 So how do we deliver TV high-quality video over the internet? We mentioned we we can differentiate between normal web-based video where we for example stream watch YouTube File-based distribution where we download a file then watch it after it's downloaded so non real-time Whereas IP TV is different where it generally refers to standard TV quality content that is large screen no disruptions and Real-time so how do we achieve that? We had a quick look at the equipment and some examples and we skipped through and said Well in a an example scenario an example home What type of content are we going to consume and? Okay, we have voice So now let's consider we want to run all of our services Via the internet so in your home. You've got one network connection via the internet You don't have a separate telephone line. There's no separate cable TV or satellite TV. Everything's across the single line so voice web browsing and TV content and Not just watching one channel at one time, but streaming model channels at the same time How much What data rate do we need to support this into our home? Well, you're talking about tens of megabits per second So we'll shortly look at what technologies will support that in our home So that's where we finished last week Let's see what we missed most Services IP TV services make use of private networks What that means is that The the company that's providing you the service is usually an internet service provider and the content in Particularly the video content is going only over that organizations network. It's not necessarily going across the public internet The reason for this and I'll show you some examples and we'll mention some different examples the reason is that When we need high quality high speed data delivery with strict performance requirements small delay Give priority to some data over others Then we need good control across the network So if it's a single organization that owns and operates the network they can control the performance of that network But if you're trying to stream high quality TV across the internet from Across multiple internet service providers Then how can one ISP? Control the quality across multiple ISP's networks. It's much harder so many IP TV services are Offered by internet service providers or As part of agreements between content providers and internet service providers And we can think of them as being private networks Here's an example of a typical setup or a very simplified view of a setup of an IP TV network We have a home here the end user And they have a set of computers or devices that they want to access the content and They have a network inside their home okay, so you have connectivity to the outside net internet and Inside your home. You have a wireless LAN or an Ethernet network So you have a home network You connect normally to an internet service provider an ISP for example your ADSL connection To the internet from your home to the rest of the network This we'll often refer to as the access network. This is the This is where the customer Accesses the the larger internet or the larger network So we have the ISP access network and From one of our first topics this this semester we distinguish between an access network and a core network Where a core network connects multiple access networks together? In this example, there's only one access network, but imagine that there are other routers and other access networks around here for example, this is for one suburb and then there's another access network for another city or another suburb another area and This is the core network that connects those access networks together and let's assume. It's the same ISP Okay, so the same company running these networks So this may be an ADSL network here so from your home, there's a router and That router connects across a telephone network into some Telephone exchange using ADSL So that we considered the access network and then from the telephone exchange and there may be multiple exchanges for multiple access networks They connect together via the ISP's core network For example optical fiber links Now where do you or the end user get access to the different services and the main different services we want as an end user Normal internet access web browsing for example access to the public internet voice calls so to be able to pick up the phone and call someone not just via someone via Using Skype, but to call someone on any telephone network Mobile phone landline telephone so via a public switch telephone network And also view view TV. That's what we're focusing on How do we get TV into the home without using or using the IP network? So in this case we see Here's our home a router to our access network and the access network connects to the core network We're another router an IP router and Then the ISP connects to the broader internet the public internet via some border router here Okay, so then we go to other ISP's in this direction So if your web browsing Accessing Facebook then your data goes via the access network the core network to the border router and then out to the public internet If you're making a voice call and calling someone on their mobile phone You use voice over IP So you use SIP for example to set up the the voice call and then RTP to send the voice traffic You use voice over IP to connect from your home phone via the access network The core network and since you're connecting for example to a mobile phone You need to connect to someone on the the the normal public switch telephone network So there may be a gateway that takes the voice over IP connection and turns it into a normal switched connection that Mobile phones and landline phones use