lab, IT Lab 2 that is based upon this course. That is we do some practical hands-on activities in a lab about setting up networks, building and testing networks. So that's next semester. And in fact next semester you have another course called ITS 325, Computer Network Architectures and Protocols, taught by Dr. Conworth, someone else. But again that also covers communications, the internet and network. So this is the first of several courses for you about computer communications and networking. Let's talk and give an introduction to data communications and networks and then when I've covered this topic, it doesn't take too long, it's just a very light introduction, then I'll talk about the course structure at the end of the lecture. So we can get straight into the technical details first. In fact this lecture which we'll finish today is just mentioning some terminology, some definitions and some concepts, the details of which we'll cover in other lectures, in later lectures. So if you don't catch all of it, you don't understand the details, don't worry too much from this lecture, you'll catch up throughout the semester. The topic is introduction to data communications. What is data communications? What do we mean by it? Well communications, when we communicate, we're sharing information. Whether it's between computers or between humans, if I'm talking to one person face to face then I'm sharing information with that person. I'm talking to you as a class, I'm trying to share information that I have. I want to get it into your brains, so I want to communicate something to you. Of course we sometimes want to communicate over a larger distance than just across a room. So we have remote sharing information across between rooms, between buildings, between cities anywhere in the world. We have remote communications or sometimes we use the word telecommunications, tele meaning over a large distance. So not just between humans, we'd also like computers or computing devices to also be able to share information. Data, data communications, well what do we mean by data here? It's the information being shared, whatever that information is. The examples being text, some textual message that we want to share from one computer device to another, numbers, images, audio and video are the main things that we want to share between computing devices. So you want to make a voice call over the internet, voice over IP then the information is audio, your voice. You want to get it from your computer, from you and your computer to your friend's computer so they can hear what you're saying. So data communications is the exchange of data and here's some examples of the data between two or more devices via some transmission medium. Exchange of data, two devices, well that's a common example we think of. I connect one computer to another. We send data from one computer to another, two devices are sharing information but there are other cases where one device will send information to many devices at once. An example not with computers but with humans is this lecture. I'm communicating information from one person to 20 or 30 people at the same time. So it's not always between just two devices, it's sometimes say from one computer send to many computers, so two or more devices. And we say via some transmission medium. The transmission medium thing at this moment is the thing between those devices. I want to get data from this laptop to this PC. Then we'd say between them we have some transmission medium. The medium over which we transmit that information. It may be a cable that's plugged into my laptop and plugs into this PC. So the transmission medium would be that cable or the copper wires inside that cable or there may be other transmission mediums. What's the medium I'm using to communicate to you in this lecture? If I ignore the microphone but me talking to you, what would you say the transmission medium is? I've never seen in the lecture before. Try someone else. Louder. Air. Air is a medium. So when I'm talking the audio, the information is going from the transmitter, me to your ears, the receivers, and the medium would say is air in this case. It's wireless transmission. So the medium think is the thing between the two devices communicating. So that's an example of wireless. Of course we also use in many cases wires or wired communications. So that's a simple explanation of what we mean by data communications. So we want to get information from one point to another, one to many others via some medium. How do we do that so that it works well? It may be that we have some technology to get information from my laptop to this PC but in fact we want it to be effective to work well. So how do we measure that? What do we mean by effective data communications, good data communications? Three different things that we can use to measure here. Delivery accuracy and timeliness. We want that information to be delivered to the correct destination. We want the information that is delivered to that destination to be an accurate representation of what was sent, to be accurate. And we often want that information to be delivered in a short amount of time, in a timely manner. Some examples, first some simple examples to do with real life. I want to send an email. I have some girl that I like and I want to express my feelings to her. So I write this email, I love you and so many other words. And I type in her address, her to address and