 In this topic called protocol architectures and internet applications There's in fact a mix of a few things to cover so today. We'll just cover the first part of it, which is what is a protocol architecture and For that we need to know what is a protocol? Okay So we'll try and cover that today Again same with the other class in the other class What are you IT section the other class CS section computer science IT third year? We have people from somewhere else From overseas exchange students. Where are you from? All four of you from France. Okay, so we have some exchange students here for this course and some of our other courses So you'll get to meet them when you meet them In tie, what do you say when you first meet someone in tie? Say in English, I would say hello Okay, you would hear that many times so at the so at the crop for a man. I'm not good at it And what about in French? Bonjour, okay, so there you go. You've learned something to how to meet people. What about in in France if you go to an interview or a business meeting and you formally greet someone What do you do? You shake the hands so you put your hand out the other person puts the hand out and they shake hands, okay? Same in tie shake hands Why shake hands In tie, there's a different greeting a different formal greeting to why okay, and I don't understand the details But they understand even less so let's explain to them or you'll explain to me and them how to why okay and So that we have a record and I know what you're gonna do. I'm gonna record and write down the instructions So you tell me how it works What is a why and tell them as well? What what what is a why? Okay How to show respect to someone when you do it when you meet people so when you say two people Come together. Let's keep it simple two together. I thank you as well when you're Leaving or saying thank you. Okay, so it's used for different reasons to communicate One of them is say simple case two people come together and they want to greet each other, okay? So we say it in in France and in Western. It's a handshake Here in Thailand. We have the why Let me write down the rules for what we do when two people come together so we'll see it's a form of communications and The reason we're doing this is we'll see that it's actually a protocol for communications And we'll see what parts what is a protocol by going through this Let's say I'm I'm the person and someone else comes in there's two people both enter the room They need to greet each other so that at the start What happens what do I do in in English you may say hello. No in Thailand. What do we do? What do I do? Give me some instructions what to do in This formal greeting of using a Y put put hands together, okay like this Okay, like this so there's there's some their format for how you Communicate this why to someone else so you put your hands together We'll come back to that exactly how to do it in a moment who put their hands together both people at the same time Two people come into the room. They want to greet each other to both of the people at the same time put their hands together like this older people Do what so something about age who does it who does it first then? The younger person Initiates so let's write this down. So from my perspective and I'll write these rules from one person's perspective if a Let's say a younger person or a Someone junior to me, okay younger than me if a junior person arrives Then what do I do? So imagine I'm here if a junior person is the one that arrives. What do I do I? Wait for a why? Okay Because it's the junior person that should initiate this communications Okay, so there's the first rule And I'll be a bit later. I'll say we'll describe what happens when we Are in this state of waiting for a why? Okay, so think of that as some state that we're in initially. I'm in the start state Someone arrives if they're junior. I'm going to go into this state of waiting for them to do something What if they were senior If they're not junior If it's a senior person that arrives, what do I do? Why okay? I initiate the communications So I send a message to them so Let's say even better. I send a message and this message is called a why we'll describe the format of this message shortly Okay, so we're just writing the rules so people can follow and communicate well Else well, I'm going to keep it simple. I've said if junior person arrives else means otherwise the senior What if they're both the same age? We won't consider that that's too hard. Okay Let's keep it simple either someone's junior to you or senior to you senior being older After I send the why to the older person what do I do? So I've done the why to the older person. What do I do now? Hmm. Okay. I say so a D to them I'm going to save space and not write everything down. Okay, and then what do I do? Start talking Always the case so I why someone else and then I just start talking Sometimes they should respond to me correct Not always, but sometimes it's a it's a two-way greeting One person the junior person gives a why to the senior person the senior person may respond Okay, so let's consider that case and again. I'm keeping it simple and only some cases So I wait for a response Because they should do the same to me Okay, and then what happens? So let's now consider We're in this state of waiting for a response and let's consider if If I receive a why from a junior person so What do I do if a junior person arrives then I wait and then if I receive the The why from the junior person, what do I do then I can why them and then what? start talking Okay, talking a simple set of steps that Junior person arrives. I wait for them to initiate the communications If they initiate I respond and then we've finished this greeting and we start our data communications We start talking That's a simple description of course What about this case? What do we do? Why? What happens now start talking? Okay, because this is the case where the scene I sent a why to the senior