so for example use voice over IP to here and then Use the normal telephone network the public switch telephone network to connect to someone who you're calling here If you're calling another user who also uses voice over IP for example, maybe they're on the same access network Then it can go direct to them Or on another access network go via the core network to that user and then what about TV content if you're watching TV then a Typical setup is that we have the TV station the organization that provides the content Channel 3 channel 5 whatever the organization has their content and They have their own TV network and that needs to be connected to the ISPs network and In this case the name of the device that connects the TV network to the ISP IP network is a video head end So the content is in whatever format it's filmed in or they they store the content in If it's live then they may be filming it and Then it's up to the TV Network that is the the company that runs this TV network to distribute that content to this video head end and Then the video head end converts the content into a format that can be sent across the IP network for example, it encodes it using MPEG for some codec and Uses RTP the real-time protocol to send that content to stream that content From the video head end through the core network to the access network and eventually to your TV in your home So the idea is all these three services TV telephone and Internet access normal internet access are all provided by an IP network and To make sure that the quality that you need to deliver these services to the end user is suitable Usually the IP network is run by a single company because if it's run by a single company then They can guarantee the performance inside their network if it's run by multiple companies Then they need to have some special agreements to make sure that they'll provide that But Required performance, so that's the general idea that we have Access to all three services via the one network connection in your home You no longer have a home telephone line Or at least you no longer have a home telephone line for making phone calls everything goes via IP Over via your ISP their core network and then to the Destination let's look at some of the requirements for this to work the the technologies for TV content we need The video head end that converts the audio and video from the the format that's provided by the TV station Into some digital format that can be sent across the network So for example The content may be sent across an analog or a digital network to the video head end then that converts it into say M M peg for and that then Packetizes that content puts it into RTP packets and sends it across the core network So that's the role of the video head end to convert it from one format And it may be analog or digital Into a format a digital format that can be sent across the network And a typical approach is to use RTP as the protocol to send it across the network to stream At the it's not shown in this diagram, but in your home you usually need some set-top box to receive the content and Distribute the content to the appropriate devices the TV The audio system and so on what protocols are used well different protocols available, but a common one For video delivery RTP the same with voice over IP RTP is not just for voice over IP. It's for in general audio and video So we went through examples last week where we took voice and depending upon the codec We put it into packets and sent those RTP packets the same thing can be applied with video content The other two parts or technologies needed for this to work are some ways to manage the network and The different technologies within those networks for network management For performance reasons usually we need to make use of multicast now we mentioned the concept of multicast remember with multicast the source creates one copy of the content and sends it through the network and Inside the network it In particular the routers inside the network Deliver that content to multiple destinations So it's one to many delivery Where we have one special multicast address where we send it to that address the data should be delivered to many hosts That's well suited to TV delivery In this example, there's one destination, but of course in an ISPs network There may be many destinations watching the same channel Okay, so there are a thousand people at the same time of the day watching one particular TV channel So what we do is that that content that TV channel is delivered to the video head end just one copy of it and Then use multicast in the network So using RTP We create one copy of the content send it and The routers inside the core network So they're not shown here, but inside this cloud there may be different routers They deliver it to the appropriate destination so that everyone who's subscribed to that Multicast group receives a copy Let's try and draw that Which extends upon the one on the board, so let's add some more users is The same network but with some more details So we have the video head end then we have our core network and Inside this core network. I've drawn the circles here to mean some routers inside that network and These three devices These routers here on the edge of the core network and this so here are some six homes our six users and We can think of this say as an ADSL connection. So our access network So going into some telephone exchange here Home a connects in via say ADSL That's our access network and inside the home. We have a home network now. We want to deliver for example We have our six users. Of course, we could expand this Let's say it covers Whole of all of Bangkok. So we have