 So after talking about the concepts of general lands and wide area networks there are many different technologies to choose from for lands and WANs and and the related technologies like personal area networks metropolitan area networks Many to choose from in terms of lands today. There are two technologies which are Most widely used one is what we think of a wired land and the common name is Ethernet So we'll talk about that and the other technology we mainly use inside local area is a wireless LAN or the the marketing name or common name being Wi-Fi and There's some similarities between Ethernet and Wi-Fi So a lot of Wi-Fi your wireless LAN access uses some similar concepts Addresses frame formats to Ethernet in this topic. We'll give a brief introduction to Ethernet. So for wired LANs For wireless LANs then we will not cover that but there's some similarities that maybe if you take some The lab next semester with me will do some more hands-on with Ethernet and wireless LANs so first we'll talk about general and Talk about one of the the groups or standards organization that creates standards regarding lands So before we get into Ethernet You probably have seen or heard of the acronym IEEE The Institute of Electrical and Electronic Engineers So it's a really a professional organization where people become members of they do many things one of the things that we see them A lot is they create standards for electrical and electronic engineering. So they write the standards such that the manufacturers different manufacturers implement products Following those standards so that they can interoperate Some of them that you may or may not have seen IEEE has created standards for firewire for cryptography Doing arithmetic in computers and many other things software development project management and so on IEEE Create standards across many different fields related to computing and telecommunications and They give their standards or their series of standards a number so a Very widely used range of standards is those regarding local area networks and originally Metropolitan area networks So they have a committee and the number associated with that is 802. So IEEE 802 And that's what we care about in data communications So they develop standards for personal local metropolitan area and even more recently wide area networks So they have many different standards and they are divided into working groups Most of their standards focus on if we think of our five layer stack And you will need to know for the exam those five layers from bottom up the physical layer data link layer That's what the 802 standards focus on the physical and data link layer How to transmit signals which is the physical layer and how to get the data efficiently across a link the data link layer In fact the data link layer They subdivide into two two layers one called medium access control that topic. We just skipped Which is about making sure the frames can be transmitted fairly and efficiently across a medium and Logical link control LLC is about giving addresses and a few other things for for a link or across a land or inside a small network So this IEEE standards organization creates these series of standards under the umbrella of 802 and There are many They keep developing so some of the older ones are more common IEEE 802.3, which is what we'll talk about ethernet IEEE 802.5 was another land technology, but not very common anymore. So it's old token ring IEEE 802.11, which you use on a regular basis Wi-Fi So this IEEE 802.11 is the formal name of the standard You can go and download the document Wi-Fi is like the marketing name It's much easier for most people to remember and think about Bluetooth so they've had input in Bluetooth Ymax and others so they create standards on wireless and wired technologies Ranging from personal area networks up into a wide area networks We're gonna focus on ethernet with respect to layers So here's our five layer Internet stack physical up to application layer The efforts of the IEEE standards are mainly in the bottom two layers So they create a physical layer for safer ethernet for wired lands 802.3 And what we call a medium access control protocol for ethernet and Similar for Wi-Fi. There's a 802.11 physical layer for how to transmit signals wirelessly And a medium access control protocol for how to share amongst all the users who want to access that access point and other things and for Bluetooth for Ymax and other standards and They have a common 802.2 Logical link control which we'll not talk much about except we'll talk about the address format that these Technologies use So over over the years that this group has been creating more standards of Improving the current wide and wireless technologies Let's just talk about ethernet and the basics of how it works It's developed ethernet was the the name given to the technology developed in the 1970s for land communications so people wanted to connect connect the different computers inside a an Office environment or inside a company together like printers computers at that stage mainframes and so on so Xerox the people who made the photocopiers they Develop this technology called ethernet and it became a standard in 1983 which means that other companies started to use it So when you buy a card like a land card This one's not quite as old as 1983, but I think it's 1990 something a land card Doesn't matter which manufacturer you buy from as long as they implement IEEE 802.3 You'll be able to communicate between different land cards because they follow the same standard