person I wait if they send one back to me then this greeting is finished and Then we start talking Okay, so if I could type that be happy this is a protocol This is a protocol for greeting people in Thailand It's for two entities to communicate with each other to do a specific purpose This is just greeting how to talk to people. Well, there's another protocol for that That is one person talks first the other person then responds If two people talk at the same time usually the conversation is not much fun. Okay, so to start the talking phase Requires a different protocol. So this is a protocol for greeting and you can see we can describe it as a set of States that we may be in and the start state. I do something in this waiting state. I do something different Some events that arrive some person arrives Someone sends me a message I Receive a message and some actions that I take I go into the wait state. I send a message I start talking so this is a very simple example of a protocol when My laptop wants to send a file to this PC If they have connected via some transmission line Then they both need to follow the same protocol to be able to communicate So another way to think of a protocol is as a language To people or two entities for them to communicate they both must speak the same language and both must use the same protocol if I Follow the protocol of a handshake and someone else follows the protocol of the why and We try to greet each other. It will not work very long. Okay as Humans we can adjust. Okay, if I go to shake someone's hand and they do something else to me Then maybe I'll respond but with computers if they speak the wrong protocol They just won't be able to communicate nothing will work so Just a quick example of a protocol in this case Any other case any other statements we need here? all right What if How long do I wait? junior person arrives and We're just both standing there junior person walks in and we're both standing there. I'm waiting for them to why me a younger than me How long do I wait? 20 minutes Okay, and still they start start the conversation. What do I do then they didn't why me? What do I do? Complain at least I have a feeling of maybe less respect from them towards me Maybe I'll just ignore them and walk away All right depends upon the person in that case of how they respond but Importantly well There are different types of events that can happen and especially with computers if we're sending and receiving messages between computers Things can go wrong. I Send a message from my laptop to the PC. I'm expecting a response message back. I'm waiting for a response My computer cannot wait forever We need some time-out mechanism that says if I don't receive a response in 100 milliseconds then Do something else? Maybe give up the communication say there's an error in this case if I don't receive a response Then I will take some action in this case walk away or whatever similar if a If I wait too long for the senior person I have given a why to them and now I'm waiting for the response then I may take a different action So the timing of what happens is important in a protocol Especially waiting for things timeouts will see them as we go through protocols this semester We'll see on the slides a protocol is describes a set of rules the entities follow in order to communicate But it also defines the set of messages that they use What do we send we send a Y in this case think of this is our message we receive this message So that's the message that we send Let's describe that well in our simple case. We have just one message one message type And it has some meaning so we need to describe what the meaning is but in fact in a Y Again, what do I do put the hands here and bow a little bit correct What if I put the hands here is that correct? No Okay, if I do this not correct. Okay, so there's a format or a structure of the message It must be defined for the communications to work Are there is there just one type of Y or there are multiple types What are some different ones is this The same as this Different meaning What's the difference the kind of people that Okay, I took towards a monk More senior person maybe to show more respect you may do it maybe higher Better than just this okay, so the the where you put the hands has some meaning That is the messages The structure of those messages have different meanings so depending upon the message type they mean something else to the receiver So whether it's the higher one the lower one and the students that do to me when they're carrying their books or their laptop the one-hand one Okay, so there's different types and they have different types of meanings Same when my computer sends a message to here This PC must know the exact format of the message So that it knows when it receives message a It knows what action to take because it knows message a means everything's okay when it receives message B It may mean there's an error so the messages that we send between computers have some meaning So what is a protocol a set of rules that to or more? peer entities So when two entities are communicating we're saying that peers with each other Set of rules that they obey in order to communicate So we saw an example of a protocol for greeting in time But there are many other things that we need protocols for So in fact there are two parts of a protocol the procedures that is those rules those if L statements that I wrote And the syntax or the format of the data message or data blocks the types of messages what do they mean? So in general that's what we mean by a protocol All of our data communications The devices that communicate in order to be successful Both devices communicating must follow the same protocol must understand the protocol that's being used So that's a protocol Now I want to communicate from laptop to PC. I want to send a file from laptop to PC. I Can write some software in my computer that implements a protocol all these if else statements Define the message