 So welcome to ITS 323, Introduction to Data Communications. My name is Steve Gordon. I'll be teaching this course. This group of students, your IT students, we're going to have a few exchange students with us as well. A few more, they're all on holiday I think, going on a long weekend. We're going to try and give you your first course on communication systems and the internet. And computer networks in general. In today's lecture we have two parts. The first part I'll try and give an example to try and introduce what we mean by communications and an example that you know about. So try and connect all the things you already know to data communications and the internet. And then we'll have a break about 240, 220, have a break. And then after that we'll get started really on the first lecture. So in the first hour or so we will not be covering much from election notes. I'll just show some examples on the screen. And when we get a bit of time we may talk about the structure of the course, like the exams, the quizzes, the website and other things. But not quite yet. Let's go straight to an example of how you... Try and demonstrate some of the things that you already know about data communications. And in particular in using the internet. So a good example of using data communications is across the internet, which we use every day. And in particular web browsing we use every day. So let's access a website and see how it works. Because this course is trying to be, how does data communications work? And a large part of that is how does the internet work? So we'd like to know how the internet works. So let's access a website and see what happens. Any recommendations of a website I should access? There's our course website. I'll not go to there. Let's try one. I'll try to type in an address. Okay, good, it worked. I gave this to the CS class on Wednesday and it didn't work. The internet didn't work. I just accessed a web page. Nothing complex. What we want to know is how did that work? What happened in that case? So let's just go back. It may be hard to see at the back. Can we zoom in a little bit? The first thing I did was typed in an address. And if you saw me, I typed in, it's not fully shown there, I typed in http colon slash slash sandylands.info slash it.html. What is that? What's the name of that thing? Again? What's the name of that domain? Part of it is a domain. So sandylands.info we call a domain. But the whole thing, http colon slash slash sandylands.info slash it.html is a URL. I think you may have heard of it, you may not know what it means, a Uniform Resource Locator, but a URL is the whole address, and part of that address is the domain. The other part is the http and also this slash it.html is a file name. So the first thing that we do when we visit websites is usually we need to specify some address. And what we're going to study in this course is different, well, what we'll come across is different addressing schemes, different ways that we identify devices using addresses, and the role of those addresses in data communications. So we type in an address, then what happened? I pressed enter, what happened? Download. Download. Browse? Yeah, what? Correct? Type. Okay, so I typed in an address and it browsed, so I think you mean it showed me the web page that this address identifies. So the address or URL identifies a resource. In this case, the resource is a web page, a file, a HTML file. Who knows HTML? Who can write HTML? Who has seen the inside of a HTML file? Okay, the HTML tags are greater than less than signs and so on. Even if you can't remember the syntax, I think many people may have seen the inside of a HTML file. So what happened when I pressed enter is that my browser, this is my web browser on my laptop, my browser browsed to this website, but what does that mean? What did my browser actually do or my computer do? Did it communicate with someone else or some other entity? Where did this web page come from? Database? Possibly, maybe. But where does this web page come from? Did it just magically appear on my laptop? Where did it come from? Anyone want to guess? Did it come from America? Did it come from Thailand? Did it come from my blue laptop? I don't know. Japan? Okay, maybe it did. What can we identify? Well, the address identifies a web server. Sandilands.info identifies the address of some web server. So with web browsing, the very simple view of web browsing is my browser, I want to visit this web page. I tell my browser by typing in the address. I press enter. My browser and my computer sends a request to a web server. The web server is identified by Sandilands.info, sends a request to some web server somewhere in the world. The web server receives the request. The request is for the page or the file it.html. The web server receives a request, looks on its hard drive to see if it has that page. If it does, it sends that page back in a response. When my browser receives the response, then it displays this text on the screen. So there were some communications happening there. My browser sends a message to a web server somewhere on the internet. The web server sends a response back containing the web page. Then my browser displays that web page on the screen. It all happened quite fast. I think from when I pressed enter until it was displayed, it was, I guess, milliseconds, less than a second. So what's the name of that mechanism for my browser sending a request and then the server sending a reply? What's the name of that technique or mechanism? A query, okay, so it's a request response. So it's a query for a web page. More specific. There's a name, and you know