At the time there was some competing technologies, but basically ethernet was the most popular for different reasons and Still is the most popular land standard it is evolved over time so in 1973 or about then It had a data rate of around three or of three megabits per second And they use co-actual cables like in some audio systems or cable TV to your TV and a bus topology You use half duplex communications Many if there are two computers connected One could transmit, but the other has to wait for that one to finish only one transmits at a time and the technology was improved over time So in 1983 around 10 megabits per second Ethernet 2 was the name Fast Ethernet 100 megabits per second and it supported a star topology It used a hub. We may say a bit more about that in a moment In 1990 a switched Ethernet 100 megabits per second full duplex links You could be transmitting and receiving data at the same time from your computer in a star topology with a switch and that's that the The main way that it's used today At that point it used twisted pair So the the LAN cables that you use today are still twisted pair cables where Inside there are four pairs of wires copper wires, and we've seen them before four pairs of copper wires inside here and basically you would transmit a signal across one pair and receive on another pair so with Fast Ethernet and switched Ethernet of the four pairs inside here you would only use two in fact So the other two were unused in most cases So that's how full duplex is achieved by Transmitting across one pair of wires and at the same time you can receive across another pair And we'll show you the topology in a moment. We'll look at the the the typical setup Gigabit Ethernet supported up to one gigabit per second still used twisted pair in some cases But used all four pairs so transmit across two pairs receive across two pairs But it also supported optical fiber So not so much used inside your home optical fiber because it's expensive and hard to deal with but inside maybe Connecting servers together inside data centers then they start to use optical fiber And in fact Ethernet has been it keeps to be developed and is used Also in metropolitan area networks across a city and between cities wide area networks and There's 10 gigabit per second Ethernet and these mainly use optical fiber 40 gigabit per second Ethernet 100 and 400 are being worked on or planned so These are mainly for say in the Google data center where they have many servers They need to connect together at a very high speed they may use variations of Ethernet there or between Buildings across a city so not so much for lands these technologies lands now they mainly use switched Ethernet in some cases gigabit Ethernet And that's what we'll focus on those two So switched Ethernet Most lands today use a star topology a star topology We have some special device a switch There we have some special device. Here's a small one a small home or office switch This has it needs power. It has eight ports on the back and you plug your LAN cable into one of those ports and Like the other land and into your PC what we call our station PC or laptop and Then your second PC or laptop you plug by another LAN cable into this switch So all the stations connect via point-to-point links to the switch So for example, this switch can support eight stations connecting if you want more then you need a bigger switch and typically switches range from two four eight ports 24 32 48 is usually the maximum number of ports so you get a rack a Unit a unit that fits in a rack and has 48 ports if you want more stations to connect you need to connect those switches together model with switches So you communicate between your computers by sending to the switch and the switch sends to the destination computer the key characteristics is That our links are full duplex I can be transmitting data to the switch To and onto someone else and at the same time be receiving data from the switch from someone else Point-to-point links so there's no sharing of the medium twisted pair cabling is Primarily used in in home and office lands not optical fiber. So these are twisted pair copper wires There are different quality of the wiring really so called different categories Sometimes it says on the on the outside of the cable. This one says category 5e so There's a category 6 which is better quality and less interference allowing for One gig per second without any problems the data rate supported in most lands Who has a laptop yes, what's the data rate supported for your LAN cable? Any idea can you find it in your operating system? What is it what data rate does it support? Not sure do you want to guess? Anyone else want to help him how fast could it send if I plug the LAN cable into your laptop and then into the switch and onto another computer When you bought the laptop did you look at the specs? Anyone want to guess how fast does a laptop today if you go shopping how fast will it be able to send over a LAN? 100 megabit per second if you bought it maybe five or ten years ago if you buy it today They'll usually support one gigabit per second. Okay, so most PCs and laptops nowadays so laptops have a a LAN port and it's the LAN card is really on the motherboard PCs you usually get a either on the motherboard or a separate independent PCI card most of them today support a Maximum of one gigabit per second But they all support the low also support the lower rates so Your laptop will be able to send it one gigabit per second 100 megabits per second and probably also 10 megabits