types The problem is with data communications all the tasks needed for that communication to be successful There are many of them and very complex So in fact, we cannot have one protocol that does everything It's just there's so much that we need to do to communicate There's not just one magic protocol for everything There's a protocol for my laptop to communicate wirelessly to the access point up there There's a different protocol for my laptop to communicate via wires to some other device and So on so we don't just have one protocol. We have many different protocols And that will lead us to the need for a protocol architecture Because data communications is very complex. There are many tasks. What we do is we apply this divide and conquer principle take one hard task Divide it into many sub tasks and try to conquer solve Those individual sub tasks separately such that that we solve the the larger tasks. That's the concept here in communications the task of communicating between computers we divide into sub tasks and We organize those sub tasks some way and that the way that we organize them is into layers That is think of a layered stack At the bottom layer, there are some there are protocols responsible for some tasks At the next layer. There's protocols responsible for different tasks and so on Such that if we combine all of those layers All of those protocols We'll be able to successfully communicate between computers The collection of the layers together and the protocols inside those layers We refer to as a protocol architecture and that's what we're trying to scribe today in the rest of this lecture We'll go back and forth between some of these slides So I'll go forward a few to just give you a quick example Here is a protocol architecture very simple view It is called the TCP IP protocol architecture and it's what we're going to use in this course And I've drawn it as five layers and some names for those five layers In fact, we'll use this throughout the course. You'll need to memorize this the physical layer Data link network transport application The idea is that my laptop to communicate with other devices on the internet Implements inside my laptop these protocols in these five layers So my laptop has some protocol Inside which we consider as part of the physical layer Another protocol or protocols there may be one or more as part of the data link layer Network layer protocols transport layer protocols and application layer protocols and when For example, I want to access a website. I Open up Firefox. I type in a URL and I press enter then the communication software in my laptop software and hardware goes to work and It follows these layers in that there's a protocol For accessing a web server that is for web browsing. What's the name of the protocol for web browsing? HTTP it's up here. So HTTP is a protocol It supports the application of web browsing It doesn't matter what your web browser is Firefox i.e. Safari some mobile browser They all use HTTP. They all use the protocol called the hypertext transfer protocol Because that's built for web browsing But it doesn't do everything that my computer needs to get data to the web server and get a response a web page back Because the tasks for communicating as we say a split into different layers It does some things for the communications and then other protocols in the other layers do other tasks perform other tasks so HTTP does something If I want to access a website and then send some data to the transport layer protocol and There are different transport layer protocols the one that HTTP uses in fact TCP We don't need to know that yet. That's just this example. That is HTTP allows me to access a web server But to get that information Reliably to the web server without any errors HTTP will not handle that for me. It leaves it to another protocol called TCP So TCP does some perform some tasks Specifically providing some reliability if something goes wrong TCP tries to fix that Instead of HTTP having to provide reliability it leaves it to someone else to do so we share the tasks amongst the different protocols TCP is used In the network layer a different protocol is used also in this case IP is the main one the internet protocol That's main its main task is to get data from my computer across the internet to the server and We'll see some more examples of that later to get data across the first link okay My computer has a wireless link to this access point That access point has a cable going up in the ceiling down to I think the third floor There's a device in there that the cable plugs into There's another cable going to another device and there's more cables and wireless links that eventually go to a web server in DUS Some Google web server The network layer is about getting data from my computer to the Google web server via these intermediate devices The data link layer and the physical layer have the tasks of getting my data just across the first link just from laptop to this wireless access point so We'll describe them again, but the data link layer is about getting data across a single link Again some reliability mechanisms and a few other mechanisms physical layer is about getting data as bits zeros and ones across a link By sending some signals some electrical signals some radio signal in the case of wireless so This is an example of a protocol architecture It's divided in the five layers and They have some names and each layer is genuinely responsible for a certain set of tasks And we'll describe those tasks a bit more shortly. So go back So that TCP IP is a real protocol architecture What about a simple protocol architecture? Do we need this I? Think you're all smart enough that we can go straight to the direct the real one instead of the simple fake one Maybe go through a little bit of the simple one So remember a protocol a set of rules that our computers follow to communicate and remember that we can't Implement everything in one protocol. We need many