I press send. And it goes into the internet, this email, out from my computer into this magic thing, the internet and it goes through the internet and it arrives not at that girl that I sent it to but at someone else's computer. That would be an example of ineffective communications because I've sent an email to someone I want to say I love you to and it's gone to someone else. So that's not good for me. We'd say that's inaccurate delivery or that's not correct delivery because the data was not delivered to the correct destination. If our communication system does not deliver to the correct destination, then it's no good. It's not good communications. So that's almost an obvious one. If I send something to computer A, it should get to computer A, not to computer B, that's delivery. Accuracy, I compose my email, I love you. It goes out into the internet and somehow the internet makes some mistakes and it arrives at that girl and it says I hate you. Again, that's not effective communications because what was received is not an accurate representation of what was sent. We have not conveyed that information correctly to the destination. So in any communication system, when we send something, what is received should be a good representation of what was sent. We say an accurate representation. In some cases it doesn't have to be 100% accurate. With an email we'd expect it to be. I type in my email, the email that a person receives should be exactly the same as what I typed in. That is 100% the same, 100% accurate. If there's a letter different, it won't be so bad but I don't think it's a good communication system. But in some applications, I have some information, I send it, even if what's received is not exactly the same as what was sent, it still may be effective communications. What's an application where that works? What's received is not the same as what was sent, but it's still effective. Think of the applications you may use on the internet, the types of applications. Not sending an email, because if I send an email and the email that the person reads is different, that's not good. Any other applications that you send? You don't need 100% accuracy. Has anyone used Skype or a similar voice over the internet application? A picture in some cases, let's use Skype, a voice call as an example, where you use your laptop and you make a call to someone and talk. What happens there is that when you talk, it goes into the microphone of the computer and the computer takes that information and sends across the internet. What the other computer receives doesn't have to be exactly the same as what you sent, because what you send is a digital representation of some audio, some sound waves. So long as when it's played back at the receiver, it sounds like my voice and that the receiver can understand what I'm saying, even if it's low quality audio, it's still okay. Same when you talk on a mobile phone. The person who talks is talking clearly, but sometimes the receiver has some bad reception and words cut in and out. It's poor quality. It still works though, you can still talk. So that's an example of even though the receiver doesn't receive exactly what was sent, we'd still consider it accurate because the receiver can still understand what was sent. So depending upon the application, we measure accuracy differently. Sometimes we need 100% accuracy, sometimes not so much. We'll see other examples of that in subsequent lectures, just a light introduction. Timeliness, I send my email, I love you, send to the girl. It arrives one year later. She's gone and got married to someone else, again ineffective for me. So we want data to arrive at the destination in a reasonable amount of time. How long for an email? You press send. How long do you think it should take to be good for the other person to receive it? What do you think? Less than a minute, okay, anyone can wait, cannot wait for one minute for an email? What about if it took one hour for an email? Would you be happy? You wouldn't care? You wouldn't know? One hour, sometimes you wouldn't know. Sometimes emails are delayed for a long time, okay, so it changes depending upon the application. What about instant messaging, you're using Line or some instant messaging application, you type in a message, press send, the other person sitting at their computer, how long do you think it should take for that message to get to the other person? One hour? One hour is not good enough, is it? One hour would mean it's not instant messaging, okay. You're talking more in terms of seconds, I don't know whether it's 10 seconds, 1 second. If it's 10 seconds, it's not so good, if it's 1 second, I can survive. So it depends upon the application as to what is a reasonable amount of time. So again, we'll look at different applications through this course and we'll talk about some examples there. So we want to communicate data from one point to another, get to the right destination, do it accurately and timely in a timely manner. That's data communications. We or people need to build computer systems that allow communications between devices. What do they need to do to build computer networks, telephone systems and so on to allow it to work? Well, we can start by simplifying communications into some model that we can follow and this is an example or this is one simple model of a communication system. We have five components in this model. We have a source. The source is some device