per second the speed that it uses Usually depends upon the switch So this switch for example can support up to one gigabit per second You plug your laptop into this one and you'd be able to transmit at one gigabit per second between laptop and switch But if you have an older switch or a cheaper one Like you find at the back of that wireless access point also has a switch in it Then it will usually only support 100 megabits per second If your laptop supports one gigabit per second and the switch only 100 megabits per second Then they basically auto negotiate They choose the highest which both support switch 100 laptop 1,000 then the laptop will go down to 100 so it can communicate with a switch, so Usually they support up to one gigabit per second But some older switches only support up to 100 megabits per second The standards for the different data rates have different names if you look them up some are called hundred base TX thousand base T100 meaning the data rate one thousand the data rate in megabits per second Different variations of that the cabling used as well The typical distance that you can have a link so from PC to switch a maximum about 100 meters You cannot have a cable longer than that Random access we haven't talked about medium access control, but random access is not used we have point-to-point links Meaning the medium is not shared When my laptop transmits It's transmitting to the switch and no one else is using that link It's dedicated from my laptop to the switch, so there's no sharing involved, which is very good for performance Any questions on Ethernet? This is one of the easier topics. I think you you all use it Whether you're aware of it or when you in the labs in the lab computers They're all connected via LAN cables Any questions on ethernet switched ethernet the star topology Here's a simple example with six stations. Let's say we have six PCs in our small land that we want to connect together We want to allow anyone to communicate with anyone else We have this switching device this switch device in the middle So we connect via cables from PC to switch in all cases Note that ethernet is for communicating inside a LAN It doesn't deal with how to talk to others on the internet It's just internal communications inside a LAN So if there's someone else out on another network ethernet doesn't deal with how to communicate with them We'll see that in the next topic on the internet in general. We call these stations that is a through to F for stations and They're either In the internet we'll see later hosts or routers a host is like your PC or laptop a Router is a station that will connect to another network We don't have that in this example work in the next topic. We'll see okay. We want to connect our LAN to someone else's LAN So one of these will become a router in that case But with respect to Ethernet, they're all just stations Full duplex twisted pair connected to the switch The switch has multiple ports so four up to 48 for example if you want The more computers you want to connect via a switch that the larger the switch the more expensive the switch and What we do is we transmit frames Because we have point-to-point link We just transmit the frames to the switch and the switch will do some magic and send it on to the destination So if a wants to transmit to D a transmits across is its link to the switch switch looks at the frame and Sends it on to D So we need to talk about a little bit about what are the frames? What do they look like and the magic that the switch does To send it on to D. So let's look at the structure of the frames that we send using ethernet and Importantly the addresses that we use First the addresses All of the 802 standards or almost all of them Whether it's Wi-Fi Ethernet and some of the older technologies use the same format of address So each station gets an address So when a wants to send to D They don't have letters like A and D. They have a 48-bit address So a 48-bit number identifies the station So the format is defined and it's common across many technologies, so it's important to be aware of it And I triple E 48-bit address Sometimes called a MAC address or a hardware address. You'll come across the different terminology It's 48 bits in length, but it's split into two parts There's the first 24 bits which identify Usually the manufacturer or some company associated with the manufacturer of the device So the manufacturer of your LAN card So whoever manufactured it has a unique ID and that's represented in the first 24 bits The second 24 bits are assigned by the manufacturer to the device so all the LAN cards or What we sometimes called network interface cards Manufactured by one company in one process would be assigned different Would have the same first 24 bits, but the next The last 24 bits will be different different amongst all devices for humans Writing down and remembering 48 bits is not easy. It's easy to make a mistake when you write 48 zeros and ones so The 48-bit addresses are converted into a slightly easier format to read and write and it's this hexadecimal format There are six two-digit hexadecimal numbers So here's an example of a 48-bit address But written in hexadecimal Remember hexadecimal goes from 0 to 15 One hex digit is four bits So here you see there are 12 hexadecimal digits or 48 bits and The pairs of hexadecimal digits are separated by a colon or sometimes a dash the different formats Let's have a look at some example addresses and talk about the split between the first 24 and the last 24 So on my computer How many network interface