different protocols to do different things and The way that we make use of the different protocols is that we would order them in some layers One layer protocol uses the lower layer Which uses the one below that and and so on and I said at the start that this is one of the hardest lectures because this These concepts are hard to connect with what you already know Let me just see if we can avoid this Let's try this example. So here's instead of the five layer protocol architecture. That's the real one To start simple. Let's use a Fake one which has just three layers just to keep it a little bit simpler What that means is that for each computer computers a b and c in this simple example network each computer implements protocols in these three grouped into these three layers and The groupings are done by the tasks that they perform have different purposes That is the application layer protocols perform tasks specific to applications What are some applications that use in the internet or in networks? Give me some examples of types of applications not not the actual software, but the general types of applications What do you use every day? What internet application or type of application? web browsing Or a browsing That's a web browsing is a type of application Of course, there's different software for a web browser and There's different software for web servers, but together when they communicate. We just say that's web browsing the web browsing application What protocol is used for web browsing? We've said HTTP So this is the application type this is the actual protocol used more applications email Okay, what's FTP used for what how do you describe it? file transfer you want to Not so much browsing, but you want to download or transfer a large file from one computer to another some of you may not you do it so much now you can use web browsing but FTP is a protocol for transferring files between computers another one email All right, everyone sends emails. I know you can use web browsers to send emails But you can also have standalone clients that do it and in fact the web browser acts as a client on your behalf What protocol protocols does email use? There are different ones and you may not some of you may not have seen them because email you don't See the name so often SMTP is one that's used IMAP is one that's used Pop I will not explain them the main ones You'll see some of these examples on some later slides. There's no need to copy that Anything else internet applications? remote connection bit torrent Voice over IP Skype type voice calls video calls instant messaging Sending instant messages games Games we use over the network Database applications businesses have their own proprietary applications. There are many types of applications That use the internet to perform that their tasks. I won't list them all That'll do because I can't think of all the other protocols, but there are others Okay, there are the types of applications and they have their own protocol We classify these all part of the application layer okay, all of these protocols a Grouped into into the application lab because all of the protocols are designed to support specific applications If I want a web browser use HTTP if I want to send an email I use SMTP and others Different because they have different goals so In our protocol architecture at the application the topmost layer we have application protocols now Consider these three how Remember yesterday we introduced the accuracy as a measure of effective communications. I need to Deliver an accurate representation of my data to the destination if it's not accurate. That's no good What level of accuracy do we need in these three? If I have a web page that transferred from the server to my browser Does the page that my browser receive have to be identical the same number of bytes the exact same bytes as What the server sent it should be the server has a web page to send me a Thousand bytes has some text in it If it sends me across the internet and my browser receives 900 bytes of course, I'm not receiving the whole web page We want to see the exact same web page at the server for web browsing. We need 100% reliability What about and we had the example yesterday? I send an email. I love you and if it's not received or it's received in error At the receiver. That's ineffective with email What we receive should be the same as what we send We need 100% reliability same with file transfer. I download a file Then if that file is incomplete or corrupt Then that's ineffective communications What if I do download a file and I notice that it's corrupt some the software tells me that this file you've downloaded There's some strange characters in it. It's done some detection of errors and finds it's it's not the correct file What do you do? You try again. Okay, so you download a file 10 gigabytes You're waiting all day to get it you get it and then you open it up and it says no this file cannot play It's corrupt Not so good. All right, so you go back to the same place and download it again waste your time But that concept of if there's an error Retry or Get the the sender to retransmit the data. This is a common concept used for reliability Okay, so many protocols implement this to provide reliability Send some data check if it's correct. If so send some more if not send the old one again Retry or retransmit all of these applications need such functionality Because in all of them we need 100% reliability So one option is within HTTP implement some retransmission scheme and In FTP implement a retransmission scheme and in SMTP implement a retransmission scheme But in fact they all require this same retransmission scheme so let's make our life easier and Have a different protocol that implements the retransmission this reliability feature and let these use that so they don't have to implement it themselves and in fact, that's one of the roles of the transport lane and The protocol that does it in real life is TCP So