different at access networks for different regions in the city and These are routers across the entire city let's say some users Tuned into a particular TV channel so three users a C&D turn on their TV and Tune into channel three Okay, so they all want to watch that TV channel so although it's not drawn here the TV station The content for channel three is being generated and sent to the video head end What the video head end does is converts it into a format that can be sent across the IP network So a particular codec that's supported by the ISPs network and probably using RTP There are other protocols, but let's stick with RTP So the video head end as the video comes in the content comes in it generates RTP packets and sends them using multicast Even though there are three destinations With multicast we just send a single copy of that packet So if we have a packet containing a portion of the video content for channel three We send a single copy of that packet. So here's our packet the source Address is the video head end whatever the IP address is for that and the destination address The destination address will be a special IP multicast address So the way multicast works is we have one special IP address which can represent multiple users and We say that those users Join or subscribe to a multicast group So we'd have a special address here. I'll just say I Were not right an actual IP address MC for multicast MC3 multicast group 3 why 3 because we're watching channel 3 but in fact, it's a IP address that would be here. This is an IP packet. We'd have a source address and a destination address This content needs to get to users AC and D But what we do with multicast is we create one copy and send it from our source to the first router These are routers inside the network and they support multicast This first router receives a copy of the packet. Where's it send that packet? Let's make it a bit easier. Let's give names to the routers One two Three The other routers in our network Video head end creates the content or at least the content it's received from the TV station puts it into an RTP packet Where the IP source address is that of the video head end and the IP destination address is a special multicast address Where does this Then it sends to router R1. Where does R1 send a packet to? Where does R1 send a packet to? Yeah, it will use its routing table correct and most likely what will it decide where to send it quite simple There are two options R2 R3 Where does R1 send to? Sends to both okay, so it receives one copy and It uses its routing table and the routing table must be set up to say that I'm not I will not try and draw it here, but to say anything going to multicast group three I Need to send to both R2 and R3 Why both R2 and R3? Because we need to send to them to reach the destinations a C and D So part of multicast is setting up them the routing tables to include this information and That relies on users subscribing to a particular multicast group, so let's keep track and say that Currently in multicast group three mc3. It corresponds to users a C and D Now the current three users in that group So R1 receives a copy sends to router 2 and router 3 Where does router 2 send to? One option that's easy Router 2 will send a router 7 router 7 will send to a Nothing works on this board router 1 Sends to router 3 router 3 sends to where? Sends to 4 only no need to send to 5 Okay router 3 It must know That since a C and D are in the multicast group In particular C and D have told router 8 very multicast group 3 and router 8 has told router 4 that someone on my network is in multicast group 3 Which also is in for informed router 3 so 3 will send to 4 and Sender 8 and 8 will send a C and D so We send one copy of the packet at the source Then it split and made into two copies as we go across these paths and as We reach R7 a single copy is sent to Home a and at R8 a copy is sent to C and another copy to D How many copies in total? Well, we count them one two three four five six seven eight nine So for that one piece of content That's one small portion of the TV In the network nine copies of the packet was sent If we didn't use multicast There's one source and three destinations if we did not use multicast The only option we'd have is to send a copy across this path One two three four packets Send another copy from source to C Which is one two three four five packets and Another copy from source to D one two three four another five packets Which is what a total of 14 packets in that case if we don't have multicast We need to send a one copy of the content for every destination with multicast We can significantly cut down on the number of copies of packets we send in the network Especially if we have many users Who are receiving the content on the same access network When we have two users on the same access network Then we send one copy of the packet until it gets to this router and then it creates the multiple copies Try and imagine now that's expanded to having thousands of users one TV station TV three sending the content of the video head end Sends the data and we have thousands of users watching that same TV station at the same time with multicast Through most of the network. We're only sending a few copies of the packet But if we didn't have multicast we'd have to send send thousands of copies of the packet all through the network So when we have many users receiving the same content then multicast is very beneficial It's especially especially so for TV because many people are watching the same content at the same time So that's when multicast is is Is important any questions on the the benefits of multicast in IP TV We