cards does my laptop have? Not one two good I have Wi-Fi and I have Wireless LAN or Wi-Fi or IEEE 802.11 and I have wired LAN or Ethernet 802.3 is the standard. So I have two interfaces In fact Wi-Fi and Ethernet use the same format of addresses. They have many similarities On my computer. I can see some details about those interfaces My interface configuration of my Ethernet 802 and it shows me some information and This is the thing of interests the hardware address So that's the address that's assigned by the manufacturer of my my LAN card It's actually a chip on board the motherboard F0 through to B7 48 bits, but expressed in hexadecimal my Wireless LAN card also has a hardware or IEEE 48 bit address different value the concept is that all devices in the world will have unique 48 bit addresses globally unique addresses There are some exceptions though The first six digits identify the manufacturer of that device or at least some company associated with a manufacturer the designer maybe and the last six digits in the hexadecimal version identify Within that manufacturer that the particular device Who manufactured my devices anyone know who manufactured my LAN card and Wireless LAN card anyone want to guess who manufactures wireless LAN chips or hardware for LAN cards have a check on your own computer and See if you can find your hardware address We'll have a look in a moment my Ethernet card is a real tech Uses real tech hardware and some model RTL811 or similar So this is the the brand name or the manufacturer for the LAN card and for the wireless LAN It's just listed as a network controller. It's an Intel wireless chip okay now the Mac addresses themselves identify the manufacturers Let's look at the wireless LAN chip first Note the first six digits eight C a nine eight two so that identifies a manufacturer and IEEE have a website They register those first six digits to particular companies So they have a website where you can look up the manufacturer that I have eight C a nine a two eight two and You do a search if my internet works And it tells me that the manufacturer for all LAN cards which start with those six hex digits is Intel Okay, so that identifies the manufacturer of that card if we do it for my Ethernet card It was real tech What do we have? F zero D E F1 We look it up and we get some company with drawn info con Okay, so it doesn't identify real tech So it doesn't necessarily identify the the brand name of the device But usually the the the company that designed it in many cases someone designs it for some other company So this is the really the manufacturer of the device in that case my LAN card Your next quiz will involve you trying to look up and and I suggest you have a look at your laptop Your mobile phone or any device with a LAN or Wi-Fi card and you can look up the the actual manufacturer of that Or who's assigned as the manufacturer? So what happens the manufacturer has this first six digits and when they Manufacture the cards they assigned a unique last six hexadecimal digits Our Mac addresses unique in the world can two people have the same Mac address Check see if you can find the Mac address on your phone It's there Your phone has a Mac address you have Wi-Fi on your phone If you look in the status In the advanced settings somewhere you find them the Mac address on your phone In theory devices shouldn't have the same Mac address They should be globally unique But in practice nowadays that they can either the manufacturer makes a mistake and assigns two devices the same address But nowadays you can set the address in software So in fact on my laptop I can change the address Which gives the possibility that two or more devices can have the same address, but in practice usually they don't so All of our stations have a Mac address and When we want to send frames from one station to another we'll see the format of frame includes the source and destination Mac address These 48 bit Mac addresses are used not just in Ethernet, but also in other technologies use them There's a new newer version which is not so common which is it uses 64 bits But it's only it's been used in some technologies like firewire We'll talk about the special case in a moment. Everyone found their Mac address on their phone You don't have a phone See if you can find your Mac address Find it Right, you may see a Mac address and a Bluetooth address Same format so Bluetooth uses the same 48 bit or 12 hexadecimal digit address Bluetooth is a different technology. You should you may see two Mac addresses one for Wi-Fi one for Bluetooth You won't have an Ethernet address because you don't have wired LAN on your phone, but on the PC on laptop You'll also have your Ethernet address Wi-Fi, but Wi-Fi uses the same format of addresses. There are many similarities between Wi-Fi and Ethernet One's 802.3 the other's 802.11 And Bluetooth has similarities as well so When one station wants to send to another They send 802.3 frames and this is the structure of the frames There's data okay our frame contains data minimum of 46 bytes normally up to 1500 bytes There's an extension that allows jumbo frames much larger, but not so common So the data up to 1500 bytes then we have a header at the front and a trailer at the end Quite simple the header contains the destination address the 48-bit address or six byte address that we're sending to and The source address who sent it it contains a two byte field called the ether type and This really identifies what type of data is inside this So our Ethernet frame contains data from other