that generates the data to be transmitted. An example is, and it's actually on the next slide, an example is my laptop. In fact, I sit at my laptop, I type in a message, think is that is the process of generating the data. That's the information I want to communicate to someone. I create the data at the source. Then we have another entity, a transmitter that takes that data, say an email, where that email is actually just a sequence of bits, zeros and ones and it converts that data into some signal that can be sent through our communication system. The next slide shows that, I said a laptop here in this old picture, it says a work station but imagine this is a laptop and maybe the transmitter device is a modem that's attached to my laptop, a home ADSL modem, which takes some digital signal and transmits some analog signal across the telephone network. We're going to spend a lot of this course before the midterm talking about to get something from one device to another, we send signals. Think of some oscillating signal, some sine wave, some electrical signal, some radio signal. That's what we're going to focus on and spend some detail in the first few lectures. That's what's sent and carries the information between devices. The source creates the data, the transmitter converts that data into a signal and sends or transmits that signal through the transmission system, through our transmission media, for example. The transmission system carries the data as a signal from source to destination. At the other end point, the receiver, it takes the signal, converts it back to the data and then the data is, let's say, consumed by the destination. The destination makes use of that data. We can treat usually the source and transmitter together as the source system and the receiver and destination as the destination system. Another example, my laptop has a socket for the LAN card or LAN cable. Think of that as the transmitter. That's inside my laptop. My laptop is the source and has a device or a chip in there that acts as the transmitter. Then the cable, when I plug it in, if I plug in one of these normal LAN cables into here and it connects to the receiving device on the back of this computer, think of this as our transmission system. It's a very simple one in this case. It's just a single cable. In more complex networks, the transmission system may consist not just of one cable but other intermediate devices connected together. So, communications is simple because all we need is these five components. But in fact, the problem is the things that each component must do to make communications work well, to be effective, are quite complex, in fact. What the transmitter must do to convert data into a signal can be very complex. The transmission system can be much more complex than a single cable. This is, as we say, a simplified view of any communication system. Source and destination transmits information to a receiver via some transmission system. That was one example, I think, maybe, okay, let's say laptop, some home ADSL modem connects via a telephone network to some server which is also attached to a modem, where we send data, the source, transmitter, transmission system, receiver, and the destination. We will see other examples that follow that model through this course. So, if we think of any communication system as this model of five components, it looks easy. But the reason why we have this course and you have courses next semester is because it's not so easy. In fact, to work in an effective manner, there are many different tasks that have to be performed. And we're going to spend this course looking at those tasks. Here are some of them listed. You don't have to understand these. We're going to go through a lot of them during this semester. Somehow we need to generate, for example, electrical signals to send across a wire. How do we generate those signals? What type of signals? Sometimes we send some signal across a system and there are some errors. There's interference. Something goes wrong. So we may want to detect if there are any errors. But if we detect errors, correct them. So there are different ways to perform error detection and error correction. So we'll look at some examples of that. I want to send a message to an individual student in this class by telling them something. How could I send a message to one particular student in this class? What do I need if I want to talk? I need their name. So if I want to send a message, if I say something, you got a D in your exam. Who receives it? Well, no one knows who it's intended to. But if I say Steve, you got a D in your exam, then Steve would know it's intended to him. So to communicate with devices, we need some addressing scheme. In your case, your address is your name. In computers, we have different addressing schemes. You would have seen IP addresses. Maybe you set up your computer for internet access. You may see an address like 192.168.1.1. That's a type of address that we use in computer networks. We need security mechanisms. In this course, we're not going to touch upon security mechanisms. Most of you will take IT security next semester. Actually, I teach that as well. And then you'll see some more aspects of security. In this course, we don't have time to cover it. And other tasks. The point is to have communications work in a large system. There are many complex things to do. And therefore, it's not as simple as this five