the name. You may not know what it means. You see it every day. What's the name of the mechanism used for requesting and retrieving web pages? It's a protocol. It starts with H. HTTP, okay. It's no longer displayed here. My browser's too smart to display it, but I typed in HTTP colon slash slash. HTTP Hypertext Transfer Protocol. That is the mechanism for, or the set of rules that define how my browser sends a request to the server and how the server sends a response. It's a protocol. It's a hypertext transfer protocol. It's a protocol for transferring hypertext. Hypertext is the name of the way for describing the format of web pages, HTML, the hypertext markup language. So we have a protocol that defines how to communicate. One of them that you always see is HTTP. Does anyone know any others in the internet? Other protocols you may have heard of. HTTP, maybe you've downloaded files, FTP from a server. Others? Has anyone... Maybe many people use web browsers to do everything nowadays, but many other applications on the internet. Email users sometimes use something like POP or IMAP or SMTP. When you had it, maybe a few years ago, you had MSN Messenger. And that used its own protocol, an instant messaging protocol to talk to other Messenger instances. Voice over IP allows you to make voice calls over the internet. VoIP, you may have seen the acronym. We'll see many acronyms which refer to protocols through this course. What's another one? IP, the internet protocol, is a core one. Web browsing. The server sends back that web page. What's the web page look like? We can view the page source and for those experts in HTML, it doesn't matter if you can't read it. You can zoom in a little bit. The HTML source of that web page saying the markup tags and welcome to ITS 323, the heading and so on. So as a web developer, you would create this page, put it on the web server, and they would see the content from this HTML page. Very simple so far. Where is the web server? Tokyo, okay. How do we know that? I know it because it's my web server. It's in Tokyo, Japan. That's why I wrote it here. Don't worry about how we know that. We know it in this case. So it's in Japan. My browser is here in Thailand. So the request went all the way to Japan and then came back. And how long did it take? If I reload, can someone time, get their stopwatch going? Okay, less than a second. So to get all the way to Japan and come back, the server to respond takes milliseconds in that case. What else do we know about this? So there are addresses that identify resources or computers like a domain name identifies a web server, identifies a file on a web server. We have protocols that define how we communicate between computers like HTTP. What else can we see from this simple example of web browsing? Other types of addresses. Does anyone know of other types of addresses? Does my laptop have an address? Do you think? Yes? Does my laptop, do you think, have a domain name? Like Steve's laptop.com? Unlikely. Does yours? Your mobile phone have a domain? What's your domain? It has an address and maybe it does have a name but it may be local to a network. But what address does your phone, tablet, laptop, home computer have? But I think you've seen, you may not understand what it means what type of address. An IP address. You may not have done much with it but if you look in the settings on your phone about the network settings you'll see something like an IP address. So an IP address is another type of address that identifies computers on the internet and it's a very important address. In the simple terms, we'll assume that all computers on the internet have a unique IP address. So my laptop has an IP address. This blue laptop has a different IP address. The web server has one and all other computers have a unique IP address. And we'll communicate by sending to a particular IP address. So I think you've heard of you've definitely used HTTP. You've seen domain names. You know URLs. You've seen websites for sure. You've probably seen or come across IP addresses. What else? What's the IP address of my laptop? Anyone let's have a look. On my laptop to see the IP address it's my network interface. IF is sure for interface. So to see the configuration of my interface my wireless LAN interface use this command. You don't have to know the command. And I see a lot of information and I see this is I know that's the IP address for my laptop at this point in time. 10.99.159. What does it mean? We'll have a topic on the structure of IP addresses after the midterm. I'm sure you can look into your mobile phone and explore the network settings. If you go into the advanced settings you'll find your IP address there. On any of your computing devices you can access. Another IP address what did I access? sandylands.info sandylands.info is the domain name of my web server. My web server is a computer in Japan. This program will show me that that domain name also corresponds to an IP address. 106.187. 