protocols. What is the other protocol? It's usually specified by the ether type In practice, you'll mainly see the ether type is the value 8 meaning the other the type of data is the internet Protocol data it's from the internet We'll see that later At the end we attach a checksum This is error detection So that when the receiver receives this it uses the checksum to make sure the data has no errors If they're errors that we need to fix it somehow There are possible jumbo frames not very common This is really at the the data link layer or the Mac layer In addition, there's one byte of extra information added at the start by the physical layer So before we transmit this we need to transmit an additional one byte at the start So how does it work in flat frame delivery? Here's an hour our example of six six stations and I've given them some fake Mac addresses Okay, I just chose some Mac addresses for our six stations The switch doesn't necessarily need a Mac address the switch is there just for sending frames on to others The the Mac or hardware address is assigned by the manufacturer So here we have our six stations. Let's say a wants to send to D. So a would create the frame Source address Sorry, the first field is the destination address 20 CF through to six seven So the destination address would be that of D Source address is that of a? Ether type identifies the type of data we have you which is usually the internet protocol we include the data and then attach a checksum, which is Some information that allows the receiver to check that there are no errors inside the data In before the midterm, I think we talked about a parody check as a very simple checksum But there are others more complex checksums that allow for error detection A wants to transmit the frame to D. Where does a send the frame? Where does a send the frame? Where is a in our picture going to send the frame? There's one option a has a cable to the switch So it transmits to the switch okay There's no other option in in a star topology or the switched ethernet. You just transmit across the cable that's plugged into your computer Which is goes to the switch So we transmit a frame to the switch and then the switch has the job to realize Destination is this 20 to the six seven address Send it on to D and the way that switch does that is the switch has some table It's a bit small on this. I should have made it bigger But the switch has a set of ports which the computers are plugged into This one has eight ports on the example I have just six ports or six computers plugged into this so we can think port one through to six are being used in this example and The switch maintains some table that maps the ports to the MAC addresses So it learns when the really when the cables are first plugged in This switch learns that on port one at the other end point is f zero four five So it maintains a table saying on port one you can reach this MAC address which identifies computer a and on port four is 20 to through to six seven so this table is maintained inside the switch It's created when the really when the cables are plugged in by one of the the protocols in operation stores them in memory and therefore it's quite simple because When a creates a frame it transmits to the switch The destination address of that frame is used to determine for the switch Destination address is 20 through to six seven switch looks in the table Realizes it needs to go on port four Transmits on port four and it's received by computer D So it just transmits to the switch which forwards it on to the destination That's almost it by ethernet any questions You use it every day whether it's at home or in the labs or in our office so wired lands Most most wired lands in use today use this technology How fast can we send from a to D? again, it depends upon The data rates supported by the LAN cards inside a and D and the data rates supported by the switch It will use the highest data rate that they all support typically 100 megabits per second or one gigabit per second in most technologies Yes, in this case just if B wants to send to E It creates a frame So if B wants to send to E it creates a frame Destination address is the MAC address of E Source address is the MAC address of B puts the data inside transmits this frame To the switch The switch recognizes that that destination address needs to go on port five and transmits across this link so Allows any pair of stations to communicate with each other note that Ethernet is only for internal LAN communications if there's some web server that we want to connect to in the US and Here's our LAN inside our office here We're in our classroom for example Then this Ethernet doesn't support communications to those outside the LAN What we would need and our next topic covers it is that one of these devices. Let's say C Has another link to it that goes to another network via a LAN or a wide area network and Then C would send on to that next network and then go for on and on until it reaches a destination So that's not what lands about lands is just internal for the local area any questions on Ethernet Quick topic So be aware of the the address formats You'll see them. I See one more example in a moment, but you'll see them a lot in practice the 48-bit addresses the frame format and the Be aware of the technologies that is it uses twisted pair full duplex communications in a star topology Data rates of 100 megabits per second or 1000 megabits per second when you go home tonight I suggest if you do a search for No, you'll be working on your assignment, but