haven't gone through the techniques for how multicast works like how to establish the routing tables There are protocols for The destinations to join a multicast group What happens if user a turns off their TV and they leave They're no longer watching TV three Then somehow we need to inform these routers That there's no need to send a copy of the packet to router to Because there's no one in this direction that should receive a copy so if we Stop watching that channel we leave the multicast group and For that to work There are some protocols for Notifying the routers of that so that they can only forward the packet in the necessary direction Similarly if someone turns on the TV and watches switches to channel three user e in this case Then again the routers in the network need to be updated so that router three will now send a copy to router four and router five So that e c and d will receive it That process of leaving and joining the multicast group or subscribing There are protocols for doing that normally in TV networks the content the The process of switching to a channel Your own channel three is switched to channel five is Equivalent to joining multicast groups So if you're watching Channel three and you use your remote control to switch to another channel Then that triggers the multicast protocols to go to work to inform the routers that now Anything to multicast group seven must be delivered to e So in IP TV often multicast Groups are associated with TV channels The similar can be applied with say radio channels are the type of content so multicast is important in IP TV Qualitative service we didn't talk about that we skip that topic But basically it's important to be able to give priority to different services What's more important making a phone call or accessing Facebook? well more important in terms of Performance requirements is the phone call that is a phone call the delay requirements are in the order of hundreds of milliseconds We need a small delay accessing Facebook if the delay of your packet is 500 milliseconds It will still be okay so Giving priority to different Types of traffic is what quality of service control does so if we can do that We can provide a better service to the end user Give priority to voice calls Compared to web browsing for example But we didn't cover that in any detail The other thing that's needed which we're not going to talk about of course some way to keep track of who's accessing the network Are they authorized to do so to log in and to charge the money for example? What technologies do we need inside these networks? Inside especially the core network the access network and the home network Well, it depends upon the speed requirements Typical technologies inside the core network are using optical fiber Things like SDH are common Access networks ADSL to optical fiber coaxial cable some cases ethernet and In shot inside the home ethernet wireless LAN remember From the end user's perspective a house a home may require a data rate of tens of megabits per second if we want high-quality TV and It turns out as we go through these three networks from core Access and home network considering these different technologies Usually the slowest one is the access network The service internet service provider access network the bottleneck link or the is that last mile that last portion of the Network to your home Let's look first at the core network. What do we need in terms of capacity? How fast should the core network be? to support IPTV Here's some example numbers for HDTV or for standard definitions, so If we can work it out With the blue line, let's focus on the blue line high definition TV in this case the Assumption is that we have about where's this About 10 or 15 megabits per second needed per per TV channel So if there's one person watching hate high definite high definition TV The network has to have capacity of about 10 to 15 megabits per second to support that channel so if we have 10 Channels that we want to support at the same time then we need 10 times as much and As we increase the number of channels we get a linear increase in the capacity requirements for the core network So this is the amount that we require in total and this is the number of channels that we want to support in the network Because if we have 10 channels So the organ the the company wants to provide the users with a choice of 10 different channels Then it means at any one time Some users may be watching each of those channels. So some users watching channel one channel two channel three and channel ten Therefore we need to be able to be streaming all ten channels through the core network at the same time if the capacity to stream one channel is Say 15 megabits per second Then the capacity needed to stream ten channels is a hundred and fifty megabits per second and As we increase the number of channels, of course the required capacity of the network goes up So this is the required capacity for the core network it's 100 channels, which is many for most networks So think of a TV network how many supply 100 channels It's close to the limit then the capacity inside the capacity net of the capacity inside the core network is Approaching two gigabits per second With optical fiber that's possible Optical fiber using SDH capacities of two and a half gigabits per second ten gigabits per second common So it's not such a challenge to provide this type of capacity inside the core network. For example a network across Bangkok where the entire network is run by one company one ISP That was the case if we have normal TV Where we use multicast The idea is that Doesn't depend upon the number of people watching the channel Because with