block model makes it look. And that's what we're going to cover this semester. How these complex things work. So the people have come in. What we're doing is we're going through a very quick introduction to some aspects of data communications. At the end of today, we're going to talk a bit more about the core structure. And the details of things that I'm mentioning today, we're going to cover in subsequent lectures. So even if you don't catch everything today, next week, the week after, it will come back and we'll repeat some of these things. It doesn't mean go to sleep, but it means don't be too stressed at the moment. To categorize different technologies we use for communications, we can roughly divide them into two groups. The technologies used for communicating across a single link. And for those for communicating across multiple links or a network. A single link is when I plug a cable into laptop, into PC, they're directly connected together. How do we get data from one to another via that link? Well, sometimes that's referred as data communications. Transmitting signals in a reliable and efficient manner across individual links. How to get it from A to B across one link. Unfortunately, most of the things we want to achieve today cannot be achieved by just communicating from one computer direct to one other computer. Because I want to connect to Google and do a search for the Google web server. I cannot plug a cable into my laptop and then another cable into the Google web server. A, I don't have a cable long enough. B, the Google web server doesn't have enough ports to have everyone's computer in the world plug into it, okay? So what we do then is we connect from one computer to another device. That connects to some other device and we keep making connections until we find a path that gets from my source computer to the Google web server. And that's a network. I think at this stage a network is when we, or networks allow communications across multiple links. And there are different problems and therefore different technologies used depending on whether we're considering communications across a single link, simply data communications, or communications across a set of links or across a network. So we sometimes distinguish the two. We'll talk about each of them just briefly. Data communications across one link. What are some of the issues? Well, in fact, we've covered it a bit. This is almost the same diagram as we saw before. And I think there's not much more to say in that. Think for a single link. We have a source system, a destination system, and we send across a single link here represented by the transmission system. So we take our data, for example, some text. We may represent it as some sequence of bits. If it's an email, we can use ASCII encoding to represent, to convert it down to a sequence of zeros and ones bits. And the transmitter takes that stream of bits and creates some signal to send across our link. If the link is made up of this cable, just a normal LAN cable, I'm sure you've used these on a regular basis, have you ever cut one in half? If you cut it in half, in fact, you can see from the end points, it's made up of eight different wires. You cannot see very well. But there are eight different wires in here, or eight white, green, blue, orange and brown-coated wiring in here. In fact, each of them are twisted around, and we get what's called twisted pair-caven. We'll cover the details of that later. But inside these wires are just copper, strands of copper. And if this is our link, the signal that we send across it is just electricity, an electrical signal, which somehow carries the information from one end point to the other end point. So from our transmitter to the receiver. Electrical signal is received, and then the receiver has the job of converting it back to some bits, some zeros and ones, which are consumed at the destination. So we're going to spend a few lectures looking at how to transmit different signals and what type of mediums, media can we have in between the transmitter and receiver? The thing in between, when we just have a single link between transmitter and receiver, this cable is sometimes simply the transmission line. It's a line between one point and another. It's important because that's where we send our data via. It's that link between transmitter and receiver. When we build a network, when we build a transmission system, you go and get a job, and your job is to design and build a link between one computer device and another computer device. Then you need to choose which transmission line to use, which one's best. And to do that, you need to think about choosing one that provides the required capacity, is reliable and is cheap. Let's explain those three. I want to get some data from this laptop to this PC. Just a single link. I want to transfer a file. It's a small file, 100 bytes, small file. I just want to get from this laptop to this PC. What are some different transmission mediums or transmission links or technologies that I could use to communicate from the laptop to PC? Can anyone name some? A USB key, okay. Correct, except it involves a human. I have to plug it in and then unplug and plug it into the other one. But yeah, that's a transmission system. It involves the human. But we can even use a USB cable. You can buy cables that plug into one USB socket and go into the other. Not so common. So USB is one. Another one. To transfer data