46.22 So most servers have a domain name as well as an IP address. Computers use IP addresses to communicate. Humans remember domain names. So we'll talk about later towards the end of the course the mapping from domain names to IP addresses and how that works called DNS the domain name system. I'm just trying to go through a very simple example of web browsing and trying to highlight some things about data communications. Let's see what else we can see. So I said with HTTP my browser sent a request to the web server. The server sent back a reply. I tried to draw this before so we have a browser and some server so two computers somewhere on the internet and we'll say that the browser and server I'll draw it as a cloud meaning or it's much more complex than just a cloud it's actually many different devices. Don't worry too much about drawing my pictures they're not so important at this stage after our break we'll move on to the first lecture notes and we'll try and cover the same concepts but maybe in a little bit more formal manner and then you can take more notes. What happens if I can draw it what happens the browser sends some request to the server I'll just write that as a request and then the server gets the web page and sends back a response and this is part of the protocol called HTTP so HTTP defines the format of the request the format of the response when to send them what should be inside those messages that's a protocol what else do we see when I accessed that website I was doing something else on my computer I was recording the messages that my computer sent and received so just before I accessed the website I started another piece of software to record everything that my computer where the browser is running every message it sends and receives let's have a look at those messages I have to bring them up and I'll go directly to hopefully and just to hide some of the details what was I 106. you don't need to understand what I'm doing here but we'll just look at the final result if it works a lot of detail here but this software shows a record of the messages that my computer sent and received I started some recording so everything that came out of my computer and went into my computer across the wireless interface was recorded and I've summarized and selected the two things of importance in these two messages the top these two show the two messages a lot of information here let's just focus on some things that we know there's a source address and a destination address the source is who sent it to and if you can recall 10.10.99.159 was my laptop and the 106 address was my server so this first message went from my laptop to the web server using protocol HTTP and the summary information in that message was this is the request going to the server saying I want to get the file flash it.html so this is my computer saying I want to get this file the length of that message was 366 bytes and then how long did it take to get the response back so the next message is the response how long does it take well if you note here there's some times relative to when I started this process the time when the request was sent was 14.96 seconds when the response came back it was 14.27 seconds so what's that about 0.3 seconds about 300 milliseconds from when my browser sent the request to Japan and until the Japanese web server sent the web page back so that's the time it takes to get the response back from this information from the web server to my laptop you're still using HTTP and the response some summary information is saying everything's okay the request was okay and the response is okay most important the response here we can zoom in on some of the detail inside the response is this what is this HTML it's the web page okay so this is the response message inside that response is the actual web page that I requested the file it.html so what happens is my browser sends the first request out server receives a request finds the file I requested puts it in the response sends the response back to my computer my browser receives the response grabs this part of it and uses that to display on the screen welcome to ITS 323 in this course what we want to get to towards the end of the semester is how some of these other things work HTTP transmission control protocol TCP the internet protocol ethernet and other communication technologies we want to study how they work how big was the response here 743 bytes what else can we determine close that one for now let's have a look at the web page I'm going to save this web page on my hard disk and we'll look at the size and look at the contents save it I'll just save it as IT .html the page the HTML page is 311 bytes the response was 700 bytes it contained the web page plus some other stuff some overhead but the page itself is 311 bytes why? why is it 311 bytes alright why 311 what does it tell you about what's inside anyone okay there are 311 bytes of data it's a hard it's a confusing question there's no one answer it tells us in fact that there are probably 311 characters inside there in the file itself it's just a text file if we look at that file and you go and count all the characters in there including the end of lines you'll see that there are 311 characters there each character is stored on disk as a single byte which is very common for most operating systems we can word count that file word count there are 13 lines words 311 characters each character represents one byte very basics we're doing nothing exciting yet let's look at that file in the binary form XXD is just a program to look at a file a text file in a binary form I have to zoom out a little bit so it will fit on a screen so this on the right hand side it shows the ASCII representation I just gave you the answer to my next question it shows some the text and here is the binary form well my next question was how do we map text to binary ASCII is the common encoding that we use the ASCII table says that the letter H is the number 104 or whatever it is which corresponds to a 7-bit value but on the hard disk we store as a 8-bit value so the letter H here in HTML is this binary number so we can map any form of text into binary and later as we go through data communications in most of the things that we want to communicate we'll represent them as binary