multicast We send one copy of the packet at the source if there's one person watching the channel We send one copy If there are ten people watching the same channel, we also send one copy so with multicast increasing the number of users Doesn't impact upon what we require for capacity. So that's if we have normal TV sometimes we'd like to have TV on demand video on demand where a user Goes to some website or some user interface and they select the video to watch at a particular point in time so With normal TV the schedule of what you watch is decided by the the TV channel But with video on demand the user can choose what they watch and when With video on demand We normally cannot use multicast Because normally there are not multiple users Wanting to watch the same content at the same time Hence we have to revert to unicast And therefore For every user that's wanting to watch a video The source has to send a single copy of that content So if user A is watching one video They want to watch a movie and they start that movie at 8 p.m. So they go to some interface and they choose that movie to watch at 8 p.m Therefore the video head end is streaming content to user A then user B at 805 Chooses to watch the same movie then We have to use unicast to stream a copy of the same content to user B We cannot use multicast because they're watching it and they want to receive the content at different times So we have to use unicast and stream the content separately in that case So that's a problem in terms of video on demand The capacity we need in the core network depends upon the number of users we want to support For example, if one user needs a capacity of 15 megabits per second to watch their movie The second user also needs another 15 megabits per second because we need to stream using unicast so The capacity needed inside the network depends upon the number of subscribers In particular the number of video on demand subscribers So this is some some data from large network, so but you can extrapolate to different numbers So this is in thousands of subscribers If we have 25,000 people in the network That we want to support with video on demand Then the capacity of the network is in the order of five gigabits per second Because the capacity requirements goes up as the number of users go up and The more users we want to support the larger the capacity requirements because we cannot make use of multicast So supporting normal TV multicast is very beneficial and The capacity required in the core network depends upon the number of channels we want to support But with video on demand The capacity depends upon the number of subscribers that we want to support So we need to weigh up those It's easy to support normal TV, but with video on demand. There's Higher requirements on the capacity of the core Even tens of gigabits per second are not too difficult with optical fiber though. What about from This router here is a core network to the home the access network or Here called the service provider access network So from your home to the core network what technologies are available? We'll go through several First use ADSL. So use the normal telephone link from your home to some telephone exchange Where this router is located in a telephone exchange? ADSL, ADSL 2 plus so their improvements What typical speeds do they provide? ADSL 2 plus in both cases depend upon the distance between Your home and the exchange if this link the distance here is say 300 meters Then with ADSL they may be able to get a speed of 12 megabits per second download With ADSL 2 plus up to 26 megabits per second if this home is three kilometers from the exchange then They're talking about speeds of less than 10 megabits per second Now if we want to support going back the entire home with multiple TV channels We spoke about a requirement of tens of megabits per second therefore If you're three kilometers from the home between the home and the exchange ADSL even ADSL 2 plus will probably not be fast enough to support IPTV If the home is close to the exchange Then it may be fast enough. We can get up to 20 25 megabits per second But further from the exchange the the speed supported by ADSL is not high enough So that's a problem. ADSL will not always be suitable for IPTV Router 8 router 7 so one option is to use ADSL But depending upon the distance it may not be sufficient because with a copper Remember ADSL makes use of the copper telephone network with a copper wire the signal quality degrades across distance and with ADSL it turns out that the limits are in the order of 20 25 megabits per second But only over very short distance the further we go the lower the data rate that's available So the solution if we need faster data rates and what's available is To reduce the length of the copper line So we see here with a short distance the speeds are okay with a longer distance the Speeds are not enough. So the idea is To reduce the distance of the copper line eventually down to zero so we do not use copper Note that normally from the router to the rest of the network is optical fiber in the core network So here's router 7 which is this zoom in from our other picture ADSL of course is use our copper telephone network. So the idea is to then Try and bring the optical fiber closer to the home and that's what we get with some of these Versions or variants of providing optical fiber to to the end user We get fiber to the node fiber to the curve fiber to the home. Let's go direct to fiber to the home The best case solution There's optical fiber coming into this router this edge router one option is to Or try and draw it all in the same diagram Use optical fiber that connects that router direct