from laptop to PC. Okay, the SATA that you use for the hard disks. Okay, yep. Bluetooth, okay, my laptop has Bluetooth. I don't think the PC does. Some PCs, you can get Bluetooth or you plug in a Bluetooth adapter, USB adapter. So then we could use Bluetooth. And Bluetooth uses what medium? What is the medium that Bluetooth uses to send data from here to here? Wireless or simply air. It's a wireless transmission system. Bluetooth, it transmits some signal through the air and it's received here. What else could I use? USB, some hard drive SATA cable, Bluetooth. This LAN cable, okay. Sometimes called Ethernet or just a LAN cable and plug it in here, connect here, set it up, send my file across there. Another one. There's an antenna here. Wi-Fi, okay. So there is different technologies I could use to get this 100-byte file between them. Okay, let's cut some. We had Wi-Fi, we had the LAN cable, Bluetooth and for simplicity, let's leave it for those three. There were others, but just keep my example simple. Now I want to transfer of burnt 10 DVDs onto my hard drive. So I've got about 50 gigabytes on my hard drive. I want to transfer that 50 gigabytes to the PC. Choice of Bluetooth, Wi-Fi or the LAN cable. We'll have a vote. Hands up for Bluetooth. Anyone? I want to get 50 gigabytes from laptop to PC, Bluetooth. Why not Bluetooth? No one put their hand up. Why not? Cheap. It's slow. If anyone's used Bluetooth to transfer much, it's quite slow to transfer a large amount of data. Usually it's in the order of one megabit per second, one million bits per second. What did I say? 50 gigabytes, which is 50,000 megabytes. We'll look at units and prefixes later, but 50,000 megabytes is the amount of data I want to get from A to B. Bluetooth allows me to send it, let's say, one megabit per second. That's the speed. How many bits in a byte? Eight. So 50,000 megabytes is 400,000 megabits. 400,000 million bits. There should be bit. So if I want to transfer my data at one megabit per second, I've got 400,000 megabits, it would take me 400,000 seconds, okay? I don't know, that's 30, 20 hours or something. So it takes a long time to transfer that data from one computer to another. That's why we wouldn't use Bluetooth. Well, that's one reason. Bluetooth is cheap. The devices are inbuilt to the laptop, but slow, Wi-Fi, both have Wi-Fi. Would you choose Wi-Fi? You've got two choices left, Wi-Fi or the LAN cable, hands up for Wi-Fi. Anyone, anyone game? You may use Wi-Fi. How fast is Wi-Fi? Bluetooth is one megabit per second. It depends. It depends upon your device, how much you paid for your laptop or how old it is. I think the one in the PC is quite old. It's around 54 megabits per second. So it's about 50 times faster than Bluetooth. So it would be taking the matter of tens of minutes, maybe an hour or so. I can't do the calculations in my head, but it would be much faster than Bluetooth if we use Wi-Fi. LAN cable, how fast? These are reasonably, well, they're not too old. The LAN cable, most recent LAN cards in computers, laptops and PCs, can go up to one gigabit per second or 1,000 megabits per second. Just plug the cable in, set them up, 400 seconds. What, seven minutes to transfer my 10 DVDs from one computer to another. There's just rough calculations. So what's all this about? These speeds, we'd say are the maximum speeds of the transmission line. That's the fastest we can go. It's also called the capacity. When we choose a technology, we want to choose one which will provide the required capacity. When I wanted to transfer this 100 byte file, 100 bytes is very small. I don't care if it's at one megabit per second or 1,000 megabits per second. It's still gonna be a few seconds to transfer. Doesn't matter. But if I have a lot of data, then I'll require a higher capacity. And therefore I may choose a different technology. I would choose a technology with a higher capacity. So when you need to design and build networks, you need to choose the transmission line, the technology for that transmission line that gives a high enough capacity. We will see many or different examples of these technologies and also wired technologies through this course. You don't need to remember this information, but we'll see some other details later. But it's good to be able to have an idea that your LAN is normally much faster than Wi-Fi, which is much faster than Bluetooth. Acceptable reliability, well, some transmission systems have more errors than others, less reliable. Especially wireless is less reliable than wired, even at the same capacity, which means if I use Wi-Fi, I transmit the data, some of the data received is not correct. It's different from what was sent, their errors. I'll have to send it again and that slows things down even more. So we need to consider not just the capacity, but also reliability, how reliable that system is. I want it to be cheap as well. I could go and buy some special device that gives me 10 gigabits per second and then buy one from here. It costs 5,000 baht for this laptop, 5,000 baht for this laptop. Gives me 10 times increase in speed, but it's cost me 10,000 baht, okay? So it may not be as cheap as I want. We need to consider the trade-off between capacity, reliability, and cost. We have a topic that's called transmission media and in that topic we'll compare what's the difference between these wires, optical fiber, coaxial cable, wireless, satellite, or different wireless technologies. We'll