what happens is that HTTP is just for web browsing For this reliability this retransmission so that you don't have to reload the web page But the protocols will do it automatic It uses TCP because TCP provides this retransmission scheme and so does FTP it uses TCP and SMTP uses TCP so This is this concept of dividing the tasks amongst different protocols and Amongst different layers, so the application layer protocols focus just on the tasks for applications Transport layer protocols one of their roles is to focus on retransmission of data So the others don't have to deal with it There are other Protocols as well here TCP is the main one. So in our example here We say there are application layer protocols transport layer protocols and the third one is just network access For simplicity, let's say this does everything else that we need to communicate across this simple network Including it gives addresses to these three computers What's the address of this computer? Tell me it's address Or a nice name for its address in this network Have a have an attempt try and give it an address or give each of those three computers an address a Name that uniquely identifies them in the network Keep it simple It's on the screen What would you call this computer? It's written there read it. What is this computer? Computer a so let's call it address a okay nothing complex here So we need some addressing scheme So in this case in this unrealistic case, we could say that the addressing scheme every computer gets a letter Okay, a b and c Not very useful because we can only have 26 computers if we limited to one the same case but there's some structure of the address in this case a letter and They unique amongst the computers So the role of the network access layer protocols may be defining these addresses Defining the structure making sure each one gets a unique address and Other things for sending across the link like generating signals to send across the link That's some of the roles of network access so when Maybe the next slide if computer a wants to send some data to computer B It needs to know the address of computer B, which is B and it creates a message to send And as we see in the next slide We think here's the computer. He's a link into the computer cable plugged in the way that we use the layers is that The user the human user sitting at the computer generates some data Which let's say the web browsing application. There's some data that comes from it that needs to be sent to be Sends that data to the transport layer protocol for example, TCP TCP does some things we will not describe what it does yet, but it does some things to make sure that there's no errors and Then sends all of that to the network access layer protocol which may do its own tasks and Then sends all of that information the data and we've attached some extra information In particular some addresses Here we attach This data comes from computer a and it's going to computer B. It's common in protocol Messages that we say where it's going to and who it's coming from Why do we need to know who it's coming from? Computer a knows it's coming from itself. Why does it say it's from a? because the other computer May want to respond Of course we need to say it's to be so when it goes into the network It doesn't go to see it needs to go to be and when be receives it it sees oh, it was from a I Can send back a response to a if I need to send a response So we usually include a from and a true to address in the messages For now ignore the from and to one and two that's an address as well, but for a different purpose We send a message across a link How do we do that? well a message is really a sequence of bits and Network access latch converts those bits into say some electrical signal and Generate some electricity that goes across the wires One way to do that conversion is when we have a bit one Generate some high voltage signal And when we have a bit zero generate some low voltage signal for a period of time So that's a way to convert bits that the data into signals It goes through our network it arrives at be be Notices okay. This is to me. I'm be Takes this sends it to the transport layer Takes the data sends it to the application and now the application has received the data If anything went wrong The data was incorrect It would have been the role of the transport layer to say ah, please send again Something went wrong. So that's what the transport layer may do here in this case. Nothing went wrong in the next ten minutes let's just Go back to our real protocol architecture the TCP IP protocol architecture and then We'll move on to something else the quiz for example So protocols rules for communicating Combine multiple protocols together to communicate between computers where they are layered They're organizing to some layers and combine those set of layers are called a protocol architecture The main protocol architecture in use today used in the internet is called Either the internet protocol architecture or maybe more commonly the TCP IP protocol architecture Named after the two main protocols at least in the past That are part of it and it's here. This is what we're going to use in this course What we're going to do in this course is describe different protocols and mechanisms as part of the physical layer how to transmit signals Some mechanisms as part of the data link layer How to get bits across the link efficiently the network layer The main one being the internet protocol so after the mid mid semester exam We'll look at the internet protocol and the last few lectures will finish on the transport and the application layer protocols So we're going to go through this protocol architecture That's why at the end of the semester Even if some things are a bit confusing now this protocol architecture will come together and Make hopefully sense to everyone and the way that like the layers combined together will make more sense What do the layers do? I think we've said for most