and deal with how to send bits across our link or network last thing with respect to our example I said that I sent from here my laptop in Thailand to the server in Japan so I told you it was in Japan which path did it take how did it get to Japan from Thailand anyone want to guess where did it go outside of think of cities or countries that it may have went via to get to Japan okay alright first question do I have a cable going from my laptop to the server in Japan no there's no cable from my laptop into the server I don't have a direct connection I send the data via other locations via other devices in fact where's the first thing that I sent the message the request message via this laptop sent a request message to where even before a server in Thailand was much closer maybe you can see it right that thing on the wall up there okay the wireless the first thing because I was using wifi on my laptop the first thing that it does is it sends a radio signal out of the laptop and it's received by this wireless access point or wireless router on the wall okay so that first step is that wireless communications then this one okay but there's a cable going out of the back and it goes up in the ceiling down the wall into the I think into the third floor there's a computer center into another device and it keeps going to another device and another device until it gets to the server in Tokyo via different devices I haven't checked today but when I tried this at home I found the path that it takes or roughly the path it may be a little bit different if I did it today but when I tried it before I found the path I'll try and bring it up the path this was actually from home not from SIT but it's almost the same from the web browser to the server where did it go via this message and actually goes via different companies networks or different organizations networks those organizations are referred to as usually internet service providers ISPs or telecom companies so in this case actually from home it went because my ISP at home is TOT TOT is the local government telco in Thailand and they are an ISP so it went to TOT's network some devices inside there so not just a particular device but this represents there ISP's network and then it went to another device or another network of TOT called the TOT International Internet Gateway IIG and the way the internet structured in Thailand is that there are many ISPs that you can subscribe to you pay monthly to access and most of them then connect into five or six different international gateways and then those international gateways connect to ISPs in other countries and in my case the data went to the TOT International Internet Gateway which had a connection to NT&T, actually a Japanese company in Singapore so it went from Bangkok to Singapore and then it went via Singapore to Japan probably into Tokyo, I don't know NT&T is the other company it's the national telecom company of Japan then it went to another telecom company or ISP in Japan called KDDI and then it went to the company that hosts the web server called Linode just the company that I pay per month for this server so that's the rough path between the browser and the server that the data took and again today from my laptop it may be different if you access a server in the US or in Europe or in some other region the path will be different one of our topics or several of our topics will look at how do we find a good path between browser and server or generally between two computers in a network and it's called routing and it hosts the destination that will be a topic that we cover after the midterm any questions so far nothing much new just some basics of how web browsing works and a little bit about the internet structure come back to this international internet gateway maybe more detail what does the internet in Thailand look like anyone seen a picture of the internet in Thailand or the structure of the internet I'm sure you've seen one I think most people here have seen a picture of the internet in Thailand see if I can bring one up Thailand international internet gateway a map of the international connections from Thailand to other countries I think everyone's seen that it's on the front page of your handout of your booklet it's hard to see both on the screen and also in the black and white version on your handout it's probably best to see on your own computer so you can zoom in and find the information but the general structure is that these blue ones in the center are the international internet gateways this is TOT IIG here the one that we connected to but there are a few others the grey ones around the outside ISPs in other countries the blue ones are some special ISPs inside Thailand and all the lines are the links the communication links between all those organizations we'll just zoom in on on some small parts and again this is where you need to look in on your own computer so one of the bigger gateways is run by CAT CAT the government based telecom companies here and these are international ISPs or companies overseas which connect into the CAT IIG and other international gateways you can notice that maybe you'll recognize the names of some companies or ISPs the countries Singapore, Hong Kong Google from Malaysia and Singapore so Google has their own links into Thailand so when you access Google services including YouTube going to the servers in the US it can go direct to the servers nearby in Singapore Malaysia and so on and you can scroll around best in your own time to see many other companies there mostly around Asia some in the US and so on and the lines are the links so think of them