compare them. And some of the things that we'll answer in those later lectures are, how do we, for the transmission system, how do we convert data into a signal? What media to use, wired versus wireless? Which one's better? Which one has the different trade-offs? How do we, this is similar to the first one, how do we take the data and convert it into a signal and code? What happens if there are errors? What if there are many people wanting to send at the same time? How do we share that media? We'll answer those questions in subsequent topics. That's briefly about communicating across a link. Networks allow us to communicate across more than one link, across a set of links, a series of links. Allows us to go further and communicate with more people. Because we'd like to be able to allow any user to communicate with any other user. By user it could be a human, it could be a machine. I shouldn't be restricted to be able to communicate from this laptop to any PC in this room. I should be able to communicate from this laptop to any computer in the world. That would be much better. And that's what the internet allows us to do effectively. For this to work, to be able to communicate with more than just nearby machines, we need some special software. And we'll see that we'll refer to that as, well, that comes up when we look at the internet and the internet protocol. And we often distinguish between different types of networks as well. So let's just talk about them first. Wands and lands. So networks now. Not just one link, but many links. That's categorized into two different types of networks. It's not a very accurate classification. There are types in between and slightly different, but it's a common one that we'll see. We'll distinguish between wide area networks and the next slide, local area networks. And the difference is, one's a network that covers a wide area and one covers a not so wide area or a local area. So the difference is about how much geographical area they cover. Roughly, we say a wide area network is a network that covers a city. So different points across Bangkok, maybe a wide area network, connects between cities, Bangkok to Chiang Mai. That may be a wide area network between countries across the globe. Classify them as wide area networks. They span a large geographical area. Local area networks across a campus, across an office building, inside an office, inside a home, around you. They're generally local area networks. There's no exact definition, just a rough one. But they differ not just on the size, but also how they're built and the technologies available. Wide area networks, before I describe that, let's consider an example of a wide area network. We have a campus here and we connect to the campus in Rangsit. It's about 15 kilometers. So we wanna connect the two campuses together so we can communicate. So that would be classified as a wide area network. Connecting these two remote locations would say we could use a wide area network technology to connect them. And we do, we have a connection between them. Let's say SIT wants to build their own link using wires, using cables from this campus to Rangsit. What we would need to do is we'd need to dig a hole in the ground all the way and put some cables down and then we could connect some devices and transmit through there. That's not easy because we don't own the land between this campus and the other campus. If we wanna dig some holes, we need to get the permissions of the people who own the land between our campus and the Rangsit campus. Very hard to do. Time-consuming, complex, very costly. Because you need to get access to all the land. You need to cross public land and also private land. So most companies, SIT and most individuals, you and me, we don't build our own wide area network. There are other companies whose specific purpose is to build wide area networks. Telecommunication companies, TOT, True, Cat in Thailand and different companies, it's their job. They build wide area networks and then they rent them to users like SIT and other companies. So what SIT does is we pay a telecommunications company to use their network to connect between our two campuses. We don't have our own network. And that's common for wide area networks. Large companies, telecom companies, internet service providers, sometimes called common carriers, they build the wide area network and then they get customers to use that network. So that network may carry data of many companies, many organizations. Whereas a local area network is a network that we build or we use inside, say an office or inside your home. Think of your home. You may have your dorm, you may have an ADSL router for internet access and you plug a LAN cable for your PC maybe, maybe even to your TV for streaming TV and maybe Wi-Fi for your laptop and mobile phone. That's a small local area network. Think of the devices. You own all of those devices. You own the PC, TV, mobile phone and you own the cables most likely, maybe the ISP, the internet service provider, let you borrow the cables and the router but you could own that. Usually with a local area network, the person who owns the end devices, the computers, the computers also owns and operates the actual network. You build the network, you maintain it how you want. With a wide area network, the person who uses the network doesn't usually own the network. A telecom company builds a network and rents it to the person