of them Application layer deals with application specific things So what I'm about to say is on the next These two slides which gives a brief description of those five layers We'll go through here physical layer at the bottom is Provide some physical interface between the device the computer and the transmission medium So in my computer, I have a LAN card. It's in built. It's on the motherboard Here's an old one from 15 years ago. Okay, that's just an old LAN card We have the socket you plug your your cable in and Of course the cable goes to another LAN card on another computer or on a switch another device so The physical layer defines how we connect from the hardware here to the transmission medium So the physical interface What type of signals do we send out of here under this under these copper wires? What those signals mean? How fast do we send those signals the data rate? In this case the device can send at 100 million bits per second 100 megabits per second It's is limited to that and that limitation is imposed by the physical layer protocol Other protocols like Wi-Fi have a different physical layer and they have other limitations so physical layer specifies these things about How fast the data can trend be transmitted the frequencies used for the transmissions codex modems Some things part of the physical layer We'll spend three or four lectures or topics going through these things If you don't know what a codec is that's okay or mom the data link layer You think the physical layer takes bits zeros and ones and sends signals It doesn't really care Whether the signals get to the other end or not It's the role of the data link layer to make sure that that data sent across the link gets to the other end in a reliable manner and efficiently and So the data link layer may provide reliability and other features that make sure that the performance is good and We'll only see that once we get to an example in later lectures It may also provide addresses This device if you look to plug into a computer if it still worked has an address the manufacturer Allocated an address to it the format of that address We can think of is part of the data link layer the structure of the address a Mac address you may heard of I'm going through this five layer TCP IP protocol architecture Other people give the layers different names I've used data link layer some people call it network access some call it Mac link or even hardware layer So we'll use data link layer in this class Just go back one Flicking between slides This diagram shows three devices One's called the source host one's the destination host and this intermediate device a router here. They are source host is my laptop intermediate device is this Router it's an a wireless router. In fact, it's got some It's got wireless capabilities is the antennas and it's got some sockets on the back to plug LAN cables into and the Destination host is this PC. Of course, it's not on but we'll pretend it is and I plug Unplug that one and if everything was on plug it in and Let's say I want to communicate now laptop to PC So the the network is laptop will connect wirelessly to this Device this intermediate device this device will then send a signal across the copper wires to the PC So first we have a radio signal and then an electrical signal. So the three devices here this diagram shows the Typical setup of the layers implemented in each of these three devices The end goal is To get data from my source host to destination host between an application on my laptop To an application on the PC. That's what I want to achieve to do that I Use on each of those computers an application layer protocol the same one For example, HTTP. Maybe that's a web server. This is has a web browser So they must speak the same language to communicate that is the protocol used here is The same or is supported by the protocol used here at our application layer To make sure that the data is sent across this network is sent reliable reliably We'll use a transport layer protocol both here and here the same for example TCP So inside my laptop There is an implementation of an application layer protocol like firefox has HTTP My operating system has the implementation of TCP. So it's inside the OS and the same in this computer now will skip the network and go to the bottom Look at the link from my laptop to the intermediate device There's no cable. It's actually a wireless link, but we still call it a link here. It's drawn as a black line the physical layer inside my Laptop determines how to send wireless signals from a laptop to here What frequency? What power to transmit at the characteristics of those signals are determined by the physical layer The wireless LAN physical layer The physical layer used by my laptop is the same as used by the intermediate device here and That's shown on this diagram These two are the same speak the same language Same with the data link layer the data link layer of my laptop Is the same as what's used on that intermediate device the router. They must be the same to be able to communicate But there's a second link the second link from this router to the PC The physical layer used here and also the data link layer may be different from what's used here And in fact they are in our case in my case. It's Wi-Fi a wireless LAN across the first link that has some Protocols for physical and data link and then across the second link is a wired LAN Called ethernet is the protocol used so remember physical and data link layers apply across links normally They determine how to get data across one link But in real cases in a network we have multiple links It's the role of the network layer to get data across those multiple links across a network So my PC sorry my laptop Has a network layer protocol The PC has a network layer protocol, which is the same as my laptop and Also this intermediate device the router has a network layer protocol, which is the same as my Laptop and PC they all speak the same language