Hello friends, Welcome to Gate Smashers, the topic is topology. Topology basically tells that how the devices are connected with each other means topology tells about the arrangement of devices and generally we have these topology mesh, star, bus, ring and hybrid. Although this is a very simple topic but in UGC net especially on this topic many questions have already come and what happens sometimes that a simple topic creates problem. We feel that this topic is simple and I can do it easily but sometimes such questions come which we have not expected that such questions can also be there. So here in topology we are going to discuss on various topics on various questions actually the concept is very simple but what questions can come that I am going to discuss here. So in this video first we will talk about Mesh topology. Mesh topology means where all devices are connected with each other means here you can see this diagram there are four devices and all four are connected with each other, if I say five device let’s say five devices, so how five devices will be connected to each other, like that this is the way. Here all devices are connected to one another, So here what question comes first? On number of cables, so let’s say here there are four devices all are connected with each other how much cable is required? So here I can count 1 2 3 4 5 6. We can count here also but if number of devices is 10 or 20 or 30 then how will we calculate? We can’t make diagram because here when the number of nodes will increase cables will also increase, so direct formula for this is NC2 or you can also say as n x (n-1) divide by 2. Here what is n, number of nodes, number of nodes means all the devices which are connected. all the devices that are connected then you can calculate how much cables are needed, that is a simple point. This is actually a formula of complete graph also. In this graph if you have to find the edges then also the formula will be same. Second question may be number of ports, if you are given mesh topology and where there are simply 10 devices then on each device how many ports will be there? So if you look carefully what the port means, port means connectors where wires are connected you might have seen in laptops, mobiles there are ports especially in laptops there are HDMI port, VGA port various ports are there Ethernet ports are there so that is the port. So here if we see in device A how many ports are there? Three, how many port are there on each device? Three and how many nodes are there? Four, if there are four nodes then on each devices how many ports are required? Three Now if you see here one, two, three, four, five five devices are connected together. How many on each, one, two, three, four How many ports are needed? Four, so you can directly calculate its formula, number of ports, how many? n – 1, this is (n – 1) on each device, If you are asked total, then you multiply this with n, then it would become n x (n-1), if asked for one device then n – 1 Reliability, this point also comes whether mesh topology is reliable or not? It provides reliability or not? What does it mean by reliability? Sometimes it happens in our system that failure occurs one cable fails or problem occurred in one cable, so is there any other way any other method to send message? Check it. Let’s say A has to send message to D, A sends message in this way to D and suppose this wire gets damaged then is there any other method? Yes there is, how? via B one more method is there via C so reliability means if there is single failure then will my system stop or will continue? So you can see here reliability is very high. Even If I say we compare all the topologies then here it is highest. You can say highest reliability provided by mesh topology. Cost, Now if we talk about the cost, cost here especially depends on the cables because devices are fixed only four, five or six but if you connect ten devices then 10 x 9 divide by 2 according to the formula so what it became? 10 x 9 divide by 2 so this is what, this is 5, = 45, means how many wires are required if you have to connect only 10 devices? 45 wires, obviously cost will also increase that much. Yes! Cost is also high because multiple devices are connected with multiple wires. Security, does mesh topology provides security? Yes, How? We will talk about the same if A is sending message to D, through this wire if A is sending message to D, then B or C will not even know, So B and C will not have any information if A and D are communicating with each other. that is what it provides the security. Yes it provides the security also. So these are all the major points which can be asked about mesh topology. Apart from this if we talk about disadvantage then you can say about maintenance also, because number of wires are more. If you connect 100 devices then many cables will be needed. So maintenance will be definitely high here and the last important point is it supports point to point communication. There are various type of communications one of them is point to point and other is multipoint or multicast. In multipoint what happens? With one wire multiple devices are connected. Which is generally in bus topology, all devices share one wire. Here there is no sharing, the cable between A and B, is anyone sharing it? No. The cable between A and D, is anyone sharing it? No, here there is no sharing only point to point communication is there. Which is you can say dedicated communication, So can dedicated communication work in LAN in small LANs where there are less devices but if you increase devices or increase area then maintenance will be more there and cost will also increase in that case you can say point to point communication is not good and this does not support, this basically supports point to point but does not support multi-casting. Next we talk about Hub. This is all about the mesh topology. If we talk about hub topology it is also called star topology. What is there? Here there is a centralised device, see there is a centralised device called hub. Hub is a multi port device multi port device and what is the functionality of hub? I have already made a video on that I will share the link of that video please check that video so that you can have more information about hub. So here multiple device are connected through hub, means they are not directly connected but are connected through hub. If A sends message to C then it will go to C through the hub. So if we talk about number of cables How many cables are required? N, means as many devices that much cables. If N number of device are there then n number of cables are required. One, two, three, four, four devices four cables. Number of ports, How many ports are required on each device? One, one, one, one means how many ports are needed on each device one so how many in total? Total you can say 1 x n that is n again same. Reliability if we talk about reliability reliability is not there. Why reliability is not there? If there is failure in the hub, there is a single point of failure, this term is popular in networking. single point of failure means in case some problem comes in hub then the four cannot communicate with each other, the whole LAN network will stop. In this case you can say reliability is very less if hub gets damaged. Cost,cost is genuine or you can say cost is normal here. As compared to mesh definitely cost is less because number of wires are less. But cost of hub is also high cost of hub but as compared to mesh still its cost is less. Security, yes security it is here also because if A is sending message to C then B and D will not know. Although hub sends message to everyone it. it works in broadcast way but if we want to not send message to B or D so we can still stop but hub by default will not do this. Hub actually is pure hardware it cannot decide that message should be sent only to C, it will broadcast to every one. So security is less here, security is less. and last point, point to point This also supports the point to point communication. Star topology also follows point to point means does not follow multipoint, from one single wire, multiple devices are not connected sharing is not there, there is a direct communication point to point communication. So this is all about basic of mesh topology and star topology rest of the topology we will discuss in the next video. Thank you.