into your home this option would be referred to as fiber to the home f TTH That is you have an optical fiber link coming direct into your home or your building sometimes you'll see In others fiber to the building FTT be There's no need for the copper link now We don't need ADSL and we're not limited by the the physical limitations of that copper link the speeds with speeds Which which which we can achieve? limited by the optical fiber so Usually in the order of gigabits per second a typical So that's the best case for the end user With a gigabit per second or even 100 megabits per second IP TV is possible What's the problem? It's expensive who has so fiber to the home Okay, it's expensive for the for the ISP to deploy because Digging the holes and laying the cables to all the homes so you get coverage of tens of thousands of different homes is very expensive So it's very expensive to to build the network Of course countries are deploying it, but it takes time and it costs a lot of money So what are some intermediate? Approaches if ADSL is not enough and it's too costly to get fiber directly into the home Then the idea is to bring the fiber closer to the home But still utilize a portion of the copper network and that's what we get with fiber to the node and fiber to the curb Let's introduce a new device We have our let's say our router which is in the telephone exchange originally, but now What we can do is what's first? introduce a new device in the network and connect Using our copper link from the home to this new device and then from that new device use optical fiber with the idea that we're reducing the Distance that we use the copper link When we use ADSL the copper link is between the home and the telephone exchange So it depends on where you are compared to the telephone exchange as to what the distance is but the ISP can then deploy new devices which are closer to the homes for example in a particular neighborhood They put some cabinets in the street Which connect into the telephone network? So from the home you have a copper link into this special device and Then the company running the network uses optical fiber From this special device back into their core network What it does is it reduces the copper line length and as you see with ADSL the shorter the distance the higher the speed which we can achieve So let's say that the first copper length was three kilometers The idea with fiber to the node is to introduce a special node Which is closer to the home? Connect using the normal copper network from the home to this special node over a shorter distance Let's say 300 meters and Then optical fiber from this device into the core network and Of course not just home a does that but home b c d and e or all the homes in that area All connect by the copper telephone network into this special node. So now we have one special node covering Multiple nodes or multiple homes in a particular area Maybe hundreds thousands of homes. So in in some neighborhood So one device in each area and to cover another area we put in another node So the cost now to deploy this network We don't need to bring optical fiber into every home We just need to build a network that brings optical fiber into these nodes where we have one node per 100 or per 1000 homes So we reduce the cost of installing the optical fiber network for the ISP But we potentially increase the data rate that's possible because remember the limitation is the copper link and The smaller the distance the higher the speed which we can achieve So now from home a to the node We only use a 300 meter copper link and we can get higher data rates and in fact you no longer need to use a DSL There are other technologies VDSL for example is Useful for very very short links hundred meters for example 30 100 meters and You can get data rates of up to 100 megabits per second across the copper link So by reducing the distance of the copper link we can increase the speed and that's the idea of Fiber to the node and also fiber to the curb exactly the same concept, but instead of having one special node per Some neighborhood per per 1000 users They put this special node closer to the home say on every street on the curb of every street As a result reducing the distance of the copper link even further in G10 meters and then optical fiber from that special node Back to the core network fiber to the curve and the middle one was fiber to the node I don't think there's any specific definition of the distances for each of them. It's just the concepts that Okay, here we think about street level so everyone on the same street Connecting to the same device here, and then there's one optical fiber link back to the core network So with fiber to the curb the company that builds this network needs more devices and therefore has a higher cost of building the network But because we have a shorter copper link we can get higher speeds again So that's what we can compare ADSL copper direct back to the core network Fiber to the home optical fiber direct back to the core network the fastest option But the most expensive or intermediate ones That reduced the copper length at the expense of building some or deploying some portion of the network to be optical fiber so the trade-off there between Speed for the user and deployment costs so eventual costs for the user and different countries different regions different ISPs of trying different approaches What is the benefit of IPTV? We no longer Well, we can start to carry all of our services across the one network eventually so Not just IPTV, but this approach of from the home's perspective There's just one Network in this case many homes now would have internet access