at the network lab anyone know what that language is What the network layer protocol is it's IP in the internet the main protocol is the internet protocol That's part of the network layer. It's for communicating across multiple different links So this is a common Setup in the end user computers. We have all five layers In intermediate devices, we may not have all five layers We don't need an application layer protocol at the router. It doesn't care that we're using web browsing It's just data to be received and sent across link to and when then something comes back It's received at this router and then sent back across link one. It doesn't care if it's web browsing email It's just data from its perspective That's a lot of information and a lot of new concepts that Lead to a lot of blank faces at least not many people are sleeping like in the morning section Any questions? I assume there'll be a few but May not receive them let's Summarize that the very basics that you need to know even if you don't understand Everything and how it all comes together know what a protocol is a set of rules for entities to communicate That we cannot just have one protocol We need multiple protocols to do different things and The way in communications that we organize those multiple protocols into is into layers One layer contains protocols For responsibility has the responsibility for specific applications the application layer. We call it one layer The physical layer has the responsibility of performing tasks of getting signals across links to represent the bits Data link layer has the role of Making sure that data just across the link is delivered efficiently and correctly just across the link Transport layer has the task of has many tasks But one of them is to get data efficiently and correctly across a network From one computer to the other one in the internet Network layer has the task of just getting the data across the network to the right destination remember the the first Measure of effective data communications was delivery I have data. I want to deliver it to this destination host One role of the network layer is to make sure It will take the right path through the internet to reach the destination This is simple. There's no choice. You go here and then there, but now imagine the internet There's connections everywhere. I want to get data from here to a web server in the US. Which path does it take? Well solving that problem is part of the network If you can capture those concepts, then I think you're going to be okay for So far Definitely try to remember these five layers the ordering of them and the names There's always a question in a quiz or an exam about them And over time you'll so try and remember their their purposes Some are described here, but not in much detail Over time you'll get a clearer knowledge of what they do and Over time you'll start to be able to link different protocols to the different layers HTTP is an application layer protocol TCP is a transport layer protocol IP network Wi-Fi wireless LAN is in fact has protocols at both data link and physical layer So there's ethernet Twisted pair or optical fiber the cable types Really correspond to the physical layer a couple more minutes, and then we'll stop this and talk about the quiz Where did this protocol architecture come from? Well, where did the internet come from I mentioned briefly yesterday that in the US there was a research network called ARPANET Connected some universities and some government organizations in the US and it grew more people connected Other countries connected together connected their networks and it grew into the internet today Okay, with all countries connected many different users So it grew into the internet The two main protocols used originally were TCP and IP and they are still used and That's why we get this name the TCP IP Well, we'll call it the protocol architecture. It's just where the name comes from the organizations that define How TCP and IP work we'll talk about next week, but importantly The TCP IP protocol architecture here. I say five layers here are the names There's no one document or standard that says these are the five layers It's just decided by different people that okay, this is a good representation of how it works If you look in different textbooks you may see different names and You may see Different numbers of layers six or four you may see in different textbooks So there's no standard way to define this the TCP IP protocol architecture for this course These five layers There are other protocol architectures. This is not the only one or has not been the only one One of the main ones in the 70s was called The open systems interconnection protocol architecture OSI had seven layers similar, but there is an extra two Extra two layers in between here. Okay, there are seven layers It's interesting to know how it worked and the history of it But for us basically at around the same time people were developing TCP IP others OSI TCP TCP IP was the most popular and one in terms of it was deployed the most OSI Was became less and less popular and sort of died off So it's not used in practice today, but some of the concepts of it You'll still see in textbooks in websites. They'll refer to the OSI seven layer model but we will not cover it in any detail and Just to finish There are even others Some older ones IBM had a protocol architecture Apple Novel had their own but again TCP IP became the standard. Most people use that So people started to switch from the old ones to TCP IP In some telephone networks, there are protocol architectures in mobile phone networks 3g 4g There are protocol architectures, which are different from TCP IP again. We're not going to cover them in this course We're going to cover the most popular one and next week we'll continue on the rest of this topic 15 minutes Let's talk about the quiz and The practice lessons quiz opens at 12 o'clock today. So we mentioned yesterday. It's online It opens at