who uses it and that has a difference on or has an impact on the different technologies used. We'll see these two types of networks come up in different topics. There's a topic on LANs. We'll cover a little bit later after the midterm and talk more about the technologies available. Answer some of the questions like, if you've got a network going from across the globe, some companies have networks that cover a large part of the earth, then you wanna get data from Bangkok to somewhere in California. Does it go on the path up to Tokyo and then across the Pacific to LA? Or does it go on the path that goes in the opposite direction across Asia and Europe and then across the Atlantic? What path does your data take to get from source to destination through the network? That's a problem that we'll try and address after the midterm with routing, finding a good path. And how do you deliver the data? And again, we'll have a topic on that. We may mention some example technologies that you probably haven't heard of, SDH, frame relay. This is not money machine. This is a different technology called asynchronous transfer mode. You don't need to remember them now. We'll come across them later. And with LANs, you should know these because you use them all the time. Wireless LAN, often called Wi-Fi, and the wired LAN, sometimes called Ethernet. They have different names. You use them on a regular basis. Half an hour ago, let's try and finish in the next 10 minutes and then talk about the structure of this course. Very quickly, the internet. So, what is the internet? Think now that inside homes, you have LANs. Inside office buildings, we have LANs as well. In each office building, every company has their own LAN. Between, maybe between buildings across cities, between cities, we have wide area networks. We have many different networks. They may all use different technologies. What the internet allows us to do is to communicate from one network to any other network irrespective of what technology is used in between. Effectively, it connects all the LANs and all the wide area networks together and we get the internet. We may say more about where it come from when we look after the midterm about the internet protocol. It came from a US research effort about 40 years ago and the internet or the technology the internet is based upon is often referred to these two protocols, TCP and IP. So, you may see this come up. But we'll explain them later. I think no need to go into the details here. What is the internet? Collection of networks, a collection of LANs and wide area networks connected together using one common thing. So it doesn't matter if my LAN is Wi-Fi, the wide area network is SDH and some other LAN is using Bluetooth or whatever. The common thing amongst the devices is a piece of software called the internet protocol, or IP, the internet protocol. The idea is that if the devices in our computer networks use IP, it doesn't matter if the technologies differ, all computers can communicate with any other computer. And that's what we effectively can do with the internet. I can communicate with some computer in the US. I don't care what technology that's using as long as it's using the internet protocol. And we will, after the midterm, explain what is the internet protocol and how it works. It'll be a large topic. What does the internet look like? There are several examples in these, but let's go straight to this one we can mention. Ignore the details here, but imagine this is a LAN, a local area network. Imagine there's a cloud drawn here. This is another LAN, another local area network. And a third local area network here. These are two wide area networks. So we have three LANs, two wide area networks, five networks, all connected together by some special devices. Combined, we'd call this an internet. By connecting them together, we get an internet. And in the internet we have today, you think of it as just much larger than that. Many different LANs and WANs connected together. There are some other examples there. This one, one about SIT. But this one is what I want to finish on. And I don't have it here. I'll show you the pictures. From this website, you can access, and it's good to do in your own time. You'll see why. You can access two maps showing different views of the internet in Thailand. I'll show you the two maps. So if you go to that website, and I think follow some links, it's provided by Nectec. Nectec is part of NASDA, which is in Science Park at Rung SIT. Thailand Science Park there. And they provide some maps of the internet connectivity inside this country. Up-to-date maps. You can click on them and download them. Here's the first one. Of course, I didn't print this out because it's too hard to read on paper without color and a small scale. But you can read this at the back, clear. If I ask a quiz question, you can read this. Not very easily. It's all right. Relax. I'll zoom in in a moment. Let's just look at the structure. What it shows is the connections between internet service providers inside the country. So it's called the Thailand Domestic Internet Exchange. It is just focusing on internet inside the country. If you want to communicate from your home via some internet service provider who you pay on a regular basis to access their network and communicate with someone else, how does that work? Well, these blue ones around the edge, when we zoom in, we'll see our internet service