you pay a company for internet access You could pay another company or pay a different bill for your home telephone line All right, some people go without home telephone and then again, maybe for satellite TV or cable TV All of those are using three different networks, so your Well, your telephone uses the same network, but eventually splits out into two different networks Your TV is using a different network either the satellite or a separate cable So the benefit for the companies in this case is that they only need to maintain one network Okay, one physical network so they cut down on the infrastructure required The potential benefit for the users is it simplifies things everything is via the one network technology So long as it's fast enough That is your access network is fast enough. It should be suitable in terms of quality Simplifies the management internal of the of the network. So not just having less routers and less links for the company, but Maintaining who the subscribers are managing the payment managing Who can access the network simplifies the operations of that network maintaining the network is expensive? so Potentially in the long term it would be much cheaper for the company providing the network and hopefully then cheaper for the end-user and There are others that you can do services that a Normal TV network cannot provide by using IP You now basically have access to two-way communications. So now You can stream TV But by your TV you can be sending data back to the TV station and then getting customized content And different interactive applications. So that's some of the benefits So you can support more services in that case So in terms of the capacity requirements Let's summarize inside the core network owned by say the ISP They need enough capacity in there to support The number of channels that they want to deliver across that network With normal TV channels, we can use multicast and therefore the capacity scales related to the number of channels If we want to support video on demand, then we cannot use multicast. We must use unicast and therefore the capacity depends upon the number of subscribers and number of users For the access network We usually need 10 20 giga 20 megabits per second depending upon the quality of TV ADSL sometimes is not enough So some alternatives to try to bring the optical fiber closer to the home either direct into the foam into the home and As an alternative if that's too expensive To nodes which are closer to the home to reduce the copper link the technology inside the home Usually wireless LAN ethernet are sufficient for the speeds that we require with the latest wireless LAN standards We can stream 10 20 30 megabits per second possible Ethernet no problem, and that finishes our IPTV any questions Try and understand the advantages of using multicast The idea of well the correspondence between TV stations and multicast that is we can think of Multiple users watching one TV station at the same time We can take advantage of multicast because those users are a set of destinations In some multicast group and with multicast we send to one special multicast address and the routers deliver that content to each of the destinations in that group and with video and demand that's not possible because Usually there's no one user watching the same content at the same time Because people start the videos and watch different videos or movies and at different times and hence you revert to unicast And then in terms of the technologies inside the core network. Typically we use optical fiber Inside the access network We use either the existing telephone network and ADSL or some Network that makes use also of fiber in the access network fiber to the home fiber to the curb fiber to the node and Inside the home wireless LAN and ethernet are the main technologies There are a few others, but they're the main ones any questions to finish on that topic Easy topic. We've got one topic remaining Let's just introduce it and then we'll finish for today Although there are two sets of slides. It's all on the one topic. This last topic is about peer-to-peer systems. So using Using our a network of computers a distributed system to Take advantage of the multiple different computers that are in the network which are used by the end users to Provide improved services by sharing resources amongst those end users We because we're we're limited on time We've got just tomorrow and next week remaining. We will not go through all of the slides I think most of you know of peer-to-peer systems from peer-to-peer file sharing. Okay, anyone not heard of things like BitTorrent Anyone used it? No, no, we're going to explain how it works. It's not illegal. It's okay. Anyone use BitTorrent? we'll show an example of a download with BitTorrent and there are other peer-to-peer file sharing systems which allow users and users To share files between them Of course, there are a lot of issues about the content that's shared maybe illegal Copyright infringements and so on but the technology for sharing that content is of course not illegal and We'll explain how that works because it's not just for sharing movies amongst people but for Sharing other types of content and also some applications make use of these We're not going to go through the motivation here and so on we're going to go direct into the technologies But one thing that we want to distinguish is will appear to peer system compared to a client-server system so a client-server system if We go use the example of file sharing or or distributing a file a client-server system is when a client accesses a server and Downloads the file from that server and Of course if there are