almost not always but most of them are cables and the numbers specify the speed that we can transfer the data between those two entities for example KDDI in Hong Kong there's this red line going somewhere and the speed of that link is 1 gigabit per second that's what the 1G means here so you can see the speeds of different links of the connectivity inside the country again in this course we want to study things about the speed what technologies give us different speeds the connectivity between what technologies we'll use to communicate between these entities and a few other things about the structure of the internet you can find this map from some website I think I'll add a link to the course website you'll search if you search for Thailand internet map you'll find it I'm pretty sure run by Nectec so they've got an international map showing connections to other ISPs and an internal map how the internal ISPs connect inside the country updated quite often last thing if we zoom in on our communications from my laptop to the server in Japan and just look at the portion inside this campus it looks roughly like this here's my laptop it communicates with this wireless access point on the wall there's no link, there's no cable there there's a link but no physical cable we use wireless communications there so I send some radio signal to this access point it's got the antennas that pick up the signal the access point then has a cable going up through the wall and it goes down into what's called a switch in I think in the third floor there's a small computer center there and eventually it goes out to something called a gateway for this campus which connects this campus to the rest of the world with respect to the internet it's a gateway between our network inside the campus to all the other networks out on the internet there's a gateway at Bankadee and that actually has a link going to Runksit if I think we have at least two links one of them is a wireless link if you go to the top of the other building there's an antenna up there that points at Runksit and we have a wireless link but we also have a wide link that we use to connect to the other campus so this just draws the internal campus communications so another part of this topic is how do the communications inside a LAN work a wireless or a wired LAN a local area network and we'll look at some of the techniques there so there's our introduction to the course and some of the things that we'll try and cover in this course how internet applications like web browsing work how the internet is structured this is almost going backwards towards the end we'll look at the applications before that we'll look at the internet structure how do we connect across a local area network and how do we connect say between countries a wide area network or WANs and before that we'll look at things about how to find a route from source to destination how to find a path before that we need to look at the details of just a single link say from access point to switch over one cable how do we get data across a cable what do we do how do we send just imagine here to the switch what do we send send a signal what shape up down up down alright we could send some signal in general yes correct we send some signal across this link where that signal represents the information the information is usually bits whether it's a web page an email a video we'll often look at digital data sometimes we'll look at analog but if we have bits we map those bits of information to a signal whether it's a digital signal like square wave or an analog signal think of a sine wave we send some signal across here such that that represents the information being communicated the receiver receives the signal and interprets what that information was so we'll actually spend the first part of this course looking at those signals defining what they are how we encode data on those signals and how to do it efficiently let's stop there at least on this introduction part any questions everyone's confident they're going to be successful in this course they know what it's about it's about how do we communicate first across links and then how do we communicate across including the internet this course data communications is a rather complex and large topic this is just the introduction to data communications those that stick around past this semester next semester that you have a course on computer networks and network architectures I think it's called ITS 327 that sort of extends or continues on from this course here we just do the basics in the next course taught by Dr. Comet will be more detailed about the internet and some networks next semester also we'll do a lab so we'll do some hands on with what we learn in this course and a little bit from the ITS 327 so I will teach the lab next semester so IT program another aspect of the internet and data communications is security how do we make sure our communications are secure so next semester we also have a course called IT security that I think all of you will take and I will teach you that as well some of you may choose the ICT option inside IT so you may get some more details about communications there's tele-services and services architectures internet technologies and applications usually they are taught by adjuncts or external people so the topics change a little bit but related to the internet and telecommunications and maybe even mobile computing next year so it's important that you're successful in this course so that you can be successful in the subsequent courses so make sure you get through this course so that you can find the next courses much easier