providers. They're companies that provide customers access to the internet. They have lines going from them and connecting mainly into these central ones, which are what's called national internet exchanges. We'll see IX here, IX, IX, IX, an internet exchange. So these links represent connections. These lines represent connections between an internet service provider and an internet exchange. If I'm here at home, I subscribe to this ISP. I pay them every month to use their internet. You can think I connect into this ISP, into their network. If I want to communicate with someone connected to this ISP, my data goes to their network, follows one of these lines to an internet exchange and then goes to this ISP and then to their destination. That's the general way to read this. Let's zoom in and see some details. First, the central ones and see some of their names. These internet exchanges, there are what, eight or nine, are provided by different companies or organisations inside Thailand. CAT is the main one, one of the government communication organisations. They have two internet exchanges across Metropolitan Bangkok. Sorry, I've gone the wrong way. We have CAT. ADC is a commercial company for internet access. I think affiliated with AIS, everyone would be familiar with AIS for mobile phone. CS LOCKS INFO you may have heard of, provided internet exchange, Jasmine Telecommunications, SBN, TCCT, and this one you would have heard of is TRU, the TRU Internet Gateway and TOT, another government organisation. These are six or seven organisations that provide these national exchanges in Thailand. Everyone's internet inside Thailand goes through one of these, not always true, unless you're communicating with someone on the same ISP. If you're communicating with someone on a different ISP, your traffic would normally go through one of these internet exchanges. Some of the ISPs at the top here. If you can't see from the back, this is TRU Internet. So if you at home subscribe to TRU Internet, then you connect into this network and they have connections from these lines into different internet exchanges. TRU, TCCT, TOT, others that you probably, some will recognise the names at least of ISPs or telecom companies. So you subscribe to these blue ones, connect to their network, their networks connected to these internet exchanges. Each line has a number on it which represents the capacity. For example, TRU Internet has a 90 gigabit per second capacity if we follow it to the cat internet exchange. That's the amount of data, 90 gigabits per second equivalent to 90 LAN cables going in. Here's a 60 gigabits per second to someone else. I can't see over here. 200 megabits per second from this ISP into wherever it goes down here. So you can follow those lines around and see which ISPs have how much capacity to the different internet exchanges. Of course, they're upgrading them on a regular basis so increasing that capacity because more people are wanting internet access inside the country. This is, again, as I say because there's so much detail in this picture it's best to look on your own computer in your own time and you'll be able to explore the detail. I'll just give you the outline. This is just domestic. What about we want to access the internet outside of the country? This map is similar structure but it shows we'll see similar companies here. These are not national internet exchanges. We'll see when we zoom in IIG it's an international internet gateway. It's a gateway between ISPs in Thailand to ISPs in other countries. So we have gateways operated by CAT, ADC and so on the same as in the national internet exchanges. We have some local ISPs the blue ones and all these grey ones are along the outside international companies. Overseas let's zoom in on the grey ones see if we recognize some. Sprint in the US so an ISP in the US Star Hub is in fact in Singapore I think Singtel, Singapore SG so several from Singapore here so these are internet service providers in Singapore and they have links into the different international internet gateways which are down here. So when you're accessing say some website in Singapore which may go through Singtel then your data goes from your ISP to either a national exchange or direct to an international internet gateway and then to Singtel's network in Singapore and then once it's inside Singapore it goes through Singapore's internet which may have a similar structure Hong Kong NTNT the Japanese company UK not just internet service providers here, Microsoft and we'll see later there's Google Facebook, Yahoo they are connected into Thailand so that when we access their information their websites we have fast access to their content called content providers so when I download something from Microsoft Microsoft's website I'm not downloading it from Microsoft's server in the US I'm probably downloading from a Microsoft server in Singapore maybe Hong Kong I cannot tell from here Microsoft have servers located around the world so they're closer to us, the end users so you can go through and see there's Google and many other international companies there, Equinix Korea France and many different countries represented so that's the connectivity inside the country was the previous diagram and the connectivity from Thailand to the rest of the world so it's one view of the internet from Thailand's perspective there's more information you can read down the bottom but we're out of time for today