many clients that want that same file They all go to the same server and download from that same server In a peer-to-peer system the idea is that many clients want that same file Some of those clients download from the original server The other clients can then download from the clients that have already downloaded the file from the original server The result is that of those many clients With a peer-to-peer system we distribute the the task of downloading the file amongst all the devices or amongst many many clients in a client-server system That should disappear in a client-server system We depend upon the original server So and these comparison of a client-server system versus a peer-to-peer system and the same or essentially the same a trade-offs as a client-server versus a or a centralized versus a distributed system in a client-server system whether it's downloading a file or Accessing some resource or requesting some service The clients request data or functionality from some server now if There may be a large number of clients accessing that server Then the server may be replicated so that Think of the google web server. There's not just one computer that runs the google web server The same website is replicated across many physical servers in fact geographically separated But conceptually there's one server in that case The problem with a client-server system is that if the server fails No clients can access that service So the entire service becomes unusable if that server fails and the other main problem is that all of the Traffic all of the requests to the server and the responses from the server go via that server and The link to that server the network link So if we have one server Say this computer is the server and there are thousands of clients sending requests to retrieve a file from this server Then the link coming into this server is the usually the bottleneck link in that so The rate at which the data can be transferred between the clients and server depends upon the link going into that server and That becomes a problem because if that link is not fast enough then the clients get a slow transfer speed The advantages as we'll see against a peer-to-peer system is that we can easily control access to resources and functionality If this server is distributing some file clients download a file from it Then every client that wants to download that file must contact the server We can control at the server who accesses that file we can provide a username and password login system So that each client needs the right credentials to access that resource So it's easy to control access if we have one central server So good for providing security in that case and it turns out that the algorithms needed to search for resources quite efficient and simple Because quite simply if we want to if the server offers a set of files If a client wants to find it then they can just send a request To that server who can say whether or not they have the file that they're looking for What about a peer-to-peer system where? We now have many clients and they're all trying to provide the same functionality They're all peers with each other a decentralized system We do not distinguish between clients and servers. We just call each computer a peer Although they may take a role or Maybe another way is to think that each computer can be either a client or a server So they can take both roles in the exchange They may sometimes be a client and then change to be a server the peers must cooperate with each other So that again if we have this ability to transfer files then if we have ten clients then The peers must allow those other Peers to contact them and and download the file from them There must be some form of cooperation the advantages of a peer-to-peer system compared to client server opposite the the Opposite so the advantages of the negative of the disadvantages Is that right? The advantages are the negatives of the yeah the disadvantages for a client service system We have a single point of failure failure with a peer-to-peer system There is no single point of failure Because there's no one server that we rely on So if one device fails in a peer-to-peer system the system can keep running that's an advantage and With a client service system we have this performance bottleneck at the server Everything depends upon the server the speed of the server the speed of the network link into the server with a peer-to-peer system We'll see that's not the case and It turns out with a peer-to-peer system In some cases as we add more users The network gets better it scales up The problem with a peer-to-peer system is that it's harder to control access Because if we think of the file sharing If there are 10 peers that have the same file and a new peer wants to access that file Then it's difficult to say who or to restrict that new peer from accessing that file All 10 of the peers would have to have some login mechanism with a server the server can control who accesses that file one point of control and We'll see as we go through this topic that the algorithms needed to search to find resources to find files Are more complex than a client service system? So what we're going to do and we'll start tomorrow is go through some different approaches for peer-to-peer systems We'll skip a few of those slides and go through an Example of approach similar to Napster, which was used for file sharing and then Two other approaches Nutella and fast track and compare the general approaches and Then next week will go through the specifics of how a protocol works for the exchanging of files and that's bit time Let's stop there and we'll go through these techniques tomorrow