while you have a break you do a search You found your MAC address on your phone Just search on on a website search on the internet for IEEE Registration or IEEE addresses and you'll come across this website Which allows you to look up Given the first six digits of the MAC address find the manufacturer note that it expects it in the dashed format One last example on Ethernet. I think we may have seen something like this or similar at the start of the course this is a Capture of some packets sent in a network seven different packets What was happening in this packet capture? Have a look at mainly the info There. What do you think was happening? What do the user do? When I recorded the packets being sent across a network in this case So this is a this software shows a record of packet sent and or received from a computer and I did this while I was running an application on my computer and This case it recorded or I've filtered out and shown just seven packets across what about? 45 milliseconds the this exchange took place place source and destination address not MAC addresses IP addresses That's our next topic. What happened in this exchange? What did I do on my computer look at the info in those seven packets something you may recognize What did I do? The things you don't recognize skip over, but there's some words there. You would at least recognize What did I do in this case? What's here act? Yeah, there's some acts there Even simpler. What did I want to get it. HTML? Get is part of web browsing when we use our web browser to visit web pages we use a protocol called HTTP and We send a request message from our browser to the server saying I want to get some web page and The server sends back that web page this fourth message was my Computer sending a message to a web server saying I want to get the file in the the root directory in slash directory called it. HTML and Where's the response back? Where's the web page? Seven packets, which one do you think contains the web page? not five The web page this is the request for the web page Here's the response Let's zoom in Some of the other details we we were not trying to explain yet the request if I double-click I can zoom in on that particular packet. This is the request We use HTTP the request I Did this one actually two years ago? No, I didn't do it at the start of this course the request at that time was to it.sittuac.th slash it.html So this was my browser Sending a request what browser my firefox browser sending a request to a web server the protocols used HTTP We haven't covered it yet, but TCP and IP and Ethernet here. It's listed as Ethernet 2 but generally Ethernet the Ethernet frame destination address Which station my computer was sending it to? So 0050 and so on Source address That was the address of my computer at that stage So my computer sent it and the type is that ether type field which just identifies What's inside this Ethernet frame is an IP packet? So it says what is the data? This software doesn't show the trailer doesn't show the checks. Um, that's hidden from this software It's usually done in hardware the frame was 367 bytes So six byte destination a six byte source two byte type and the rest was really data with respect to that frame and the response that came from a Web server came most likely I can't remember whether I was using LAN or Wi-Fi But maybe came from a wireless access point to my laptop at the time was 569 bytes It was an Ethernet frame Destination source type It contained an IP packet and our next topic took talks about IP the internet protocol and TCP and inside was our web page or the response the response contains some Okay message the request was okay. Here's the response some other information about the server the data the response and so on and most importantly if we scroll down It contains line-based text data, which is That was the web page that the server sent back to my laptop. So when my laptop received that That response it displayed the HTML on the screen So that's just a simple example showing the Ethernet frames in the context of a web page request and response Questions on Ethernet Look at your phones again. Okay, stop playing your games. Look out your phone and find another address on your phone Try and find another address Go to back to where you found your Mac address and see if there are any other types of addresses in your phone I am II the I am I am II as some identifier for the for the mobile phone or the SIM card Signal strength is not an address. It's how strong the signal is that you're receiving Maybe you'll see another address or It may be in a different screen when you access a particular network connection like Wi-Fi But I think you've seen him before and and in the last 10 minutes we'll talk about another type of address When you connect to Wi-Fi When you connect to a wireless access point it sometimes takes a few seconds to connect and sometimes you see Looking for IP address or something about an IP address That's another type of address which we'll introduce now and then tomorrow we'll talk about the internet and the role of IP addresses But because I think most of you have seen IP addresses Let's just introduce them in the last 10 minutes and we see some other examples up here Mac addresses identify computers inside a LAN What we'll see the internet is made up of is many lands and wide area networks separate ones Connected together to create one large network the internet and in the case of communicating between computers in the internet We have a second type of address called an IP address