noon today. So directly in 15 minutes and it closes Monday at noon. Okay Monday 12 So you have five days to complete the quiz How many minutes does the quiz run for Ten minutes this one some may be longer, but you will see on the web page, but 10s typical How do you pass this quiz? You get 50% or higher. There are seven questions in this one. So you need four or more correct How many attempts do you get? Three okay, everyone knows fine. So if you don't get 50% in the first attempt go back and study a bit more and Try again You get three attempts in total So do the quiz get more than 50% and if you do that for all quizzes in the semester, you'll get the full 15% But there's more Sorry Sometimes I'll also create what I'll call practice Practice questions or practice lessons These are not marked the practice ones They're not marked. They're just for you to learn or to refresh your memory on some topic or practice some topic so If you don't do them, it won't affect your grade directly Of course, if you do them you may learn more and the quizzes may be easier and the exams may be easier But these two practice lessons that are there I think they're there for the next three weeks at least so you can do them almost any time in the next few weeks units and prefixes is about Sorry, I think you have this handout Units and prefixes well, it's just a summary of the common units we see in this course. What's a unit? Well Seconds, meters, bits, hertz Radiance or degrees watts that are the common units we see There are many questions later that okay. What is the speed of this and people will say 100? But you must give the correct unit 100 bits per second or 100 watts has completely different meaning so Just refresh your memory on what the units are. I think this is obvious for most people What about prefixes? well When we deal with very large or very small numbers to make things more convenient we use kilo mega giga terra Millie micro nano and picot for smaller numbers Okay, so we use these prefixes to make the writing of the numbers easier. You must remember them Okay, I'm not going to teach them If you don't remember them it goes through the practice lesson And it'll give a little bit of a description of things Okay, so you must remember that mega is ten to the power of six Nano is ten to the power of minus nine There are others of course, but in this course those eight are the main ones that will see you I think we will not see any others Sorry So the practice lesson They may differ You start the lesson there's no time limit you can do it at any time over any period and You give some description of what you should do there You can read through and just follow next follow the it describes those units So if you know them already you browse through here give some summary of what you should know If you understand units already then you click on This link and you'll get some questions about those units to see if you do understand them If you don't in this case you want to hear more than I have a short video That gives some more examples of those units so you can spend five minutes watching the video here and then go next and Just answer the few questions again not mark, but if you answer them correctly you can proceed to the next part of the What's the answer? What is the symbol of the unit used to measure information the symbol of the unit or what is the unit used to measure information? Bits so information we usually measure in bits a bit multiple bits and the symbol we use is a lowercase b okay, and you just submit your answer and Okay, give some description. Yes a lowercase b is used as the symbol and allow you to continue and In this case not always, but in this case you get another question You download You download 10,000 bits of data in a duration of 20 seconds. What is the average rate of the data transfer? so Some people look a bit confused, but really it's the same as you've done in high school physics or maths of okay, you drive 100 kilometers and it takes you two hours to drive that distance. How fast did you drive on average? Okay, how many kilometers per hour? so a Few simple questions like that and then once you get them correct you proceed on to some other topic the second practice lesson is on Exponentiation and logarithms 10 to the power of 6 exponentiation log of log based 2 of 32. What is it? Okay in later topics will use Exponentiation exponents and logarithms a little bit, but nothing more than high school maths. Okay, so Refresh your memory and then you'll be fine Exponentiation, okay, just a few properties some useful ones not so much you can use a calculator in this class That's okay, but sometimes it's much easier to do it in your head Or to confirm that what you're doing is correct and this lesson will give you some help in that it gives some examples of remembering for example, what is the log base 2 of a thousand Okay, some ways to approximate that what is the log in base 2 of a million And so on so because we'll start to use base 2 because we deal with bits It will come up in some of our court and some of our topics Enough talking for me. Any questions? Don't see or hear many questions So the assessment Assessment items the quiz 15% these online quizzes Homework well, there's no assessed homework. For example, you think of these practice lessons as homework But if you they don't count directly towards your grade There'll be one assignment Released around midterm a bit before midterm and run for several weeks after midterm, which will be a group assignment to Write a report on some topic do some experiments and the rest are exams Okay, so in terms of assessment quizzes one assignment and two exam Any other homework type things will come up on the website like these practice Okay, let's finish for today and next week will continue on protocol architectures and You'll see or you'll do your quiz before Monday 12 noon, okay? if anyone wants to change their passwords or Set their password they can come and see me now