and The examples from my packet capture and these two columns of source and destination This one source address is 203.131.209.72 and the destination 10.10.99.251 They are a different type of address called an IP address So this is not specific to Ethernet anymore, but moving on to the internet How long is a MAC address or an Ethernet address? The topic we just covered how long is the address? How many bits? Look at your slides with the MAC address. How many bits? When we talk about addresses, they usually represented in binary Even though we write them in hexadecimal or some other format the the raw format is binary. It's not 64. It's 48 bits Okay, well done. I triple ea to two dot addresses of 48 bits. There's a variation which is 64 bits, but we're not touching them 48 bits Convert nine hexadecimal nine into a four-bit into a four-bit number and Do that for every other hex digit and we get 48 bits so when your computer creates a frame and Transmits that frame the address contained inside is a 48-bit number But just to make it easier for humans to look at Computers often convert them when they display those addresses into hexadecimal. It's the same with IP addresses How long are IP addresses anyone know I want to take a guess They're not 48 bits IP addresses different type of address, but you may have seen or heard of the length Anyone know the length of an IP address in bits? Let's write some down Or maybe look at an example on my computer first My wireless LAN interface had a hardware address or MAC address. This is the 48-bit ethernet address But it also has an internet address INET and My IP address is 32 bits in length 10 dot 10 dot 10.107 dot 238 This is the human friendly form But the computer stores it as actually a 32-bit number So this is an IP address or most precisely an IP version for address Let's just do an example and talk about the conversion between the human friendly form and The 32-bit computer friendly form So where do we get 32 bits from that one 10 dot 10 dot 10.107 dot 238 So an example IP address What was it 10 dot 10 dot 10.107 238 This is the human friendly form for IP version 4 addresses and It represents 32 bits the scheme is there are four four decimal numbers not hexadecimal now we use decimal numbers and Each decimal number is separated by a dot. This is not a decimal point. It's just a dot and We represent each decimal number as an 8-bit binary value So convert 10 decimal 10 to the binary as an 8-bit number What do we get? 8 bits okay, so our 8-bit number for decimal 10 and 10 decimal well luckily that'll be the same 107 no seven you will check with your calculator and 238 I'm gonna run out of space Can you tell me one? 1110 Almost fit it in quite simply just convert those four decimal numbers into 8-bit binary values That's a real IP address the 32-bit value that your computer Stores in memory and sends when it sends an IP packet But when your computer displays it to us It shows in a the human friendly form of what's called the dotted decimal notation Take each 8-bit value convert it to decimal separate those four decimal numbers by dots Every IP address that we would deal with in this course in the remainder of the course is in this format It's either 32-bit value or the dotted decimal format any questions on this conversion That's we've got some slides on it that we'll see in the next topic But I think that's quite easy to capture that if you've got an IP address The dotted decimal notation you should be able to convert to binary or If you've got a binary address you should be able to convert the dotted decimal Okay, we're moving beyond the ethernet now up to the internet How many possible addresses? IP addresses About how many? 32 bits while there are two to the power of 32 possible values Which is about four billion so they're about four billion possible IP addresses Now there are some exceptions some some are not allowed to be used some are reserved for special purposes But with a 32-bit address there are about four billion possible values meaning in the world if we use this IP address we can Give addresses to about four billion different devices How many devices in the world that want IP addresses? How many mobile phones in the world? many Add up the mobile phones PCs laptops all the servers all the access points all the different devices Nowadays cars washing machines and into the future and it's much more than four billion So if we want to give a unique address to every device in the world Assigning them a 32-bit value is not enough Now there are some schemes to try and work around that the fact that there's not enough There's some way special ways to make sure that we do have enough But what people have done over the last 10 or 20 years is developed a new version IP version 6 Which uses 128 bits? 128 bits is something like billions and billions and billions for each person in the world Okay, so 128 bits is not a problem on my computer That's called an IPv6 address and it's using a different format It's shown here this strange set of hexadecimal digits That's all we're going to say about IPv6 in this course We'll focus on the more widely used the older version IP version for so what we do tomorrow is we'll talk about What is the internet and? Then we'll look at how to computers get IP addresses and how they use them But I'll assume from now on if I present any IP address in Dot a decimal notation you can convert that to binary and vice versa Let's stop there and tomorrow we'll move on to the internet slides, and that's our last topic We'll cover tomorrow and next week